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457 Cards in this Set
- Front
- Back
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How long does it take humans to identify things after seeing their images?
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100 ms
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How many dimensions do retinal images have? How do we interpret them?
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Retinal images are 2D, so any image is consistent with many 3D shapes. And to see the world the brain must choose the best interpretation, which is often the most common.
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What is the light-from-above assumption?
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It assumes that light comes from above and so it forms a perspective that is not necessarily what it is. It is partly innate and partly learned: children will learn to interpret pictures this way as they grow older.
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Why is it very unlikely to see the concave face of a mask?
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Because it is very unlikely to see it in real-life. So the assumption that faces are convex overrides the one that light comes from above. It is nearly impossible for adults to see the right-most image as a hollow face.
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What does it mean to say sensory systems have hierarchies of assumptions?
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The sensory system uses these rules to better understand the world. Stronger ones override weaker ones, so it all makes sense.
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What is Bayesian inference?
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They are the rules for optimal guessing. And our sensory apps know these rules.
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How long would it take for the eye to arise by natural selection?
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Less than 400,000 generations or half a million years. So very short.
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What is the structure of the simple eye of a flatworm planarium?
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It is composed of a cup of light-sensitive cells. The cup shape is crucial because it means light in different places excite different cells. Planaria will use this fact to infer where light is coming from, so they can swim away from it.
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What is the next evolutionary step after developing a cup-shaped eye?
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To close the walls and create a pinhole at the front which casts inverted images on the back of the eye.
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What is the pinhole eye?
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It ensures that each point on the image at the back receives light from just one direction in space - the result is perfect focus, but very dim.
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What does adding a lens to a pinhole eye accomplish?
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It will improve the image, but it doesn’t necessarily need to.
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What is a simple eye?
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It is a cup-based design. A chamber where light enters through a small hole at the front and is focused on the inner surface, called the retina.
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What organisms use the simple eye design?
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All vertebrates, squids and octopuses, spiders, and Nautilus.
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What is the eye of Nautilius?
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It is a spherical, lenseless pinhole camera, 1 cm across. its pupil widens in darkness to admit more light; in bright light it constricts to improve focus.
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How can pupil size be modulated in humans?
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It is controlled by a ring of colored muscle called the iris. These muscles can reduce the pupil diameter from a maximum of 8mm down to 2mm. The pupil area shrinks from an area of 50 to 3mm(2) - a 17-fold decrease.
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What is the range of illumination that the eye operates over?
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a 10-billion-fold range of illumination, so the pupil contributes little to compensating for brightness.
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What does enlarging the hole of a pinhole eye do?
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It makes the images brighter because more light comes in, but it also makes it blurrier because it lands on multiple spots on the retina.
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How is the image focused in human eyes?
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By the lens and the cornea. They are both lenses optically speaking but our focus is on the ‘lens’ of the eye.
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What is the cornea composed of, and how is it arranged to make it transparent?
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It is made of collagen, like the sclera, but its fibers are arranged to make it transparent.
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What is the lens composed of?
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Long (12mm) cells without nuclei, that are packed with clear proteins called crystallins. There is no blood supply (must be transparent) but absorb nutrients from the aqueous humor.
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How are the cells of the lens arranged to be transparent?
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They are ‘zippered’ together in concentric layers for flexibility.
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Why do our corneas bend light? Why do we focus poorly in water?
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Due to the difference in refractive indexes of the medium and the collagen in the corneas. In air, this difference is large and this is the reason why we can see clearly. But, in water, we focus poorly because the difference is small (hence the refractive indices are similar).
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How may we improve our underwater vision?
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Constrict our pupils more.
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What is meant when we say depth of field? Compare a lens to a pinhole.
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Meaning that, for a lens, they focus on images only of objects near a single focal distance. Where objects closer or further away are blurred. Pinholes have an infinite depth of field, so everything is focused. This is a reason why we constrict our pupils in bright light, to increase our depth of field.
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Does the cornea or lens focus light more, is it adjustable?
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About 2/3 of our focusing is accomplished by our cornea.
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If most of the focusing is accomplished by the cornea, why is our lens useful?
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It can change its shape. We can alter our focal distance: a flatter lends refracts light less and so focuses more distant objects; a rounder lens focuses things up close. (In cameras and some fish, adjusting the focal distance is accomplished by sliding the lens forward and back).
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How many photoreceptors does the eye have?
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126 million photoreceptors
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How many fibers does the optic nerve have?
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1 million
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How much percentage of data does the retina send to the brain?
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Approximately 1% (since 126 photoreceptors:1 fiber)
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How does the eye compress its message before transmission?
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Most images are redundant (i.e. neighboring pixels are similar) and so the eye doesn’t need to tell the brain the image properties at each photoreceptor.
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What came first cones or rods?
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Cones, rods evolved from them
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How many rods and cones does the human retina contain?
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More rods than cones. ~120 million rods and only 6 million cones.
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What are cones useful for?
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They are less sensitive than rods; they are responsible for vision in bright light conditions and for distinguishing colors, but they don’t operate in dim conditions.
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What are rods useful for?
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They are more sensitive than cones. They can detect single photons, but they operate only in low light conditions. In daylight they are ‘bleached out’, meaning that their photopigment rhodopsin is broken down so they can’t sense light.
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How do human eyes adapt to dim lighting/darkness?
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The rods will dark adapt, they will rebuild their stores of rhodopsin over ~30 minutes.
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How can we treat night blindness?
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(liver) Vitamin A, which is used to make retinal, a component of rhodopsin.
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Where are photoreceptors more densely packed?
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In the macula, it is a central region 5 mm across, and especially in a central pit called the fovea, 1.5 mm across.
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What is the density of the fovea?
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200,000mm(2)
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How large is the fovea? In mm and in º?
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It is 1.5 mm and 2º of visual angle, or twice as wide as your thumb viewed at arm’s length.
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How does detailed vision decline as we move away from the fovea?
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5º off center, acuity is quartered. at 20º is falls below the standard for legal blindness.
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What is the blind-spot?
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There are no receptors in the blind-spot. It is the hole where the ganglion-cell axons exit the eyeball to form the optic nerve.
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Analyze this graph.
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This graph shows that the fovea contains almost exclusively cones, and outside the fovea the proportion of rods increases, also note the blind spot. This is why we can see a dim star better by slightly looking away from it, because rods have greater acuity for the darkness.
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What are opsin molecules? Where are they located?
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Each photoreceptor contains millions of opsin molecules (~100 million per rod). When light hits them, these molecules change shape, starting a chemical cascade that hyperpolarizes the cell membrane, making it more negative.
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What effect does hyperpolarization have in photoreceptors?
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It reduces the release of glutamate that excites or inhibits bipolar neurons, which project to the retinal ganglion cells. Less neurotranmitter can either stimulate (depolarize) or inhibit (hyperpolarize) the bipolar cell (characteristic of on/off mapping)
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How sensitive are ganglion cells near the fovea? Away from it?
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Near the fovea, a single ganglion cell may get input from only a few photoreceptors, mostly cones. Farther out, each ganglion cell gets input from many receptors (up to 75000) mostly rods.
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What are the ganglion cells sensitive to in the periphery of the retina?
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Each cell is sensitive to light, but not to spatial detail because it blends information from a large variety of receptors.
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What are the ganglion cells in the fovea sensitive to?
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They are less sensitive to light, but have better spatial resolution because each one gets input from just a few densely packed cones.
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What is the rate at which neurons may fire? Why? Given an example of the neocortex (its rate and what % of energy it uses)
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Although the brain consumes 1/2 the body’s glucose, it can only support a low firing rate with only about 2-4% of neurons firing at any moment. E.g. the neocortex uses 44% of the brain’s energy and the average rate per cell is 0.16 spike/s
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What is meant when we say that retinal ganglion cells report changes?
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For example, when a light suddenly brightens or dims, many retinal ganglion cells respond briefly and then return to a resting rate of ~20 spikes/s. The response is only to the change.
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What are phasic cells?
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Phasic cells respond briefly to any change in input and then return to their baseline firing rate.
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What are tonic cells?
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Cells that respond to any change in input and maintain firing to signal the current level of a stimulus.
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What is phasic-tonic cells?
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They are also called incompletely adapting, cells respond and then go partway back to their baseline activity.
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What type of changes do phasic cells measure?
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Temporal changes, it is more efficient to report changes than to repeat the same messages over and over.
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What type of changes do temporal cells measure?
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Spatial changes, it is more efficient for cells to report only when they are on an edge between 2 kinds of things.
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What is a receptive field of the retina?
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A region of the retina where light affects the cell’s activity.
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What are center-surround receptive fields? On-center and Off-center?
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On-center are excited by light in the center of the field and inhibited by light anywhere in a ring around the center (and unaffected by light anywhere else on the retina). Off-center do the opposite.
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What is lateral inhibition? Explain centre-surround receptive fields.
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It is when cells inhibit their neighbors or the cells their neighbours excite. For an on-venter ganglion cell, a disk of photoreceptors excites the ganglion cell and a surrounding ring of photoreceptors inhibits it (excitation and inhibition occur through interneurons). Off-center is opposite.
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How does lateral inhibition reduce redundancy?
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It accentuates differences between ganglion cells, so their signals are less similar than those of the photoreceptors. Hence, it decorrelates the signals to create a more efficient representation of the image which can be transmitted with less duplication.
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What is the firing rate of the following on-center receptive field?
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The entire field is in the light and so the excitatory photoreceptors and inhibitory photoreceptors cancel.
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What is the firing rate of the following on-center receptive field?
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The cell’s field is mainly in the light and only part of the inhibitory ring is in the dark. Hence more excitation than inhibition and so the firing rate increases.
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What is the firing rate of the following on-center receptive field?
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Most of the field is in the dark with only a portion of the inhibitory ring in the dark, hence more inhibition than excitation and the response is well below baseline.
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What is the firing rate of the following on-center receptive field?
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The cell’s field is entirely in the dark and so it is neither excited nor inhibited, baseline.
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How does lateral inhibition explain the Chevreul Illusion?
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The bands are each a uniform shade of grey, but they look ‘fluted’: they seem darker at their left-hand edges and lighter at their right-hand edges. Since perceived brightness shows a wave-shaped ripple near each edge, like the activity profile of a ganglion cell.
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What are the three different classes of retinal ganglion cells and what are their proportions?
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10% are parsol cells. 80% are midget cells. <10% are bistratified cells.
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What are parasol cells?
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They are ganglion cells that get input from many photoreceptors, mainly rods, over a large receptive field. They respond to achromatic (greyscale) contrast and low-luminance stimuli. They are phasic, and detect motion.
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What are midget cells?
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They are ganglion cells that get their input mainly from a small number of cones in a small receptive field. Some respond to achromatic contrast, some to colour. They are tonic.
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What are bistratified cells?
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They are ganglion cells that are excited by blue light and inhibited by yellow light.
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What is the optic nerve?
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It is the bundle of fiber beginning at the blindspot in the retina, composed of the axons of the ganglion cells.
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What fibers cross the chiasm in the optic nerve? Which don’t?
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Fibers from the nasal retina half cross. Fibers from the temporal retina do not cross.
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What is the temporal side and what is the nasal side?
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Temporal is the outside (think of temporal cortex). Nasal is inside.
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What parts of the left and right retina does the right visual hemifield project on to?
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It projects onto the LEFT SIDE of EACH retina. In other words, the nasal side of the right retina and the temporal side of the left retina.
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What parts of the left and right retina does the left visual hemifield project on to?
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The left visual hemifield projects onto the RIGHT SIDE of EACH retina. In other words, the nasal retina of the left eye and the temporal retina of the right eye.
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What are the optic tracts?
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They are the two nerve bundles that emerge from the chiasm and connect to the LGN.
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Where are the LGN located?
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In the thalamus and project primarily to the primary visual cortex V1.
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What does LGN stand for?
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lateral geniculate nuclei.
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How many neurons does the LGN have?
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Approximately two million.
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What does retinotopic mean? What areas are retinotopic?
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It means that neighboring cells in the area get input from neighboring ganglion cells in the retina. Hence, cells that are closer together represent things that are closer together in the real world. An example is the LGN.
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What is the structure of the LGN, and how is it organized?
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Each layer represents the contralateral visual hemifield e.g. in the left LGN each layer represents information from the left half of one or the other retina, representing the right hemifield. It is retinotopic. The 6 layers are in register.
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What do the 6 layers of the LGN get their input from? Starting from the bottom to the top.
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C I I C I C, where C is contralateral and I is ipsilateral.
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What are the main factors that determine whether a response is initiated in LGN cells?
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They depend more on non-retinal inputs, such as feedback signals from V1.
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What are the magnocellular layers of the LGN?
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They are the two lower layers, populated by large neurons which receive input from the parasol retinal ganglion cells. Hence, they also have large receptive fields and encode both motion and achromatic contrast.
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What is the magno, or M, processing stream?
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Begins with parasol retinal ganglionic cells, to magnocellular LGN
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What are the parvocellular layers of the LGN?
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They are the 4 upper layers, populated with small neurons which receive input from midget retinal ganglion cells, so like those cells they encode color and static form.
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What is the visual parvo, or P, processing stream?
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It begins with the midget retinal ganglion cells, to parvocellular LGN.
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What are the konio layers of the LGN?
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They are present at the bottom of each magno and parvo layer, they are very thin. And cells in at least some of these layers receive input from bistratified cells and so like them, they respond to blue light by increasing firing and to yellow light by decreasing firing.
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How many layers are present in the LGN?
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There are 6 visible layers, but 12 functional layers: 2 magno, 4 parvo, 6 konio
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How is the primary visual cortex organized?
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It is retinotopic, but the areas are not preserved. The fovea which covers only a small part of the retina projects to large areas in LGN and V1. This is because it needs to process a lot of information received from the photoreceptors of the densely packed fovea.
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How many layers does V1 have and how are they organized?
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There are 6 layers, with layer 1 on the surface of the neocortex.
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Why is V1 also called the striate cortex?
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It has a stripe called the stria of Gennari running through layer 4 where projections from LGN end (LGN projects only to V1).
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What do the magnocellular parts of the LGN project to in V1?
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4Cα
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What do the parvocellular parts of the LGN project to in V1?
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4Cβ
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What do the konio parts of the LGN project to in V1?
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To layers 1-3
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What do V1 layer 6 cells do?
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LGN axons project to them, and they project back to the LGN cells that innervate them. In fact, more inputs come to LGN from V1 than from the retina.
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What are simple cells of V1?
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They are mainly found in layer 4, and respond most strongly to a bar or a luminance edge at a specific orientation and in a specific place on the retina. This is due to line of on- and off-center LGN cells.
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What are complex cells of V1?
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They receive input from simple cells. They are mainly in layers 2,3,5,6. Respond to bars or edges at specific orientations, but they are less particular than simple cells about where the line is - respond to favored orientation over a larger region of the retina. (e.g. of specific length or movement in a particular direction)
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How is V1 organized?
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Into columns, where cells in the same column respond to the same line orientation and adjacent cells (parallel to the surface) change orientation preference gradually (excepting color blob jumps)
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What pathway do color blobs belong to?
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Parvo, or P. But get input from both 4Cβ and 4Cα, and from konio cells from V1 layers 1-3.
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What does it mean when we say that different cells in V1 are ocular dominant?
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Although most cells in V1 are binocular, usually one eye evokes a stronger response. The degree of ocular dominance changes gradually.
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What is the packing problem?
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It is the job of mapping high dimensions efficiently onto low dimensions. Such as V1 mapping line orientation, motion, color, ocularity onto 2-D image - impossible without jumps.
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Why do we have color blobs?
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Since singularities are mathematically inevitable, it is useful to have cells that use the singularity to process some unrelated (i.e. not orientation) parameter such as color. They are also called orientation singularities or pinwheels. They are the points when all colours converge.
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How is V2 organized?
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Dark thick and thin stripes, as well as pale stripes called inter stripes. It is also retinotopic.
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What do thick strips in V2 get their input from?
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It is part of the magno, or M, pathway and it gets its input from 4Cα via 4B. Hence cells sense orientation and movement but not color. Responds best when a line appears at slightly different places on the 2 retinas (stereodisparity).
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What do the thin stripes from V2 get their input from?
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They get their input from colour blobs, Parvo, or P, pathway. Hence, they sense color or brightness but not orientation or motion.
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What do interstripes in V2 get their input from?
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From V1 layer 4Cβ (Parvo pathway) via V1 layers 2 and 3. Hence, the cells sense orientation but nor motion or colour.
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What is V4?
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It is called the color cortex and parts of the parvo pathway project here. Hence, it senses simple shapes, squeezes colour, shape and retinal location parameters into a 2D space. It is not retinotopic.
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What is V5 and where does it receive its input from? [Take note of the location]
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It is also called the medial temporal cortex, or motion cortex because it receives its information from thick stripes of V2, part of the magno pathway. But, it can also respond to other features such as stereo disparity. It is very weakly retinotopic.
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Are V5 cells specific?
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They have a preffered range of speeds, directions, and disparities.
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What is the interotemporal cortex?
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It prefers complex features such as faces…(different specific things). Within each region is a map of related objects (e.g. different views of a face are adjacent to eachoteher)
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How do our senses compute conditional probability?
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They do so given our current sensory input and our expectations based on past experience.
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P(A U B) = ?
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P(A U B) = P(A | B) P(B)
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What is Bayes’ rule?
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P(A | B) = P(A | B) x P(A) ÷ P(B)
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In Bayes’ rule what is P(A | B)?
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It is the posterior probability, or the posterior, because it is the probability of A after we have considered B.
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In Bayes’ rule what is P(B | A)?
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It is called the likelihood.
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In Bayes’ rule what is P(A) and P(B)?
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They are the prior probability of A and B, or priors.
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What is P(B) in Bayes’ rule? Why is it not required?
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We WANT to know which value of A is most probable given B. The actual values of the probabilities don’t matter, since we only want which is the largest. In this way, we can eliminate P(B) because it simply scales posteriors.
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What is another way we can state Bayes’ rule?
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Posterior is proportional to likelihood times prior.
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What is the convexivity parameter c? For the below image?
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c = 1 means a cube-shaped box. c = -1 means a cube-shaped room. c = 0 means a flat board, c = 0.5 means a slightly squashed box with a shape halfway between a flat board and a cube.
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What is the likelihood of image i given convexity c.
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If we assume that they are all squares not parallelograms than it is unlikely to be c = 0, and so only likely to be -1 or 1. So the likelihood P(i | c) peaks near c = ±1
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What do we need to compute P(c | i) given that we know P (i | c)?
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We need the prior probabilities of different values of c. This is based upon our experience. E.g. if cubelike boxes are more common than cubelike rooms. And if perfectly cubelike images are not common, then they will be a ± of 1.
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Hence what is the probability P (c | i) if we now know P(i | c) and P(c)?
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According to Bayes’ rule P(c | i) is proportional to P(i | c)xP(c). So superimposing the graphs of these two, we can find the peak of the posterior probability. Hence, Bayesian inference combines the prior (based on past experience) with the likelihood (takes into account the current image) to form an estimate that is a compromise between them.
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What is P(i | c) for the following image? State all assumptions.
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If c = 1 means a normal convex face, c = -1 means a hollow face, c =0.5 means flattened etc. This means that c = 1 means that light comes from below, and c = -1 means that the light source is high. c = 0 means that you wouldn’t see a face and so equals 0. There is a low chance you would see the face if seen from below, and a high chance if you would see it from above.
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What is the c function for the following image?
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Since normal convex face is much more common than any other shape it peaks at c = 1 and is 0 everywhere else.
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What is P(i | c) for the following image?
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Explains how the stronger faces-are-convex assumption can overpower the weaker light-comes-from-above assumption.
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What is the visible light spectrum? What is the wavelength of red and of purple? Which has higher energy?
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The spectrum is from 400nm to 700nm. Purple is 400nm and has more energy than red at 700nm.
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Why did evolution give us eyes that see 400-700nm?
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The power in sunlight peaks there. Earth’s atmosphere is most transparent to these wavelength. In sea water, it is most transparent <500nm.
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What is color constancy?
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Since every object has certain reflectances that it allows, colour vision infers these reflectances. We can only infer intrinsic reflectances. It is possible when there are at least two different wavelengths being reflected present.
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What kinds of cones are there? And in what proportions?
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63% of cones are red. 31% of cones are green. 6% of cones are blue.
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Which evolved first, red and green or blue?
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Blue cones did (b/c blue light penetrates sea water better than longer wavelengths?). Red and green cones evolved from a common ancestor 35 million years ago.
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Do red cones specifically absorb red light? What about blue and green?
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No, in fact they have these things called tuning curves which is the range and rate of absorption that their photopigment opsin can absorb.
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What wavelength does the photopigment of red-cones prefer?
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564 nm, which is yellow
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What wavelength does the photopigment for green-cones prefer?
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533 nm, which is a greenish-yellow
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What wavelength does the photopigment of blue-cones prefer?
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420 nm
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What wavelength do rods prefer?
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498 nm
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What are trichromats?
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We have three types of cones, and so our color sense is three-dimensional - corresponding to some pattern of activity in just 3 types of cone.
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What are spectral colors?
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They are those that can be evoked by light of a single wavelength. They are the rainbow colours, from violet through red.
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What are extraspectral colors?
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They are colors evoked only by a mix of wavelengths.
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What is chromatic aberration of the lens of our eye?
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Light rays of different wavelengths are refracted to different degrees, and so they don’t all come into focus the same distance behind the lens and so it blurs.
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How do we resolve chromatic aberration?
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We can place the blue cone farther back since it focuses 0.5mm in front of the red and green cones. Or we can simply remove it from our foveas.
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How do we decorrelate ganglion cells for color? Why is this necessary?
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We use sum-difference recoding for Green and Red cones because they are very similar and can be easily redundant. Doesn’t matter with blue since their information is very different.
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What is sum-difference recoding?
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We create a sum curve (R + G)/2 and a difference curve (R - G). They represent two types of ganglion cells that carry this type of signal. This is because for any value (R + G)/2 there could be any value of (R - G), and so they are uncorrelated and it becomes a very efficient source of information - none is redundant. It also allows for more messages to be equally likely, so entropy is higher and there is an improved information flow.
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What does it mean when informatione equals surprise?
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If a message tells you something you already strongly suspected, then it doesn’t surprise you and so it doesn’t give you much information.
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What does information inversely depend on according to Shannon’s Information Theory?
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probability
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What is a bit of information?
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It is the amount of information that lets you choose correctly between 2 equally likely possibilities.
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How do we maximize entropy? (average information)
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We should code messages that are equally likely.
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Which ganglion cells carry the (R + G)/2 signal? What is this pathway called?
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Parasol (and some midget) ganglion cells. They are called the yellow channel (because red and green mix to make yellow) or the luminance channel (because they report total cone activity)
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Which ganglion cells carry the R-G or G-R signals? What is this called?
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Other midget cells. They are called the red-green opponent channel.
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What ganglion cells carry the B - Y or B - (R + G)/2 signals?
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bistratified ganglion cells and it is called the blue-yellow opponent channel.
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How do opponent channels explain after-images?
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For example, if we stare at something green for a really long time our G - R channels gradually fatigue but our R - G are still active and so when we look away we see red.
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Describe the genetics of color blindness.
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The genes for red and green opsins lie on the X-chromosome. Problems at the loci underlie 95% of all variations in color vision (no problems with blue because it exists on a more stable chromosome 7).
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What does the speed of sound depend on? What is that speed in water? In air?
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When there is fast movement of a boundary the medium is compressed or rarified, causing a pressure difference which propagates at a speed v depending on density and elasticity. It is 340 m/s in air and 1400 m/s in water.
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What is frequency (or Fourier) analysis?
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It is the process of breaking a wave into its sine-components. The set of all these components is its frequency spectrum.
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What is the pressure of a point on a sine wave?
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P = Asin(2πft) where A is amplitude, and f is the frequency in Hz.
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What is the equation for wavelength?
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λ = v/f
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What is the period of a wave?
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1/f
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What determines our sense of pitch?
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Frequency, higher frequencies appear to have a higher pitch as well.
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What is the range humans can hear? How many octaves is this and when is acuity highest?
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We hear sounds in the range 16 - 20,000 Hz, which is approximately 10 octaves. We hear best between 1000 - 3000 Hz.
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What is the eardrum? What are its alternative names?
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The tympanic membrane or tympanum separates the outer ear from the middle ear, an air-filled chamber in the petrous bone of the skull.
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What are the names of the three bones that the eardrum vibrates?
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The malleus (hammer), the incus (anvil) and the stapes (stirrup).
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What is the oval window of the ear?
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It is a membrane between the middle and inner ear. It carries the vibrations from the middle ear and opens into the cochlea.
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How do the ossicles function?
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The eardrum vibrates the malleus, which moves the incus, which moves the stapes. They act as a level system to transfer vibrations from the eardrum to the much smaller oval window.
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What are the series of ducts that connects the oval window to the helicotrema?
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The vestibular duct leads into the cochlear duct which leads into the tympanic duct which reaches the cochlear apex at the helicotrema. They are layers rather than sections, (vestibular top, tympanic bottom)
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What is the round window?
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it is a membrane in the inner ear that separates the tympanic duct from the middle ear.
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Where is the basilar membrane situated?
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between the cochlear and tympanic ducts, it supports the organ of Corti.
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How does sound energy travel once it moves through the oval window?
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The energy moves through either the helicotrema or the cochlear duct. When transversing the cochlear duct the energy vibrates the basilar membrane.
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What is the organ of Corti? How does it function??
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It sits on top of the basilar membrane in the cochlear duct. They have receptors called hair cells which have 50-100 stiff hairs or stereocilia on their surface. The stereocilia extend near or into the tectorial membrane and when sound energy vibrates the basilar membrane then it bends the hairs and depolarizes the cell.
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How do different parts along the length of the basilar membrane respond maximally to different sound frequencies?
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Since the basilar membrane is wider and floppier near the helicotrema it responds maximally to low frequencies. Hence, near the oval window it is narrower and responds better to higher frequencies.
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How is the basilar membrane an auditory prism?
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It sorts vibrations of different frequencies into different positions.
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How does the brain distinguish frequencies?
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Based on the pattern of vibrations.
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What are the two types of hair cells, and what can they be related to?
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outer hair cells (OHC) and inner hair cells (IHC), which are similar to rods and cones respectively.
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What are OHCs?
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They are outer hair cells, they are very numerous and sensitive. Large numbers of them converge on single afferent neurons (of the auditory nerve, part of cranial nerve VIII)
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What are IHCs?
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They are inner hair cells, they are less sensitive than OHCs but each one is connected to a single neuron and so provide high-acuity information about sound frequency.
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How many IHCs are there per octave?
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~400
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How are fibers in the auditory nerv frequency-selective?
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Each fiber has a preferred frequency, where the threshold is lowest.
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How is frequency selectivity sharpened in auditory nerve fibers?
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By lateral inhibition, if a cell is responding to a single tone at its preferred frequency then you can reduce its activity by adding a second tone at a nearby frequency. So in terms of frequency, each cell has a central excitatory band and an inhibitory surround.
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How does the basilar membrane analyze low frequency?
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Fourier analysis won’t work and we need to phase lock the sound wave. This means that they coordinate their firing rate with the oscillations of the sound wave.
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How does phase locking underlie our sense of pitch?
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Frequencies that are too high to phase lock (>4kHz) are not usually heard as pitches.
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What happens to short and long wavelengths of sound as they travel?
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The short wavelengths tend to be absorbed or reflected by objects while long wavelengths are unaffected, so the farther the sound source, the more higher frequencies are lost.
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What are the three ways that we can infer the direction of sound?
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1. altering of sound by the whorls of fhte pinna, 2. interaural differences in phase and 3. interaural differences in intensity.
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How can we infer direction from the whorls of the pinna?
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The whorls of the pinna alter the frequency spectrum in ways that depend on direction, and which the brain can decipher.
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What is a sound shadow?
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It is an area with none of that type of wavelength coming through. But the head only casts shadow for wavelengths that are about its own size or smaller. So for frequencies greater than 2 kHz there is no sound shadow.
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What happens when a sound reaches the 2 ears at different times? How do we calculate this interaural time difference?
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The wave peaks will arrive at different times and so the ears will be phase shifted. If the head is d m wide, and the wavefront is at an angle θ to the interaural line then the time difference = dsinθ/v. [Assume sinθ(deg) = θ (rad), wher 1 rad = 57º]
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What do phase differences tell us about a source?
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It tell us if there is a 1º motion of a source, hence we can sense time differences between the two ears of just 10 μs (1% of the duration of an AP)
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What is tonotopic?
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Neighboring cell prefer similar frequencies
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What is the pathway of the auditory nerve projecting from the cochlea?
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It projects into the cochlear nuclei (CN) which projects to the inferior colliculus (IC), directly and via the superior olive (SO). The IC projects to the medial geniculate nucleus (MGN) in the thalamus.
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What are the differences between the lateral superior olive and the medial superior olive?
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Cells in the lateral superior olive typically receive information ipsilaterally, and are inhibited by contralateral ones. They respond to high frequencies and judge sound direction from interaural intensity differences. On the other hand, medial superior olive cells respond to low frequencies and prefer a particular time lapse between the signals from the 2 ears, and judge direction from phase differences.
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What is the medial MGN? Where is it located?
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It is part of the thalamus. The medial MGN projects to the primary auditory cortex A1, which is tonotopic. At right angles to its frequency axis, there are stripes where cells respond alternateely to the sum and difference between the signals from the 2 ears.
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What is the lateral MGN? What is A2?
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The lateral MGN is part of the thalamus and connects the IC to A2. A2 specializes in complex sounds (clicks, whistles, hisses, voices). It is not strongly tonotopic, some are and some aren’t
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What is conductive hearing loss?
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It occurs when something hampers the transmission of sound to the inner ear, e.g. a foreign body in the ear canal, ruptured tympanum, middle ear infection, fixation of the ossicle chain.
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What is the sensorineural loss of hearing?
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There is a problem with the cochlea or auditory nerve. 90% of hearing loss in the elderly is this type.
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How can we test for conductive loss or sensorineural loss of hearing?
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If Rinne’s test is normal on both sides but Weber’s is asymmetric then there is sensorineural loss. But if in Rinne’s test it is louder through the bone, there is conductive loss
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What is Rinne’s test?
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Hold a tuning fork to the mastoid bone and then beside the ear, ask which is louder.
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What is Weber’s test?
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Hold a tuning fork to the patient’s head and ask in which ear the sound is loudest
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What are the type of skin receptors?
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1. Free and 2. Encapsulated (including Merkel, Meissner and Pacinian mechanoreceptors)
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What sort of receptors are mechanoreceptors (phasic or tonic)?
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It s phasic, within 3 ms it returns to baseline and so measures changes.
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What do skin receptors with free nerve endings sense?
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They detect mechanical stimuli, temperature and chemicals.
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What do Merkel disks sense?
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They look like saucer shaped disks under the epidermis. They are sensitive to deformation of the skin, and are more tonic than phasic (as long as deformation persists it sends signal). They signal contact.
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What do Meissner corpuscles sense? Where are they located?
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Mainly in tongue and hairless skin (e.g. erogenous zones). There are loop ending within each corpuscle, they register sideways sheering (e.g. lifting something with fingertips). They are phasic.
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How many Meissner corpuscles do we have?
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5000/cm(2) when we are 10 but only 1000/cm(2) when we are 50
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What are Pacinian corpuscles?
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They are nerve endings sheathed in many layers like an onion. It senses displacement of about 10μm (1.5x width of blood cell) if the motion is quick. They are phasic (hence responds quickly to vibration and other fast changing stimuli)
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What are the two groups of somatosensory afferents?
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Small fibers (C and Aδ) and Large Fibers (Aβ)
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What are small somatosensory afferents (C and Aδ)? Are they myelinated? What is their conduction speeds?
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They are called C and Aδ, they have mostly free endings. C fibers are unmyelinated and and conduct spikes up to 2 m/s. Aδ are thicker than C, are myelinated and conduct up to 35 m/s.
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What are large somatosensory afferents? (Aβ)
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They end in mechanoreceptors, are myelinated and conduct at speeds up to 75 m/s.
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What are some key features about temperature receptors?
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Some signal warmth and some signal cold. Warm sensors respond maximally at ~45ªC and cold at ~30ºC. They are phasic-tonic, which is why our body can adjust to a hot bath or cold lake. There are hot spots of temperature, touching somewhere in between these hot spots we don’t notice temperature.
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What is paradoxical cold?
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It is when cold receptors briefly respond to temperatures >45ºC.
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How do somatosensory fibers arrive at the CNS?
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Signals from below the chin enters the spinal cord through fiber bundles called the dorsal roots. Signals from the face and head enter the brain via cranial nerve V, the trigeminal.
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How do large somatosensory fibers project to the CNS?
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They turn upwards on reaching the spinal cord, and run ipsilaterally up to the medulla through the dorsal column. In the medulla they will synapse on cells whose axons will cross the midline.
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How do small somatosensory fibers project to the CNS?
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They synapse directly or via interneurons on motoneurons (for reflex responses) or on cells whose axons cross the midline and run up the spinothalamic tract into the brain.
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What somatosensory afferent fiber is part of the epicritic system?
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It is phylogenetically new, the large fibers provide feedback to the brain, especially to the motor cortex as it manipulated objects.
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What somatosensory afferent fiber is part of the protopathic system?
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It is phylogenetically old, the small fibers evoke responses to specific stimuli: withdrwaing from pain or tickling, brushing away a bug, sexual and thermoregulatory responses - all not under conscious control.
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How does lateral inhibition work among somatosensory fibers?
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Detects edges, e.g. when we step into a bath it is hottest right where the rim of the water meets the cool air.
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Where do somatosensory signals arrive in the brain?
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From the spinal cord they must travel via the ventroposterolateral (VPL) nucleus of the thalamus. From the head they must travel via the ventroposteromedial (VPM) nucleus. They are then passed on to the primary somatosensory cortex, S1.
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What is congenital analgesia? What are its consequences?
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It is the inability to feel pain. And so they are susceptible to injury and infection and usually die before age 20.
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What are the two types of pain? How do they differ?
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Fast pain, carried by Aδ fibers, results in quick withdrawal (to get away from the painful thing). And slow pain, carried by C fibers, results in prolonged immobilization (to promote healing).
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What does it mean to say that visceral pain is referred?
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It means that internal organ pain is felt on the body surface (e.g. heart attack is felt in the left arm). This is because visceral and cutaneous fibers converge on the same neuron in the spinal cord.
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What are the receptive fields like for spinothalamic neurons?
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They have centre-surround receptive fields, excited in the center by C fibers signaling damage, inhibited in the surround by A fibers signalling touch. So touch in the surround ‘gates’/cancels pain from the center.
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Where must we stimulate in the brain to stimulate pain? How can we alter pain perception?
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We must stimulate the thalamus, not S1. And pain can be perceived differently due to different cognitive factors. Pain can evoke a response in the somatosensory and temporal cortex, but seeing pain only causes activation in temporal cortex.
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How many taste buds do adult humans have?
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2000 - 8000
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Where are taste buds located on the tongue?
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Mainly on the top of the tongue, but also on the soft palette, epiglottis, and upper esophagus.
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How many taste receptor cells does a human taste bud have? How long do they live?
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They have approximately 50 taste receptor cells, overlapping like petals and they survive for 10 days.
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What are the biological roles for the 5 different kinds of taste receptors?
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sweet receptors detect sugar (for energy). umami receptors detect amino acids (protein). bitter receptors detect poison. salty receptors detect Na+ ions. sour receptors detect H+ ions.
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Why does mint feel cool and pepper feel hot?
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Capsaicin in chili peppers is sensed by oral pain receptors. Mint feels cool because it reacts to the receptor that reacts to cold.
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How many olfactory receptors do we have? Where are they located?
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They lie on the olfactory epithelium at the top of the nasal cavity, In humans, this area covers 10cm(2) with only 10 million receptors [much less than other species].
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How many primary odors are there?
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"There are approximately 400 receptor cells, meaning that there are this many primary odors.
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How sensitive are olfactory receptor cells?
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They are very sensitive and can detect as few as 2 molecules of their preferred chemicals. The only reason dog’s have better smell is because they have more receptors.
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How are olfactory receptor cells pinocytotic?
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They continually sip in fluid and send it along nerves to the brain.
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How long do olfactory receptor cells exist?
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They are short-lived, degenerating after a month or two to be replaced by new ones under it.
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What is the cribriform plate?
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It is the bone at the base of the cranial cavity that olfactory receptors send their axons through into the brain.
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How do olfactory receptor cells connect to the brain?
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Many receptors converge on each bulb neuron, enhances sensitivity but discards spatial information (to decorrelate outputs), it bypasses the thalamus.
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Where does the olfactory bulb project?
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It projects to the limbic system, involved in motivation and emotion. (makes sense since primitive animals, motivation was closely linked to smells to identify food and mate), even though not linked entirely to smell nowadays, still involve din motivation.
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How is olfactory signals processed?
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No idea, individual fibers may be excited by one chemical and inhibited by another that is very similar and smells almost identical. Smells combine to form strange and unexpected combinations of good from bad, none from strong and other.
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What is the vomeronasal organ (VMO) or Jacboson’s Organ?
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In rodents, it is an accessory olfactory structure in the nasal cavity. Involved in behavioural responses to sex pheromones.
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Can humans have echolocation?
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Yes, and they can sense many properties of an object by echolocation including direction, distance, size, shape and material. *NOTE - nearsighted people are better.
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How do we echolocate?
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We sense 2 things: 1. the time delay between our emitting a sound and its echo returning to our ears. and 2. the loudness ratio between the emitted sound and its echo. BUT we also use sound reflections based on the decay rate of sound reflections even when we can’t hear any emitted sound.
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How can we become an optimal estimator from the Bayesian viewpoint? In vision?
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An optimal estimator takes into account the reliability of its data. For vision, the reliability is greater in the fovea and less in the peripherals.
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What multisensory integrative activities activate teh auditory cortex? The visual cortex?
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All of lipreading, silent portrayals of noisy things, sign language…auditory cortex. Visual areas are activated when we search for, or identify, objects by touch.
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What is the dorsal horn?
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It receives sensory input (afferent) on the dorsal part of the spinal cord.
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What is grey matter?
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It is regions of the CNS that contain the neuronal cell bodies.
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What is the ventral zone of the spinal cord?
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It contains motoneurons that send motor commands to the muscle.
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What is the intermediate zone of the spinal cord?
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It integrates sensory input.
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What are simple reflexes?
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Sensory neurons make synapses with spinal cord motoneurons to mediate simple reflexes. This is the simplest form of motor control.
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What are central pattern generators (CPG)?
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They are networks of interneurons in the spinal cord and brainstem that coordinate the interaction of many different motor groups (locomotion, respiration)
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What are complex/volitional movements?
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They are motor outputs that are planned and refined by the motor cortex, basal ganglia, and cerebellum.
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What is the basic pathway of a reflex?
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It is helpful to regulate a particular variable via feedback to a higher centre of control - by bending back the sensory stimuli within the CNS to produce a response.
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What is a monosynaptic reflex?
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It is when the afferent (receptor) neuron synapses directly with the efferent (motor) neuron.
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What is a polysynaptic reflex?
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This means that there are more than one synapses, often accomodated by an interneuron, and processed in the CNS.
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Can we control the stretch reflex?
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No, it operates at the subconscious level.
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What is the stimulus for the stretch reflex?
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Passive stretch of a muscle by applied load or contraction of antagonist muscle. The sensory organ found deep inside muscle will sense the stretching.
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What is the reponse for the stretch reflex?
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The active contraction of muscle (e.g. patellar tendon reflex)
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How quick is the stretch reflex? What neurons is it carried by?
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It is very sensitive and fast due to muscle spindle afferents of the Group 1A type. It is the fastest group of afferent neurons to carry info to the spinal cord. It is also very fast because it involved a monosynaptic pathway, directly connecting to the motoneuron. Takes about 25ms from forearm and 37ms from ankle
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What is white matter?
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They are regions of the CNS that contain the axonal tracts of neurons.
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What is the stretch reflex?
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You stretch it, it will contract. When we place a load on the hand, it will activate muscle spindles and activate the motoneuron which contracts the same muscle that was stretched.
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What is the stretch reflex essential for? Where?
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It is essential for stabilizing posture, hence it is strongest in postural muscles (aka extensor muscles) that keep us upright in the face of gravity.
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What pathway does the stretch reflex take?
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Aside from a monosynaptic pathway it can take a parallel multisynaptic pathway through the spinal cord and a transcortical path. Both use interneurons. In the transcortical path, the afferent neuron enters the dorsal horn where the afferents will branch and some will travel medially up to S1 and synapse on adjacent motor cortex.
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What is the stimulus for the Golgi tendon reflex?
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Active tension in muscle, sensed by the Golgi tendon organ.
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What is the ultimate response of the Golgi tendon reflex?
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The relaxation or reduction of tension.
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How quick is the Golgi tendon reflex? What afferents does it use? What type of pathway?
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Golgi tendon organ (GTO) afferents are of teh 1B type (which are slower than 1A). 1B neurons inhibit α-neurons of the same muscle. 1B neurons synapse on interneurons in the intermediate zone of the spinal cord.
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What is the Golgi tendon reflex?
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You contract, it will relax. The over-exertion of a muscle will activate the GTO, which will synapse onto interneurons that will inhibit the motor neurons that it came from and reduce contraction. Useful because if there is an excessive load we drop it to save the muscle.
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How are the Golgi tendon reflex and the Stretch reflex complementary?
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If during the maintenance of posture we over contract the muscle, then the GTO will be activated and relax. So that the stretch reflex does not over-act.
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When is the golgi tendon reflex suppressed?
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When net motion is required.
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What is the stimuli for the flexion withdrawal reflex?
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noxious injury of limb
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What is the response of the flexion withdrawal reflex?
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the flexion of joints proximal to stimulus (extension distal to stimulus). This is to remove the limb from the dangerous area. It is protective. There is also distal extension away from the dangerous area.
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How quick is the flexion withdrawal reflex? What afferents does it use? What type of pathway?
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It is slow because it uses polysynaptic pathways. Also uses Aδ and C nociceptor afferents which are very slow, and they synapse on interneurons in the superficial dorsal horn.
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What is the flexion withdrawal reflex?
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You touch a hot stove, flex your arm. E.g. holding a glass and then reach hand over a hot candle. This will activate the pain receptors in the forearm and flexion of the biceps but the extension of the hand to release the glass.
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What is reciprocal inhibition?
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It is the activation of one motor nucleus coupled to inhibition of antagonistic motor nuclei. E.g. the activation of flexor motor neurons elicits inhibition of antagonistic extensors (of the same muscle).
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What is co-contraction?
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When antagonistic motor neurons are activated. This causes the joint to become very stiff.
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What is the patellar tendon reflex?
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You bang your knee, you kick. We tap on the patellar tendon which stretches the quads and causes the contraction of the quads. We simultaneously inhibit contraction of the hamstrings.
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What is the cross extension reflex?
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You step on something sharp, flex your leg where there is pain and extend the other leg. This is a form of full-fledged flexion withdrawal reflex, since it involves contralateral extension for increased postural support (in legs).
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What are commissural interneurons?
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They carry the signal to the contralateral spinal cord (across te midline)
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What is the stimuli for the extensor thrust reflex?
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Pressure on sole of foot (innocuous - not painful)
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What is the response for the extensor thrust reflex?
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Activation of leg extensors.
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What is the extensor thrust reflex?
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Pressure is sensed on the sole of the foot. This activates Aβ mechanoreceptors which are pretty fast and project to intermediate zone interneurons that synapse on extensor motoneurons. ONLY exists when we are standing and there is a need.
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What is the Babinski sign?
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It is a way to test if the corticospinal tract is damaged, and is based off of the extensor thrust reflex. This is because this reflex is influenced by the corticospinal tract. Normally, toes will point downwards but if there is damage then the reflex is switched to flexion withdrawal.
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What is the stimulus for the vestibule-spinal reflex?
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It is the downward deviation of head on one side -> which activates the otolith (ear-stone) afferents.
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What is the response for the vestibulo-spinal reflex?
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‘downhill’ limbs extend
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What is the vestibulo-spinal reflex?
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You tilt your head, you extend leg where there is tilt. The ear-stone/otolith afferents activate the lateral vestibulo-spinal tract, which leads to ipsilateral projection to extensors of motor nuclei.
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How quick is the vestibulo-spinal reflex?
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It takes about 80 ms to reach the legs.
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What is the stimulus for the vestibular-ocular reflex?
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head angular rotation, excites semicircular canals (rightward rotation excites right horizontal canal afferents)
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What is the response for the the vestibular-ocular reflex?
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eye movement in the opposite angular velocity to head rotation.
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What is the vestibulo-ocular reflex?
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You shake your head, keep eyes focused. Eye saccade occurs first when tracking something or someone since this is easier than moving head. As soon as eye foveates target, VOR is locked on and so as we move our head we can keep our gaze on target.
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Why do we need CPGs and not just simple reflexes?
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This is because reflexes cannot perform complex patterns, e.g. they are not able to recover posture after a perturbation. Things like posture and movement are programmed by CPGs, or fuctional networks of neurons.
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Where are CPGs located? What are they important for?
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Principally in the spinal cord and brainstem, activated in order of relevance and very important in behavioural responses. Primarily important in locomotion and motor control.
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What is the leg step cycle?
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The step cycle of each leg during walking is programmed by a network of neurons within the intermediate zone of the lumbar cord.
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What are the properties of a CPG network?
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1. Pacemaker neurons, diffuse excitation, 2. Reciprocal inhibition, 3. Phase-dependent reflexes.
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What is the half-center structure of the CPG?
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Divided into 2 half-centers: 1. Flexor burst generator drives flexor motor nuclei, 2. Extensor burst generator drives extensors. They mutually inhibit one another and both are spontaneously active when not inhibited.
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What is the flexor burst generator?
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It is the flexion phase of swing that has a fixed duration, regardless of speed of locomotion. It has a build-up of inhibition that eventually stops the burst of AP (STOPS the flexor motoneurons). Reciprocal inhibition of extensor burst network ceases, meaning that the extensor network can become active.
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What is the stance phase of the leg step cycle?
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It has a variable duration, depending on speed and is regulated by sensory feedback. Has phase-dependent reflexes (Stretch reflex, Golgi tendon reflex, Extensor thrust reflex).
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What informs the CPG to proceed from the step phase and begin the next swing phase?
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Sensory cues, it is essential to match muscle contraction to loading conditions on the leg and so reflexes provide automatic adjustment of extensor contraction to load experienced.
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How do we transition to Leg Swing from stance phase?
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E3 phase stops (and stops inhibiting the flexor burst generator) ONLY WHEN 1. the leg is not bearing weight, 2. the hip is extended, 3. the opposite leg isin stance (bearing weight). There are projections that cross and provide correct phase-linking of CPGs on each side of the body.
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What programs arm swings during locomotion? How is it synchronized?
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CPGs in cervical cord program motion of arms during walking. Flexion phase synchronous with contra-lateral flexion in leg: diagonal pattern to cancel torque on trunk. Phase-linking via propriospinal tracts (from one segment of cord to another).
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How do bipeds maintain stability on top of moving legs?
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We must produce postural compensations in trunk and head. This requires postural CPGs in reticular formation to coordinate upper body motion with spinal step cycles. Hence, spinally injured patients cannot walk without trunk support.
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How is head angle maintained during walking.
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There are combinations of visual, vestibular and propioceptive reflexes.
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What three sensory sources do we rely on to maintain posture?
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1. somatosensory; especially proprioceptive, 2. vestibular; gravitational reference, 3. visual: slower system, but important vertical cues, and motion cues.
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Where is postural maintenance organized in the brain?
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in the reticular formation of pons and medulla.
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Where is eye-head coordination programmed in the brain? How does it accomplish this?
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In the superior colliculus. It computes how much and in what direction gaze must be shifted to ‘foveate’ target. And, it sends the same motor signal to extraocular and neck motor centers. (VOR)
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What is the red nucleus?
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It is located in the midbrain. Rubrospinal cells within the red nucleus activate localized synergies, especially in distal limbs and in the face (e.g. gripping and twisting movements of hands).
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What is synergy?
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A group of muscles contracting together for a specific purpose. The ones organized by the reticulospinal tract are very widespread for generating support postures. The ones from the rubrospinal tract are highly localized
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Where do the descending axons project from the motor cortex?
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Mostly to the spinal cord interneurons (through corticospinal tract). But there are direct corticospinal synapses on motoneurons to distal limb and speech motor nuclei.
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What are the different tracts of the motor cortex as it travels through the brain stem?
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Most corticospinal pathways cross the midline at the pyramids of the brainstem (under medulla), this tract is called the lateral corticospinal tract. The fibers that did not cross project ipsilaterally and is called the anterior corticospinal tract.
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In the motor cortex, where/how are single motor nuclei (muscles) represented?
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They have multiple representations at many different loci (apart from eachother). Each muscle column is in a different group of columns. Each cortical locus represents a different synergy; muscles which participate in most synergies have the biggest representation.
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How do cortical loci represent motor neurons?
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E.g. a neuron has a direct synaptic connection with the thumb motor neurons. And when we perform a precision grip, the cortical representation is very active. However, when we perform a power grip the cortical representation is not very active.
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What is the motor field?
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It is how one corticospinal axon synapses with a set of motor nuclei in more than one spinal segment. However, many synapses are silent. But the existence of a motor field provides potential for plasticity.
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How do somatosensory inputs relay to the motor cortex?
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They are propriocetpive inputs that input directly from the thalamus or from the somatic association cortex. Or they can be cutaneous input which comes from the somatic association areas which are related to postural and motion information.
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What is a transcortical stretch reflex?
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It is the same as the spinal stretch reflex but takes longer (60 ms from forearm). It is much more versatile and modifiable. And it can be used to trigger contractions in other muscles to synchronize action at several joints.
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What is the transcortical proprioceptiv reflex?
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It coordinates motion, when these afferents are lost, the individual cannot synchronize reversals of motion at elbow and shoulder. Hence, arm trajectories are arbitrary and inconsistent.
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What is the grasp reflex?
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It is the trancortical cutaneous reflex. The slippage of objects in fingers activates mechanoreceptors, the direction of slip is computed in somatosensory association areas, and increased finger tension is triggered.
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What are the premotor areas?
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They are a set of regions projecting into the motor cortex (but also have parallel routes to motor nuclei). They select motor cortical synergies into proper sequence for a given movement. This happens from well learned, highly evolved movements.
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What does the premotor cortex do?
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It processes sensory inputs, especially visual and auditory for cueing movement phases. (e.g. dorsal visual stream to dorsal half [spatial location], ventral vision to ventral half [object form -> shape hand])
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What are sensorimotor cues?
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They are environmental cues that trigger motor reactions (e.g. button). Sensory association areas recognize the cues and forward the signal to the frontal lobe (prefrontal and premotor cortex). The premotor cortex selects appropriate response synergies in the motor cortex.
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What is a visuomotor response?
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It is a coordinated set of activities and cues to initiate synergies. E.g. when approaching doorknob we shape our hand to fit it.
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What is preparatory activity?
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This refers to when premotor neurons set up the motor cortex. Hence, they often are not active during performance. They are typically active during preparatory phases of movement: by facilitating appropriate synergies in the motor cortex.
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What is the supplementary motor area? Where is it located?
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It is on the medial wall of the hemisphere; with a somatotopic representation of the body, but less detail than the motor cortex. It controls bilateral coordination of limbs when different motions are done on each side. Processes internal ‘volitional’ signals that drive movement.
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What is the cingulate motor area?
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It is located within the cingulate sulcus. It is a gross somatotopic representation of the body. It processes emotional, and motivational drive to movements. The limbic/motor center is important in many epileptic seizures.
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What does the ANS control?
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internal organs, blood flow, smooth muscles of the eye, viscera etc.
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What is the preganglionic component of the ANS?
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The preganglionic neuron cell bodies are located in the CNS, either in the brainstem or the spinal cord. They project to postganglionic neurons located between the CNS and the target tissue. In both the parasympathetic and sympathetic systems, they use ACh as their neurotransmitter and the postganglionic cell has nicotinic receptors.
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What is the postganglionic component of the ANS?
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ACh from the preganglionic neuron binds to their nicotinic receptors, and this stimulates an AP. Most postganglionic sympathetic secrete norepinephrine onto andrenergic receptors. Most postganglionic parasympathetic secrete ACh onto muscarinic receptors.
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Where do preganglionic neurons originate in the sympathetic ANS?
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In the thoracolumbar spinal cord.
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How does the sympathetic ANS relay information? (long/short ??)
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Short preganglionic neurons synapse onto the sympathetic chain. Then long postganglionic neurons project from the chain to effector organs.
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Where do parasympathetic preganglionic neurons originate?
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in the brainstem or sacral spinal cord.
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How does the parasympathetic ANS relay information?
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Long preganglionic neurons synapse onto ganglia near effector organ. Short postganglionic neurons from ganglia to effector neurons. Hence, it doesn’t need a chain like the sympathetic ANS since it is already very close to the target tissue.
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Where do sympathetic efferents emerge from (specifically)?
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intermedio-lateral horn of the thoracic cord.
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What is the only exception where ACh is the neurotransmitter of the postganglionic neuron in the sympathetic system?
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ACh is the neurotransmitter to the sweat glands of the skin.
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What are sympathetic activities?
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Fight-or-flight response, prepare for emergency or stress and exercise, increase heart rate and blood pressure, mobilize energy stores, pupillary dilation, decrease gastrointestinal and urinary function, release epinephrine.
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How is epinephrine released?
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Preganglionic sympathetic neuron synapses on chromaffin cells (modified postganglionic neuron) which releases epinephrine into the blood stream. IN ADRENAL MEDULLA.
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Where do parasympathetic efferents originate (specifically)?
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In cranial motor nuclei (III, VII, IX and X-vagus) and intermediolateral part of sacral cord.
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What is the exception that ACh is the neurotransmitter in the PNS?
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NO is the neurotransmitter in penile erection
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What are some parasympathetic activities?
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quiet, relaxed states, active in rest and digest, increase gastrointestinal activity, decrease heart rate and blood pressure.
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What are duel innervations of the ANS?
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At rest there is tonic activity of the PNS and SNS. PNS dominates. They are actual complementary systems. Sympathetic: cardiac output increased, skin vasoconstriction, sweating, piloerection, blood diverted from gut and skin to muscle. Parasympathetic: digestion promoted, cardiac output reduced, slow breathing, urination.
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What is a neuroeffector junction?
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In place of a synapse the ANS forms neuroeffector junctions between the postganglionic neuron and its target cells.
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What are varicosities?
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They are the replacement of terminal boutons in the ANS. There is axon swelling, contains vesicles filled with neurotransmitters.
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What type of reflexes are part of the autonomic system?
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It is linked to the sensory system to produce functional reflexes (that are critical for homeostasis), they are involved in negative feedback loops.
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What is the pupillary light reflex?
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Involves ON and OFF afferents that activate to luminance and darkness detectors, respectively. When it is too bright there is a parasympathetic reflex via the 3rd cranial nerve to ciliary ganglion and circular iris muscles (short and fast). When it is too dark there is a sympathetic reflex via the thoracic cord, sympathetic chain to radial muscles (long and slow)
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Where is the pupillary light reflex organized?
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in the pretectal area of the midbrain.
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What is the ON pathway in the pupillary light reflex?
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In the ANS, detectors sense luminance and activate a parasympathetic reflex via the 3rd cranial nerve to ciliary ganglion and circular iris muscles. This is short and fast.
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What is the OFF pathway in the pupillary light reflex?
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In the ANS, darkness detectors activate a sympathetic reflex via the thoracic cord which activates a sympathetic chain to the radial muscles. This is long and slow.
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What is melanopsin?
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It is a light-absorbing pigment (chromophore) that retinal ganglion cells have.
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Where is the baroreflex organized?
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In the cardiovascular centre, the ventrolateral medulla (Rostral and Caudal VLM)
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What does the Rostral half of the VLM accomplish?
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It excites sympathetic efferents which ultimately raises BP and HR.
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What does the Caudal half of the VLM accomplish?
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It inhibits the Rostral half which ultimately drops BP.
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What is the baroreflex?
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Baroreceptors sense change in pressure if too low, which relays its information to the nucleus solitary tract (NTS) which inhibits the caudal half of the VLM. This has the effect of uninhibiting the Rostral half of the VLM and increasing sympathetic output.
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What are some sympathetic effects on muscle?
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It influences norepinephrine vasoconstriction, and is tonically active to maintain blood pressure. It is extremely important for regulation of BP (baroreflex). And metabolite accumulation during muscle contraction causes vasodilation.
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What are the autonomic control centers?
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The hypothalamus, the pons, and the medulla all work with the ANS to regulate blood pressure, body temperature..etc
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What are the brainstem autonomic centers responsible for?
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They are the cardiovascular centre, and respiratory pattern generators in the lateral medulla and pons. The PAG is a midbrain ‘premotor’ cortex center for autonomic behavioural patterns (flight, fear, feeding, sex)
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What is the PAG? How is it organized?
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It is the Periaqueductal Gray, it is organized into longitudinal columns according to behavioural patterns. And interacts very much with the hypothalamus.
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How does the fight (rage) response work in the PAG?
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The fight (rage) column projects to the cardiovascular center in the medulla, and raphé nuclei release serotonin in the spinal cord. This depolarizes all motoneurons and inhibits pain transmission in the dorsal horn.
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What are the reticular activating systems?
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modulatory, cholinergic, serotonergic, adrenergic, dopaminergic, histaminergic
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What is the modulatory system?
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It causes a global shift in CNS activity, mainly metabotropic mechanisms.
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What is the cholinergic system?
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It determines level of attention, and sleep-wake cycle; mainly ascending.
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What is the serotonergic system?
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In upper nuclei it is for stressful situations, influences mood and the sleep-wake cycle. In lower nuclei, it is involved in pain and locomotion.
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What is the adrenergic system?
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For stressful situations to remain vigilant
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What is the dopaminergic system?
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It is the reward center. It is also involved in motor control.
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What is the histaminergic system?
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For sleep-wake control, supports the waking state.
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Where do the neurons originate in the cholinergic system?
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base of the cerebrum; pons and medulla.
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Where do the neurons terminate in the cholinergic system?
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In the cerebrum, hippocampus and thalamus.
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What is the neurotransmitter used in the cholinergic system?
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ACh
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Where do the neurons originate in the serotonergic system?
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raphé nuclei along brainstem midline
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Where do the neurons terminate in the serotonergic system?
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1. lower nuclei project to spinal cord, 2. upper nuclei project to most of brain
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What is the neurotransmitter in the serotonergic system?
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serotonin
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Where do the neurons originate in the adrenergic/noradrenergic system?
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locus coeruleus of the pons
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Where do the neurons terminate in the adrenergic/noradrenergic system?
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the cerebral cortex, thalamus, hypothalamus, olfactory bulb, cerebellum, midbrain, spinal cord.
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What is the neurotransmitter for the adrenergic/noradrenergic system?
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norepineprhine
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Where do the neurons originate in the dopaminergic system?
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1. substantia nigra in midbrain (for motor control), 2. ventral tegmentum in midbrain (reward)
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Where do the neurons terminate in the dopaminergic system?
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1. cortex (motor control), 2. cortex and parts of the limbic system (reward)
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What is the neurotransmitter in the dopaminergic system?
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dopamine
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Where do the neurons originate in the histaminergic system?
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in the posterior thalamus.
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Where do the neurons terminate in the histaminergic system?
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throughout the forebrain and others.
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What is the neurotransmitter in the histaminergic system?
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histamine
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What does the hypothalamus interact with?
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It interacts with the brainstem motor and autonomic centers via axonal projections. It interacts witht he endocrine system throught he pituitary. Hence, the hypothalamus can coordinate complete physiological response to challenes to internal environment.
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Where does the hypothalamus receive its information?
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1. nucleus of the solitary tract (inputs from visceral sensory information) 2. reticular formation (inputs from spinal cord) 3. retina (light/dark information), 4. limbic and olfactory systems (regulate eating and reproduction), 5. Brainstem PAG
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What nuclei in the hypothalamus project to the posterior pituitary?
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The supraoptic nucleus, it originates in the hypothalamus and terminates in the posterior pituitary and releases hormones such as ADH.
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What nucleus in the hypothalamus projects to the anterior pituitary?
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The paraventricular nuclei release a hormone intermediary from the hypothalamus into a portal capillary system leading to the anterior pituitary.
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Where are the thermoreceptors located that stimulate the hypothalamus?
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They are located at the base of the hypothalamus, hence temperature regulation is based on internal temperature rather than external.
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What occurs when when thermoregulators determine that we are too cold?
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Skin vasoconstriction, piloerection, decreased cardiac output (parasympathetic), shivering via posterior thalamus (sympathetic)
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What occurs when the thermoregulators determine that we’re too hot?
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skin vasodilation, sweating, increased cardiac output (sympathetic), ADH release via anterior hypothalamus
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What is the warm-sensitive neurons located in the hypothalamus? When are they activate? inhibited?
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They are located in the anterior hypothalamus, primarily in the preoptic area. They are activated when there is an increase in body temperature. They are inhibited when there is a decrease in body temperature (so they won’t act to decrease it even further)
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Where is the cold-sensitive neurons located in the hypothalamus? When are they activate? inhibited?
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They are located in the posterior hypothalamus, primarily in the dorsomedial nucleus. They are active when there is a decrease in body temperature, and they act to prevent heat loss. They are inhibited when there is an increase in body temperature (so as not to increase temp too high)
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What is the control center for the regulation of feeding in the hypothalamus?
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The arcuate nucleus control. Neuro-peptide Y neurons drive feeding and melanocortin neurons suppress feeding.
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What acts as glucoreceptors for the regulation of feeding? What do they do?
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neurons in the ventromedial and arcuate nucleus. They discharge in relation to ambient glucose levels and inhibit NPY mediated drive to eat while simultaneously activating melanocortin neurons.
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What does leptin do?
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It is secreted by adipose tissue, and provide long-term suppression of feeding by inhibiting NPY containing neurons within the arcuate nucleus, also activates melanocortin neurons.
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How is feeding regulated by hormones and vagal feedback?
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Ghrelin from an empty stomach promotes feeding, Leptin from liver and PYY from intestine and insulin from pancreas inhibit feeding. Molecules like CCK, OEA, GLP-1 secreted by the duodenum active vagal afferent to inhibit feeding.
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Why does nicotine give a sense of satiety?
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Melanocortin neurons contain nicotinic receptors and so when we intake nicotine it activates the satiety pathway.
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What is the paraventricular nucleus involved in?
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Functions like feeding, metabolic balance, BP, HR, and sexual behavior including erectile function.
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How does an erection happen?
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There is activation of the parasympathetic nerve, which releases NO and relaxes smooth muscle. This allows the sinusoids in the penis to shrink, and increases space for blood flow. The increased blood flow leads to an erection.
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How are gaseous transmitters released?
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They are not able to be stored in vesicles since they diffuse, so synthesis is triggered like for steroid hormones. Calcium influx into pre-synaptic terminal and synthesis begins. Examples include NO, CO and H2S (all are volatile gases)
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What is the pathway for NO to vasodilation?
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Calcium influx and forms a Ca+/CaM complex which activates NO synthase. It convert L-arganine to NO which diffuses out of the membrane to activate guanylyl cyclase to convert GTP to cGMP and resulting cascade leads to vasodilation.
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Why does prolonged psycho-social stress lead to deleterious effects on health?
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Due to excessive stimulation of hippocampal neurons and consequent neuronal degeneration and conversion of negative to positive feedback loop via the hippocampus.
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Where does the amygdala usually project?
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It outputs inhibitory neurons to the PAG and the hypothalamus.
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What part of the visual light spectrum does melanopsin react to?
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Blue-Green but not red
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Where do retinal projections involved in circadian rhythms go?
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1. suprachiasmatic nucleus, 2. pretectal area -> sympathetic efferent -> superior cervical ganglion -> pineal body
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What is the suprachiasmatic nucleus?
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It is the master regulator of rhythms. Sits on top of the optic chasm (which carries information from the retina), and all it looks for is if there is green-blue light or not. It is a paired structure on either side of the 3rd ventricle. It has highest activity during the day and lowest activity at night. It projects to all autonomic regions of the brain.
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What is the pineal body responsible for?
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It sits in the middle of the brain, its a gland and is only important for releasing melatonin.
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What sorts of thicks are modulated by circadian rhythms?
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hormone synthesis and secretion, body temperature, autonomic behaviors (e.g. feeding), mood, alertness, sleep-wake cycle.
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What type of activity is responsible for the oscillations of a circadian rhythm?
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Based on gene transcription and translation: gene and protein product interactions form a negative feedback loop.
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What sort of biological clocks do our bodies have?
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The suprachiasmatic nucleus, the liver and the kidney. The suprachiasmatic nucleus is the only clock, however, that receives light information from outside and so keeps the other clocks in sync.
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What is the SCN modulated by?
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retinal input, pineal input (e.g. based on the seasons), reticular activating systems (serotonin)
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When is the pineal body activated?
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It is activated by the sympathetic system in darkness (pupillary light reflex).
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What is melatonin?
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It is a neurohormone that is secreted by the pineal body (blocked by even small amounts of blue-green light). It is involved in sleep-induction and maximal secretion occurs at 2 am. There are seasonal variations.
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Where is the pineal gland located?
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It sits on top of the thalamus and 3rd ventricle, surrounded by CSF and blood vessels. Hence it can secrete melatonin into CSF and blood.
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What are the two centers for the sleep-wake cycles?
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1. sleep switch, 2. waking switch.
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What is the sleep switch? Where is it located?
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It is located in the ventrolateral preoptic nucleus of the anterior hypothalamus: activated by 1) circadian clock, 2) sleep debt (decreased brain glycogen and increased adenosine). It inhibits the brainstem activating systems.
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What is the waking switch, where is it located?
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It is in the tubermamillary nucleus, part of the histamine activating system. It is excitatory to brainstem activating systems. in posterior hypothalamus.
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What are the orexinergic neurons?
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They are located in the dorsal hypothalamus, and are the primary response from the SCN. They activate the TMN. It secretes orexin (hypocretin)
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What is orexin (hypocretin)?
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It stabilizes the waking state in relation to the circadian cycle. Lesions will results in narcolepsy, it also provides a circadian drive for feeding (via paraventricular nucleus).
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What are the stages of sleep?
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REM sleep (same as awake), Light sleep (stages 1 and 2), Deep sleep (stages 3 and 4, ‘slow wave’),
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What is the ultradian cycle?
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We alternate between different stages of sleep, or levels of alertness throughout the day. Cycles are 90 minutes. It is not controlled by the SCN.
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What is sleep atonia? How is it caused?
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Large reticulospinal and corticospinal tract neurons are very active in REM sleep, but no body movement just eye movement (REM). In other words, sleep paralysis. This is because spinal motoneurons all become hyperpolarized up to 10mV by inhibitory reticulospinal system from the pons.
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What does explicit memories required to be consolidated in the hippocampus?
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REM and slow wave sleep
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Explain the hierarchy of zones in the hippocampus.
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As we move closer inside the hippocampus we have memories for more complete/individual objects compared to the surface which are very general. We have memories for individual objects in the perirhinal cortex.
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What is LTP?
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It is a synaptic mechanism of memory formation. It is the facilitation of synaptic connections, to do this we need a high frequency of stimulation (lots of AP being fired within a short time). After LTP there will be a greter effect of stimulation from the response, the EPSP is greater. but this effect will not persist. It will last for up to a week then it will revert to normal stimulation. Occurs in all of the amygdala, hippocampus and sensory systems.
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At the cellular level, how is LTP mediated?
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It is mediated by a special glutamate receptor called NMDA. This receptor opens calcium channels. BUT the receptor must be depolarized before it will open a channel for calcium diffusion. In other word, the receptor will only open when bound to glutamate and the membrane is already depolarized. If it sits at the resting membrane potential then it is bound to Mg and will not allow Ca to go through.
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What is the cellular mechanism of LTP?
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Influx of calcium ions activate enzymes. Phosphorylation of membrane proteins enhance ionotropic EPSPs. The generation of retrograde transmitters (e.g. NO) travel to presynaptic terminal to increase vesicle release probability. This triggers transcription/translation and creates more postsynaptic receptors.
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What are the three types of muscle?
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skeletal muscle, smooth muscle, cardiac muscle
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What is skeletal muscle activated by?
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The somatic nervous system
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What is a motor unit composed of?
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A motor neuron + associated muscle fibers
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What is the neuro-muscular junction?
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It is the synapse between a motor neuron and a muscle finer (motor neuron’s axon terminal, muscle fiber). Chemical signalling occurs here.
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What is skeletal muscle?
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It is contractile filaments in sarcomeres; striated. And it has a well developed sarcoplasmic reticulum (best out of three types of muscle).
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What is the sarcoplasmic reticulum?
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It is an intracellular organelle specialized for the storage of calcium.
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What is a muscle fascicle? And what do groups of them make?
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It is a bundle of fibers, that when grouped make skeletal muscle.
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How long do muscles extend?
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They extend the length of the muscle from tendon to tendon.
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What are T-tubules?
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They are within skeletal muscle fibers. They are invaginations of the sarcolemma that run deep inside the muscle fibers. The T-tubule system allows for the spread of AP that normally occurs at the membrane (or else would be trapped at the border).
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How are motor units organized? What about muscle?
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There are three categories of motor unit: slow twitch-oxidative, fast twitch-oxidative and fast twitch-glycolytic. The muscle fiber of a motor unit are of only one type BUT the entire muscle contains a combination of different motor units.
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What does smootness and precision of movement depend on (RE: motor units)?
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The number and timing of motor units that are activated.
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In regards to diameter, what do the relative sizes of motor neurons innervate?
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Small diameter motor neurons innervate slow oxidative fibres. Large diameter motor neurons innervate fast glycolytic fibres. Small diameter motor neurons are more easily excited than are large diameter motor neurons.
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What is the motor end plate?
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It is a specialized muscle membrane at the neuro-muscular junction.
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What neurotransmitter is used at the NMJ?
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ACh
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Are synapses excitatory, inhibitory, or both at the NMJ?
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They are excitatory.
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What is the process of communication at the NMJ?
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1. AP arrives at terminal bouton of motor neuron. 2. voltage-gated calcium channels open, 3. calcium influx triggers release of ACh, 4. ACh diffuses across cleft and binds to nicotinic receptors on motor end plate. 5. ACh binding triggers opening of channels for small cations (Na and K - ionotropic), 6. Net movement of positive charge in depolarizes the membrane, 7. Causes AP in muscle cell, 8. AP spreads through muscle causing contraction.
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What are the three types of toxins that can block the NMJ?
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1. nicotinic receptor blocker, 2. exocytosis blocker, 3. ACh-esterase inhibitor
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How do nicotinic receptor blockers poison the NMJ? What are examples of this toxin?
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It prevents binding of ACh to the motor end plate. Thus preventing the creation of an AP. Examples include curare and curariform drugs used as muscle relaxants.
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How do exocytosis blockers poison the NMJ? What is an example?
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It works to prevent the release of neurotransmitters (ACh). If terminal boutons do not release ACh then there is no response from the muscle. An example can include botox.
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How does ACh-esterase inhibition poison the NMJ? What is an example?
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ACh-esterase breaks down ACh. Hence if it is inhibited, then ACh is still present and will continue to depolarize the cell. This is bad because once the cell reaches a peak of depolarization the Na channel becomes inactivated until after-hyperpolarization. Hence the muscles will become paralyzed. Examples include nerve-gases and pesticides.
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What is a myofibril?
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It is composed of a thick filament and a thin filament. Actin makes up the general structure of the thin filament. Myosin makes up the general structure of the thick filament.
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What is a sarcomere?
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It is a single unit of the myofibril
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What is the thick myofilament composed of?
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It is composed primarily of myosin. There are myosin heads which are binding sites of ATP and ATPase. It is this part that performs the power stroke with the energy provided by ATP (given off by ATPase).
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What is the thin myofilament composed of?
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It is primarily composed of two polymerized actin strands. But also has tropomyosin and troponin bound to it. Each actin site has a binding site for myosin, but it does not appear until Ca is bound to troponin.
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What happens when there is no calcium present on the thin myofibrils?
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In this situation troponin holds tropomyosin over myosin binding sites on actin. This means that no crossbridges may form between actin and myosin. The muscle is relaxed.
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What happens when there is calcium bound to the thin myofibril?
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The calcium will bind to troponin, and will cause movement of troponin that will move tropomyosin and expose binding sites for myosin on actin. Crossbridges may form between actin and myosin, and muscle is able to contract.
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What is the crossbridge cycle?
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1. ATP binds to myosin so it can release actin, 2. Myosin hydrolyzes ATP. Energy from ATP releases the myosin head to the cocked position. Myosin binds weakly to actin, 3. Ca2+ signal arrives and Myosin binds strongly to actin, the power stroke can begin, 4. Myosin releases ADP at the end of the power stroke.
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What is excitation-contraction coupling?
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It is a sequence of events whereby an action potential in the sarcolemma causes contraction. It is dependent on neural input from the motor neuron. And requires calcium release.
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How do we terminate contraction?
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To accomplish this we need to remove calcium from its binding site. To do this we use Ca2+ ATPase in sarcoplasmic reticulum which transports calcium from cytosol to sarcoplasmic reticulum.
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What is twitch contraction?
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It is a muscle twitch or a single contraction-relaxation cycle. Rise-time and duration of twitch force varies with muscle fiber type (e.g. fast glycolytic fibers have a rise-time of about 50ms, and duration of about 120ms). To generate force we need many twitches working together.
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What is summation?
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It is when the interval time is not sufficient to relax completely between two stimuli, and this results in a more forceful contraction.
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What is tetanus?
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It is a state of maximal contraction, caused by stimulation of the muscle fiber repeatedly at short intervals.
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What is incomplete, or unfused, tetanus?
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It occurs when the stimulation rate of the muscle fiber is not at a maximum value, and consequently the fiber releaxes slightly between stimuli.
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What is complete, fused, tetanus?
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It occurs when the stimulation rate is fast enough that the muscle fiber does not have time to relax. Instead it reaches maximum tension and remains there.
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Where is smooth muscle found?
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in internal organs and blood vessels such as GI tracts, urinary, reproductive, respiratory.
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Can we control smooth muscle?
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No it is under involuntary control by ANS
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Compare smooth muscle contraction rate and organization to skeletal muscle?
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It is not organized into sarcomeres, it must operate over a range of lengths and its layers may run in several directions. This allows it to contract and relax more slowly, so it uses less energy and can sustain contractions for a longer period of time.
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How do we classify smooth muscle?
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1. by location (e.g. vascular, gastrointestinal, urinary, respiratory, reproductive, ocular), 2. by communication with neighbouring cells (single-unit smooth muscle/visceral smooth muscle or multi-unit smooth muscle)
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What do singleu-units smooth muscle/visceral form?How is single-unit smooth muscle organized?
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The fibers are connected to one another by gap junctions. An electrical signal in one cell is spread rapidly through the entire sheet of tissue to create a coordinated contraction. It is called visceral muscle because it forms the walls of internal organs such as the intestinal tract.
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Where is multi-unit smooth muscle found? How is it organized?
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It is foundin the iris, ciliary body of the eye, male reproductive tract, uterus (prior to labor). These cells are not linked together and so must be stimulated independently to contract, Hence each individual muscle cell is closely associated with an axon terminal or varicosity. Hence we can finely control which muscles will be activated.
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How does excitation-contraction coupling occur in smooth muscle?
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1. Calcium channels open in the plasma membrane, 2. Calcium influx triggers release of calcium from sarcoplasmic reticulum, 3. Calcium binds to CaM, 4. Ca++/CaM activates MLCK, 5. MLCK phosphorylates myosin, 6. Crossbridge cycling occurs.
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How is smooth muscle able to relax?
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Phosphatase removes phosphate from myosin. Calcium removed from cytoplasm by Ca-ATPase and Ca-Na counter transport.
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How is cardiac muscle organized? Where is it found?
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It is found in contractile cells and conductile cells. There are contractile filaments organized into striated sarcomeres. And they have intermediate development of SR. There are gap junctions between cells for synchrony.
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What nervous system is cardiac muscle organized by?
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the ANS
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What is the AP duration in ventricles?
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300ms
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Why can cardiac muscle have a very forceful and long contraction (300ms) from a single AP?
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This is because the AP plateaus due to slow Ca++ channels, and gives it enough time.
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How can we increase the force of cardiac muscle contraction?
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We can increase force of contraction by increasing muscle length, this will increase the amount of blood coming in which increases the amount of blood going out (Frank-Starling Law). WE CANNOT, increase force of contraction by recruiting more motor units or enhancing excitation-contraction coupling or by increasing stimulation frequency to tetanus.
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