Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
73 Cards in this Set
- Front
- Back
|
What functions are served by each of the 3 branches of the visual pathway?
|
1) The branch to the superior colliculus provides info for visually guided eye movements
2) The branch to the pretectum provides information for pupillary reflexes 3) The branch to the LGN relays information to the visual cortex and processes that information for perception |
|
|
Which neurons in the LGN receive synaptic contact from M ganglion neuron axons?
|
The two ventral layers (the magnocellular layers)
|
|
|
Which neurons in the LGN receive synaptic contact from P ganglion neuron axons?
|
The four dorsal layers (the parvocellular layers)
|
|
|
How do the receptive fields of ganglion neurons in the retina compare to the receptive fields of neurons in the LGN?
|
The receptive fields of LGN neurons are concentric, like ganglion receptive fields, and are of similar size. This is because each geniculate neuron receives its main retinal input from only a few ganglion cells.
|
|
|
What is color contrast?
|
The difference between colors of similar brightness.
|
|
|
What is luminance contrast?
|
The difference between the brightest and darkest parts of an image
|
|
|
What is spatial frequency?
|
The number of repetitions of a pattern over a given distance.
|
|
|
What is temporal frequency?
|
How rapidly a pattern changes over time.
|
|
|
Compare and contrast the ability of the P and M pathways to detect the qualities of color contrast, luminance contrast, spatial frequency, and temporal frequency.
|
P pathways are important for color vision, high spatial frequency, and low temporal resolution vision.
M pathways are important for low spatial and high temporal vision. |
|
|
Describe the flow of information into the visual cortex for all 3 visual pathways.
|
From the thalamus:
1) Magnocellular pathways project to spiny stellate cells in the 4Calpha layer 2) Parvocellular pathways project to spiny stellate cells in the 4Cbeta layers 3) Intralaminar zones project to layers 3 and 2 (blob regions) |
|
|
Describe the flow of information within the visual cortex.
|
1) Pyramidal axons from layers 3 and 2 project to layer 5 pyramidal cells.
2) Pyramidal cells in layer 5 have axon collaterals that project back up to layers 3 and 2, and axons that project to layer 6. 3) Layer 6 pyramidal cells project to layer 4C smooth stellate cells. |
|
|
Describe the outflow of information from the visual cortex.
|
The outflow of the visual cortex originates from each layer, except for 4C.
1) Layers 2,3, and 4B project to other (extrastriate) visual cortical areas. 2) Layer 5 projects to the superior colliculus, pons, and pulvinar. 3) Layer 6 projects back to the LGN and also to the claustrum. |
|
|
What is the principle neurotransmitter of pyramidal neurons? Is it excitatory or inhibitory?
|
Glutamate or Aspartate - excitatory
|
|
|
What is the principle neurotransmitter of the spiny stellate neurons? Is it excitatory or inhibitory?
|
Glutamate or Aspartate - excitatory
|
|
|
What is the principle neurotransmitter of the smooth stellate neurons? Is it excitatory or inhibitory?
|
GABA - inhibitory
|
|
|
What are the two types of pyramidal neurons in the visual cortex?
|
simple and complex
|
|
|
What kind of visual stimulus do ganglion neurons respond to?
|
specifically oriented bars of light
|
|
|
What are the 3 features of the receptive fields of simple ganglion neurons?
|
1) They have specific retinal position
2) They have discrete excitatory and inhibitory zones 3) They have a specific axis of rotation |
|
|
How does convergent input from neurons at earlier stages of the visual pathway "construct" the elongated or linear receptive fields of simple ganglion neurons?
|
Simple cortical neurons receive convergent excitatory connections from three or more on-center ganglion cells that together represent light falling along a straight line in the retina.
|
|
|
How do complex ganglion neurons differ from simple ganglion neurons?
|
The receptive fields of complex ganglion neurons are determined by the pattern of inputs. Each complex cell receives convergent excitatory input from several simple cortical cells, each of which has a receptive field with the same organization: a central rectilinear excitation zone and flanking inhibitory regions. In this way, the receptive field of a complex cell is built up from the individual fields of the presynpatic cells.
|
|
|
What is an orientation column?
|
It contains simple cells whose receptive fields monitor almost identical retinal positions and have identical axes of orientations.
|
|
|
What is a blob?
|
A peg shaped region of cells, prominent in layers 2 and 3, that frequently respond to different color stimuli and have receptive fields that - like those cells in the LGN - have no specific orientation.
|
|
|
What is an ocular dominance column?
|
It receives input from one eye or the other and is important for binocular interaction
|
|
|
What is a hypercolumn?
|
A column response to all lines of orientation from a particular region in space.
|
|
|
What is the range of wavelengths in the visible spectrum?
|
400-700 nm
|
|
|
How would a dichromatic photoreceptor system allow one to distinguish between different wavelengths in the visible spectrum?
|
It would generate two different signals for each wavelength. By comparing the two signals, the brain can distinguish lights of difference wavelengths. When an object reflects longer wavelengths, the receptors for longer wavelengths will transduce stronger signals than the other receptors and the brain can interpret the object as being red or yellow. Shorter wavelengths indicate blue. Objects reflecting all wavelengths equally would be seen as colorless (black, gray, or white).
|
|
|
What is the advantage of a trichromatic system over a dichromatic system?
|
With dichromatic photoreceptor systems, it is possible for two different-colored surface to have similar reflectance signatures and be perceived as the same color. Trichromatic systems reduce the likelihood of misperceiving color differences by generating more signals to describe surfaces.
|
|
|
What type of photoreceptor is responsible for perceiving color?
|
Cone
|
|
|
What are the three types of cone photopigments? What wavelength of light does each absorb most strongly?
|
S (short wavelengths): 420 nm
M (middle wavelengths): 530 nm L (long wavelengths): 560 nm |
|
|
What wavelength of light does rhodopsin absorb most strongly?
|
500 nm
|
|
|
What part of a photopigment in a rod or cone makes it selective for particular ranges of the visible spectrum?
|
each different photopigment contains a different opsin
|
|
|
What is the color opponent process of color vision?
|
Vision depends on 3 distinct opponent (one inhibited by the other) mechanisms or mutually exclusive pairs:
Achromatic or light/dark Green/red Blue/yellow |
|
|
What are the roles of P and M ganglion neurons in conveying information about color?
|
M cells: important for the analysis of image movement, but cannot resolve detail or spatial variation in brightness
P cells: convey information about brightness and color; they respond well to brightness variation in the fine structure and color variation in the coarse structure of the image |
|
|
Describe the pathway for information about color.
|
Color is mainly confined to pathways that convey information from the striate cortex, through areas V2 and V4, to the temporal lobe.
|
|
|
What is the basis of color blindness?
|
The afflicted individual has a dichromatic photoreceptor system instead of the normal trichromatic photoreceptor system.
|
|
|
What are the types of color blindness? What is the frequency of each in terms of gender and overall population?
|
Protanopia (loss of L cones) and deuteranopia (loss of M cones) almost always occur in males, each with a frequency of 1%.
Tritanopia (loss of S cones) afflicts genders equally and is rare: 1 in 10,000 |
|
|
What does the "sound pressure level" (SPL) of a sound indicate?
|
Loudness
|
|
|
What are the units of SPL?
|
decibels
|
|
|
Why are sound pressure levels of 0 decibels and 120 decibels meaningful in terms of human hearing?
|
0 dB is equivalent to the softest sound that can be heard at 4 kHz, the frequency at which humans have the most sensitive hearing. 120 dB is the loudest sound tolerable.
|
|
|
Describe the mechanics of sound transmission from the tympanic membrane into the fluid filled cochlea.
|
Air pressure vibrations (sound) move the tympanum back and forth. The tympanum movements displace the malleus. The malleus moves the incus, which moves the stapes in the oval window like a piston. The stapes cyclically pushes and pulls the fluid in the scala vestibule.
|
|
|
What is the difference between conductive hearing loss and sensorineural hearing loss?
|
Conductive hearing loss is due to compromise of the middle ear's normal structure and function.
Sensorineural hearing loss is due to disruption of function of the inner ear (damage to CN VIII or loss of cochlear hair cells). |
|
|
How is the Rinne test conducted?
|
The patient is asked to compare the loudness of sound from a vibrating tuning fork held in the air near the affected ear with that perceived when the base of the tuning fork is placed against the head just behind the auricle. If the latter is louder, the conductive pathway may be damaged. If there is no difference, there is sensorineural hearing loss.
|
|
|
How are conductive and sensorineural hearing loss treated?
|
Conductive hearing loss can be effectively treated through surgical intervention, while sensorineural hearing loss cannot be treated this way.
|
|
|
What are the two systemic variations in the mechanical properties of the basilar membrane?
|
1) The cochlea varies in width, or breadth, along it's length; width is greatest at the apex.
2) The cochlea varies in thickness and tautness along its length; it is thickest and tautest at its base. |
|
|
How do the basilar membrane's systemic variations allow it to "deconstruct" a sound?
|
The cochlea deconstructs sound by confining the action of each component of a complex sound to discrete segments of the basilar membrane. Because different regions of the basilar membrane are "tuned" to different sound frequencies, it is said to be a "tonotopic map".
|
|
|
What is the range of sound frequencies that can be detected by the human ear?
|
20 Hz - 20,000 Hz
|
|
|
Which part of the basilar membrane vibrates maximally at 20 Hz?
|
helicotrema/apex
|
|
|
Which part of the basilar membrane vibrates maximally at 20,000 Hz?
|
oval window/base
|
|
|
Which part of the basilar membrane vibrates maximally to a pure tone of 1000 Hz?
|
middle of the basilar membrane
|
|
|
In which direction are the hair bundles on hair cells bent by an upward deflection of the basilar membrane? What is the effect on membrane potential?
|
They are bent toward the tall edge
Depolarizing - excitatory |
|
|
In what direction are hair bundles on hair cells bent by a downward deflection of the basilar membrane?
|
Toward their short edge
Hyperpolarizing - inhibitory |
|
|
What two features of sound are encoded by the afferent cochlear nerve fibers that make synaptic contact with hair cells?
|
Frequency and intensity
|
|
|
How do afferent fibers convey information about sound frequency?
|
The CNS gains this info in two ways: sound is carried in a place code (carried in a tonotopic map, where position = frequency), and a frequency code (in which the rate of firing reflects the frequency of the stimulus)
|
|
|
What two types of information are used by neurons of the auditory pathway to localize sounds in space?
|
1) Sound arrival delays are used primarily with low-frequency sounds. Longer delays mean greater distance from the mid-sagittal plane.
2) Sound intensity differences are analyzed, primarily in high-frequency sounds. Greater intensity differences mean the source is closer to the ear that receives more intense sounds. |
|
|
What are some far-reaching consequences of deafness for children and the elderly?
|
Children are deprived of the normal avenue to the development of speech, reading, and writing.
For the elderly, hearing loss can result in painful and protracted estrangement form family, friends, and colleagues. |
|
|
What are some possible consequences of abrupt loss of hearing for an adult?
|
Results in loss of psychological well-being, which can result in loneliness, depression, and suicide. It can also result in ominous vulnerability because hearing serves as an early-warning system for the environment and through alarms like fire alarms and emergency vehicles.
|
|
|
What is a major improvement in modern hearing aids?
|
They can be customized to amplify only the frequencies that the person has a deficit in.
|
|
|
How does a cochlear prosthesis work?
|
It is an array of tiny electrodes that can electrically stimulate nerve fibers at various positions along the spiral course of the cochlea. A pocket-sized receiver decomposes the sound and projects signals that stimulate the cochlear nerve fibers. This therapy takes advantage of the regular and predictable tonotropic organization to reproduce sounds for normal perception.
|
|
|
What are the two general categories of sign language?
|
Signed English mirrors spoken language and obeys the rules of spoken English.
ASL diverges from spoken languages radically and tend to be more effective. |
|
|
How do linguists regard ASL?
|
It is recognized as its own language that matches or exceeds expressiveness of spoken English.
|
|
|
Describe the structure of a hair cell.
|
They are columnar epithelial-shaped cells, without dendrites or axons. They are bound to surrounding support cells with tight junctions and belt desmosomes which provide compartmentalization and strength respectively. The apical surface projects 20-300 stereocilia. The basal surface has contact with efferent and sometimes afferent nerve fibers.
|
|
|
Describe a hair cell bundle.
|
It consists of stereocilia that extend from the apical surface of the hair cell in a hexagonal array and form a beveled tip due to graded length variation.
|
|
|
Describe a stereocilium.
|
It is a rigid cylinder whose cytoskeleton consists of a fascicle of actin filaments cross-linked by fibrin. The core is covered by a tubular sheath of plasma membrane. Most actin filaments terminate near the apical surface of the hair cell, resulting in a narrower base. This allows the projection to pivot at the base when mechanical force is applied to the tip.
|
|
|
Describe a kinocilium.
|
A true cilium, found at the tallest edge of each hair bundle. It possesses an axoneme (array of 9 paired microtubules) at its core, and sometimes an additional, central pair of microtubules.
|
|
|
What type of potentials do sound waves produce in hair cells?
|
graded membrane potentials
|
|
|
Which ions are responsible for hair cell depolarization when deflection is towards the tallest stereocilium?
|
Cations: K+ forms most of the transduction current
|
|
|
Describe mechanoelectrical transduction in hair cells.
|
Mechanically gated ion channels are found in the tips of the stereocilia and elastic strain opens and gates them. The gating spring is called a tip link, which is a filamentous connection between stereocilia. When the stereocilia are bent toward the tallest cilia, the tip links are strained and pull open the physical gate on the ion channel in the taller of the two stereocilia because of the increased distance between the tip of the shorter stereocilium and the ion channel gate of the taller stereocilium.
|
|
|
What is the effect of high doses of aminoglycoside antibiotics such as streptomycin, gentamicin, and tobramycin on hair cells?
|
These drugs block the mechanically gated ion channels and can damage or kill the hair cells in large concentrations by inhibiting mitochondrial ribosomes.
|
|
|
Why are individual hair cells said to be tuned to a particular sound frequency?
|
Mechanical properties tune hair cells to particular frequencies; the length, mass, and flexibility all vary along the length of the cochlea in a systematic, tonotropic way.
Electrical properties vary in a tonotropic fashion as well. Specific frequencies evoke the greatest receptor potential |
|
|
Describe the cycle of ionic fluxes into and out of hair cells that underlies electrical tuning.
|
1) K+ influx at the tip of stereocilia depolarizes the cell
2) This opens voltage-sensitive Ca2+ channels and permit Ca2+ influx 3) The rise in Ca2+ concentration opens K+ channels which repolarizes the cell by allowing K+ efflux 4) Ca2+ is sequestered and pumped out |
|
|
What neurotransmitter is released from the basal end of hair cells at the point of synaptic contact with afferent nerve fibers?
|
glutamate
|
|
|
Describe the release of neurotransmitter from resting (unstimulated) hair cells.
|
Ca2+ channels are stimulated at the resting potential, which allows a steady, slow influx of Ca2+ that causes neurotransmitter release from unstimulated cells.
|
|
|
Describe the effect of stimulation by sound waves on a hair membrane's potential and on neurotransmitter release.
|
As the hair cells are bent in an oscillatory patter, the receptor membrane potential undergoes coordinating oscillating changes and neurotransmitter release is modulated upward and downward in the same frequency.
Bending toward the tallest stereocilia = depolarization = upward modulation of NT release Bending away from the tallest stereocilia = hyperpolarization = downward modulation of NT release |
