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292 Cards in this Set
- Front
- Back
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layered structure of retina
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-ganglion cell layer
-inner plexiform layer -inner nuclear layer -outer plexiform layer -outer nuclear layer -layer of photoreceptor outer segments -pigmented epithelium |
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what cells does the foveal pit contain
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only photoreceptor cells!
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describe blind spot
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light falling on the optic nerve head can't be detected
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why are we normally unaware of the blind spot
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perceptual "fill-in" by the visual cortex
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why can't we see our own blood vessels
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stabilized image fades rapidly with time
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why can you sometimes see white blood cells traversing thin retinal vessels
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because they are moving and don't contain hemoglobin, you can see a white spot moving within the vessel
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retinal diseases
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-macular degeneration
-retinitis pigmentosa -glaucoma -diabetic retinopathy |
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describe phototransduction
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1.molecule absorbs photons in th visible part of the electromagnetic spectrum
2. absorption of light by the photosensory molecule must initiate some sort of cellular signal 3.ionic permeability of the plasma membrane must be altered by opening or closing ion channels |
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what is rhodopsin
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combination of a protein molecule opsin & a light absorbing chromophore molecule, retinal
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retinal
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derivative of vitamin A, which is in turn derived from beta-carotene
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retinal in dark state
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retinal is attached to opsin in the "bent" form (11-cis retinal)
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retinal in light state
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retinal absorbs a photon, it photoisomerizes to the "straight" form (all-trans retinal)
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rhodopsin
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G-protein couple receptor
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rhodopsin ligand in the dark
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inactive state (11-cis retinal)
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rhodopsin ligand upon photoisomerization
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ligand converts to active state (all-trans retinal) and the G-protein-couple receptor is activated
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what G protein does rhodopsin activate
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transducin
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transducin
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heterotrimeric G protein
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describe phototransduction cycle
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cGMP-gated channel->channel opens with cGMP bound->Na and Ca influx -> depolarization
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what does phosphodiesterase do
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it hydrolyzes cGMP to GMP
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what is turning off rhodopsin dependent on
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interaction between arrestin & rhodopsin
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do photoreceptors show adaptation? if so, when
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YES, during continued presence of light
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photoreceptors responses in light
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maximally sensitive to light, their responses are large & slow
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photoreceptors response in the presence of background light
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less sensitive, faster response
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what is the adaptation process controlled by
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calcium concentration inside the photoreceptor outer segment
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path of Ca+2 in darkness
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Ca+2 enters through open cGMP-gated channels and binds to two target proteins: recoverin & GCAP
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effect of Ca+2 binding on recoverin
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inhibits rhodopsin kinase which prolongs and strengthens the light response (good in darkness)
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what occurs when Ca+2 isn't bound
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GCAP binds to and activates guanylate cyclase, which then synthesizes cGMP at a higher rate. This promotes fast recovery & makes responses smaller (good in background light)
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what do bipolar cells and horizontal cells receive synaptic inputs from
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photoreceptors
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2 types of bipolar cells
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On and Off
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receptors for Off bipolar cell
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ionotropic glutamate receptors (AMPA & Kainate receptors)
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receptors for On bipolar cell
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metabotropic glutamate receptors (mGluR6)
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what does mGluR6 act through
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G_o-alpha
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what are horizontal cells depolarized by
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glutamate released from photoreceptor synapses
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what do horizontal cells express
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ionotropic glutamate receptors (AMPA receptors) at the tips of their dendrites
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response of horizontal cells to illumination
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hyperpolarize in response to illumination of their synaptically connected photoreceptor cells
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what kind of feedback do horizontal cells provide
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lateral inhibitory feedback at the synapses between photoreceptors and bipolar cells
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when is neurotransmitter release from horizontal cells highest
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in darkness, when they are depolarized
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when is neurotransmitter release from horizontal cell lowest
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during illumination
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what is GABA
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neurotransmitter released by horizontal cells
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what effect do horizontal cells produce
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synaptic effect in bipolar cells that opposes the effect of illuminating the photoreceptors that are directly connected to the bipolar cell
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effect of Off-type bipolar cell
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depolarizes
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effect of On-type bipolar cell
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hyperpolarizes
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mechanism #1 of lateral inhibitory feedback
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horizontal cell feedback mediated by GABA onto photoreceptor terminals.-cuz this mechanism affects glutamate release from presynaptic terminal, it will have the appropriate negative effect on the light response of both On and Off bipolar cells
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mechanism #2 of lateral inhibitory feedback
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GABA released from horizontal cells onto dendrites of bipolar cells (mammals)
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what do On bipolar cells express
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NKCC, which generates chloride influx
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what do Off bipolar cells express
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KCC2, which generated chloride efflux
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effect of GABA released from horizontal cells
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depolarizes On bipolar cells and hyperpolarizes Off bipolar cells
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what occurs during illumination
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reduced GABA release contributes hyperpolarization to On bipolar cells and depolarization to Off bipolar cells
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mechanism #3 of lateral inhibitory feedback
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shift in activation range of Ca+2 current in photoreceptor synaptic terminals (all species)
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effect of illumination on photoreceptor calcium channels, what is it mediated by
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illumination shifts the activation of photoreceptor calcium channels in the negative direction, mediated by feedback from horizontal cells
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effect of activation of photoreceptor Ca+2 channels in neg. direction
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causes Ca+2 channels to activate at more hyperpolarized membrane potential of the photoreceptors in the light, restoring some transmitter release.
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what do horizontal cells produce
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negative feedback at the synapse between photoreceptors and bipolar cells
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effect of horizontal cells in the case of Off-type bipolar cells
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cause the bipolar cells to depolarize
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do horizontal cell receive inputs from more or less photoreceptors than bipolar cells typically do
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MORE photoreceptors -spatial extent of the response mediated by horizontal cell feedback is larger
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receptive field of a bipolar cell
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center-surround receptive field- bipolar cell responds best to spatial contrast of illumination
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receptive field of retinal ganglion cells
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center-surround organization: it's an ON-center cell
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what is information about illumination encoded by
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frequency of action potentials
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where does the blood supply for the eye come from
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arterial supply of the brain (carotid artery)
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what area in retina has the highest visual acuity
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fovea
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what is the retina a part of
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CNS- diencephalon
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what is the sclera continuous with
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the meniges of the brain
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where does light come into
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pupil
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where must light be focused to
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back of the eye (retina)
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lens
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30% of the refractive element; optical focusing element
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cornea
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70% of refractive element
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what occurs at fovea
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light coming in from center-view is brought into sharp focus here
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what do we see the world through
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ganglion cell axons
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what is the purpose of black pigmented cells
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so scattered light is absorbed
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where is the exit point for retinal ganglion cells
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near the optic nerve
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why is there a blind spot by the optic nerve
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because there are no photoreceptors or anything to give it light sensitivity
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where does the fovea get oxygen supply & nutrients from
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diffusion from choroid
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position of blood vessels in relation to retina
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they're attached to surface of the retina
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what occurs in macular degeneration
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there are extracellular deposits of lipids & proteins around macula ->kills photoreceptors (no more fovea)
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what occurs in retinitis pigmentosa
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disintegration of the retinal causes back pigmented epithelial cells to proliferate into that empty space
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what kind of vision do you lose in retinitis pigmentosa
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peripheral vision
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what does glaucoma result from
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intraocular pressure getting too high, which cuts off blood supply and damages retina
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what are the eye sockets kept inflated by
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aqueous humor fluid (balance betw. production & drainage)
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what occurs in diabetic retinopathy
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-cells that line blood vessels die and blood vessels become leaky
-vessels aren't efficient in carrying blood and the oxygen-starved retinal will generate signals to make new blood vessels -small new blood vessels are weak and leak blood into anterior of the eye |
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what photoreceptors does the fovea contain
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only RODS
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where does phototransduction occur
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in outer segment- light sensitive part of rod
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purpose of connecting cilium
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connects outer segment to the rest of the cell
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what is the membrane potential of photoreceptor cell at rest in darkness
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DEPOLARIZED
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response of photoreceptor during dim lighting
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graded hyperpolarization
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what do visual pigment molecules in photoreceptors do
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absorb light
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which part of rhodopsin absorbs light? what occurs next
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retinal absorbs photon of light & isomerizes from bent form to straightened form
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what does isomerization of retinal result in
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uncoiling of the cytoplasmic tail to reveal binding sites
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what does light cause? how?
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hyperpolarization by closing cyclic-nucleotide gated channels
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explain herring grid illusion
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brain only knows about intensity of light at a point in space from the frequency of action potentials in the ganglion cells whose receptive fields coincide with that point.
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why does the perceived gray spot disappear when you gaze directly at a particular intersection
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because the receptive fields of ganglion cells in the central part of the visual field are much smaller, so both the center and surround fall within the white area without overlapping the black zones.
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what does lateral inhibition do
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it enhances the perceived contrast in brightness at the border between light and dark regions of the visual field
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what are mach bands
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dark stripe at dim side of the transition and the bright stripe on the bright side
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can we distinguish colors (wavelength of light) based on the output of a single type of photoreceptor
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NO
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what are the 3 different types of cone photoreceptors
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S, M, and L
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what are cone signals carried to and how?
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subsets of ganglion cells by special types of bipolar cells
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what kind of receptive fields do color-sensitive ganglion cells have
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center-surround receptive fields whose center and surround arise from different types of cones
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what cones does the red/green opponent ganglion cell arise from
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L cones and M cones
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what cones does the blue/yellow opponent ganglion cells arise from
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S cones and M cones
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what is the red/green opponent ganglion cell strongly excited by
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a white light that covers only the center of the receptive field.
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Vision: Higher visual pathways
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-thalamus: lateral geniculate nucleus
-accessory optic system -primary visual cortex -higher cortical areas |
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what is the pathway for conscious parts of vision
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geniculo-striate visual pathway
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phylogenetically older targets (non-cortical) of retinal ganglion cells in the brain
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-suprachiasmatic nucleus
-superior colliculus -accessory optic system |
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thalamocortical/geniculostriate pathway in brain
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retinal ganglion cells target the lateral geniculate nucleus->striate cortex
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organization of retinal inputs to the thalamus in animals with frontally placed eyes
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Light from the left visual field is focused onto the temporal retina of the right eye and the nasal retinal of the left eye. Light from the right visual field falls on the nasal retinal of the right eye and the temporal retinal of the left eye.
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how do points from the same region of space project to the same side of the brain
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axons of ganglion cells from nasal and temporal retina have to sort as shown at the point of crossover (optic chiasm)
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where are inputs from contralateral and ipsilateral eyes segregated
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within the lateral geniculate nucleus
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where do parvo-cellular cells project to
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layers 3-6 in the lateral geniculae nucleus
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where do magno-cellular cells project to
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layers 1-2 in the lateral geniculate nucleus
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what are the three classes of retinal ganglion cells in non-primate mammals
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X, Y, W cells
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What is the equivalent of X,Y,and W cells in primates
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X= P cells
Y= M cells |
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Y cells
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-large cells bodies
-large dendritic fields -large center-surround receptive fields -respond transiently to illumination -prefer moving stimuli -not sensitive to color |
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X cells
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-medium size cell bodies
-small dense dendritic fields -small center-surround receptive fields -produce sustained responses to illumination -sensitive to color |
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W cells
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-small cell bodies
-widely spreading dendritic fields -functionally diverse with many different kinds of light responses -don't participate in thalamocortical system |
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What do X cells (or P cells) and Y cells (M cells) represent
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parallel streams of information
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what do sleep centers inhibit
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reticular formation neurons
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where do retinal ganglion cells project to
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projection neurons and local interneurons
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what are simple cells sensitive to
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bars or lines of a particular orientation
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what is receptive field defined in terms of
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surface of retina
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what are complex cells sensitive to
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stimulus orientation independent of stimulus location, within broad limits
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what are hypercomplex cells stimulated best by
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lines of a particular orientation and length
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what system are hypercomplex cells a part of
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cortical systems that analyze the form or shape of an object, without strong constraint on its location
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what is the columnar organization of V1
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orientation columns
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what are color-sensitive cells in V1 called
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double opponent neurons- not sensitive to white light or to full-field, uniform color
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what are double opponent cells not sensitive to
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white light or full field, uniform color
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when is the best response in color sensitive V1 cells
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red spots on green background
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where do "blobs" containing color-sensitive cells receive inputs from
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parvocellular layers of the LGN, which in turn receive inputs from X cells
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what subsystem are the X cells a part of
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color-analysis subsystem
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where do blobs (color-sensitive) (parvocellular or X-cells) project to
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thin stripes
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where do thin stripes project to
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area V4- color and form vision
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where do orientation sensitive (parvocellular or X-Cell) project to
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interstripe regions
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where do interstripe regions project to
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area V4- color & form vision
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where do orientation sensitive (magnocellular or Y-cell) & motion-sensitive and orientation sensitive (magnocellular or Y-cell) project to
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thick stripes
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where do thick stripes project to
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area V3 (form vision) and area V5 (visual motion)
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what do cells in V5 (or MT middle temporal area) do
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detect stimulus movement, independent of stimulus shape
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what are directionally selective neurons in V5 organized in
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columns, and neurons in a particular column share the same preferred direction while neighboring columns prefer other directions
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what is the auditory system interested in
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FREQUENCY->changes in sounds pressure
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what are sounds
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pressure changes that impinge on the ear
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what are pressure changes a result of
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air molecule density alternately compressing (compression) and expanding (rarefraction)
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what is frequency
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1/cycle time of wave in seconds
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what is frequency measured as
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Hertz (Hz)
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what hertz do humans hear
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between 20 Hz and 20,000 Hz (20 kHz)
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what are sounds with frequencies >20kHz called
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ultrasounds
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what are sounds with frequencies <20 Hz called
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infrasounds
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when does absorption occur
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when a sound wave is smaller than on object it encounters, the object absorbs (reduces) the sound wave
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when does reflection occur
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when a sound wave in air hits something of higher density (e.g. water) the majority of the wave is reflected back and a smaller portion is transmitted into the denser medium.
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what is impedance mismatch created by
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the difference in density between 2 mediums
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what characteristics do sound waves exhibit
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frequency and spatial characteristics
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how much spaces does a low freq sound wave occupy compared to high freq
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MORE SPACE
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what is sound power
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the amount of energy released per unit time in all directions (E/t)
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what is sound intensity
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sound power per unit area (W/m^2)
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what does sound pressure measure
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the pressure (force per m^2 perpendicular to the direction of the sound) at an observer's location
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peak to peak
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difference in pressure betw peak and trough
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relative pressure equation
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decibel (db)= 20*log (measured sound pressure/20 micropascals) RMS
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is the measure of sound intensity relative or absolute
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relative
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what change in sound pressure results from a 20 dB increase
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a 10 fold increase in sound pressure
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what does decibel measurement compress
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enormous range into a useable scale
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what movements do we hear at threshold
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movements of air that are only 1 billionth of a centimeter
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resonant frequency
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the natural frequency of vibration for an object
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what frequency is all speech
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1000-8000Hz
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what is the resonant frequency of the outer ear
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2.1 kHz
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what does the outer ear do
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it funnels sound to tympanic membrane
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3 bones of middle ear
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malleus, incus, and stapes
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what does stapes connect to and how
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connects to the cochlea via oval window
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2 muscles in middle ear
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1. stapedius
2. tensor tympani |
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what is stapedius innervated by and act on
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VII, acts on stapes
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what is tensor tympani innervated by and act on
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motor V, acts on malleus
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cochlea
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closed, liquid filled tube that converts sound pressure into neural activity
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at what frequencies does the base vibrate best at
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HIGH frequencies
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at what frequencies does the apex vibrate best at
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LOW frequencies
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what does basilar membrane perform
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biological Fourier transform
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what does the Fourier transform determine
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amplitude, frequency, and phase of the sine waves that sum to make any complex form
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cells in stria vascularis
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absorb Na+ and secrete K+ against their concentration gradients
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effect of movement of basilar membrane
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causes the stereocilia of the inner hair cells to bend their interactions with the fluid around the tectorial membrane
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outer hair cells response to basilar membrane
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outer hair cells touch the tectorial membrane and bend with vibrations of the basilar membrane
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what does basilar membrane cause
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cilia movement
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when do hair cells depolarize
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when the sterocilia bend toward the kinocilium
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when do hair cells hyperpolarize
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when the sterocilia bend away from kinocilium
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effect of cilia bending
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ion channels open
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what do hair cells exhibit
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receptor potentials
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response of outer hair cells to depolarization
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shorten their length
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how do outer hair cells shorten
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with depolarization, Cl- dissociates and prestin acts as a motor to shorten OHC length (at rest Cl- is bound to protein prestin)
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place code
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the brain determines the sound frequency by keeping track of the origin of the VIIIth n (auditory nerve) afferent along the basilar membrane
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what does the brain use the place code for
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to identify 1.4-20 kHz frequencies and only uses the place code to identify frequencies >5kHz
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what does the brain use the period code for
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to identify 20-5000 Hz frequencies and only uses the period code to identify frequencies <1400 Hz
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what do all nuclei contain
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tonotopic map of frequencies
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where does cochlear nucleus receive inputs from
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one ear, monaural
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where do binaural interactions first occur
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in the superior olive
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what kind of input does the nucleus of lateral lemniscus have
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monaural input from contralateral cochlear nucleus
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what has a map of auditory space not frequencies
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one portion of inferior colliculus
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what is the medial geniculate
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thalamic input to primary auditory cortex
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what do neurons in belt region respond to
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conspecific sounds
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where do nuclei in superior olive get inputs from
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both eyes
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what are the groups of cells in A1 cortex divided into
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those that are excited by inputs from either ear (EE neurons) or excited by one ear and inhibited by the other (EI neurons)
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what do surrounding auditory cortices respond to
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complex sound stimuli important in normal behavior such as speech sounds
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which part of belt region of cortex is more active in listening to speech
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left belt region
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which part of belt region of cortex is more active in listening to music
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right belt region
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for frequencies <1.4 kHz,what does the medial superior olive (MSO) do
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measures the time difference between when the sound reaches the two ears, interaural time delay, to determine the location of the sound in auditory space
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what does the MSO contain
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'delay lines' that detect the coincidence of inputs from the left and right ears.
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what kind of neurons are in MSO
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E-E neurons
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for frequencies >1.4 kHz, what does the lateral superior olive (LSO) measure
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the difference in the sound intensity reaching the 2 ears, interaural intensity difference, to determine the location of the sound in auditory space
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what does the LSP compare
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excitatory inputs from the ipsilateral ear and inhibitory inputs (via medial nucleus trapezoid body) from the contralateral ear.
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what kind of neurons are in LSO
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E-I neurons
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what causes constructive interference
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at low frequencies, the direct & indirect waves are in phase
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what causes destructive interference
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at high frequencies, the indirect and direct sound waves are out of phase
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what does sound localization in the vertical plane rely on
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spectral cues between the direct & indirect (reflected) inputs to the ear
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cochlear implants
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electrodes stimulate at different points along the basilar membrane and a speech processor does Fourier transformation
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3 sensory systems that determine posture
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1.proprioceptive
2.vestibular 3.visual |
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proprioceptive system
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stretches muscles around the ankle joint
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vestibular system
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activates inner ear receptors of head movement
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visual system
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retinal slip opposite direction of head movement
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what occurs when the 3 sensory systems don't agree
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sensory conflict occurs- leading to motion sickness
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postural reflexes
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1.first muscles to contract act on ankle
2.muscles around the knee begin to contract next 3. muscles around the hips contract |
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what is sensory-motor conflict
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when the NS chooses to weigh the info. from each source differently.
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what modifies postural reflexes?
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experience
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what do the 3 semicircular canals respond to
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angular acceleration in the plane of the canal
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what are semicircular canals insensitive to
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angular acceleration perpendicular to the plane of the canal
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what are the opposing pairs formed by the canals on the opposite side of the head
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1.left & right horizontal canals
2.left anterior and right posterior canal 3.left posterior and right anterior canals |
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what is inside each bony semicircular canal
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an endolymph filled membranous labyrinth with an expanded region, the ampulla
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whats inside the ampulla
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gelatinous mass, the cupula
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what's embedded in the cupula
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sterocilia and kinocilium of vestibular hair cells
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how do semicircular canals work
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because of the inertia of endolymph
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what are cilia of hair cells in vestibular system bathed in
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endolymph
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what are hair cells depolarized by
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cilia movement toward kinocilium
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what are hair cells hyperpolarized by
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movement away from kinocilium
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what channels do hair cells of vestibular system use
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TRPA1 channels
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what does hair cell orientation determine
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the direction of activation for vestibular end organs
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what do otoliths do
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sense linear acceleration
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what does utricle respond best to
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linear acceleration of the head moving forwards and backwards and side to side
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what do saccule respond best to
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up and down linear acceleration of the head (gravity)
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what are the hair cell tips in contact with
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Ca+ carbonate mass, otoconia
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what occurs when the head undergoes linear acceleration
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inertia of the otoconia causes it to lag behind the head and bend the sterocilia
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what does hair cell orientation determine
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sensitivity to direction of linear acceleration
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discharge of semicircular canal afferents with the head stationary
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~90 spikes/s
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what does angular head acceleration produce
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excitation of one VIIIth nerve and inhibition of the contralateral VIII nerve in the opposing semicircular canal
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effect of rotation to the left
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excites left horizontal canal and inhibits right horizontal canal
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effect of rotating head downward (forward)
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excites anterior canals and inhibits the posterior canals
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effect of rotating head up (backward)
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excites the posterior canals and inhibits the anterior canals
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what do the vestibular neurons in the brain look at
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the difference in activity between the left and right vestibular nerves to determine the direction of rotation
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two types of semicircular canal afferents
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Type 1 afferents and Type 2 afferents
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Type 1 afferents
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irregular pattern of discharge, time between spikes is variable
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type II afferents
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exhibit regular discharge pattern in which there is little variability in the interval between action potentials
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what info do type II afferents provide
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info about head rotation
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what do type I afferents act as
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event detectors for high frequency head rotations
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what do the semicircular canals respond to
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angular acceleration
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what do otoliths respond to
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linear acceleration
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what inputs does area 2v receive
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visual and proprioceptive inputs
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what does electrical stimulation of 2v evoke
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sensations of spinning or dizziness
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what inputs does 3a receive
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somatosensory inputs, may be involved in head movements
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where does vestibulospinal travel
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to the spinal cord in the lateral and medial vestibulospinal tracts
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what are vestibulospinal tracts involved in
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maintaining posture
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what is benign paroxysmal positional vertigo (BPPV) due to
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displaced otoconia that has settled in the utricle
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symptoms of BPPV
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dizziness, light headedness, imbalance, and nausea
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what are BPPV symptoms due to
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shift in the position of the head relative to gravity
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what is meniere's disease characterized by
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episodes of vertigo, tinnitus, sensation of fullness in the ear, and fluctuating hear loss
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what is meniere's disease presumes to develop from
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inc endolymph in labrynth and cochlea
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3 axis of eye rotation
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1. elevation & depression
2. abduction & adduction 3. extorsion and intorsion |
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what are the three antagonistic extraocular muscle pairs
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1. medial rectus-ADduction
lateral rectus- ABduction 2. inferior oblique-extorsion superior oblique- intorsion 3. superior rectus-elevation inferior rectus- depression |
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where do the MR & LR rotate the eye
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in a plane parallel to the horizontal canals
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where do the SR & IR rotate the eye
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in a plane parallel to the ipsilateral anterior canal
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where do the SO & IO rotate the eye
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in a plane parallel to the ipsilateral posterior canal
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hering's law
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corresponding muscles of the 2 eyes are equally innervated during conjugate gaze
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5 types of eye movements
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1. saccadic eye movements: conjugate
2. vestibular eye movements: vestibulo-ocular reflex conjugate 3. optokinetic eye movements: conjugate 4. smooth pursuit eye movements: conjugate 5. vergence eye movements: dysconjugate |
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2 goals of eye movements
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1. redirect line of sight
2. maintain image stability (ex: eliminate retinal slip) |
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what are rapid flicks of eyes
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saccadic eye movements (saccades)
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fixations
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time between saccades when the eyes are stationary
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when do we take in visual information
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during fixations
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why do we change the direction of gaze
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because our point of highest acuity, the fovea, only looks at a small region of the visual world
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what do abnormal saccades reveal, why
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brainstem problems because humans can't voluntarily change the speed of saccadic eye movements
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what do saccadic eye movements reveal
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visual attention
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when is vision suppressed
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during saccadic eye movements
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how does vestibulo-ocular reflex (VOR) eliminate retinal slip
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by rotating the eyes opposite to the direction of head rotation
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what activates the vestibulo-ocular reflex (VOR)
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angular acceleration of the semicircular canals
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what is nystagmus defined by
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direction of its fast phase
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what produces nystagmus
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constant velocity head rotation in the dark
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what is nystagmus
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eye slowly moving opposite to the direction of head rotation (slow phase) interrupted by a saccade in the direction of head rotation (fast phase) to reset the eye
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what does optokinetic nystagmus (OKN) do and how
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it elimates retinal slip by moving the eyes at the same speed and direction as the retinals lip
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what are optokinetic eye movements driven by
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motion of the entire visual field
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what does OKN require
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visual stimulus
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what can stabilize head motion
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optokinetic system
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what do the optokinetic and vestibular systems work together for
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to provide an accurate measure of head rotation
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at what frequencies does the VOR work best
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HIGH
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at what frequencies does the OKN work best
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LOW frequencies
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what do smooth pursuit eye movements do
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redirect the line of sight
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what do smooth pursuit eye movements occur in response to
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a small, slowly moving target and only achieve max peak velocities of ~60-80 deg/s
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what do vergence eye movements do
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dysconjugate & redirect the line of sight
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what increases the speed of the vergence eye movements
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combining vergence eye movements with saccades
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whats the near triad
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1. convergence
2. accommodation 3. pupil constriction |
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what is the fastest eye movement
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saccades
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what initiates and programs saccades
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superior colliculus (SC)
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where are horizontal saccades organized in
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pontine paramedian reticular formation (PPRF)
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where are vertical saccades organized in
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mesencephalic reticular formation (MRF)
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what controls eye movements
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frontal eye fields (FEF) work with the superior colliculus (SC)
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what causes saccadic eye movement
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"burst" of motoneuron activity
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