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002 - Neurobiology (part II) > (12) Visual System > Flashcards

(12) Visual System Flashcards

1
Q

(RETINA)

1-3. eyeball is composed of three concentric layers - name them (and where they are)

A
  1. outer, fibrous layer
  2. middle, vascular layer (uvea)
  3. retina (inner layer of eyeball)
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2
Q

(Eyeball)

  1. What are the 2 components of the outer, fibrous layer (+ are they clear or transparent?)
  2. What are the three components of the middle, vascular layer (uvea)? what does the third one contain and what is it present in?
  3. Retina. What of the retina lines the iris, ciliary body, and choroid? What lines the fundus to the level of the ora serrata?

Consists of how many histological layers? Including what that gives rise to the optic nerve?

A
  1. sclera (white) and cornea (transparent)
  2. iris; ciliary body; choroid - contains a tapetum lucidum in most domestic animals (not pig)
  3. the pigmented epithelium; the functional optic part; retinal ganglion cells
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3
Q

(Clinical relevance of Eyeball)

  1. What is formed by the retinal pigmented epithelium and the endothelium of retinal capillaries? Which lie within what? Breakdown of this barrier leads to what?
A
  1. Blood ocular barrier; nerve fiber layer of the retina; uveitis
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4
Q

(Clinical relevance of eyeball pt 2)

  1. What is the interior part of the eye consisting of retina, choroid, and optic disk that can be observed with an opthalmoscope?

2-5. What four things are you looking at here?

  1. increased reflectivity of the tapetum lucidum suggests what?
A
  1. fundus
  2. appearance of optic disk (blind spot - no photoreceptors)
  3. appearance of vasculature
  4. reflectivity of tapetum lucidum
  5. retina attachment
  6. retinal damage
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5
Q

(Embryonic Development)

  1. The retina develops from what?
  2. optic nerve is histologically a what tract?
  3. the optical part of the retina develops from what?
  4. The outer wall becomes what?
A
  1. optic cup of diencephalon
  2. CNS tract
  3. inner wall of the optic cup
  4. pigmented epithelial layer
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6
Q

(Histological Organization)

1-10 Then layers are recognized in the optic part of the retina - name them in order…

  1. Where does light come in?
  2. Light must penetrate how many of these layers? to reach what? where what happens?
  3. What surrounds the outer segments of rods and cones?
A
  1. pigmented epithelium
  2. rods and cones
  3. external limiting membrane
  4. outer nuclear layer
  5. outer plexiform layer
  6. inner nuclear layer
  7. inner plexiform layer
  8. ganglion cell layer
  9. optic nerve fibers
  10. internal limiting membrane
  11. from bottom
  12. 8; outer segments of rods and cones; photons are absorbed
  13. processes of pigmented epithelial cells
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7
Q

(Hisological organization cont)

  1. What run to the optic disk and then exit the eyeball as myelinated axons that comprise the optic nerve?
  2. What are absent at the optic disk (blind spot)? What enter at the disc and course along the retinal surface?
  3. Which area of the retina has the highest visual acuity?
A
  1. nonmyelinated axons
  2. photoreceptor cells; retinal vessels
  3. area centralis (visual streak)
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8
Q

(Cell types in the retina)

  1. What transduce light energy to neural electrical activity? They are what in the dark and what in the light?
  2. What receive input from photoreceptors and synapse on ganglion cells (as well as some amacrine cells)? They are either what or what in response to light?
A
  1. photoreceptors; excited in the dark (depolarized); inhibited (hyperpolarized) by light
  2. bipolar cells; depolarized (on) or hyperpolarized (off) in response to light
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9
Q

(cell types in the retina cont.)

  1. Their axons leave the retina and form the optic nerve. How are the unlike all other retinal cells? The rate of fiiring is increased or decreased by what?
  2. Are always inhibitory? They have complex interactions with what? modulate the activity of what indirectly? They are primarily responsible for what?

3.

A
  1. ganglion cells; they generate action potentials; visual stimuli
  2. Horizontal cells; photoreceptors; bipolar cell; lateral inhibition (inhibition of cells as a result of activity in a neighboring cell)
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10
Q

(Cell types in retina cont.)

  1. often inhibitory neurons that make synaptic contact with bipolar and ganglion cells?
  2. What are modified astrocytes which provide structural and metabolic support? Like astrocytes they do what? Processes of these cels form what?
A
  1. amacrine cells
  2. Radial Glial cells (Mueller cells); take up excess ions and NT molecules to maintain homeostasis; the internal and external limiting membranes
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11
Q

allows differentiation of all the layers

A
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12
Q

(Transduction of visual signal by photoreceptors)

  1. what are the two populations of photoreceptors?
  2. The outer segments of rods and cones contain stacked membranous discs that are continually produced, sloughed, and phagocytized by what?
  3. The discs contain the photosensitive molecule what that does what?
A
  1. rods and cones
  2. pigmented epithelium
  3. rhodopsin (retinal + protein) that intercepts photons
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13
Q
  1. Photoreceptors are what in the dark and what in the light?
  2. Do they generate AP?
  3. They respond to visual stimuli with graded depolarization (excitation) and hyperpolarization (inhibtion), which results in what?
  4. Rods form what kinds of circuits with bipolar cells, which improves what but at the expense of what?
  5. Cones form what kinds of circuits with bipolar cells, which provides what but requires what?
A
  1. excited (depolarized) in the dark; inhibited (hyperpolarized) by light (photons)
  2. no
  3. proportional release of glutamate neurotransmitter
  4. convergent; improves vision in dim light at expense of image resolution
  5. relay circuits; provides good visual detail but requires bright light
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14
Q

RODS VS CONES

  1. % of human retina?
  2. where?
  3. single or multiple populations?
  4. performance in light conditions?
  5. participate in what circuits that provide what?
  6. sensitivity?
A
  1. 95% – 5%
  2. widely distributed throughout retina – conc in Area Centralis
  3. single population, all contain rhodopsin (protein + retinal) no color sensitivty – multiple populations, based on different wavelength (color) sensitivies, due to protein differences (protein + retinal)
  4. functional in dim light, response saturates in daylight – operate under bright light
  5. highly convergent circuits (>1000 rods converge on one ganglion); low spatial resolution – participate in relay circuits (few cones per ganglion cell); high spatial resolution
  6. high sensivity (respond to single photon) – lower sensitivty (need hundreds of photons for response)
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15
Q

(Transduction)

(Dark Condition in Rods)

  1. What build up in the outer rod segment? What is it?
  2. What is abundant and acts to keeps channels open?
  3. Influx of what depolarizes the rod cell in a graded electrotonic manner (-40 mV).
  4. The depolarized rod cell releases what at its junction with what and what?
A
  1. rhodopsin; rhodopsin = protein (scotopsin) bound to retinal (11-cis Vitamin A Aldehyde)
  2. cGMP
  3. Na+ and Ca++
  4. gluatamate; bipolar and horizontal cells
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16
Q

(Transduction)

(Photon Effects in rods)

  1. Photon energy converts cis-retinal to all what? Which causes what?
  2. Activated rhodopsin triggers a what to activate what to do what?
  3. What do cation channels do in the absence of cGMP? Rod cell becomes what?
  4. One photon activates how many rhodopsin molecules which triggers what?
  5. The rod cell relases less or more glutamate at its synapse?

*Transduction is the same in cones, except for what?

A
  1. all trans-retinal; destabliizes rhodopsin which becomes enzymatically active as it dissociates
  2. triggers a G protein (transducin) to activate many phosphodiesterase molecules which enzymatically convert cGMP to GMP
  3. cation channels close; polarized (-70 mV)
  4. one; closure of hundreds of cation channels
  5. less

*protein is different (not scotopsin)

17
Q

(Processing of Visual Stimuli)

  1. Processing of visual stimuli in the retina (and in the visual system in general) is organized in a way that optimizes what?
  2. What type of visual information is most useful to the animal?

*For example, contrast at the edges of an object defines its shape and motion involves both spatial and temporal contrast

A
  1. the detection of contrast
  2. the pattern of contrast in the visual scene
18
Q

(Vertical and lateral pathways in the retina)

  1. Cells in the vertical pathways (photoreceptors –> bipolar cells –> ganglion cells) are specialized to detect what?
  2. Bipolar and ganglion cells that specialize in detecting increases in brightness/illumination (ie bright object on a dark background) are termed what?
  3. Bipolar and ganglion cells that specialize in deteceting decreases in brightness/illumination (eg a dark object on a bright background) are termed what?
  4. Cells in the lateral pathways (horizontal and amacrine cells) contribute to what?
A
  1. changes in contrast
  2. “ON” cells
  3. “OFF” cells
  4. contrast enhancement
19
Q
  1. The detection of contrast is based on the organization of what?
  2. What is the region of the retina that must be illuminated in order to obtain a response in a visual neuron?
  3. Receptive fields of retinal ganglion cells are round and have a what?
  4. Responses in the center are mediated by what?
  5. Responses in the surround are based on what that is mediated by what?
  6. The receptive fields ganglion cells are overlapping so that every point of the retinal surface is analyzed by several on-center and off-center ganglion cells
  7. Center-surround receptive fields are first established at the level of what and persist at what?
A
  1. receptive fields
  2. the receptive field
  3. center and a surround with antagonistic properties
  4. vertical pathways
  5. lateral inhibition mediated by lateral pathways
  6. -
  7. established at level of bipolar cells; persist at CNS levels of visual processing (ie lateral geniculate nucleus and visual cortex)
20
Q

(3. Responses of ON-center and OFF-center ganglion cells)
1. On-center ganglion cells _____ their rate of firing when the center is illuminated and _____ it when the surround is illuminated.
2. Off-center ganglion cells _____ their rate of firing when the center is illuminated and _____ it when the surround is illuminated.
3. The firing rate of a ganglion cell is a measure of what?

A
  1. incrase, decrease
  2. decrease, increase
  3. the contrast between the illumination of the center and the surround
21
Q

(Principles of Parallel Processing)

  1. The visual system uses what to process information about different features of the visual scene (eg form, motion, color)?
  2. The parallel pathways originate where and form what?
  3. Ninety percent of primate ganglion cells fall into two functional classes designated as what and what?
  4. Which type have larger receptive fields and signal motion, position, and depth?
  5. Which have small receptive fields and provide info about fine detail and color?
A
  1. parallel pathways
  2. in the retina from functionally distinct classes of ganglion cells
  3. M (magni, large) and P (parvi, small)
  4. M cells
  5. P cells
22
Q
  1. Retinotopic mapping occurs where? lost at level of what? In the primary visual cortex representation of what is greatly enlarged compared to cortical surface area devoted to the rest of retina?
  2. What is it called that receptive fields become larger and more complex at each level?
A
  1. lateral geniculate nucleus and primary visual cortex; lost at level of association cortex; area centralis
  2. Hierarchial processing
23
Q

(Color Vision)

  1. Humans have how many populations of color sensitive cones?
  2. Vision in dogs is similar to people who are what?
  3. Are dogs di or trichromatic? can they see blue and yellow? green and orange-red?
  4. Can horses distinguish read and blue from gray? How many horses can distinguish yellow and green from gray?
  5. Two populations of color sensitive cones are found in other species.. like what?
  6. Are nocturnal animals color-blind?
A
  1. 3 (we are trichromatic)
  2. red-green color blind
  3. di; yes; no
  4. yes; some
  5. cat and pig
  6. yes
24
Q

(Non-image forming vision)

  1. Mediated by what? which contain what? Where is peak sensitivty?
  2. used to detect what? involved in what?
A
  1. intrinsically photosensitive retinal ganglion cells; melanopsin; blue/green range
  2. ambient light; circadian clock
25
Q
  1. What are axons from retinal ganglion cells called?
  2. What is the decussation of optic nerve axons called? *depending on species, percentage of axons from the lateral side of each retina do not cross
  3. What are the axons from both eyes? This conveys what kind of visual field information?
A
  1. the optic nerve
  2. optic chiasm
  3. optic tract; contralateral (ex axons from the lateral part of the retina of the ipsilateral eye & the medial & central parts of the retina of the contralateral eye)
26
Q

(Visual Pathways)

  1. Concious pathway is what?

2-3. What are the two reflex pathways?

A
  1. retina –> lateal geniculate –> cortex
  2. retina –> rostral colliculus (eye, ear and head turning to orient a visual stimulus)
  3. retina –> pretectal region (pupil size regulation to compensate for light intensity)
27
Q
  1. What is important for depth perception?
  2. requires what?
  3. “corresponding” ganglion cells in each eyes send their axons through what?
  4. The visual cortex in one cerebral hemisphere receives info about and object from one or both eyes?
  5. In visual cortex, some colums monitor simulation in what?
A
  1. binocular vision
  2. visual field overlap so that individual objects can be viewed simultaneously by both eyes
  3. the same optic tract
  4. both
  5. corresponding loci of the two eyes
28
Q

(Concious Visual Pathway)

  1. Optic tract fibers synapse in the what? Neurons of the lateral geniculate nucleus send their axons in the what of the what? then to where?
A
  1. lateral geniculate nucleus; optic radiation of the internal capsule; primary visual cortex
29
Q
  1. The primary visual cortex exhibits what type of organization? Columns respond to what?

* A cell column within visual cortex becomes excited in response to light-dark boundaries oriented at a certain angle, moving in a certain direction, affecting either or both eyes. Some cell columns are activated by what?

A
  1. typical columnar organization of neocortex; geometric and dynamic elements of an image

* certain colors

30
Q
  1. What cortex is required to associate meaning and significance to the elements of the primary image? What does it surround?

There are two separate visual integrations…

  1. A phylogenetically older “where” system that analyses what?
  2. 1-4 What does damage produce (4 things)?
  3. A phylogenetically newer “what” system that analyzes what and what?
  4. 1-2 Damage produces what?
A
  1. the association cortex; the primary visual cortex
  2. motion and depth
  3. 1 faild occular pursuit of a moving target (ie inaccurate eye saccades (tiny movements))
    1. poor depth perception
  5. 3 deficient visually guided movements (eg reaching)
  6. 4 deficits in visual attention
  7. form and color
  8. 1 loss of color vision
  9. 2 impaired pattern recognition, including face/object recognition
31
Q

(Reflex Visual Pathways)

  1. Axons participating in subconcious visual reflexes leave the optic tract and travel in the what to reach two visual reflex centers, the what and what?
  2. Eye, ear and head turning to orient a sudden, prominent visual stimulus involves the what? Neurons of the rostral colliculus send their axons to appropriate motor nuclei via what two tracts?
A
  1. brachium of the rostral colliculus; rostral colliculus and pretectal region (axons also leave the optic tract to reach the hypthalamus)
  2. rostral colliculus; tectobulbar and tectospinal tracts
32
Q

(Reflex Visual Pathways cont)

  1. Pupil size regulation to compensate for light intensity involves what region? with fiber decussation in the what? Axons go to where for pupillary constriciton? dilation is achieved by what?
  2. The pupillary light reflex is important for diagnosing what?
A

1. pretectal region; caudal commisure; parasympathetic nucleus of the oculomotor nerve; less constriction

  1. diagnosing lesions in the visual pathways

002 - Neurobiology (part II) (7 decks)

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