FINAL EXAM Lecture 12 Visual System

Question 1

The eyeball is made up of 3 concentric layers:

1.

2.

3.

Answer 1

1. Outer, fibrous layer
2. Middle, vascular layer (uvea)
3. Retina

Question 2

The outer, fibrous layer of the eye is made up of:

1.

2.

Answer 2

1. Sclera - White
2. Cornea - Transparent

Question 3

The middle, vascular layer ( _____ ) is made up of:

1.

2.

3. ________; contains a _______ in most domestic animals. (Absent in the pig)

Answer 3

1. Iris
2. Ciliary body
3. Choroid; Tapetum Lucidum

Question 4

Retina = _____ _____ of the eyeball

The ______ ______ of the retina lines the Iris, _____ ______ and ________.

The functional ____ ____ of retina lines the fundus to the level of the ora serrata.

Consists of ___ histological layers, including retinal ganglion cells, which give rise to the _____ ______.

Answer 4

Inner Layer

Pigmented Epithelium; Ciliary Body; Choroid

Optic Part

10; Optic Nerve

Question 5

_____ _____ ______:

Formed by the retinal pigmented epithelium & the endothelium of retinal capillaries, which lie within the nerve fiber layer of the retina.

Breakdown of the barriers leads to _________

Answer 5

Blood Ocular Barrier

Uveitis

Question 6

Fundus:

________ part of the eye consisting of:

1.

2.

3.

Can be observed with an opthalmoscope

• Appearance of ____ ____
• Appearance of ________
• Reflectivity of ______ _________
• _________ attachment

Answer 6

Interior

1. Retina
2. Choroid
3. Optic Disk
   - Optic Disk
   - Vasculature
   - Tapetum Lucidum
   - Retina

Question 7

Embryonic Development of the Retina

The retina develops from the ___ ___ of the _______, and the optic nerve is histologically a _____ tract. The optical part of the retina develops from the inner wall of the optic cup.

The outer wall becomes the _____ ______ layer.

Answer 7

Optic Cup

Diencephalon

CNS

Pigmented Epithelial

Question 8

Histological Organization

______ histological layers are recognized in the optic part of the retina:

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.

Answer 8

10

1. Pigmented Epithelium
2. Rods & 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

Question 9

Retina Organization

Light must penetrate _____ of the layers to reach outer segments of rods & cones where ______ are absorbed. Processes of ______ ______ cells surround the outer segments of rods and cones.

_________ axons of ganglion cells run to the ______ _____ and then exit the eyeball as _______ axons that comprise the _____ ______.

Photoreceptor cells are absent at the ____ _____ (blind spot). Retinal vessels enter at the disc and course along the retinal surface.

The area ______ (visual streak) of the retina has highest visual acuity.

Answer 9

8; photons

pigmented epithelium

Nonmyelinated; optic disc; myelinated; optic nerve

Optic Disc

Centralis

Question 10

______________ transduce light energy to neural electrical activity. They are excited ( ______ ) in the _____ and inhibited ( ______ ) by _______.

Answer 10

Photoreceptors

Polarized; dark

Hyperpolarized; light

Question 11

_____ _____ receive input from photoreceptors and synapse on ____ ____ (as well as some amacrine cells).

These are depolarized (ON) or hyperpolarized (OFF) in response to light.

Answer 11

Bipolar cells

Ganglion Cells

Question 12

Ganglion Cells:

Their axons leave the ____ and form the ____ _____.

Unlike all other retinal cells, ganglion cells generate _____ ______.

Their rate of firing is increased or decreased by ______ stimuli.

Answer 12

Retina; Optic Nerve

Action Potentials

Visual

Question 13

Horizontal cells:

are always ________. They have complex interactions with _________ and modulate the activity of _____ ____ indirectly.

They are primarily responsible for ______ inhibition (inhibition of cells as a result of activity in a neighboring cell).

Answer 13

inhibitory

Photoreceptors; Bipolar cells

Lateral

Question 14

Amacrine Cells:

are often _____ neurons that make synaptic contact with ____ & _____ ______.

Some respond to the onset.offset of light, others are responsive to direction of light movement. The optic nerve contains _____ axons, which synapse on amacrine cells to provide brain control of ______ activity.

There are ____ different populations of amacrine cells with respect to morphoology and neurotransmitters released.

Answer 14

inhibitory; bipolar; ganglion cells

efferent; retinal

30

Question 15

Radial Glial Cell

AKA _______ ________

Modified astrocytes which provide ______ and _______ support. Like astrocytes they take up excess ions and neurotransmitter molecules to maintain homeostasis. Processes of these cells form the internal and external limiting membranes.

Answer 15

Mueller Cells

Structural

Metabolic

Question 16

Transduction of Visual Signals by Photoreceptors

There are two populations of photoreceptors: ____ & ___.

The outer segments of rods & cones contain stacked membranous discs that are continually produced, sloughed, and phagocytized by pigmented epithelium. The discs contain the photosensitive molecule _____ (retinal + protein) that intercepts _____.

Answer 16

Rods & Cones

Rhodopsin

Photons

Question 17

Transduction of Visual Signals by Photoreceptors

Photoreceptor cells are excited ( _____ ) in the ____ and inhibited ( _______ ) in the _____.

They do NOT generate _____ _____. They repond to ______ stimuli with graded depolarization and hyperpolarization, which results in proportional release of _____ neurotransmitter.

Answer 17

Depolarized; dark

Hyperpolarized; light (photons)

Action Potentials; Visual; Glutamate

Rods; Dim

Cones; Bright Light

Question 18

Transduction of Visual Signals by Photoreceptors

______ form convergent circuits with bipolar cells, which improves vision in ____ light but at the expensve of image _______.

________ form relay circuits with bipolar cells, which provides good visual detail but requires ____ _____.

Answer 18

Rods; Dim

Cones; Bright Light

Question 19

Rods

_____ of photoreceptor cells

Widely distributed throughout the retina

Single population all containing _______ (protein + retinal); No ____ sensitivity

Functional in ____ light, response saturates in daylight

Participate in highly _______ circuits (>1,000 rods _____ on one ganglion cell); low spatial resolution

High _______ – can response to a single photon

Answer 19

95%

Rhodopsin; color

Dim

Convergent; Converge

Sensitivity

Question 20

Cones

_____ of photoreceptor cells

Concentrated in ____ ______

Multiple populations, base on different _______ (color) sensitivities, due to protein differences (Protein + Retinal)

Operate under ____ light conditions

Participate in _____ circuits (few cones per ganglion cell); high spatial resolution

______ sensitivity – need hundreds of photons for a response

Answer 20

5%

Area Centralis

wavelength

Bright

Relay

Lower

Question 21

_Processing of Visual Stimuli _

Processing of visual stimuli in the retina (and in the visual system in general) is organizerd in a way that optimizes the detection of ________.

This pattern in the visual scene is the type of visual information most useful to the animal.

For example, contrast at the edges of an object defines it shape and motion involves both _____ and ____ contrast.

Answer 21

Contrast

Temporal; Spatial

Question 22

Vertical and lateral pathways in the retina

Cells in the vertical pathways
( ______ –>_______ _______ –> ______ _____ )
are specialized to detect changes in _________.

______ and _____ ______ that specialize in detecting increases in brightness/illumination (e.g. a bright object on a dark background) are termed “ ____” cells.

These cells that specialize in detecting decreases in brightness/illumination are termed “ _____” cells.

Answer 22

Photoreceptors –> Bipolar Cells –> Ganglion Cells

Contrast

Bipolar & Ganglion CElls

ON

OFF

Question 23

Vertical & Lateral Pathways in the retina

Cells in the _______ pathways ( _____ and _____ cells) contribute to contrast enhancement.

Answer 23

Lateral

Horizontal & Amacrine Cells

Question 24

_The detection of contrast is based on the organization of receptive fields _

The ____ _____is the region of the retina that must be illuminated in order to obtain a response in a visual neuron.

_____ ______ of retinal ganglion cells are round and have a _____ and a ______ with _______ properties. Responses in the center are mediated by _______ pathways. Responses in the surround are based on _______ inhibition mediated by ______ pathways.

Answer 24

Receptive Field

Receptive Fields

Center

Surround

Anatgonistic

Vertical

Lateral; Lateral

Question 25

**_The detection of contrast is based on the organization of receptive fields_** The receptive fields of _______ cells are overlappingso that every point of the retinal surface is analyzed by several on-center and off-center _____ cells. Center-surround receptive fields are first established at the level of ______ cels and persist at the _____ levels of visual processing (i.e., lateral geniculate nucleus and visual cortex).

Answer 25

Ganglion; Ganglion Bipolar; CNS

Question 26

**_Responses of ON-center and OFF-center ganglion cells_** On-center ganglion cells _____ their rate of firing when the center is illuminated and ____ it when the surround is illuminated. Off-center cells ____ their fire when the center is illuminated and ____ it hen the surround is illuminated. The firing rate of a ganglion cell is a measure of the ______ between the illumination of the center and the surround.

Answer 26

Increase; Decrease Decrease; Increase Contrast

Question 27

**_Principles of Visual Processing_** The visual system uses ______ \_\_\_\_\_\_ to process information abotu different features of the visual scene (e.g. form, motion, color). These originate in the ____ from functionally distinct clases of ganglion cells. 90% of the primate ganglion cells fall into 2 functional classes desginated as ____ (magni, large) and _____ (parvi, small)

Answer 27

Parallel Pathways Retina M; P

Question 28

M cells have _____ receptive fields and signal \_\_\_\_\_, ____ and \_\_\_\_\_ P cells have _____ receptive fields and provide information about ____ \_\_\_\_\_ and \_\_\_\_\_. The parallel pathways remain separate from retina to cortex.

Answer 28

Larger; Motion, Position, Depth Small; Fine Detail & Color

Question 29

\_\_\_\_\_\_ _____ in lateral geniculate nucleus and primary visual cortext (lost at level of association cortex). In the primary visual cortex representation of the area centralis is graetly enlarged compared to cortical surface area devoted to the rest of the retina.

Answer 29

Retinotopic Mapping

Question 30

\_\_\_\_\_ \_\_\_\_\_\_: receptive fields become larger and more complex at each level.

Answer 30

Hierarchial Processing

Question 31

Color Vision Humans have ____ populations of color sensitive \_\_\_\_\_. We are trichromatic and can distinguish the range of colors with which you are familiar. Color vision in dogs is said to be comparable to people are are \_\_\_\_-\_\_\_\_\_ color blind. Dogs are ______ and seem to see _____ and ____ but not green or orange-red. All of several horses tested could distinguish ____ and _____ from gray. Some but not all of the horses could also distinguish ____ & ____ from gray. Nocturnal animals are completeley color blind (rat, hampster, etc.)

Answer 31

3; Cones Red-Green Dichromatic Blue; Yellow Red; Blue Yellow; Green

Question 32

**_Non-Image Forming Vision_** - Mediated by intrinsically photosensitive _____ \_\_\_\_\_ cells, which contain melanopsin (peak sensitivity in the \_\_\_\_/\_\_\_\_\_ range of the spectrum) - Detect _____ light - Involved in ______ clock

Answer 32

Retinal Ganglion Blue/Green Ambient Circadian

Question 33

**_Visual Pathways_** Conscious Pathway: \_\_\_\_ --\> _____ --\> \_\_\_\_\_\_

Answer 33

Retina ---\> Lateral Geniculate --\> Cortex

Question 34

**_Visual Pathways_** Reflex Pathways Retina --\> _______ \_\_\_\_\_\_ (eye, ear, and head turning to oreitn to a visual stimulus) Retina --\> _______ \_\_\_\_\_ (pupil size regulation to compensate for light intensity)

Answer 34

Rostral Colliculus Pretectal Region

Question 35

**_Optic Nerve:_** axons from ____ \_\_\_\_ cells

Answer 35

Retinal Ganglion Cells

Question 36

**_Optic Chiasm:_** decussation of ____ \_\_\_\_\_axons; depending on species, percentage of axons from the lateral side of each retina do not cross

Answer 36

Optic Nerve

Question 37

**_Optic Tract:_** axons from both eyes. The optic tract conveys _____ visual field information

Answer 37

contralateral

Question 38

Binocular Vision: Important for _____ \_\_\_\_\_\_ - Requires visual field overlap so that individual objects can be viewed simulatneously by both eyes. - "corresponding" ganglion cells in each eye send their axons through the same optic tract - The visual cortex in one cerebral hemisphere receives info about an object from both eyes. In visual cotex, some columnds monitor stimulation in corresponding loci of the 2 eyes.

Answer 38

Depth Perception

Question 39

**_Concious Visual Pathway_** Optic tract fibers synapse in the ____ \_\_\_\_\_ nucleus. Neurons of this nucleus send their axons into the optic radiation of the internal capsule and the nto the primary visual cortex.

Answer 39

Lateral Geniculate Nucleus

Question 40

**_Conscious Visual Pathway_** The ____ \_\_\_\_ _____ exhibits the typical columnar organization of neocortex. Colums respond to geometric & dynamic elemnts of an image. 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, etc. Some cell columns are activated by particular colors.

Answer 40

Primary Visual Cortex

Question 41

Conscious Visual Pathway The ____ \_\_\_\_, surrounding the primary visual cortex, is required to associated meaning and significance to the elements of the primary image. There are two separate visual integrations: - A phylogenetically older "\_\_\_\_" system that analyzes motion and depth. Damage produces: Failed ocular pursuit of a moving target Poor depth perception Deficient visuall guided movements deficits in visual attention - A phylogenetically newer "\_\_\_\_\_" sysmte that analzyes form and color. Damage produces: Loss of color Vision Impaired pattern recognition, including face/object recognition

Answer 41

Association Cortex Where What

Question 42

**_Reflex Visual Pathways_** Axons participating in subconscious visual reflexes leave the optic tract and travel in the ______ of the _____ \_\_\_\_ to reach two visual reflex centers, the 1. _____ \_\_\_\_\_\_ 2. _______ \_\_\_\_\_\_\_ (Axons also leave the optic tract to reach the hypothalamus)

Answer 42

Brahcium of the Rostral Colliculus 1. Rostral Colliculus 2. Pretectal Region

Question 43

Eye, ear and head turning to orient to a sudden, prominent visual stimulus inolves the ______ \_\_\_\_\_\_. Neurons of this send their axons to appropriate motor nuclei via tecto\_\_\_\_\_ and tecto\_\_\_\_\_ tracts.

Answer 43

Rostral Colliculus Tectobulbar & Tectospinal

Question 44

Pupil size regulation to compensate for light intensity involves the ______ \_\_\_\_\_\_, with fiber decussation in the ________ \_\_\_\_\_\_\_\_. Axons go to the ________ nucleus of the ________ nerve for pupillary constriction (dilation is achieved by less constriction).

Answer 44

Pretectal Region Caudal Commissure Parasympathetic Oculomotor

Question 45

The pupillary light reflex is important for diagnosing lesions in the _______ pathways.

Answer 45

Visual