Physiology of the Visual System

Question 1

Rounder lens =

Flatter lens =

Answer 1

More refraction

Less refraction

Question 2

To increase curvature of the lens:

What’s it used for?

Answer 2

Ciliary m. contracts, allowing suspensory l. to loosen. Lens becomes rounder.

Used for near vision.

Question 3

To decrease curvature of the lens:

What’s it used for?

Answer 3

Ciliary m. relaxes, which causes suspensory l. to tighten. Lens flattens.

Used for far vision.

Question 4

Presbyopia

Answer 4

When the lens becomes stiffer in aging, w/ loss of elasticity.

Question 5

Near response (3 steps)

Answer 5

1. Contraction of ciliary ms.
2. Convergence of eyes to point of focus.
3. Constriction of pupil.

Question 6

Vertically oriented cells in the retina (3)

Answer 6

Receptor cells (rods and cones)
Bipolar cells
Ganglion cells

Question 7

Horizontally oriented cells (2)

Answer 7

Horizontal cells

Amacrine cells

Question 8

Rod system

Answer 8

Convergence: Many rods and bipolars converge onto 1 ganglion cells.
This allows rods to operate in dim light.

Question 9

Cone system

Answer 9

Less convergence: Cone goes to 1 bipolar cell which goes to 1 ganglion cell.

Question 10

Where do amount of cones peak in the retina?

Where do rods peak?

Answer 10

Cones: at fovea.

Rods: eccentricity of 20 degrees.

Question 11

When is glutamate release greatest?

When is it lowest?

Answer 11

Greatest when it is dark.

Lowest when there is light.

Glutamate is constantly being released, though.

Question 12

ON-center bipolar cells

Answer 12

Activation in the center causes depolarization.

Activation of the periphery causes hyperpolarization.

Question 13

OFF-center bipolar cells

Answer 13

Activation in the center causes hyperpolarization.

Activation in the periphery causes depolarization.

Question 14

Activation of ON-center bipolar cell by cone photoreceptor in the dark (3)

Center only

Answer 14

1. Glutamate activates Gi on the ON-center cell.
2. Decrease in Na+ influx into cell.
3. Hyperpolarizes cell.

Question 15

Activation of ON-center bipolar cell by a cone photoreceptor when light is present (4)

Center only

Answer 15

1. Light decreases glutamate levels.
2. Less activation of Gi.
3. Increase in Na+ influx.
4. Depolarization.

Question 16

Activation of OFF-center cell by a cone photoreceptor in the dark (3)

Center only

Answer 16

1. Glutamate activates AMPA/kainate.
2. Increase in Na+.
3. Depolarizes cell.

Question 17

Activation of OFF-center cell by a cone when light is present (4)

Center only

Answer 17

1. Less light –> less glutamate.
2. Less activation of AMPA/kainate.
3. Less influx of Na+.
4. Hyperpolarization.

Question 18

Activation of bipolar cell by rod photoreceptor (4)

Answer 18

1. Many rods converge on one ON-center cell.
2. Connects to a “rod-bipolar cell” and a “rod amacrine cell” which act as interneurons.
3. Connects to a “cone-bipolar cell”.
4. Connects to a ganglion cell.

Question 19

ON-center cells tell us where _______

OFF-center cells tell us where _______

Answer 19

Where something is.

Where something ends.

Question 20

What’s the function of the amacrine and horizontal cells?

Answer 20

They provide inhibitory modulation of nearby cells in the retina.

Question 21

Direct targets of the retina (5)

Answer 21

LGN
Superior colliculus
Pretectum
Hypothalamus
Accessory optic nuclei (AON)

Question 22

Function of the LGN/LGB

Answer 22

1. Control motion of eyes to converge on a point.
2. Control focus of eyes based on distance.
3. Determine relative position of objects to map them in space.
4. Detect movement relative to an object.

Question 23

Brodmann’s areas of:
Primary visual cortex
Parastriate cortex
Peristriate cortex

Answer 23

Primary visual cortex - 17
Parastriate cortex - 18
Peristriate cortex - 19

Question 24

Visual areas
V1
V2
V3
V4
V5

Answer 24

V1 - primary visual cortex (17)
V2 - greater part of Brodmann 18.
V3 - narrow strip of Brodmann 18.
V4 - area 19
V5 - middle temporal area (part of 19)

Question 25

Which layers of the retina receive input from LGB?

Which layers are main output from LGB?

Answer 25

Layer IV

Layers V and VI.

Question 26

Ocular dominance column

Answer 26

A slab of cells that preferentially respond to input from one eye or the other.

Question 27

Orientation columns

How are they oriented?

Answer 27

Region of neurons that are excited by visual line stimuli of varying angles.

Perpendicular to cortex.

Question 28

Blobs in primary visual cortex

Answer 28

Neurons that are sensitive to color. Requires all 3-colo-coding cones for accurate detection.

Question 29

Which colors are absorbed at lowest wavelength to highest wavelength?

Answer 29

Lowest to highest: blue, green, red.

Question 30

Major job of V1

Answer 30

Identify edges and contours of objects

Question 31

Major job of V2

Answer 31

Detects depth perception by analyzing disparities between two eyes.

Question 32

Major job of V3a

Answer 32

Identifies motion

Question 33

Major job of V4

Answer 33

Complete color processing of color inputs.

Question 34

Dorsal pathway

Answer 34

From primary visual cortex and goes to parietal/frontal cortex.
Primary path associating vision w/ movement.
Completes motor acts based on visual input.
Passes thru V3.

Question 35

Ventral pathway

Answer 35

From primary visual cortex to inferior temporal cortex.

Primarily involved in interpreting images and complex patterns.

Question 36

Explain melanopsin and circadian rhythms

Answer 36

MG cells detect light via melanopsin.
Lights, via melanopsin, causes changes in Ca++ levels in MG cells.
This is considered a non-image-forming light-responsive system.
Projects to thalamus.