Physiology of the Visual System

Question 1

How does the shape of the lens affect incoming light refraction?

Answer 1

rounder = more refraction

flatter = less refraction

Question 2

How does the ciliary m affect the shape of the lens?

Answer 2

contracts –> allows suspensory L to loosen –> rounder lens –> near vision

relaxes –> suspensory L tight –> flatter lens –> far vision

Question 3

What is presbyopia?

Answer 3

the lens becomes stiffer in aging, loss of elasticity

Question 4

What are the 5 neuron types in the retina?

Answer 4

vertically oriented:

receptor cells - rods and cones

bipolar cells

ganglion cells (subtype: MG cells)

Horizontally oriented cells:

horizontal cells

amacrine cells

Question 5

What do rod cells detect and how do they converge?

Answer 5

a lot of convergence: many rods + many bipolars –> one ganglion cell

operates in dim light

sacrifice acuity to gain sensitivity

Question 6

What does the cone system detect?

Answer 6

less convergence: receptor –> one bipolar cell –> one ganglion cell

maximizes acuity

colors and bright light

Question 7

Wher are rods and cones most dense on the retina?

Answer 7

cones: most dense at fovea
rods: peak laterally about 20 degrees

Question 8

What is glutamate release like in dark and light?

Answer 8

Highest when it is dark –> no stimulation by photons

Glutamate is Lowest when there is Light –> cells hyperpolarize

Question 9

How do cones activate bipolar cells?

Answer 9

photon stimulates photoreceptor

photoreceptor hyperpolarizes

glutamate release on bipolar cell decreases

Question 10

How do ON-center bipolar cells react to light?

Answer 10

Light: less glutamate –> activation of photoreceptor in center –> depolarization of bipolar cell

dark: glutamate –> Gi activation in periphery –> hyperpolarization of cell

tell you where something is

Question 11

How do OFF-center bipolar cells react to light?

Answer 11

activation of photoreceptor in center of receptive field –> hyperpolarization of cell

activation of photoreceptor in pheriphery –> depolarization

Dark: glutamate –> AMPA receptor –> increase cation influx –> depolarization

tell you where something ends

Question 12

How does glutamate affect ganglion cells?

Answer 12

bipolar cell activated –> glutamate –> depolarizes ganglion

Question 13

How do rods affect bipolar cells?

Answer 13

many rods converge on one ON-center bipolar –> connects to a rod-bipolar cell and a rod amacrine cell –> cone-bipolar cell –> ganglion cell

Question 14

How do amacrine and horizontal cells affect other cells in the retina?

Answer 14

provide inhibitory GABA/glycine to other cells

Question 15

What does the pretectum do in vision?

Answer 15

modulates the pupillary light reflex

Question 16

What is V1?

Answer 16

primary visual cortex

brodmann area 17

identifies contours

Question 17

What is V2?

Answer 17

greater part of brodmann 18

parastriate complex

identifies depth perception

Question 18

What is V3?

Answer 18

narrow strip of Brodmann 18

parastriate cortex

V3a: identification of motion

Question 19

What is V4?

Answer 19

brodmann 18

completes processing of color inputs

Question 20

WHat is V5?

Answer 20

middle temporal area (part of 19)

Question 21

What do the layers of the primary visual cortex do?

Answer 21

I, II, III allow for networking btw V1 and other areas of the cortex

Layer IV: receives input frm LGB (large here)

Layers V and VI: main output layers to LGB, thalamus, subcortical regions

Question 22

What are ocular dominance columns?

Answer 22

span all 6 layers

cells in one column respond to one eye, the next column responds to the other eye

columns alternate btw L and R eyes

Question 23

What do orientation columns do?

Answer 23

in primary visual cortex

span all 6 layers

excited by visual line stimuli of varying angles

oriented perpendicular to cortical surface

Question 24

What do blobs do in the primary visual cortex?

Answer 24

span all 6 layers

organized region of neurons that are sensitivet to color

all 3 color-coding cones are required for accurate color detection

Question 25

What are the 3 types of cones?

Answer 25

S cone = blue cone

M cone = green cone

L cone = red

Question 26

What are the patterns of mapping each type of column in the primary visual cortex?

Answer 26

ocular dominance = stripes

orientation columns = swirls

blobs = blobs

Question 27

What is the dorsal pathway?

Answer 27

the “where” pathway

from V1 –> thru V3 –> to parietal/frontal cortex

completes motor acts based on visual input

Question 28

What is the ventral pathway?

Answer 28

the “what” pathway

Vfrom V1 –> inferior temporal cortex

interprets images and complex patterns

copying and naming are separate fxns

facial recognition is a specialized area

Question 29

What are MG cells?

Answer 29

subset of ganglion cells

detect light directly via blue-sensitive pigment melanopsin –> change in Ca levels in MG –> project directly to suprachiasmatic nucleus of hypothalamus

manages circadian rhythms

Question 30

How does glutamate affect metabotropic and ionotropic receptors and where are they found?

Answer 30

glutamate –> Gi –> closes channels –> cell hyperpolarizes

light –> less glutamate –> less Gi signaling –> depolarization = On-center bipolar cells

dark –> glutamate –> AMPA –> depolarizes cell

see AMPA in off-center bipolar cells = tell you where light/object stops