L3 pt 2 Vision

Question 1

Retina

Answer 1

innermost layer, contains neurons sensitive to light and transmit via central targets

Question 2

Uveal tract

Answer 2

compoased of choroid, ciliary body, and iris

Question 3

Choroid

Answer 3

rich capillary bed nourishes photoreceptors, high concentration of light absorbing pigment melanin

Question 4

Ciliary body

Answer 4

ring of tissue encircling the lens
has a muscular and vascular portion

Question 5

Iris

Answer 5

colored portion of the eye seen through the cornea
controls pupillary constriction and dilation

Question 6

Sclera

Answer 6

outermost tissue layer and comprised of white fibrous tissue

Question 7

Cornea

Answer 7

outer layer in front of eye with specialized transparent tissue that permits light rays to enter the eye

Question 8

Humors of eye

Answer 8

Aqueous = front of eye
Vitreous = back of lens and retina

Question 9

Accommodation

Answer 9

dynamic changes in the shape of the lens

Distance = lens is thin and flat, has least refractive power. high tension in zonule fibers

Near = lens is thick and round, most refractive power, relaxed zonule fibers, contracted ciliary muscle

Question 10

How does accommodation occur?

Answer 10

tension of the ciliary muscle that surrounds the lens and zonule fibers

elasticity of the lens and tension of zonule fibers create counteracting forces

Question 11

Adjustments of the pupil

Answer 11

help to clarify images and adjust how much light enters the eye

controlled by sympathetic and parasympathetic NS

Question 12

Zonule fibers

Answer 12

radially arranged connective tissues bands that attach to the ciliary muscle

Question 13

Which nervous system is the retina a part of?

Answer 13

central
forms from the diencephalon

Question 14

Retinal Circuitry

Answer 14

retina converts graded electrical activity of photoreceptors (rods and cones) into action potentials . possible b/c of short distances

pathway goes from photoreceptor to bipolar to ganglion (projection neuron) cell located in optic nerve

Question 15

Phototransduction

Answer 15

absorption of light by photopigment in photoreceptors initiates a cascade of events that changes the membrane potential of the receptor, causing NT release

Question 16

Horizontal cells

Answer 16

allow for lateral interactions between photoreceptors and bipolar cells

help with sensitivity to light/contrast

Question 17

Pigment Epithelium

Answer 17

light rays must pass through various non-light-sensitive elements of the retina and vasculature before reaching photoreceptors.

reason for it: provides vasculature for photoreceptors, helps to generate new cells and remove old ones

Question 18

Hyperpolarization and photoreceptors

Answer 18

light stimulus causes hyperpolarization and not depolarization

causes membrane to go from -40 to -65

hyperpolarization causes the number of Ca2+ channels opened to be reduced, and rate of NT is reduced.

Question 19

Rods

Answer 19

low spatial resolution
sensitive to light
good for low light
multiple inputs to one ganglion, making it better at detecting light
more rods than cones
greater density in retina

less photons cause a reaction vs cones

Question 20

Cones

Answer 20

very high spatial resolution
insensitive to light
good for color
only one cone per ganglion, making it better at spatial resolution
greater density in fovea

responses to light are more quickly adapted in cones vs rods because it does not saturate at high levels of steady illumination–> membrane potential of individual cones still vary

Question 21

Cones and colors

Answer 21

-three types of cones, each defined by the photopigment they contain
-each is differentially sensitive to different wavelengths
-cones are colorblind, just reactive to different amounts of photons

Blue: short
Green: medium
Red: long

Question 22

On/Off Retinal Cells

Answer 22

On center = burst of action potentials with light directly on it
Off center = burst of action potential with light off

help to detect edges in vision

Question 23

On-center/Off-center Bipolar cells

Answer 23

help with the perception of contrast

both types of cells get the same input, more glutamate in the dark, less glutamate in light

Question 24

Off center bipolar cells

Answer 24

Are excited by baseline glutamate release; light/decrease in glutamate causes these to become more hyperpolarized

have ionotropic receptors that cause bipolar cells to depolarize in response to INCREASED OR BASELINE glutamate release

Question 25

On center bipolar cells

Answer 25

express a G-protein that when bound to glutamate, close sodium channels and hyperpolarize the cell

decreased levels of glutamate cause depolarization

1. Light enters IN THE CENTER, causing decreased glutamate
2. Reduction of inhibitory signals on on-center bipolar cells
3. Allows for transmission of excitatory signals to on-center ganglion cells

Question 26

Luminance contrast

Answer 26

differences in level of illumination that falls on the receptive field center and the level of illumination that falls on the surround

most ganglion cells respond better to small spots of light confined to the receptive field vs uniform illumination

Question 27

Horizontal cells and glutamate

Answer 27

these cells influence the amount of glutamate the photoreceptors will release onto bipolar cell dendrites

glutamate released by photoreceptors depolarizes horizontal cells, Horizontal cells have a hyperpolarizing effect on photoreceptors

overall effect is to oppose changes in the membrane potential of photoreceptors that are induced in phototransduction events in outer segment

Question 28

Decreased glutamate and horizontal cells

Answer 28

decreased glutamate from on-center light = reduces inhibitory feedback from horizontal cells onto bipolar cells

provide feedback inhibition to on-center receptors that can be changed with decreased glutamate