(40) The Visual System

Question 1

What part of the brain in responsible for visual perception?

Answer 1

occipital cortex

Question 2

What part of the brain in responsible for visual memory?

Answer 2

parietal an temporal

Question 3

What part of the brain in responsible for visual reflexes?

Answer 3

brainstem and spinal cord

Question 4

What part of the brain in responsible for circadian rhythm

Answer 4

pineal gland and dienchephalon

Question 5

what focuses the incoming light from objects we see to create a crisp image

Answer 5

fovea

Question 6

What happens to the light from an object after it enters our eye to get to the retina?

Answer 6

refracted by cornea 
inverted through pupil 
refracted by lens 
projected onto fovea 
fovea focuses/fine tunes light 
light hits retina

Question 7

how is the image of the object we are seeing oriented on the fovea in our eye?

Answer 7

inverted and smaller

*due to refraction by cornea and lens

Question 8

What muscle controls lens refraction and how it is innervated

Answer 8

cilliary muscle via sympathetic and parasympathetic control

Question 9

protective later to the retinal and choroid

Answer 9

sclers

Question 10

choroid provides blood flow and nutrients to….

Answer 10

photoreceptors and RPE cells = OUTER retina

Question 11

describe the circulation in the fovea

Answer 11

there is NONE = no blood vessels bc blood distorts the image

Question 12

describe the cellular organization of the retina

Answer 12

photoreceptor cell bodies lie in outer nuclear layer and project to outer flexiform layer where they synapse with bipolar cells who’s cell bodies are found in the inner nuclear layer. these bipolar cells project to ganglion cells in the ganglion layer. the ganglion cell projections coalesce to form the optic N

Question 13

provides the barrier between the retina and the choroid

Answer 13

retinal pigmented cells

Question 14

support the photoreceptor by providing nutrients

Answer 14

RPE

Question 15

What are the interneurons that lie in the retina and what cells do they synapse with and what is their function?

Answer 15

horizontal (outer plexiform layer) –modulate photoreceptors and bipolar cells
amacrines (inner plexiform layer) –modulate bipolar cells

Question 16

what form the blind spot?

Answer 16

optic N entry into retina

Question 17

how are the retinal cells arranged in the fovea?

Answer 17

radially to minimizes distortion of the image

Question 18

Macular degeneration results when blood vessels damage the ____ and break through to grow into the ___ region of the eye

Answer 18

RPE and macular region

Question 19

2 main functions of the RPE

Answer 19

1. provide barrier between retina and choroid

2. eat outer rod segments every 10 days (prevents macular degeneration/drusen production)

Question 20

function of rods

Answer 20

produces black and white vision

Question 21

what is the spherule?

Answer 21

synapse of rods with bipolar cells and horizontal interneurons

Question 22

which cones are carried on X chromosome

Answer 22

M and L

Question 23

what is the purpose of the photoreceptors

Answer 23

abs photons and convert it into electrical signal

Question 24

what is the response that rods and cones have to light

Answer 24

hyperpolarize

**only sensory cells that hyperpolarize in response to a signal, all others depolarize

Question 25

describe the bichem that is going on in a photoreceptor that allows for a photon to be converted into an electrical signal

Answer 25

light converts cis retinal to trans retinal which activates rod opsin-rhodopsin which converts GDP to GTP which activates PDE. active PDC lowers cGMP levels which closes the cGMP-gated ion channel (Ca and Na). no cations coming in = hyperpolarization = electrical signal that is the visual response

Question 26

how is the hyperpolarized state of the photoreceptor reversed?

Answer 26

decreased Ca levels activate guanyl cyclase and inhibits PDE which increases cGMP and allows the cations (Ca and Na) channels to reopen

Question 27

how is the trans retinal converted back to cis retinal so that another photon can activate it

Answer 27

active rhodopsin-GTP is dephosphorylated back to GDP and allows all the trans to go back to cis **rhodopsin kinase P-rhodompsin which binds arrestin to make the moleucle inactive untl the photon shows up

Question 28

At the bipolar ganglion cell synapse, ______ cells detect major changes in activity levels

Answer 28

amacrine

Question 29

cones and rods have thier own bipolar cells. which ones are found in the periphery and which ones are centrally?

Answer 29

periph = rods cones = central

Question 30

what cells help converve the signals from multiple rod photoreceptors to fewer rob bipolar cells? (i.e. convergence)

Answer 30

horizontal cells

Question 31

what ganglion cells are found in the periphery and receive most of their input from rods

Answer 31

alpha-ganglion cells

Question 32

alpha ganglion cells project to _____ and function to....

Answer 32

magnocellular layer of lateral geniculate nucleus and function to determine the location of object in space

Question 33

what ganglion cells are found in the central retianl and receive most of their input from cones

Answer 33

beta ganglion cells

Question 34

beta ganglion cells project to _____ and function to....

Answer 34

parvocellular region in lateral geniculate nucleus to define color and texture

Question 35

the foves has (rods, cones, or both)

Answer 35

cones

Question 36

what ganglion cells decussate in the optic chiasm

Answer 36

only nasal fibers

Question 37

left visual field is processed by what side of the cortex

Answer 37

right

Question 38

M pathway originates in the ______ cells and projects to lateral geniculate layers _____ then to layer ____ in the cortex. This pathway relays ____ info

Answer 38

originates in magnocellular ganglion cells layer 1-2 in LGN 4C-alpha in cortex space information

Question 39

P pathway originates in the ______ cells and projects to lateral geniculate layers _____ then to layer ____ in the cortex. This pathway relays ____ info

Answer 39

originates in parvocellular ganglion cells layer 3-6 in LGN 4C-beta in cortex form information

Question 40

high glc causes damage to what cells in the eye

Answer 40

retinal epiptheral cells and pericytes and neurons **damage activates growth facotrs

Question 41

what vasculature is damaged in diabetic retinopathy vs macular degeneration

Answer 41

``` DR = retinal AMD = choroid ```

Question 42

how is vision field loss compared in DR and AMD

Answer 42

``` DR = central AMD = all vision ```

Question 43

how is dry AMD different than wet AMD

Answer 43

Dry more common than wet dry has less vision loss and is usually unilateral while wet is bilateral dry has drusen and wet sometimes foes

Question 44

What are the treatments for AMD

Answer 44

Avastin and Macugen injections that block vasculature growth **they halt progression and do not reverse***