physiology of the visual field

Question 1

refraction

Answer 1

the fact or phenomenon of light, radio waves, etc being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density

Question 2

first sight of refraction

Answer 2

cornea

• not variable
• 2/3 of light bending

Question 3

second sight of refraction

Answer 3

lens

• variable
• depends on curvature of lens under physiologic control
• rounder = more refraction
• flatter = less refraction

Question 4

what is required to change the curvature of the lens?

Answer 4

• ciliary muscle
• suspensory ligaments
• normal lens

Question 5

increase curvature of lens

Answer 5

• ciliary m contracts
• allows suspensory ligaments to loosen
• lens more rounded shape by natural recoil
• near vision

Question 6

decrease curvature

Answer 6

• ciliary m relaxes
• suspensory ligaments tighten
• lens pulled tight flattening it
• used for far vision

Question 7

presbyopia

Answer 7

lens becomes stiffer in aging, loss of elasticity

Question 8

near response

Answer 8

1. contraction of ciliary ms
2. convergence of eyes to the point of focus
3. constriction of pupil
   - reduces opening for light to enter
   - eliminates diverging light rays
   - allows better focus

Question 9

path of light from when it enters at cornea to activating photoreceptor

Answer 9

cornea, lens, hummor, vitreous, GCL, IP, INL, OPL, ONL

Question 10

5 neuron types in the retina

Answer 10

vertically oriented

1. receptor cells (rod and cone)
2. bipolar cells
3. ganglion cells - MG cells

horizontally oriented

4. horizontal cells
5. amacrine cells

Question 11

photoreceptors

Answer 11

rods and cones

Question 12

rod system

Answer 12

• convergence: many rods + many bipolars –> 1 ganglion cell
• allows to see in dim light
• sacrifices acuity to gain sensitivity
• off center

Question 13

cone system

Answer 13

• less convergence: 1 receptor –> 1 bipolar cell –> 1 ganglion cell
• maximizes acuity
• bright light
• center

Question 14

what do rods and cones constantly release?

Answer 14

glutamate

Question 15

when is glutamate release highest?

Answer 15

dark

Question 16

when is glutamate release lowest?

Answer 16

light

-stimulation by photons –> hyperpolarize –> less glutamate release

Question 17

activation of bipolar cell by cone

Answer 17

1 photon stimulates photoreceptor
2 photoreceptor hyperpolarizes
3 glutamate release onto the bipolar cell DECREASES

Question 18

ON center

Answer 18

CENTER: causes depolarization
PERIPHERY: causes hyperpolarization
increase discharge rate to luminance increments in the receptive field center

Question 19

OFF center

Answer 19

CENTER: hyperpolarizes
PERIPHERY: depolarizes
increase discharge rate to luminance decrements in the receptive field center

Question 20

ON center bipolar cell in darkness

Answer 20

1. glutamate would activate Gi GPCR metabotropic receptor on the ON-center bipolar cell
2. results in a decrease in cation influx into the bipolar cell
3. hyperpolaries cell

Question 21

ON center bipolar cell in brightness

Answer 21

1. light photons decrease the presence of glutamate
2. less glutamate around
3. less activation of metabotropic receptor on the ON center bipolar cell
4. less Gi signaling
5. results in an INCREASE in cation influx into the bipolar ell
6. depolarizes the cell

Question 22

OFF center bipolar cell in darkness

Answer 22

1. glutamate would activate AMPA receptor on the OFF center bipolar cell
2. results in an increase in cation influx into the bipolar cell
3. depolarizes cell

Question 23

OFF center bipolar cell in brightness

Answer 23

1. light photons decrease presence of glutamate
2. less glutamate around
3. less activation of AMPA receptor on the OFF center bipolar cell
4. results in decrease in cation influx into the bipolar cell
5. hyperpolarizes the cell

Question 24

Do ganglion cells have ON center and OFF center varieties?

Answer 24

yes –> activated/deactivated by glutamate released when bipolar cells depolarize

• ganglion cell axons become fibers of optic nerve
• in cortex, ganglion cells will release glutamate

Question 25

activation of bipolar cell by rod photoreceptors

Answer 25

1. many rods converge on one ON center bipolar cell 2. connects to a "rod-bipolar cell" and "rod amacrine cell" which both function as interneurons inhibiting the cones with glycine or GABA 3. connects to a "cone-bipolar cell" 4. connects to ganglion cell

Question 26

direct targets of the retina

Answer 26

- LGB - superior colliculus - pretectum - hypothalamus - accessory optic nuclei

Question 27

LGB functions

Answer 27

1. control the motions of the eyes to converge on a point of interest 2. control the focus of the eyes based on distance 3. determine relative position of objects to map them in space 4. detect movement relative to an object

Question 28

optic radiations

Answer 28

axons of LGB relay cells to visual cortex on same side | -maintains retinotopic organization

Question 29

anatomical areas of visual processing

Answer 29

17 primary visual cortex 18 parastriate cortex 19 peristriate cortex

Question 30

functional areas of visual processing

Answer 30

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

Question 31

primary visual cortex layers

Answer 31

I, II, III - networking with IV IV receives input from LGB V and VI main output layers: LGB, thalamus, subcortical regions

Question 32

What layers of the cortex do columns span?

Answer 32

all 6 layers

Question 33

ocular dominance columns

Answer 33

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

Question 34

orientation columns

Answer 34

organized region of neurons that are excited by visual line stimuli of varying angles spanning 6 layers of cortex oriented perpendicular to cortical surface

Question 35

blobs in primary visual corex

Answer 35

collections of 6 layers of the cortex organized region of neurons that are sensitive to color assemble into cylindrical shapes. -3 color coding cones required for color detection

Question 36

S-cone

Answer 36

blue 437 nm

Question 37

rod

Answer 37

498 nm

Question 38

M-cone

Answer 38

green 533 nm

Question 39

L-cone

Answer 39

red 564 nm

Question 40

stripes

Answer 40

ocular dominance

Question 41

swirls

Answer 41

orientation columns

Question 42

cytochrome oxidase stain

Answer 42

blobs

Question 43

V1 major job

Answer 43

edges and contours of objects

Question 44

V2 major job

Answer 44

depth

Question 45

V3 major job

Answer 45

ID of motion

Question 46

V4 major job

Answer 46

color processing

Question 47

dorsal pathway

Answer 47

from primary visual cortex and goes tot the parietal/frontal cortex - primary path associating vision with movement - completes motor acts based on visual input - passes through V3

Question 48

ventral pathway

Answer 48

from primary visual cortex to the inferior temporal cortex - primarily involved in interpreting images (recognizing or copying shapes, forms, faces) and complex patterns - copying/naming objects are separate functions in temporal lobe. damage to one area is possible without damaging the other - facial recognition is a specialized area

Question 49

what are MG cells?

Answer 49

a subset of ganglion cells detects light directly via the blue-sensitive photopigment melanopsin

Question 50

What does melanopsin do?

Answer 50

light, via melanopsin causes changes in calcium levels in MG cells -non-image-forming light -responsive system --> project to hypothalamus (suprachiasmatic nucleus) (circaidian rhythms)