Vision

Question 1

What are the advantages of compound eyes?

Answer 1

Better sensitivity to movement and wider range of wavelengths. Bugs can see UV light!

Question 2

What are the advantages of the refractive eye?

Answer 2

Better for resolving power. Visual acuity

Question 3

how would you increase the visual acuity of a compound eye?

Answer 3

By increasing the number of cells

Question 4

What causes glaucoma?

Answer 4

Blockage of the canal of schlemm. Without a place for aqueous humor to drain, pressure builds up in the anterior chamber of the eye. This pinches off blood vessles and damage neurons of the retina causing blindness

Question 5

What is accomodation?

Answer 5

Change in the refractive power of the lens by changing its shape

Question 6

What happens when the ciliary muscle is relaxed?

Answer 6

Suspensory ligaments are taught and the lens is flat for far vision

Question 7

What happens when the ciliary muscles contract?

Answer 7

Suspensory ligaments become slack and lens rounds for near vision

Question 8

What is myopia?

Answer 8

Near-sightedness. Focal point occurs before the retina.

Question 9

What is hyperopia?

Answer 9

Far-sightedness. Focus of image is behind the retina

Question 10

What do you use to correct myopia? Hyperopia?

Answer 10

Myopia=concave lens

Hyperopia=convex lens

Question 11

What is cataracts?

Answer 11

Opacities in the lens of the eye that interfere with vision. Caused by changes in lens proteins called crystallins

Question 12

What sort of receptor cells are predominantly in the fovea? Outside the fovea?

Answer 12

Fovea is mostly cones. Outside of the fovea is mostly rods

Question 13

What is the tapetum?

Answer 13

Reflective layer in nocturnal animals. Helps reflect light that was not absorbed by retina. Second chance to be absorbed to increase sensitivity to light

Question 14

What is the tapetum made of? What are the disadvantages?

Answer 14

Made up of guanine crystals. Disadvantage=decreases acuity

Question 15

What is retinal detachment?

Answer 15

Separation of the retina from the pigment epithelium, which deprives it of its blood supply

Question 16

What is the macula?

Answer 16

Yelowish pigmented spot surrounding the fovea

Question 17

What is macular degeneration

Answer 17

Loss of pigment epithelial cells and then photoreceptors causing central vision loss and sometimes retinal detachment

Question 18

Drusen

Answer 18

Yellow or white accumulations of protein and lipids seen around the retina. Seen in dry macular degeneration

Question 19

What do amacrine cells do?

Answer 19

Modulates bipolar cell output to ganglion cells.

Question 20

What do horizontal cells do?

Answer 20

regulate and integrate information from photoreceptor cells

Question 21

What do Muller cells do?

Answer 21

Support neuronal cells of the retina. Can help with regeneration of retinal cells after damage

Question 22

What happens to the disks in rods and cones?

Answer 22

They move towards the pigment epithelial cells where they are phagocytosed

Question 23

What are the advantages and disadvantages of rods (sensitivity to light? resolution? Acuity? Color?)

Answer 23

High sensitivity for night vision. Low resolution and acuity. No color. Only one type of rod pigment

Question 24

What are the advantages and disadvantages of cones (sensitivity to light? resolution? Acuity? Color?)

Answer 24

Lower sensitivity to light, high resolution and acuity, and detects color with three types of cones (RBG)

Question 25

What is convergence? Which cells have higher convergence? What are the advantages and disadvantages of having convergence?

Answer 25

Convergence means that many photoreceptor cells feed signals into a single bipolar cell. Rods have high convergence while cones have low convergence. Increase convergence has the advantage of increased sensitivity to light but the disadvantage of lower acuity, since the light signal cannot be pinpointed to a single cell on the pigmented epithelium

Question 26

What is the response of photoreceptors to light?

Answer 26

They HYPERpolarize!

Question 27

Describe the processes (channels, ions, etc) that occur when a photoreceptor is in the dark vs. light

Answer 27

``` DARK: High cGMP concentration cGMP-gated channels are open Na/Ca enter into the cell "dark current" Slight depolarization of cell causes neurotransmitter release ``` ``` LIGHT Lower cGMP cGMP channels closed No Na/Ca in, no "dark current" Cell hyperpolarizes Less neurotransmitter release ```

Question 28

What molecule is essential for conversion of the light signal into an electrical response?

Answer 28

11-cis-retinal is converted to 11-trans retinal in the rhodopsin molecule. This causes a conformational change that activates phosphodiesterase, which breaks down cGMP to 5'GMP.

Question 29

What is rhodopsin made out of?

Answer 29

11-cis-retinal + opsin

Question 30

What are the two ways in which the response to light is terminated?

Answer 30

1. Retinal recycling: Retinal binding protein transports trans retinol back to pigment epithelial cells to convert it back to 11-cis retinal. SLOW STEP 2. Calcium levels decrease inside cell. With less calcium available to inhibit rhodopsin kinase, it phosphorylates and thus inactivates rhodopsin. Also decreases Ca inhibition of guanylate cyclase, returning cGMP levels back to normal

Question 31

The optimal wavelength at which a photopigment will absorb light is determined by...??

Answer 31

The type of OPSIN it contains. Rods only have one rod opsin while cones have three

Question 32

Where would you find the rod opsin gene?

Answer 32

Chromosome 3

Question 33

Where would you find the blue opsin gene?

Answer 33

Chromosome 7

Question 34

Where would you find the green and red opsin genes?

Answer 34

X chromosome. Hence male color-blindness

Question 35

What is the function of M-type ganglion cells?

Answer 35

involved in motion detection--has larger receptive field

Question 36

What is the function of P-type ganglion cells?

Answer 36

Involved in color vision and has a smaller receptive field

Question 37

What is special about the W type ganglion cell?

Answer 37

They have melanopsin and there is NO center-surround receptive field

Question 38

What happens when an on center cell undergoes stimulation from light?

Answer 38

HYPERpolarizes This causes reduced release of inhibitory neurotransmitter. This increases firing of the bipolar cell which releases increased transmitter Ganglion cell then has increased firing rate

Question 39

What happens when an off-surround cell undergoes light stimulation?

Answer 39

Surround cells are hyperpolarized Less inhibitory neurotransmitter released Horizontal cell then has fewer inhibitory signals to the postsynaptic terminal of the center cell. Increased inhibitory neurotransmitter release Bipolar cell hyperpolarized Decreased transmitter release to ganglionic cell Decreased firing rate of ganglionic cell

Question 40

What determines whether a cell is On-center or Off-center?

Answer 40

The type of glutamate receptor expressed by the bipolar cell. On-Center: Metabotropic mGluR6 receptors. These are inhibited by neurotransmitter release by the center cone. Off-center=Ionotropic NMDA/AMPA receptors on the bipolar cell. They are stimulated by neurotransmitter released by the center cone

Question 41

What is the purpose of the W type ganglion cells?

Answer 41

Internal circadian rhythm

Question 42

What is the purpose of the superior coliculus?

Answer 42

Orienting movements of head and eyes

Question 43

What is the purpose of the pretectum?

Answer 43

Reflex control of pupil/lens

Question 44

Neurons from which part of the retina decussate?

Answer 44

The right sides of both eyes

Question 45

You notice that the right pupil is not responsive to light. However, when you shine the light into the right eye, you observe a normal pupillary contraction in the left eye. Where is the lesion?

Answer 45

Damaged right oculomotor nerve.

Question 46

You notice that when you shine a light into the right eye, there is no pupillary response. However, when you shine the light into the left eye, you have a NORMAL pupillary response in BOTH eyes. Where is the lesion?

Answer 46

In the right optic nerve

Question 47

Where do P type ganglion cells project to?

Answer 47

Layers 3-6 of the lateral geniculate nucleus. Info on color vision

Question 48

Where do M type ganglion cells project to?

Answer 48

Layers 1-2 of the lateral geniculate nucleus. Info on Movement.