Ocular Physiology

Question 1

Order this in the correct sequence:

1. All-trans retinol is transported to the RPE cells
2. Light is absorbed by the photoreceptor
3. All-trans retinal is reduced to all-trans retinol
4. 11-cis retinal is converted to all-trans retinal
5. 11-cis retinal is shuttled back to the photoreceptors to be incorporated into the photopigments in the disc outer segment
6. All-trans retinal moves from the disc lumen into the cytoplasm
7. All- trans retinol is converted to 11-cis retinol in the RPE

Answer 1

2 –> 4 –> 6 –> 3 –> 1 –> 7 –> 5

Question 2

Photoreceptors have approx what electrical charge in the dark?

Answer 2

-50 mV

Question 3

The Na/K ATPase pump pumps Na (in/out) while moving K (in/out) in the inner segment?

Answer 3

Na OUT
K in

NOTE: Na reenters inner segment iva Na+ channels located in the OUTER segment

Question 4

When PR are depolarized what NT do they release and onto what cell (“ON” cells)?

Answer 4

They release GLUTAMATE onto BIPOLAR CELLS

Question 5

Which enzyme keeps Na+ channels open to promote depolarization with regard to the retina and PR?

Answer 5

cGMP

keeps Na+ channels open to promote depolarization

Question 6

What is unique about PR, horizontal cells and OFF-center cone bipolar cells?

Answer 6

they HYPERPOLARIZE to LIGHT

Question 7

What is the key event during phototransduction?

Answer 7

CLOSURE of Na+ channels & effectively “shutting off” the PR by DEC their release of glutamate

Question 8

Dissociation of which protein triggers the activation of G proteins, TRANSDUCIN, which leads to a cascade that unltimatel results in a DEC in [cGMP] when light is absorbed?

Answer 8

Rhodopsin

This triggers phototransduction

Question 9

What does DEC in cGMP result in?

Answer 9

Closure of Na+ channels thus INCREASING negative charge in the cell to -65 mV –> AKA hyperpolarization –> DEC glutamate to bipolar cells

Question 10

Which retinal NT is excitatory and released by ALL rods, cones, bipolar cells & MOST ganglion cells?

Answer 10

Glutamate

Question 11

Which retinal NT is inhibitory and released by horizontal and amacrine cells?

Answer 11

GABA & glycine

Question 12

What happen to ON-center bipolar cells in the light?

Answer 12

They depolarize due to less glutamate being released which results in depolarization

RECALL that this type of bipolar cell is inhibited by glutamate

Question 13

What happens to OFF-center bipolar cells in the light?

Answer 13

They hyperpolarize due to a DEC in glutamate which results in hyperpolarization

RECALL that this type of bipolar cell is EXCITED by glutamate

Question 14

Which bipolar cell always depolarizes in response to light?

Answer 14

ROD bipolar cells

Question 15

True or False. Horizontal cells do not have a center surround receptive field.

Answer 15

True

Question 16

Horizontal cells hyperpolarize or depolarize in the presence of light?

Answer 16

Hyperpolarize

NOTE: they also respond w graded potentials the same way off-center bipolar cells and PR do in light.

Question 17

True or False. Amacrine cells have center/surround receptive fields & respond with graded potentials.

Answer 17

FALSE.

They do have a center/surround receptive field; however, respond w ACTION POTENTIALS

Question 18

Amacrine cells always depolarize or hyperpolarize in response to light?

Answer 18

DEPOLARIZE

NOTE; amacrine cells fine-tune the signal btwn bipolar and ganglion cells

Question 19

ON-center/OFF-surround ganglion cells do what in the presence of light (de or hyper polarize?)

Answer 19

DEPOLARIZE

ON-center = depolarize in light (less glutamate which inhibits)

NOTE: ON-center/OFF-surround also synapse w ON-center bipolar cells

Question 20

OFF-center/ON-surround ganglion cells do what in light?

Answer 20

HYPERPOLARIZE

NOTE: OFF-center/ON-surround synapse w OFF-center bipolar cells

Question 21

Outer plexiform layer has axons of which 3 cells?

Answer 21

1. Bipolar
2. Photoreceptors
3. Horizontal

“BPH”
All from the INL

Question 22

Inner plexiform layer has axons from which 3 cells?

Answer 22

1. Bipolar
2. Amacrine
3. Ganglion

in the “BAG”

Question 23

What causes the foveal reflex to dim with age?

Answer 23

Thickening of the ILM

Question 24

Rod density decreases with age. Does that mean the scotopic function declines as well?

Answer 24

NO

Question 25

How does atrophy that increases with age manifest throughout the retina?

Answer 25

1. PPA (optic disc)
2. DEC pigmentation in RPE/choroid (throughout posterior pole)
3. Periphery (paving stone degeneration)