Physiology II

Question 1

Describe the passage of light inside the retinal cells

Answer 1

1. Photoreceptors
2. Bipolar cells
3. ganglion cells

Question 2

What is the role of horizontal cells?

Answer 2

Receive input from photoreceptors and project to other photoreceptors and bipolar cells

Question 3

What is the role of amacrine cells?

Answer 3

Receive input from bipolar cells and project to ganglion cells, bipolar cells and other amacrine cells

Question 4

What are the four main regions of the photoreceptor cell?

Answer 4

Outer segment
Inner segment
Cell body
Synaptic terminals

Question 5

What are the types of photoreceptor?

Answer 5

Rods and cones

Cones- short, medium, long wave

Question 6

What causes cells to release glutamate?

Answer 6

Light causes conversion of chemicals in photopigment regions causing the cell to release glutamate

Question 7

What is the membrane potential of vertebrate photoreceptors?

Answer 7

Depolarised -20mV

Question 8

What happens to membrane potential in photoreceptors with light exposure?

Answer 8

Hyperpolarisation

Question 9

What is the dark current?

Answer 9

A cGMP gated Na+ channel that is open in the dark and closes in light

Question 10

Describe the dark current in the dark

Answer 10

PNa = PK (Na channels in the outer segment)

Vm therefore between ENa and EK

Question 11

Describe the dark current in the light

Answer 11

PNa is reduced (outer segment channels close), PK > PNa

therefore, Vm —> EK, hyperpolarizes

Question 12

Why are photoreceptor signals amplified?

Answer 12

so we can interpret a small change in light

Question 13

What is the visual pigment in rods?

Answer 13

Rhodopsin- vitamin A derivative + opsin (GPCR)

Question 14

Where is rhodopsin present?

Answer 14

membrane folds (called discs in outer segment)

Question 15

What does light convert 11-cis-retinal to?

Answer 15

all-trans-retinal (activated form)

Question 16

In the dark there is … glutamate

Answer 16

more

Question 17

What is visual acuity?

Answer 17

ability to distinguish two nearby points.

determined largely by photoreceptor spacing and refractive power

Question 18

When do rods/cones see?

Answer 18

rods= see in dim light

cones= see in normal daylight

Question 19

Where is the highest density of cones?

Answer 19

Fovea

Question 20

Why do rods have such a high convergence?

Answer 20

Many rods can access one ganglion giving poor acuity but allowing you to see in the dark; the signals assimilate to one larger signals

Question 21

What allows us to see in colour?

Answer 21

differnet rods and cones for specific spectra

Question 22

What does our visual system detect?

Answer 22

local differences in light intensity- not the absolute amounts of light

Question 23

What is our visual system good at?

Answer 23

Identifying differences

Question 24

What causes amblyopia?

Answer 24

multitude of issue

No problem with optics and retina

Question 25

What happens to the visual cortex in amblyopia?

Answer 25

The dominant eye will take over

Question 26

Describe hebb’s postulate

Answer 26

Cells that fire together, wire together

Question 27

What are the 5 characteristics of rods and cones

Answer 27

Rods : Cones

Achromatic : Chromatic

Peripheral retina : Central retina

High convergence : low convergence

High light sensitivity : low light sensitivity

Low visual acuity : high visual acuity