1.8: Physiology 2

Question 1

Give a quick summary of how vision works?

Answer 1

1. The amount of light hitting the retina is regulated by the eye 2. Lights falls upon the rods and cones in the retina 3. Energy from waves of photons is changed into signals 4. Brain receives and interprets signals

Question 2

Describe the order of the cells of the retina involved in signal transmission? (Front of the eye to the back)

Answer 2

• Optic Nerve Cells - Ganglion Axons - Ganglion Cells - Bipolar Cells - Photoreceptors

Question 3

Describe the direct pathway for signal transmission?

Answer 3

• Photoreceptors - Bipolar Cells - Ganglion Cells - Ganglion Axons - Optic Nerve

Question 4

Describe how the retina is considered ‘back to front’ when it comes to signal transmission?

Answer 4

The optic nerve cells and ganglion axons are furthest forward The Photoreceptors are furthest back However, light hits the photoreceptors first then travels forward

Question 5

What are the two types of photoreceptors?

Answer 5

Rods Cones

Question 6

Function of photoreceptors?

Answer 6

Convert light into neural signs

Question 7

Describe rods and cones?

Answer 7

Rods are found on the periphery and work best in dark, low level light conditions (Eg: Night) Cones are central and work best in high level light conditions (Eg: Daytime) and colour

Question 8

Describe the structure of a photoreceptor?

Answer 8

Synaptic Terminal Inner Segment Cell Body Outer Segment

Question 9

What is in the outer segment of photoreceptors?

Answer 9

There is are membranous disks containing photopigment

Question 10

Describe the physiology of phototransduction?

Answer 10

Photoreceptors have a depolarized resting membrane potential When light is shone, a cGMP-gated Na+ channel closes This causes hyperpolarization The change in Na+ is the signal that allows the brain to perceive objects in the visual field

Question 11

What channel is involved in phototransduction? When is it open, when is it closed? What is this current called?

Answer 11

cGMP-gated Na+ channel Closed during light, open during dark This is the dark current

Question 12

What is the dark current?

Answer 12

This is a cGMP-gated Na+ channel that is open during the dark and closed during the light

Question 13

What is the photopigment in rods called?

Answer 13

Rhodopsin

Question 14

What is retinal? Where is it found?

Answer 14

Retinal is the light-absorbing part of photopigment Opsin (the G-protein coupled receptor) makes a pocket where retinal is found

Question 15

Rhodopsin = X + Y What does X mean? What does Y mean?

Answer 15

Rhodopsin = Opsin + Retinal Opsin is a G-protein coupled receptor Retinal is the light absorbing part

Question 16

What confirmation of Retinal is used in phototransduction?

Answer 16

11-Cis-Retinal

Question 17

What is retinal derived from?

Answer 17

Vitamin A

Question 18

What happens when 11-cis-retinal absorbs a photon of light?

Answer 18

It becomes all-trans retinal This is the active form

Question 19

What happens once 11-cis-retinal has been converted into all-trans-retinal?

Answer 19

This causes closure of cGMP Na+ Gate There is reduced Na+ entry This results in hyperpolarization

Question 20

http://sites.sinauer.com/neuroscience5e/animations11.02.html Watch this animation

Answer 20

…

Question 21

What molecule regulates the dark current?

Answer 21

Rhodopsin

Question 22

What facilitates visual acuity?

Answer 22

Photoreceptor spacing

Question 23

Where is the highest number of cones?

Answer 23

Fovea

Question 24

Where is the highest number of rods?

Answer 24

Periphery

Question 25

What part of the electromagnetic spectrum can we detect?

Answer 25

Only visible light

Question 26

What colour do the short wave cones detect?

Answer 26

Blue

Question 27

What colour do the medium wave cones detect?

Answer 27

Green

Question 28

What colour do the long wave cones detect?

Answer 28

Red

Question 29

Compare visual acuity between rods and cones?

Answer 29

Rods = Low Visual Acuity Cones = High Visual Acuity

Question 30

Compare convergence between rods and cones?

Answer 30

High Convergence = Rods Low convergence = Cones

Question 31

Describe light sensitivity between rods and cones?

Answer 31

Rods = High sensitivity Cones = Low Light Sensitivity

Question 32

Nerve fibres from the XXX half of each retina cross at the optic chiasm. XXX =?

Answer 32

Nerve fibres from the NASAL half of each retina cross at the optic chiasm