9.7 Detection of light by mammals

Question 1

What are the two types of photoreceptors in found in the retina

Answer 1

• Rod cells
• Cone cells

Question 2

What is the purpose of rod cells

Answer 2

• To provide grayscale vision

Question 3

What is the purpose of cone cells

Answer 3

• To provide colour vision

Question 4

Why are rod cells more sensitive to light

Answer 4

• Due to convergence
• Many rod cells synapse with one bipolar nerve fibre so action potential is easily generated

Question 5

What is the pigment found in rod cells

Answer 5

• Rhodopsin

Question 6

How do rod cells differ from normal neurones ?

Answer 6

• They are normally permeable to sodium ions

Question 7

Explain how no action potential is generated when the rod cells are at rest

Answer 7

1 - Na+ ions are actively being pumped out via active transport but they are moving back in via open sodium ion channels.
2 - This causes inside of the cell to become partially negative than the outside, membrane is partially depolarised
3 - This triggers release of inhibitory neurotransmitter
4- This neurotransmitter inhibits the bipolar neurone so no info goes to brain

Question 8

Explain what happens to rhodopsin when light hits the rod cells

Answer 8

• Rhodopsin is converted into opsin and transretinal.(bleaching)

Question 9

Explain the role of rhodopsin in the generation of a nerve impulse in the bipolar neurone

Answer 9

• Rhodopsin broken into opsin and transretinal
• This causes Na+ channels on rod cells to close
• This leads to rod cell hyperpolarising
• Less inhibitory transmitter is released

Question 10

Describe how light causes a change in the release of glutamate from rod cells.

Answer 10

• Rhodopsin breaks down into opsin and transretinal
• This causes Na+ channels to close
• Na+ still diffusing out of rod cell, causing hyperpolarisation
• Hyperpolarisation stops the release of glutamate