Vision

Question 1

Where is light focused?

Answer 1

A region on the retina called the fovea, containing photoreceptors rod + cone cells

Question 2

How does light enter the eye?

Answer 2

Amount of light entering controlled by the iris; focused by the lens using ciliary muscles and suspensory ligaments

Question 3

Describe rod cells

Answer 3

Found on outer retina
Sensitive to intensity of light
Images generated are black and white

Question 4

Describe cone cells

Answer 4

Found grouped together in fovea
Sensitive to different wavelengths of light
So can determine different colours

Question 6

Describe general structure of nerves carrying impulse from photoreceptors to optic neerve

Answer 6

Cone cell —> each connected to one bipolar neuron—> ganglion cells to optic nerve
Rod cell —> multiple connect to one bipolar neurone —> single ganglion cell

Question 7

What occurs in rod cells in absence of light ?

Answer 7

1) Sodium ions are actively pumped out of rod cell by active transport
2) Sodium ions diffuse back down this concentration gradient into the rod cell via sodium/cation channels
3) little difference in charge between the outside and inside of the rod cell, and the cell is said to be depolarised
4) The depolarised rod cell releases neurotransmitters which diffuse across a synapse to a bipolar neurone
5) this neurotransmitter inhibits the generation of an action potential, preventing a nerve impulse from being sent to the optic nerve

Question 8

What occurs in rod cells in presence of light?

Answer 8

1) Light bleaches rhodopsin, causing it to break apart into retinal and opsin
2) This causes the sodium ion channels in the cell surface membrane of the rod cell to close, preventing sodium ions from diffusing back into the rod cell
- but are still being actively transported out
3) The lack of positively charged ions entering the rod cell causes inside to become more negative until it reaches a hyperpolarised state
4) The hyperpolarised rod cell stops releasing an inhibitory neurotransmitter, so the generation of an action potential in the neighbouring bipolar neurone is no longer inhibited
5) An action potential is generated in the bipolar neurone attached to the rod cell and an impulse is sent to the optic nerve

Question 9

How do pupils change size?

Answer 9

Dim light —> Radial muscles contract to dilate pupils
Bright light —> Circular muscles contract to constrict pupils