Physiology 3 (seems niche)

Question 1

Describe the cellular structure of the retina

Answer 1

From outer to inner:

1. Ganglion cells
2. Bipolar cells
3. Photoreceptors

Has horizontal cells at the junction between photoreceptor cells and bipolar cells

Has amacrine cells at the junction between bipolar and ganglion cells

Question 2

Which cells convert the light signals into electrical signals to sense what we are seeing ?

Answer 2

Photoreceptor cells (this is weird as they are the innermost cells)

Question 3

What is phototransduction and describe how it occurs

Answer 3

1. Unstimulated photoreceptors have a depolarised Vm (membrane potential)
2. When light hits the photoreceptors it hyperpolarises them due to the ‘dark current’

Question 4

Describe what the ‘dark current’ is and how this results in electrical signals when photoreceptors are stimulated by light

Answer 4

This is where a cGMP-gated Na+ channel that is open in the dark and closes in the light this change in light is what enables the brain to perceive objects

Essentially in light the Na+ channels close, there is more eflux of K+ which hyperpolarises the membrane hence neurotrasmitter release and signal produced

Question 5

What is visual acuity and what is it determined by ?

Answer 5

• Refers to the clarity of someones vision
• Determined by photoreceptor spacing and refractive power

Question 6

What do rod photoreceptors help us do ?

Answer 6

See in dim light

Question 7

What do cone photoreceptors help us do ?

Answer 7

See in normal daylight

Question 8

Explain the basis of colour discrimination

Answer 8

Basically there is different sub-types of cone photoreceptors which pick up different wavelengths corresponding to different colours of light

Question 9

What is retinotopy ?

Answer 9

This is the mapping of the visual field which is done in the retina, LGN, superior colliculus, & cortex

Question 10

What do people with congenital cataracts (so these are present at birth) have trouble with after they’ve been removed ?

Answer 10

Trouble with perceiving shape and form due to the fact the cataracts arent removed till roughly 10-20 yrs old as too yuong to operate otherwise

Question 11

What is Amblyopia or cotical blindness ?

Answer 11

No problem with the eye but one eye has better vision than the other

Question 12

What are the causes of amblyopia and how is it treated ?

Answer 12

Strabismus (wandering eye)

Until old enough to be corrected surgically then cover the infant’s good eye with a patch for a few hours each day so the brain has to rely on the weaker one