PHYS: Visual and Auditory Physiology

Question 1

4 steps/processes required for vision

Answer 1

1. ACCOMODATION - the image must be focused on the back of the retina
2. LIGHT REFLEX - the pupil must dilate/constrict enough so that the appropriate amount of light falls on the retina so that light can be detected but the rods/cones aren’t bleached out
3. PHOTOTRANSDUCTION - light causes change vitA/retinol conformation to generate an AP
4. VISUAL PATHWAYS - the AP must travel through the visual pathways to the visual cortex.

Question 2

What is lateral inhibition?

Answer 2

The ‘pruning’ of a light signal, the capacity of an excited neuron to reduce the activity of its neighbors.

This allows sharp edges to be visualised.

Question 3

How and why does accomodation occur?

Answer 3

Ciliary muscles relax/contract to change the shape of the lens and hence the amount that the light is refracted as it passes through, changing the focal point so that the image falls on the retina (so we can have a range of distances at which an image can be focused).

Question 4

To accomodate to see a near object what will the ciliary muscles do and what effect does this have on the lens?

Answer 4

NEAR: the muscles contract, this reduces tension on the lens and makes it rounder/more swollen = more refraction.

(FAR: ciliary relaxation, tension on lens, flatter & thinner)

Question 5

What is an astigmatism?

Answer 5

Imperfection/irregularity in the curvature of the cornea, creating an irregular pattern of vision

Question 6

What is the term for the age related stiffening of the lens? What is the effect of this?

Answer 6

Presbyopia.

Difficulty with focusing near objects.

Question 7

What is the medical term for near-sightedness/far-sightedness? Normal sight?

What is the mechanism/pathology in each case?’

Answer 7

Myopia & hyperopia. Emmetropia.

Myopia = too much convergence, focal point in front of retina, need diverging lenses.

Hyperopia = not enough convergence through the lens, focal point behind retina, need converging lenses.

Question 8

Which muscle and motor system constricts the pupil? Relaxes?

Answer 8

CONSTRICT: inner, circular iris muscle/sphincter. Parasympathetic.

DILATE: outer, radial iris muscle. Sympathetic (fight or flight, lets in more light).

Question 9

What is the term for the reflex where shining light in one eye makes the opposite pupil constrict?

Answer 9

Consensual pupillary reflex

Question 10

What is the fovea?

Answer 10

Area in the centre of the macula which has the highest density of cones in the eye and is hence specialised for high-acuity visions.