Vision: The Eye

Question 1

accommodation

Answer 1

like a camera lens, lens must be shaped correctly so that the image of an object at a distance is focused at the retina. ciliary muscles can change the lens shape. if the accommodation is inaccurate, then poor focus which leads to glasses. age related changes are common

Question 2

iris (light control)

Answer 2

opens and closes to wary the amount of light entering the eye. the hole itself is the pupil. controlled at the brainstem level by a single nucleus which leads to coordination of pupil size in both eyes.

Question 3

what is intraocular movement?

Answer 3

accommodation and iris

Question 4

what is extraocular movement?

Answer 4

extremely precise movements of the eyeball which are done by 3 pairs of muscles: superior/inferior rectus, medial/lateral rectus, and superior/inferior oblique

Question 5

what does the superior/inferior rectus do?

Answer 5

up and down

Question 6

what does the medial/lateral rectus do?

Answer 6

side to side

Question 7

what does the superior/inferior oblique do?

Answer 7

rotation

Question 8

which cranial nerves are involved in eye movement control?

Answer 8

trochlear IV - superior oblique
abducens VI - lateral rectus
oculomotor III - everything else

Question 9

convergence

Answer 9

several receptors connect to individual bipolar cells, which may connect to a single ganglion cell. amacrine and horizontal cells provid lateral communication with neighbouring retina.

Question 10

is convergence greater for rods or cones?

Answer 10

rods

Question 11

why is convergence greater for rods?

Answer 11

there are hundreds of rods per ganglion cells, sometimes only a few cones per ganglion cell. it reflects differences in acuity.

Question 12

scotopic system

Answer 12

works in dim light and mediated by rods, about 90M/eye. it lowers acuity, especially away from fovea.

Question 13

photopic system

Answer 13

needs more light and mediated by cones, about 4.5M/eye. it displays colours, high acuity, especially in and near fovea.

Question 14

receptive fields

Answer 14

convergence of receptors on bipolar and ganglion cells. they record graded potentials from bipolar cells, or AP from ganglion cells. the receptive field looks likea donut, where light falling on the centre excites the cell, and light falling on the surround does vise versa. if light falls on both, centre holds more priority

Question 15

adaptation

Answer 15

receptors shift their range to work around light condition

Question 16

what happens to receptors when going through adaptation?

Answer 16

pupillary size, range fractionation, Ca++ currents altered to change responsiveness, fusion of rentinal and opsin back into pigment is slow

Question 17

Range fractionation

Answer 17

scotopic vision in low light, phototopic in bright light

Question 18

enzyme photsphodiesterase

Answer 18

messenger system that opens Na+ channels