Visual System

Question 1

Path of light to electrical activity

Answer 1

pigment epi -> photo-receptor outer segments -> outer nuclear layer -> outer plexiform layer -> inner nuclear layer -> inner plexiform layer -> ganglion cell layer -> nerve fibre layer

Question 2

Rods

Answer 2

black & white and dim light, high sensitivity to light, 100 million per retina, low visual acuity, periphery of retina, high degree of convergence with bipolar cells, blue-green light

Question 3

Cones

Answer 3

colour, day light, low sensitivity to light, 3 million per retina, high visual acuity, fovea, low degree of convergence with bipolar cells, blue, green and red cones

Question 4

Phototransduction

Answer 4

light exposure dissociates retinal from opsin -> decreases levels of cGMP inside the cell -> hyperpolarisation with high light -> depolarisation of bipolar cells release transmitters that signal GANGLION CELLS -> axon exits eye at optic disk -> optic nerve -> optic tract -> enter brainstem

Question 5

Eyes project to?

Answer 5

Visual cortex, hypothalamus (circadian rhythms), pretectum (reflex control of pupils & lens), Superior colliculus (orientating the movements of head and eyes)

Question 6

Pupillary constriction

Answer 6

retina -> optic n. -> optic chiasm -> optic tract -> pretectal nucleus -> parasym. nucleus of oculomotor n. -> preganglionic CNIII fibres -> ciliary ganglion -> post-ganglionic parasymp. to circular constriction

Question 7

Menance response

Answer 7

eye -> optic n/chiams/tract -> lat. geniculate -> optic rad. -> visual cortex -> motor cortex -> facial m.

Question 8

Pupillary dilation

Answer 8

midbrain -> Spinal cord -> tectotegmental -> ramus communicans -> vagosymp. trunk -> ganglions -> eye

Question 9

Horners

Answer 9

Dog & Horse:
miosis, enophthalmas, ptosis, 3rd eyelid prolapse
Horse extra:
sweating of face and neck

Question 10

Damage: Right optic nerve

Answer 10

Present:
left menace, left PLR (both)
Absent:
right menace, right PLR (neither)
Dilation:
L: normal, R: normal to partial

Question 11

Damage: Right CN III

Answer 11

Present:
left menace, right menace, 
Absent:
Right PLR (only left), left PLR (only left)
dilation:
L: normal R: complete

Question 12

Damage: Right retrobulbar

Answer 12

Present:
left menace, 
Absent:
right menace, left PLR (left only), right PLR (neither)
Dilation:
L: normal R: complete

Question 13

Damage: Right optic tract

Answer 13

Present:

Absent:
Dilation: