Optic tracts

Question 1

Where are the optic tracts located?

Answer 1

wind round the cerebral peduncles of the rostral midbrain

Question 2

What does each optic tract split into?

Answer 2

• large lateral root
• smaller medial root

Question 3

Where do the large lateral roots of the optic tracts terminate?

Answer 3

posteriorly in the lateral geniculate body

Question 4

What is the lateral root of the optic tracts concerned with?

Answer 4

conscious visual sensation

Question 5

What is the smaller medial root of the optic tract connected to?

Answer 5

connected to the pretectal area and superior colliculus by the superior brachium

Question 6

What proportion of optic tract fibres are carried by the medial root?

Answer 6

10%

Question 7

What are the 6 groups of fibres in the medial optic tract (not concerned with conscious vision)?

Answer 7

3 target superior colliculus:

1. visual grasp reflex
2. automatic scanning of images
3. visual association pathways

Remaining 3:

1. enter pretectal nucleus (pupillary light reflex)
2. enter parvocellular reticular formation (arousal function)
3. enter retinohypothalamic tract (?photoperiod regulation - effect of light on mood)

Question 8

What are the 3 different types of fibres from the medial root of the optic tract that target the superior colliculus?

Answer 8

1. visual grasp reflex
2. automatic scanning of images
3. visual association pathways

Question 9

What is the function of the group of fibres from the medial root of the optic tract that enter the pretectal nucleus?

Answer 9

serve pupillary light reflex

Question 10

What is the function of the group of fibres from the medial root of the optic tract that enter the parvocellular reticular formation?

Answer 10

arousal function

Question 11

What is the function of the group of fibres from the medial root of the optic tract that enter the retinohypothalamic tract?

Answer 11

terminates in suprachiasmatic nucleus of hypothalamus → possibly involved in photoperiod regulation, has been invoked to account for beneficial effect of bright artifical light or sunshine on mood

Question 12

Where does the retinohypothalamic tract terminate?

Answer 12

in the suprachiasmatic nucleus of the hypothalamus

Question 13

What are the superior colliculi?

Answer 13

2 small rounded elevations located on the dorsal surface of the midbrain above the inferior colliuli, visible on external examinatin of the brainstem

Question 14

What lies between and above the superior colliculi?

Answer 14

pineal body

Question 15

What are the 2 pairs of colliculi collectively referred to as?

Answer 15

the tectum

Question 16

How does the age of the mesencephalic or tectal termination of optic tract fibres compare with the forebrain termination (visual cortex)?

Answer 16

the mesencephalic/tectal termination of fibres is phylogenetically older than forebrain termination in visual cortex

Question 17

What is the pathway of the lateral root of the optic tract?

Answer 17

passes backwards, a little upwards, and terminates in lateral geniculate nucleus (LGN) part of the thalamus (relay station for ascending sensory info)

Question 18

Why isn’t the lateral root of the optic tract completely free?

Answer 18

its medial aspect is attached to the outer wall of the third ventricle by a narrow band of tissue

Question 19

What happens to the orientation of the lateral root of the optic tract as it passes around the cerebral peduncles?

Answer 19

rotates slightly on its own axis - 90 degrees inward twist

Question 20

What are 2 key structures that the optic tract runs superiorly to?

Answer 20

1. dorsum sella
2. third nerve - crosses it from medial to lateral

Question 21

What structure does the optic tract run below?

Answer 21

runs below and parallel to the posterior cerebral artery

Question 22

What 2 structures overlap the middle portion of the optic tract?

Answer 22

1. uncus
2. parahippocampal gyrus