Midbrain

Question 1

What is the midbrain also known as?

Answer 1

mesencephalon

Question 2

Where is the midbrain in relation to the other components of the brainstem?

Answer 2

most superior

Question 3

The midbrain can be divided into two main parts, what are they?

Answer 3

1. tectum = located posterior to the cerebral aqueduct
2. paired cerebral peduncles

Question 4

Internally, the paired cerebral peduncles are further separated by the substantia nigra into what?

Answer 4

the crus cerebri (anterior)
tegmentum (posterior)

Question 5

The tectum houses 4 rounded prominences called what?

Answer 5

Colliculi - collective called the corpora quadrigemina which sit directly inferior to the pineal gland. There are two superior and inferior colliculi

Question 6

What separates the colliculi?

Answer 6

cruciform sulcus

Question 7

What are the superior colliculi concerned with?

Answer 7

part of the visual system, concerned with eye reflexes

Question 8

What are the inferior colliculi concerned with?

Answer 8

part of the auditory system, concerned with the reflex of looking towards a loud noise

Question 9

What extends laterally from each colliculi?

Answer 9

The quadrigeminal brachium

Question 10

What does the superior quadrigeminal bracium do?

Answer 10

Forms a pathway between the superior colliculus and the retina of the eye
Conveys visual information from the lateral geniculate body to the superior colliculi

Question 11

What does the inferior quadrigeminal brachium do?

Answer 11

conveys auditory information from the medial geniculate body to the inferior colliculi

Question 12

Where do the cerebral peduncles extend from?

Answer 12

Extend from the cerebral hemispheres to converge as they meet at the pons

Question 13

What separates the cerebral peduncles anteriorly in the midline?

Answer 13

Interpeduncular fossa - floor of which is termed the posterior perforated substance

Question 14

Which cranial nerve is seen exiting from between the peduncles?

Answer 14

oculomotor nerve (CN III)

Question 15

What is the function of the pineal gland?

Answer 15

an endocrine gland that synthesises melatonin which modulates sleep patterns in both circadian and seasonal rhythms

Question 16

Name the 4 fibre tracts which run within the crus cerebri

Answer 16

1. frontopontine fibres - located most medially
2. corticospinal fibres - motor fibres from the primary motor cortex
3. corticobulbar tracts - motor fibres from the primary motor cortex
4. temporopontine fibres - located posterolaterally

Question 17

Where is the tegmentum located in relation to the substantia nigra?

Answer 17

tegmentum is located posterior to the substantia nigra

Question 18

What is the cerebral aqueduct surrounded by?

Answer 18

periaqueductal grey matter - within this lies the mesencephalic nucleus of the trigeminal nerve as well as the trochlear nucleus

Question 19

What lies between the central grey matter and the substantia nigra?

Answer 19

4 lemnisci = bundles of fibres
moving anterior to posterior they are the medial, spinal, trigeminal and lateral lemnisci

Question 20

How does the internal structure of the midbrain differ at the level of the inferior and superior colliculus? - think central portion, cranial nerve nucleus and lemnisci differences

Answer 20

Most of the internal structure from the level of the inferior colliculus to the superior colliculus is unchanged. However, the central portion which was occupied by the decussation of the superior cerebellar peduncles at the level of the inferior colliculus now contains large paired red nuclei, with some decussation of the rubrospinal tract occurring anterior to this at the level of the superior colliculus. The trochlear nucleus is replaced with the oculomotor nucleus. The medial, spinal and trigeminal lemnisci are all present but the lateral lemnisci does not reach this level

Question 21

Where does the midbrain receive its blood supply from?

Answer 21

Basilar artery and its branches:
- posterior cerebral artery and its peduncular branch
- superior cerebellar artery
- posterior choroidal artery
- interpeduncular branches of the basilar artery