The Midbrain

Question 1

What makes up the brainstem?

Answer 1

From superior to inferior:

1) Midbrain (acts as a conduit between the cerebrum above and the pons and cerebellum below).
2) Pons
3) Medulla

Question 2

What are the main parts of the midbrain (mesencephalon)?

Answer 2

1) Tectum

2) Peduncles

Question 3

What are the main features of the tectum posteriorly?

Answer 3

1) Colliculi (rounded prominences) that sit inferiorly to the pineal gland. There are two siperior and two inferior colliculi.
2) Brachium - these extend from each colliculi.

Superior quadrigeminal brachium - forms a pathway between the superior colliculus and the retina of the eye.

Inferior quadrigeminal brachium - forms a pathway between the inferior colliculus and the medial geniculate body.

Inferior to the colliculi, the trochlear nerve (CN IV) emerges before sweeping across to the anterior surface.

Question 4

What are do the cerebral peduncles

Answer 4

The cerebral peduncles are located on either side of the colliculi.

They extend from the cerebral hemispheres to converge as they meet the pons.

They are separated anteriorly in the midline by the interpeduncular fossa - the floor of which is termed the posterior perforated substance (where many perforating blood vessels can be found).

The oculomotor nerve (CN III) can be seen exiting between the peduncles while the optic tract runs around the superior border of the midbrain.