[Note] The Midbrain & Rule of 4.

The brain stem is a stalk like structure found in the brian, made up of the midbrain, pons and medulla oblongaia.

Each feature has its own important function, but all together the brain stems has the following functions:
- Communication between Cerebrum, Cerebellum, and Spinal Cord.
- Cardiovascular, Respiratory, Vomiting and Vasomotor Centers.
- Passageway for neuropathway.
- Home of Cranial Nerve Neuclei.

The brain stem begins at the level of the Cerebral Peduncles, and Corpora Quadrigemina. It ends at the level of the Foramen Magnum and Decussation of the Pyramids.

The Midbrain is the superior and widest part.
The Pons is in the middle.
The Medulla Oblongaia is at the bottom and is the narrowest part.

Blood Supply, is derived of the Vertebral and Bastilar Arteries. The midbrains vascular supply is from the posterior cerebral artery and its pedunclar branches, the superior cerebellar artery, the posterior chorodial artery, and the interpedunclar branches of the basilar artery.

Majority of the vascular supply of the pons comes from the Pontine artery, the anterior inferior cerebellar artery (AICA), and the Superior Cerebellar Artery (SCA).

the Medullas vascular supply is complex and changes depending on the level. In general:
- The spinal artery
- the posterior inferior cerebellar artery (PICA)
- the anterior inferior cerebellar artery (AICA)
- the vertebra artery

The rules of 4 for the brain stem:

basically everything to do with 4s.
There are 4 structures in the midline beginning with M.
- Motorpathway (Corticospinal Tract)
- Medial Lemniscus
- Medial Longitudinal Fasculus (MLF)
- Motor Nucleus and Nerves

4 structures in the sides beginning with S:
- Spinocerebellae pathways
- Spinothalamic pathway
- Sensory nuclei of 5th cranial nerve
- sympathetic pathway

4 cranial nerves in the medulla, pons AND above the pons (2 in midbrain).
Midbrain: 3, 4
Pons: 5 6 7 8
Medulla: 9, 10, 11, 12

4 motor cranial nerve nuclei in the midline, divide equally into 12.