Untitled Quiz

Study Notes

Brain Stem

The brain stem is comprised of the medulla oblongata, pons, and midbrain. It connects the spinal cord to the cerebrum.
The brain stem is directly continuous with the diencephalon above and the spinal cord below.

Medulla Oblongata

The medulla oblongata is 3 cm long and conical in shape.
The medulla oblongata is divided into the open medulla (upper half) and the closed medulla (lower half).
The open medulla forms part of the floor of the fourth ventricle while the closed medulla contains the central canal, which is continuous with the spinal cord.

External Features

Ventrolateral Surface:
- Anterior median fissure: Continuous with the spinal cord.
- Pyramid: An elevation caused by the corticospinal tract.
- Olive: An oval elevation overlying the inferior olivary nucleus. The hypoglossal nerve (XII) exits between the olive and pyramid.
- Inferior cerebellar peduncle: A bundle of nerve fibers connecting the medulla to the cerebellum. The glossopharyngeal, vagus, and cranial root of the accessory nerves exit between the olive and inferior cerebellar peduncle.
Dorsal Surface of the Open Medulla:
- Forms the lower part of the floor of the fourth ventricle.
- Separated from the pons by the medullary stria.
- Bounded laterally by the inferior cerebellar peduncles.
- Contains a vertical median sulcus and an inverted V-shaped depression called the inferior fovea.
- The inferior fovea divides the medullary part into three areas:
  - Hypoglossal trigone: Overlies the nucleus of the hypoglossal nerve.
  - Vagal trigone: Overlies the dorsal nucleus of the vagus nerve.
  - Vestibular area: Overlies the inferior and medial vestibular nuclei.
- Area postrema: A protuberance at the inferoposterior limit of the fourth ventricle.
Dorsal Surface of the Closed Medulla:
- Contains a posterior median sulcus (continuous with the spinal cord).
- Gracile tract and tubercle: Overlying the gracile nucleus.
- Cuneate tract and tubercle: Overlying the cuneate nucleus.
- Tuberculum cinereum: Overlies the spinal nucleus of the trigeminal.
- Inferior cerebellar peduncle: Two bundles that extend upwards and laterally along the sides of the fourth ventricle.

Blood Supply of the Medulla

Anterolateral surface: Supplied by the anterior spinal and 4th part of the vertebral arteries.
Postero-lateral surface: Supplied by the posterior inferior cerebellar artery.
Gracile and cuneate tracts and nuclei: Supplied by the posterior spinal artery.

Pons

The pons is a bridge that connects the medulla oblongata to the midbrain.

Blood Supply of the Pons

Basis pontis: Supplied by the pontine branches of the basilar artery.
Tegmentum:
- Lower pons: Supplied by the posterior inferior cerebellar artery.
- Upper pons: Supplied by the superior cerebellar artery.

Midbrain

The midbrain is 2 cm long and connects the pons and cerebellum with the forebrain.
The midbrain lies between the pons and the diencephalon.
The trochlear nerve (IV) emerges from the dorsal surface of the midbrain just below the inferior colliculus.