Medulla oblongata

The medulla oblongata is the lower portion of the brainstem. By anatomical terms of location, it is rostral to the spinal cord and caudal to the pons, which is in turn ventral to the cerebellum. For a human or other bipedal species, this means it is above the spinal cord, below the pons, and anterior to the cerebellum. It controls autonomic functions and relays nerve signals between the brain and spinal cord.

The medulla is often thought of as being in two parts, an open part (close to the pons), and a closed part (further down towards the spinal cord). The 'opening' referred to is on the dorsal side of the medulla, and forms part of the fourth ventricle of the brain.

Running down the ventral aspect of the medulla are the pyramids which contain corticospinal fibres. On the open medulla, there is a slight bulge just behind the pyramids called the olive or olivary nuclei. Cranial nerve XII (the hypoglossal nerve) emerges between these two structures. Cranial nerves IX and X (glossopharyngeal and vagus nerves) also emerge from the medulla.

The base of the medulla is defined by the commissural fibres, crossing over from the ipsilateral side in the spinal cord to the contralateral side in the brain stem - below this is the spinal cord.

Function of the medulla oblongata

 * 1) To control autonomic functions (such as breathing and heartbeat)
 * 2) To relay nerve messages from the brain to the spinal cord
 * 3) Processing of inter-aural time differences for sound localization (olivary nuclei)
 * 4) Function control of sneeze-, cough-, swallow-, suck-reflex and of vomiting.

Blood supply
Blood to the medulla is supplied by a number of arteries.
 * Direct branches of the vertebral artery
 * Posterior inferior cerebellar artery (PICA)
 * Anterior spinal artery

The anterior spinal artery supplies the whole medial part of the medulla oblongata. A blockage (such as in a stroke) will injure the pyramidal tract, medial lemniscus and the hypoglossal nucleus. This causes a syndrome called medial medullary syndrome.

The posterior inferior cerebellar artery, a major branch of the vertebral artery, supplies the posterolateral part of the medulla, where the main sensory tracts run and synapse. (As the name implies, it also supplies some of the cerebellum.)

The vertebral artery supplies an area between the other two main arteries, including the nucleus solitarius and other sensory nuclei and fibres. Lateral medullary syndrome can be caused by occlusion of either the PICA or the vertebral arteries.