Medulla oblongata
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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.
Function of the medulla oblongata
- To control automatic functions (such as breathing and heartbeat)
- To relay nerve messages from the brain to the spinal cord
- Processing of inter-aural time differences for sound localization (olivary nuclei)
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.
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