The myelencephalon is categorized as a secondary vesicle in the development of the central nervous system. The prefix "myelen" is derived from Greek for medulla (myelos). The myelencephalon differentiates primarily into the medulla oblongata and a caudal portion of the fourth ventricle, but will also contain portions of the following cranial nerves: vestibulocochlear nerve (CN VIII), glossopharyngeal nerve (CN IX), vagus nerve (CN X), accessory nerve (CN XI), and hypoglossal nerve (CN XII).
The myelencephalon develops from the primary vesicular structure called the rhombencephalon (or hindbrain), which is present in all vertebrate embryos. The rhombencephalon normally begins its differentiation into the myelencephalon and the metencephalon at approximately 5 weeks of gestational development in humans. Evolutionarily, the myelencephalon is the area of the brain which is the most ancestral, eventually controlling visceral mechanisms (basic bodily functions) such as breathing, heart and blood vessel activity, digestions, and peristalsis.
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Grey: Raphe/
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