Chapter 11 - The Medulla Oblongata

Abstract

The medulla (myelencephalon) is caudally continuous with the C1 level of the spinal cord and rostrally with the caudal pons at the pons-medulla junction. Characteristic structures of the medulla include the pyramid (containing corticospinal fibers), olivary eminence, pre- and post-olivary sulci, restiform body, and tubercles formed by the gracile and cuneate nuclei and fibers of the spinal trigeminal tract. Medullary nuclei derived from the basal plate include the hypoglossal, dorsal motor vagal, and nucleus ambiguus; the vestibular, cochlear, and solitary nuclei, and the spinal trigeminal tract and nucleus arise from the alar plate. The level of the motor decussation is at caudal medullary levels and followed immediately rostral by the sensory decussation (crossing of posterior column-medial lemniscus fibers). At midolivary levels the principal olivary nucleus, pre- and post-olivary sulci, and restiform body, and reticular formation are especially obvious. The hypoglossal, vestibular, and solitary nuclei, and the spinal trigeminal nucleus and tract are also clear at this level. The cochlear nuclei are specifically characteristic of the medulla-pons junction while the spinal trigeminal tract and nucleus extends throughout the length of the medulla. Lesions of the medulla may damage nuclei and/or exiting roots of cranial nerves located therein as well as long tracts traversing the medulla. The blood supply to the medulla is primarily via anterior spinal, vertebral, and posterior inferior cerebellar arteries.