Cranial nerves IX, X, XI and XII originate from the medulla. The ascending and descending tracts of the spinal cord pass through the medulla. Because the architecture differs from that of the spinal cord the tracts are located differently than in the cord; closed medullary levels are more similar to the cord than open medullary levels.
Functions of the medulla include: 1) control of somatic motor reflexes of the larynx, pharynx and tongue which are important in speech and swallowing; 2) control of visceral motor reflexes, e.g., coughing, swallowing, salivating, vomiting, secretion, sneezing; the medulla receives taste and other visceral sensations; 3) the MLF contains fibers for the regulation of the position of the head and neck and for coordinated eye movements; 4) the medulla is a relay for the cochlear and vestibular responses; 5) the reticular formation regulates a variety of functions including skeletal motor activity, consciousness, visceral functions, conduction of sensation, etc. The features of medullary syndromes reflect its anatomy and physiology, i.e., the ascending sensory tracts, the descending motor systems, cranial nerves IX - XI exiting at this level, and the cranial nerves that are associated at or near this level, viz., CN VIII.
In the closed medulla the corticospinal tracts are located in the pyramids on its anterior surface. Posterior white column tracts terminate in the nuclei gracilis and cuneatus, internal arcuate fibers pass ventral to the central canal and central gray. Thus the crossed discriminatory touch pathway continues as the medial lemniscus, located interiorly, just astride the midline. The posterior gray horn of the cord is joined (replaced) by the spinal nucleus and tract of CN V carrying temperature, pain and touch sensation from the head. Located laterally at the surface of the medulla, distant from the medial lemniscus, are the spinothalamic tracts. Near the midline in the central gray, the motor neurons of CN XII send exiting fibers just lateral to the pyramids. Just lateral to the nuclei of cells of CN XII in the central gray is the dorsal motor nucleus of CN X and the nucleus and tractus solitarius; fibers of these nuclei pass laterally to exit the medulla. The posterior spinocerebellar tract is located laterally as in the cord and joins the inferior cerebellar peduncle to enter the cerebellum. Upper extremity fibers for unconscious proprioception terminate on the accessory cuneate nucleus which also sends fibers to the inferior cerebellar peduncle (without crossing). The inferior olivary nucleus, which contributes crossed fibers to the inferior cerebellar peduncle, is lateral to the pyramids.
In the open medulla the nuclei gracilis and cuneatus are not present, the inferior olives are more fully developed, and the central canal has become open to the fourth ventricle. As at closed medullary levels the nucleus of CN XII, the dorsal motor nucleus of CN X, and nucleus solitarius are located sequentially from medial to lateral. Lateral to the preceding nuclei, in the floor of the fourth ventricle, are the vestibular nuclei which give rise to the vestibulospinal tracts. The MLF lies just ventral to the nucleus of CN XII carrying vestibular and lateral reticulospinal fibers. Exiting fibers of CN XII pass between the pyramids and olives to the pre-olivary sulcus; exiting fibers of CN IX, X and IX pass laterally through the medulla to the post-olivary sulcus.
Since vascular lesions occur more commonly in the brainstem than in the spinal cord it is important to understand the distribution of the major vessels of the medulla. Other lesions are due to neoplasms which grow from within the medulla or derive from distant metastases; neoplasms may press on the medulla from its meninges, the cerebellum, or from nearby cranial nerves. Additional causes of medullary syndromes are infections, metabolic, hereditary, traumatic, toxic, etc.
The blood supply of the medulla derives from the vertebral arteries and its anterior and posterior spinal branches. The perforating branches of each vessel perfuse a longitudinal zone of tissue. The anterior zone of the medulla contains the pyramids, MLF, internal arcuate fibers and/or medial lemniscus, and CN XII (nucleus and exiting fibers). Caudally this area is supplied by branches of the anterior spinal artery; rostrally it is supplied by branches from the vertebral and basilar arteries. The lateral zone contains the nucleus ambiguous of the CN X, exiting fibers of CN IX and X, portions of the spinal nucleus and tract of CN V, ventral part of the inferior cerebellar peduncle, spinothalamic tracts, descending autonomics and the inferior olivary nucleus. Caudally this lateral area is supplied by direct branches of the vertebral artery and through its posterior inferior cerebellar artery (PICA) branch; rostrally it is supplied by branches of the basilar artery and through its anterior inferior cerebellar artery (AICA). The posterior zone of the medulla contains the posterior white columns and their nuclei (gracilis and cuneatus), caudal part of the vestibular nuclei, dorsal motor nucleus of CN X, nucleus and tractus solitarius, inferior cerebellar peduncle and the spinal nucleus and tract of V. It is primarily served by branches of the posterior spinal artery.