Brainstem Summary

Caudal Medulla

• 1.

  Nucleus gracilis. Second-order somatosensory neurons whose axons cross at this level to form the leg portion of the medial lemniscus.

• 2.

  Fasciculus cuneatus. Uncrossed branches of primary afferents, carrying tactile and proprioceptive information from the arm.

• 3.

  Nucleus cuneatus. Second-order somatosensory neurons whose axons cross at this level to form the arm portion of the medial lemniscus.

• 4.

  Nucleus of the solitary tract, surrounding the solitary tract. This is much like a posterior column system for information from viscera and taste buds: central branches of afferents from cranial nerves VII, IX, and X travel through the tract to reach the nucleus. Only information from viscera reaches this caudal level.

• 5.

  Dorsal motor nucleus of the vagus. Preganglionic parasympathetic neurons for thoracic and abdominal viscera.

• 6.

  Central canal. Continuous rostrally with the fourth ventricle and caudally with the central canal of the spinal cord.

• 7.

  Spinal trigeminal tract. Primary afferents from the ipsilateral side of the face, at this caudal level conveying information about pain and temperature.

• 8.

  Spinal trigeminal nucleus. At this caudal level, second-order pain and temperature neurons whose axons cross the midline and join the anterolateral pathway. Trigeminal pain and temperature afferents from the ipsilateral face reach the nucleus via the spinal trigeminal tract.

• 9.

  Hypoglossal nucleus. Lower motor neurons for ipsilateral tongue muscles.

• 10.

  Anterolateral pathway. Mostly crossed fibers of second-order spinal neurons conveying pain and temperature information to the thalamus (spinothalamic tract), reticular formation, and midbrain.

• 11.

  Location of nucleus ambiguus. Lower motor neurons for laryngeal and pharyngeal muscles (also contains preganglionic parasympathetic neurons for the heart).

• 12.

  Reticular formation.

• 13.

  Medial longitudinal fasciculus (MLF). At this level, the fibers of the medial vestibulospinal tract.

• 14.

  Medial lemniscus, the principal ascending pathway for tactile and proprioceptive information. Originates in the contralateral posterior column nuclei and terminates in the thalamus (ventral posterolateral nucleus [VPL]).

• 15.

  Raphe nuclei. Widely projecting serotonergic neurons that collectively blanket the CNS. Those in caudal brainstem levels like this project mainly to the spinal cord.

• 16.

  Pyramid. Corticospinal fibers from the ipsilateral precentral gyrus and adjacent areas of cerebral cortex.

Important brainstem structures caudal to this level (i.e., between here and the spinal cord): pyramidal decussation (at the spinomedullary junction), where most fibers of the pyramids cross to form the lateral corticospinal tracts.