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Lab 9 (ƒ 10) - Cranial Nerve Nuclei and Brain Stem Circulation

Cranial Nerve VII - Review

This section was taken at mid-pontine level. The lateral and superior vestibular nuclei (vestibular afferents in Cranial Nerve VIII) occupy the region lateral to the sulcus limitans. The spinal trigeminal nucleus and tract (somatosensory afferents of Cranial Nerve V, VII, IX, X) continue to be located anterior to the vestibular nuclei. Notice that the descending root fibers of the facial nerve are located medial to the spinal trigeminal nucleus and tract.

The facial nucleus (axons exit brain in Cranial Nerve VII) is reduced in size and is medial to the descending facial nerve rootlets and posterior to the superior olivary nucleus. The abducens nucleus (axons exit brain in Cranial Nerve VI) and the axons of the facial nucleus that sweep around it form the facial colliculus. The cortical input to the abducens nucleus are indirect and mediated by midbrain (superior colliculus for involuntary saccades and supraoculomotor area for vergence) and pontine structures (paramedian pontine reticular formation, PPRF, for conjugate lateral gaze and medial vestibular nucleus for smooth pursuit). The corticofugal fibers are located in the basis pontis, surrounded by the pontine nuclei.

Blood Supply

Branches of the basilar artery continue to supply blood to pontine structures. The medial area of the basis pontis, which contains the pontine nuclei, corticofugal fibers, abducens nerve rootlets, and decussating pontine nuclei axons that travel laterally to form the middle cerebellar peduncle, continues to be supplied by the paramedian branches of the basilar artery. The short circumferential branches of the basilar artery supply more lateral areas of the basis pontis, which contain the decussated axons of pontine nuclei that form the middle cerebellar peduncle. Branches of the anterior inferior cerebellar artery (AICA) also supply the middle cerebellar peduncle. The long circumferential branches of the basilar artery penetrate the pons tegmentum to supply the abducens nucleus, medial longitudinal fasciculus, tectospinal tract, facial nerve rootlets, lateral and superior vestibular nuclei, solitary tract and nucleus, spinal trigeminal tract and nucleus, pons reticular formation, central tegmental tract, trapezoid body and superior olivary nucleus, facial nucleus, medial lemniscus, ventral trigeminal lemniscus, spinothalamic tract, rubrospinal tract.