Cranial Nerve VII

This is the facial nerve, which has a primary motor function. The facial nerve originates from the facial nucleus in the pons, where it receives input from the corticobulbar tract, the source of motor innervation from the precentral gyrus of the cerebral cortex. After its axons leave the pons, the facial nerve innervates the ipsilateral muscles of facial expression. Damage to the facial nerve or its nucleus thus produces weakness of one entire side of the face. However, damage to the corticobulbar fibers arriving at the facial nucleus in the brain stem produces a somewhat different pattern of weakness. In this instance, typically following a contralateral stroke in the brain, only the muscles of the lower face are weak because the upper facial muscles are supplied by corticobulbar fibers from both hemispheres and the intact side can compensate for the damaged side. This anatomic feature permits the crucial clinical distinction between a stroke and the less ominous situation of weakness from seventh nerve



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