Point 14











Point: 14. Motor nucleus of cranial nerve VII

Neurons innervate the muscles of facial expression including orbicularis oculi (closes eyelid), the stapedius, the stylohyoid, and the posterior belly of the digastric.

Motor VII lies in the pontine tegmentum dorsal to the superior olive (which you might confuse it with) and ventral and medial to the spinal tract and nucleus V. Cells in motor VII possess axons that pass medially, rostrally and dorsally to course over the abducens nucleus (causes a bump in the floor of the fourth ventricle=facial colliculus). The motor VII axons then pass ventrally and laterally to exit the pons. Corticobulbar input to motor VII is tough to remember. Top part of the nucleus, which contains cells that innervate the muscles of the upper one-half of the face, receives BILATERAL corticobulbar input. This is GOOD. The bottom one-half of the nucleus, which contains cells that innervate muscles of the lower one-half of the face, receives ONLY CROSSED corticobulbar input. This is BAD.

Lesion in motor VII or its fibers results in atrophy of muscles of facial expression IPSI. to the lesion. Can not close eyelid due to atrophy of orbicularis oculi muscle. Drooling from IPSI. side of the mouth. Atrophy of stapedius muscle in the middle ear results in hyperacusis, which is increased sensitivity to sounds. A lesion of the corticobulbar input to motor VII results in weakness (NO ATROPHY) of the muscles of the lower face on the CONTRA. side. Remember, you can always wrinkle your forehead!

Other Note:
Lesion of C.N. VII result in Bell's Palsy