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!
Lesion of C.N. VII result in Bell's Palsy