Point 17
Motor V
Point: 17. Motor V/Chief Sensory V
Function:
Neurons in motor V possess axons that innervate the muscles
of mastication. The chief sensory nucleus V is involved in
conveying 2pt. discrimination, conscious proprioception and
vibratory sense from the face to the thalamus (VPM) and
brainstem centers (blink or corneal reflex).
Pathway:
Axons of motor V neurons leave the pons by passing through
the middle cerebellar peduncle (where they lie next to the
entering sensory fibers) They directly innervate the IPSI.
muscles of mastication. Corticobulbar input to motor V is
bilateral. GOOD. The central processes of cells in the
trigeminal ganglion conveying 2pt. discrimination, conscious
proprioception and vibratory sense from the face terminate
in the chief sensory nucleus V. Cells in the "Chief" possess
axons that cross, enter the T.T.T. (the pain and temp.
fibers from the caudal spinal nucleus V are already there)
and ascend to the VPM. V.P.M. cells project to somatosensory
cortex. Chief sensory neurons also project bilaterally to
motor VII for the corneal reflex. Touch cornea of one eye,
both eyelids close (orbicularis oculi muscles are innervated
by motor VII cells). IPSI. eyelid closure=direct response,
while CONTRA.=is consensual.
Deficits:
Lesion of motor V or motor fibers in C.N. V results in IPSI.
atrophy of all muscles of mastication. Upon jaw opening, the
jaw will deviate IPSI. (toward the side of the lesion) due
to weakened pterygoids. Lesion of the "Chief" results in
IPSI. loss of 2pt. disc. etc. from the face. Also, with a
lesion of the "Chief", stimulation of IPSI. cornea fails to
result in closure of EITHER eyelid. Stimulate other cornea,
both eyelids will close.
Other Note:
Mesencephalic nucleus and tract V. Sorry! Read module.
Unconscious proprioception. Nitpicky!!