[UW Anatomy | Contents]

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!!