nucleus in the thoracic cord and enters the cerebellum via the inferior
cerebellar peduncle. The ventral spinocerebellar tract originates from
spinal cord gray matter and enters the cerebellum via the superior cere-
bellar peduncle.- Interruption of primary fibers in the dorsal funiculus will cause loss of
proprioception, and so forth, on the same side of the body as the lesion. - Interruption of secondary fibers in the medial lemniscus will give rise to
contralateral deficits. - Tabes dorsalis and pernicious anemia attack the dorsal funiculi.
Trigeminal Pathways
- Primary trigeminal fibers enter at the level of the pons.
- Primary afferents of the descending root terminate in the spinal trigemi-
nal nucleus. - Secondary fibers ascend through the medulla and pons as the trigeminal
lemniscus to terminate in the ventral posterior medial (VPM) nucleus of
the thalamus. - The ascending root primary tactile afferents terminate in the main sen-
sory nucleus of CN V. - Secondary fibers ascend in the trigeminal lemniscus to the VPM.
- The cell bodies of the primary proprioceptive afferents from the muscles
of mastication are located in mesencephalic nucleus of V, and thus are
“like” dorsal root ganglion cells embedded in the brain. They project to
the motor nucleus of V for a monosynaptic jaw jerk reflex. - Lesion of the descending root of V and the adjacent lateral spinothalamic
tract on one side of the medulla will result in pain and temperature
deficits on the contralateral side of the body and the ipsilateral side of the
head.
Vestibular Pathways
- Primary afferents terminate in the vestibular nuclei and in the cerebellum
on the same side. - Secondary fibers ascend or descend in the medial longitudinal fasciculus
or the ventral funiculus of the spinal cord. - Unilateral lesions of the vestibular system result in movement of the
head, body, and eyes (nystagmus) to the affected (ipsilateral) side. Symp-
toms include vertigo, nausea, and a tendency to fall to the affected side.
40 Anatomy, Histology, and Cell Biology