Point 13
Intro
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Point 13. Vestibular Nuclei and Abducens Nucleus |
You
are probably wondering why we suddenly have TWO
nuclei under ONE point. Well, over the years I've
learned that it is much easier to cover them both at the
same time because of their close functional association in
the control of eye movements. This is a very long and
tough point, but hang in there!
There are four vestibular
nuclei within the brain stem (superior, lateral, medial,
and inferior). All four can not be seen in the same cross
section, since they are present for a considerable
rostrocaudal distance from the rostral medulla to the middle
of the pons. You only have to be able to identify the
MEDIAL and INFERIOR vestibular nuclei, both of
which are present at level #4 (shown below on the left).
The vestibular nuclei receive their primary input from the vestibular portion of C.N. VIII (vestibular-auditory). The axons in the vestibular nerve are the central processes of neurons that lie in the vestibular or Scarpa's ganglion (actually two ganglia), which lie in the internal auditory meatus. The peripheral processes of these cells receive information from the receptors of the vestibular labyrinth, i.e. hair cells located in the semicircular canals and the saccule and the utricle (otolith organs).