Vestibular system
Fall 2002
The vestibular system detects 2 things:
1) Movement--tells you when your head
is moving
2) Gravity--tells you where your head
is relative to gravity
Located in the inner ear, near the cochlea.
There are two parts to the system:
1) Semicircular canals
There are three canals to detect motion along
3 planes (see Figure 11.6). The canals are filled with fluid that moves
as the head moves (i.e., accelerates). As the fluid moves it causes stereocilia
on hair cells to bend. This movement evokes IPSPs and EPSPs in the hair
cells.
2) Otoliths
There are two otoliths; one oriented horizontally,
the other vertically. Crystals within the otoliths rest on hair cells.
Gravity pulls these crystals down causing the hair cells to bend. The activity
of these hair cells allows you to know the orientation of your head relative
to gravity.
Cranial nerve #8 (auditory vestibular nerve)
carries this information from the inner ear to the vestibular nuclei in
the medulla. The medulla integrates the information with input from the
visual and proprioception systems.
Question: What causes motion sickness?
Answer: A mismatch between vestibular and visual
information.
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