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Equilibrium
The sense of equilibrium is a mechanical
sense that gives the brain information on balance and the position of
the head. Equilibrium sensory structures combined with the cochlea
(organ of hearing) comprise the inner ear.
 | The vestibule consists of two sac-like
fluid-filled spaces. On the floor of each sac is a patch of
sensory epithelium, the macula, which has hair-like
microvilli sticking up. On top of the microvilli lies a gelatinous
substance containing tiny crystals of calcium carbonate - the
otoliths. Changes in the position of the head causes
movement of the otoliths which distorts the microvilli. This
produces nerve impulses which the brain interprets as head
movements. |
| The semicircular canals are 3
fluid-filled, semicircular canals, each arranged in a different
plane at right angles to the other two. Rotation of the head in
the plane of a particular canal causes distortion of hair-like
microvilli in its receptor area (the crista). This
generates nerve impulses which the brain interprets as rotary
motion of the head. |
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