Regulation and Integration of the Body
reﬂex centers in the brain stem, rather than to the cerebral cor-
tex as with the other special senses.
Te nerve pathways connecting the vestibular apparatus
with the brain are complex. Te transmission sequence begins
when the hair cells in the vestibular apparatus are activated. As
The Equilibrium Pathway to the Brain
Our responses to body imbalance, such as when we stumble,
must be fast and reﬂexive. By the time we “thought about” cor-
recting our fall, we would already be on the ground! Accord-
ingly, information from equilibrium receptors goes directly to
At rest, the cupula stands upright.
Fibers of vestibular nerve
(c) Movement of the ampullary cupula during rotational acceleration and deceleration
Flow of endolymph
(a) Anatomy of a crista ampullaris in a semicircular canal
(b) Scanning electron micrograph of a
crista ampullaris (200
During rotational acceleration, endolymph
moves inside the semicircular canals in the
direction opposite the rotation (it lags behind
due to inertia). Endolymph flow bends the
cupula and excites the hair cells.
As rotational movement slows, endolymph
keeps moving in the direction of rotation.
Endolymph flow bends the cupula in the
opposite direction from acceleration and
inhibits the hair cells.
Location, structure, and function of a crista ampullaris in the internal ear.