582
UNIT 3
Regulation and Integration of the Body
15
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
Fibers of
vestibular
nerve
At rest, the cupula stands upright.
Fibers of vestibular nerve
Hair bundle
(kinocilium
plus stereocilia)
Hair cell
Supporting
cell
Section of
ampulla,
filled with
endolymph
(c) Movement of the ampullary cupula during rotational acceleration and deceleration
Membranous
labyrinth
Crista
ampullaris
Crista
ampullaris
Endolymph
Ampullary cupula
Cupula
Flow of endolymph
(a) Anatomy of a crista ampullaris in a semicircular canal
(b) Scanning electron micrograph of a
crista ampullaris (200
m
)
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.
Figure 15.35
Location, structure, and function of a crista ampullaris in the internal ear.
previous page 616 Human Anatomy and Physiology (9th ed ) 2012 read online next page 618 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off