CHAPTER 21
Ear
419
Vestibular System
Temporal
bone
Utricle
Temporal
bone
Saccule
Vestibule
Macula
of utricle
Crista
ampullaris
Macula
of saccule
Ampulla
Anterior
semicircular
duct
Posterior
semicircular
duct
Horizontal
semicircular
duct
A
Perilymph
Utricle
Macula utriculi
Vestibule
Fig. 21-10B
Fig. 21-9B
Crista
ampullaris
Ampulla
Position of
cupula
Temporal bone
Temporal bone
Endolymph
B
Figure 21-8A.
Sensory receptors.
The vestibular apparatus of the inner ear contains
sensory
receptors
that detect rotation of the head in space, linear accel-
eration, and the static position of the head. The sensory recep-
tors are
hair cells
that are similar in many, but not all, respects
to the hair cells of the auditory system (see Fig. 21-11A,B).
Rotational movements
of the head are detected by hair cells
located in the
crista ampullaris
of the anterior, posterior, and
horizontal
semicircular ducts
(located within their respective
semicircular canals).
Horizontal acceleration
is detected by hair
cells in the macula of the utricle;
vertical acceleration
is detected
by hair cells in the macula of the saccule.
Static
head
position
is
detected by combining signals from the maculae of the utricle
and saccule. The
dashed rectangle
indicates the approximate
position of the photomicrograph in Figure 21-8B.
Figure 21-8B.
Crista ampullaris and macula utriculi.
H&E,
3
60
A low-power photomicrograph that includes the
ampulla
of a semicircular canal, the
utricle
, and a portion of the
vestibule
is shown.
The semicircular canal within the temporal bone is ± lled with
perilymph
. The membranous labyrinth, ± lled with endolymph, fl oats
within this bony canal (Fig. 21-2). The sensory receptors of both the vestibular system and the auditory system are in contact
with the endolymph. The
crista ampullaris
contains vestibular hair cells and the sensory receptors of the vestibular system and is
described in detail in Figure 21-9A,B. A gelatinous structure, the
cupula
, surrounds the crista ampullaris and forms a wall across
the ampulla (Fig. 21-9A). The cupula is normally lost during tissue processing. Movement of the endolymph during head rotation
defl ects the cupula and, thereby, bends the cilia of the hair cells. The large fl
uid-±
lled utricle contains the
macula utriculi
, a sense
organ that measures linear acceleration and static position of the head. The macula utriculi contains vestibular hair cells with cilia
that are embedded in a gelatinous structure, the
otolithic
membrane
. This membrane is covered by tiny crystals (
otoconia
), which
have a higher speci± c gravity than the surrounding endolymph and, consequently, are infl
uenced by gravity and acceleration. The
macula is described in further detail in Figure 21-10A–C.
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