Ampulla of the semicircular canal.
Each of the three semicircular ducts has an enlargement called the
near one of the points at which the duct joins the utricle.
There is a ridge, the
, on the ﬂ
oor of each ampulla.
Partially surrounding the ridge and extending to the ceiling of the
ampulla is a wall, the
, which completely blocks the duct.
The cupula consists of a F
rm gel of proteins and polysaccharides.
This structure is normally dissolved during the tissue preparation
process and only remnants are typically seen in histological sec-
tions. When the head rotates, the
within the semicircu-
lar ducts moves (
) and exerts pressure on the cristae and
their respective cupulae, causing them to deﬂ
ect slightly. This deﬂ ec-
tion bends the hair cells in the cristae (±ig. 21-11B) and modulates
the frequency of action potentials that are going to the brainstem
vestibular centers, thereby producing the sensation of motion.
(also known as the
) is a pro-
jection of connective tissue covered with epithelium within the
ampulla. The epithelium consists of
. The cilia of the
are embedded in the gelatinous
material of the
. The hair cells are cradled by
that rest on the
of the epithelium. There are two dis-
tinct types of hair cells in the cristae, termed
type II hair
. These will be described in greater detail in ±igure 21-11A,B.
is a region of endothelium composed of
a single layer of cells called “dark cells,” because they stain more
intensely than other epithelial cells in the internal ear.
play cytological characteristics of cells with high metabolic activity
and are believed to be important in controlling the ionic composi-
tion of the endolymph. They are found in several other locations
within the labyrinthine ducts, including the stria vascularis.
is a disorder of the labyrinth of the
inner ear, characterized by intermittent episodes of
causes are uncertain but may include autoimmune dis-
orders, viral infections, genetic predisposition, aller-
gies, and head trauma. Disorders of secretory cells
in the membranous labyrinth and endolymphatic sac
may produce ionic imbalance between endolymph and
perilymph, resulting in
ing of the membranous labyrinth) and producing
many of the above symptoms. Diagnosis is based on
history, clinical symptoms, audiometry, and vestibu-
lar testing. Postmortem histopathologic F
include perisaccular F
brosis, atrophy of the endo-
lymphatic sac, and other membranous changes. Treat-
ments include reduction of caffeine and salt intake,
diuretics, antinausea medications, glucocorticoid ther-
apy, intratympanic gentamicin injection, surgical laby-
rinthectomy, and vestibular nerve section.
Dilated membranous labyrinth
in Ménière’s disease