CHAPTER 21
Ear
413
Figure 21-2.
Major structures of the inner ear.
The
bony labyrinth
is a complex cavity in the petrous portion of the
temporal
bone
, the hardest bone in the body. The cavity is lined
with endosteum and contains
perilymph
(
blue shading
), a clear fl
uid with a composition very similar to that of cerebrospinal fl uid.
The bony labyrinth is divided into three portions, the
vestibule
, the
cochlea
(anteriorly), and the
semicircular canals
(posteriorly).
The
membranous labyrinth
, consisting of the three
semicircular ducts
, the
utricle
, and the
saccule
, lies within the bony labyrinth.
The walls of the membranous labyrinth are, in general, composed of a thin layer of F
brous connective tissue; a thin layer of
more delicate, more vascularized connective tissue; and an internal lining of simple epithelium. Two saclike structures, the
utricle
and
saccule
, are found in the vestibule. A
semicircular duct
lies within each of the semicircular canals. A similar but more complicated
structure, the
cochlear duct
, lies within the bony cochlea. These membranous structures are continuous with each other and contain
endolymph
(
yellow shading
), a fl uid with a high concentration of K
+
(potassium) ions that is unique in the body. Specialized regions
within the membranous labyrinth (indicated by
thick orange lines
) contain receptor cells innervated by branches of the vestibuloco-
chlear nerve (CN VIII). These include the
cristae
(singular,
crista
, from Latin for “crest”) in each of the
ampullae
(singular,
ampulla
,
from Latin for “fl ask” or “bottle”) of the semicircular ducts, the
maculae
(singular,
macula
, from Latin for “spot”) of the utricle and
saccule, and the
organ of Corti
(
spiral organ
) in the cochlear duct. The receptor cells in all these regions are specialized epithelial cells
(
hair cells
) that transduce movements of the basilar membrane into nerve impulses (see ±igs. 21-5C, 21-7, and 21-11A).
Maculae
Maculae
Crista
Crista
Semicircular
Semicircular
canal
canal
Semicircular
Semicircular
ducts
ducts
Endolymphatic sac
Endolymphatic sac
Endo-
Endo-
lymphatic
lymphatic
duct
duct
Ampulla
Ampulla
Vestibule
Vestibule
Cochlea
Cochlea
Round
Round
window
window
Tympanic
Tympanic
membrane
membrane
Oval window
Oval window
Bone
Utricle
Ampulla
Crista
Saccule
Vestibule
Maculae
Cochlea
Mastoid
cavities
Oval window
Semicircular
ducts
Semicircular
canal
Endolymphatic sac
Endo-
lymphatic
duct
Perilymphatic duct
(cochlear duct)
Dura mater
Scala vestibuli
Cochlear duct
(scala media inside)
Scala tympani
Subarachnoid space
Brain tissue
Tympanic
membrane
Round
window
Auditory
(Eustachian)
tube
Osseous
spiral
lamina
External auditory
meatus
Scala vestibuli
(perilymph)
Bone
Scala tympani
(perilymph)
Scala media
(endolymph)
Vestibular
(Reissner)
membrane
Organ of Corti
(spiral organ)
Basilar
membrane
Cross section of cochlea
previous page 428 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online next page 430 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online Home Toggle text on/off