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The Ear
Otic; Vestibular; Auditory
External Ear (contains air); Middle Ear (contains air); Inner Ear (contains fluid)
E
M
I
pinna
tympanic membrane
external auditory
canal
Middle Ear: the ossicles
M
Malleus (tympanic membrane)
Incus
Stapes (oval window)
I
S
pharyngotympanic
(auditory) tube,
connected to
nasopharynx region
of the throat;
functions in
equalizing pressure.
Normally this tube
is flattened and
closed, but
swallowing or
yawning causes it to
open temporarily to
equalize the
pressure of the
middle ear cavity
with external air
pressure.
Middle Ear
M
air
E. A. TM
Canal
I
S
air
AT
air
Inner Ear
Two layers:
Inner Ear
Bony labyrinth filled with an aqueous fluid called perilymph.
The three subdivisions of the bony labyrinth are the
1.
2.
3.
semicircular canals
vestibule
cochlea.
Membranous labyrinth filled with endolymph. This is a
second membrane-bound system suspended in the
perilymph. The three subdivisions of the membranous
labyrinth are:
(1) the semicircular ducts
(2) the Utricle and the Saccule
(3) the cochlear duct.
Inner Ear
Semi-circular canals
(semi-circular ducts)
C
U
V
Vestibule
(utricle & saccule)
S
Cochlea
(cochlear duct)
Inner Ear: membranous labyrinth
Vestibular System: Dynamic Equilibrium
• Semicircular canals: (1) lateral (horizontal), (2) posterior
(sagittal), and (3) anterior or superior (frontal) canals.
• Contain membranous semicircular ducts, at the base of
which is an enlarged region, the ampulla.
• Each ampulla contains a crista, consisting of a tuft of hair
cells covered with a gelatinous cap, or cupola.
• Circular movements of the head move the endolymph in the
semicircular ducts, which pushes the cupola in the ampullae,
and causes the hair cells to fire impulses, which travel down
the vestibulocochlear cranial nerve VIII to the brain.
Inner Ear
Semi-circular canals
lateral (horizontal) canal
anterior (frontal) canal
C
U
V
S
posterior (sagittal) canal
vestibule
cochlea
Semi-circular canals
contain membranous
semi-circular ducts,
at the base of which
is an enlarged region,
the ampulla.
Each ampulla contains
a crista, consisting of
a tuft of hair cells
covered with a
gelatinous cap, or
cupola.
ampulla
Hair cells in ampullae
Each ampulla
contains a crista
(hair cell).
Circular movements of
the head move the
endolymph in the
semicircular ducts, which
pushes the cupola in the
ampullae, and causes the
hair cells to fire
impulses, which travel
down the
vestibulocochlear cranial
nerve VIII to the brain.
Semicircular canals
Anterior
‘YES’
Lateral
‘NO’
Posterior
TILTING
HEAD
Vestibular System: Static Equilibrium.
• The vestibule contains receptors (maculae) that respond to
static equilibrium. The maculae respond to gravitational pull,
thus providing information on which way is up or down.
•
The maculae are located in the utricle and saccule.
•
Maculae consist of hair cells whose cilia project into
gelatinous mass containing small grains of calcium carbonate
(otoliths).
• As the head moves, the otoliths also move, thus triggering
nerve impulses in cranial nerve VIII.
Vestibular System: Static Equilibrium
A
U
A
m
S
m
maculae
Vestibular System: Static Equilibrium.
maculae and otoliths
Vestibular System: Static Equilibrium
macular function
TILT HEAD BACK
Vestibular branch VIII
Sense of Hearing
• The cochlear duct separates the cochlea into an upper
chamber (scala vestibuli) and a lower chamber (scala
tympani). The scala vestibuli terminates at the oval window.
The scala tympani terminates at the round window.
• The cochlear duct supports the organ of corti, which
contains the receptors for hearing. These are sensory hair
cells resting on the basilar membrane; the cilia of these
hair cells project up into the tectorial membrane, and the
nerve endings of the cochlear division of the
vestibulocochlear cranial nerve VIII, which sends impulses
to the auditory association centre in the temporal lobe of
the brain.
cochlea
cochlea
Cochlear chambers
cd
td
sv
cd
td
Organ of Corti
tm
bm
tm
bm
Organ of Corti
Auditory Pathway
Summary of the Inner Ear
Dynamic
Equilibrium
Semicircular canals
Semicircular ducts
Bony Labryinth (Perilymph)
Static
Hearing
Equilibrium
Vestibule
Cochlea
Oval Window: Scala vestibuli
Round Window: Scala tympani
Membranous Labryinth (Endolymph)
Utricle & Saccule Cochlear Duct
Ampullae with cristae
Maculae
Organ of Corti
Cupola with hair cells
Otoliths
with hair cells
Tectorial membrane, hair cells
Basilar membrane