Dr. Nimir
Dr. Safaa
 Objectives
 Describe the structures making the external and middle ear.
 Discuss the features of the tympanic membrane.
 Describe the ossicles and related muscles.
 Describe the auditory tube, its openings and structure.
 Understand the mastoid air cells and their connection to the
middle ear.
 Describe the structure of cochlea, semicircular canals, utricle
and saccule
 Describe the course of vestibulocochlear nerve and its central
connections
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The Ear
The ear consists of:
External ear
Middle ear(tympanic cavity)
Internal ear( labyrinth)
External Ear:
The external ear has an
Auricle: It consists of a thin plate
of elastic cartilage covered by
skin.
 External auditory meatus:
 Its outer third is elastic cartilage
and inner two thirds is bone.
 The meatus is lined by skin, with
hairs,sebaceous and ceruminous
glands (secrete wax).
 Nerve supply by auriculotemporal
vagus nerves.
 Middle Ear (Tympanic Cavity):
 It is an air-containing cavity in
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petrous bone lined with
mucous membrane. It
contains the auditory ossicles.
It communicates infront with
nasopharynx through
auditory tube and behind
with the mastoid antrum.
The tympanic membrane:
Is a thin circular fibrous
membrane.
The tympanic membrane is
extremely sensitive to pain
and is innervated by
auriculotemporal and vagus.
 Auditory Ossicles
 They are the malleus, incus,
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and stapes
The malleus is attached to
tympanic membrane
The stapes is attached to
oval window.
Muscles of the Ossicles:
These are tensor tympani
supplied by mandibular
nerve and stapedius muscle
supplied by facial nerve.
 Auditory Tube:
 It connects tympanic cavity
to th nasal pharynx.
 Its posterior third is bony,
and its anterior two thirds is
cartilaginous.
 It serves to equalize air
pressures in tympanic cavity
and nasal pharynx.
 Mastoid Air Cells:
 They are a series of
communicating cavities
within the process that are
continuous above with
mastoid antrum and middle
ear . They are lined with
mucous membrane.
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Vestibulocochlear Nerve (Cranial Nerve VIII)
This nerve consists of two distinct parts:
Vestibular nerve.
Cochlear nerve.
They are concerned with transmission of afferent information from
internal ear to central nervous system.
 Vestibular Nerve:
 It conducts nerve impulses
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from :
Utricle and saccule.
Semicircular canals.
Its fibers are central processes
of nerve cells located in
vestibular ganglion (in internal
acoustic meatus).
They enter vestibular nuclear
complex by passing between
lower border of pons and
upper part of medulla
oblongata .
Fibers then divide into short
ascending and long descending
fibers
A small number of fibers bypass
the vestibular nuclei & enter
cerebellum through the inferior
cerebellar peduncle.
 The Vestibular Nuclear
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Complex:
This complex consists of a
group of nuclei situated
beneath the floor of the
fourth ventricle.
Four nuclei may be
recognized:
(1) Lateral vestibular nucleus.
(2) Superior vestibular
nucleus.
(3) Medial vestibular nucleus
(4) Inferior vestibular
nucleus.
 Vestibular nuclei receive afferent
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fibers from :
Utricle ,saccule and semicircular
canals through vestibular nerve
Cerebellum through inferior
cerebellar peduncle.
Efferent fibers from the nuclei pass to:
Cerebellum through inferior
cerebellar peduncle.
Efferent fibers also descend
uncrossed to spinal cord from lateral
vestibular nucleus and form
vestibulospinal tract.
Nuclei of oculomotor, trochlear, and
abducent nerves through medial
longitudinal fasciculus.These
connections enable maintainance
visual fixation on an object.
In addition, information received
from the internal ear can assist in
maintaining balance by influencing
muscle tone of the limbs and trunk.
 Ascending fibers also pass
upward from vestibular
nuclei to cerebral cortex, to
vestibular area in
postcentral gyrus just above
lateral fissure.
 These fibers are thought to
relay in ventral posterior
nuclei of thalamus. The
cerebral cortex probably
serves to orient the
individual consciously in
space.
 Cochlear Nerve:
 The cochlear nerve conducts
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nerve impulses concerned
with sound from hair cells in
organ of Corti in cochlea.
Fibers of cochlear nerve are
central processes of nerve
cells located in spiral
ganglion of cochlea.
They enter anterior surface
of brainstem at lower border
of pons. In pons nerve fibers
divide:
One branch entering
posterior cochlear nucleus.
Other branch entering
anterior cochlear nucleus.
 Cochlear Nuclei:
 The anterior and posterior
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cochlear nuclei are situated
on the surface of inferior
cerebellar peduncle.
They receive afferent fibers
from cochlea through the
cochlear nerve.
Cochlear nuclei send axons
(2nd order neuron fibers) that
relay in the same or opposite
side of:
Trapezoid body (posterior
nucleus).
Olivary nucleus (superior
olivary nucleus) .
 Axons pass through posterior
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part of pons and midbrain form
lateral lemniscus which consists
of third-order neurons from
both sides.
As fibers of lateral lemniscus
ascend, some of them relay in
nucleus of lateral lemniscus.
In the midbrain fibers of lateral
lemniscus terminate in:
Inferior colliculus.
Medial geniculate body and
pass to auditory cortex of
cerebral hemisphere through
acoustic radiation of internal
capsule.
 Course of Vestibulocochlear
Nerve:
 The vestibular and cochlear
parts of the nerve leave
anterior surface of the
brain between the lower
border of pons and
medulla oblongata.
 They run laterally in
posterior cranial fossa and
enter internal acoustic
meatus with facial nerve.
The fibers are then
distributed to different
parts of the internal ear .