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ANATOMY III
4. The Ear
DR. MOHAMAD BAKER ABU-SNAINA
GENERAL SURGEON

The Ear
The ear consists of:
 External ear.
 Middle ear, or tympanic
cavity.
 Internal ear, or labyrinth,
contains the organs of
hearing & balance.

External Ear
• The external ear has:
 Auricle
 External auditory meatus.
The auricle:
• Has a characteristic shape.
• Collects air vibrations.
• Consists of a thin plate of elastic
cartilage covered by skin.
• It possesses extrinsic & intrinsic
muscles, which are supplied by
the facial nerve.

External Ear
The external auditory meatus
• Is a curved tube that conducts
sound waves from the auricle to
the tympanic membrane.
• It outer 1/3 is elastic cartilage & the
inner 2/3 is bone, formed by the
tympanic plate.
• It is lined by skin & its outer 1/3 is
provided with hairs & sebaceous &
ceruminous glands (modified sweat
glands) that secrete the wax.
• Sensory supply: auriculotemporal
nerve & auricular branch of vagus.

Clinical Notes
Tympanic Membrane Examination
• Otoscopic examination of the
tympanic membrane is
facilitated by first straightening
the external auditory meatus by
gently pulling the auricle upward
& backward in the adult &
straight backward or backward
& downward in the infant.
• Normally, tympanic membrane
is pearly gray & concave.

Middle Ear (Tympanic Cavity)
• It is a small, oblique, biconvex cavity
its long axis lies parallel to the plane
of the tympanic membrane.
• It lies inside the petrous part of the
temporal bone, lined by mucous m.
• It contains the auditory ossicles,
that transmit the vibrations of the
tympanic membrane to the
perilymph of the internal ear.
• It has: roof, floor, 4 walls, ant., post,
medial & lateral, it communicates:
 In front with the nasopharynx
through the auditory tube.
 Behind with the mastoid antrum.

Roof: a thin plate of bone,
tegmen tympani, which
separates the middle ear from
the middle cranial fossa.
Floor: a thin plate of bone
which separates it from the
superior bulb of the internal
jugular vein.
Lateral wall: mainly by the
tympanic membrane.
Medial wall: separates the
middle ear from the inner ear,
shows the following features:

 The promontory: is a rounded
bulge produced by the 1st turn
of the cochlea.
 Oval window: above & behind
the promontory, it leads to the
vestibule of the inner ear.
 Rounded window: below &
behind the promontory, closed
by the 2ry tympanic membrane.
 Horizontal part of the fascial
canal: arching above the
promontory &oval window.

Anterior wall:
 Upper part, 2 openings into 2 canals:
 The upper for tensor tympani muscle.
 The lower for the auditory tube.
 Lower part, a thin plate of bone,
separates it from internal carotid artery
Posterior wall: shows the following:
 Aditus: is the inlet to mastoid antrum.
 Pyramid a small projection, its apex
transmits the tendon of stapedius
muscle
 Vertical part of the fascial canal: lies
medial to the aditus.

4._The_Ear_3 and all the anantomy of it.pdf

The tympanic membrane
• It is a thin, fibrous membrane, pearly
gray in color, circular, 1 cm diameter.
• It is obliquely placed, facing downward &
laterally.
• It is concave laterally & contains small
depression, the umbo, produced by the
handle of the malleus.
• Its greater part is tense (pars tensa), but
a small triangular part at its upper border
is lax (pars flaccida).
• Extremely sensitive to pain innervated
on its outer surface by auriculotemporal
nerve & the auricular branch of vagus.

Auditory Ossicles
• There are 3 ossicles articulating
together , from lateral to medial:
the malleus, incus & stapes.
• The malleus is fixed to the
tympanic membrane while the
stapes is fixed at the fenestra
vestibuli & the incus in between.
• The stapedius muscle in inserted to
the neck of the stapes & is supplied
by the fascial nerve.
• The tensor tempani muscle is
inserted in the handle of the
malleus.

Auditory (Eustachean) Tube
• It connects the anterior wall of
the tympanic cavity to the nasal
pharynx.
• Its posterior 1/3 is bony & its
anterior 2/3 is cartilaginous,
related superiorly to the skull,
&inferiorly it passes over the
superior constrictor muscle of
the pharynx.
• It serves to equalize air pressures in
the tympanic cavity & the nasal
pharynx.

Complications of Otitis Media
• Pathogenic organisms can gain entrance to the middle ear
by ascending through the auditory tube.
• Acute infection of the middle ear (otitis media) produces
bulging & redness of the tympanic membrane.
• Spread of the infection into the mastoid antrum & the
mastoid air cells (acute mastoiditis).
• Superior spread of the infection could produce
meningitis & a cerebral abscess in the temporal lobe.
• Medial spread of the infection can cause a facial nerve
palsy & labyrinthitis with vertigo.
• Posterior spread can cause sigmoid sinus thrombosis.
• These various complications emphasize the importance of
knowing the anatomy of this region.

Facial Nerve
• Fiber Type: Sensory, motor, (special
sensation, parasympathetic).
• Origin: Pons (Cerebellopontine
angle)
• On reaching the bottom of the
internal acoustic meatus the facial
nerve enters the facial canal.
• The nerve runs laterally above the
vestibule of the internal ear until it
reaches the medial wall of the
middle ear. Here, the nerve expands
to form the sensory geniculate
ganglion.

Facial Nerve
• The nerve then bends sharply
backward above the
promontory.
• On arriving at the posterior wall
of the middle ear, it curves
downward on the medial side of
the aditus of the mastoid
antrum.
• It descends in the posterior wall
of the middle ear, behind the
pyramid & finally emerges
through the stylomastoid
foramen into the neck.

Important Branches of the
Intrapetrous Part of the Facial Nerve
• The greater petrosal nerve arises from the facial nerve at the
geniculate ganglion It contains preganglionic parasympathetic
fibers.
• The nerve to the stapedius arises from the facial nerve as it
descends in the facial canal behind the pyramid ,It supplies
the muscle within the pyramid.
• The chorda tympani arises from the facial nerve just above
the stylomastoid foramen
• The chorda tympani contains:
 Taste fibers from the mucous membrane covering the
anterior two thirds of the tongue & the floor of the mouth.
 Preganglionic parasympathetic secretomotor fibers that
reach the submandibular ganglion & are there relayed to the
submandibular & sublingual salivary glands. 19

Tympanic Nerve
• Arises from the glossopharyngeal
nerve, just below the jugular
foramen.
• It passes through the floor of the
middle ear & onto the promontory.
• Here it splits into branches, which
form the tympanic plexus.
• The tympanic plexus supplies the
lining of the middle ear & gives off
the lesser petrosal nerve, which
sends secretomotor fibers to the
parotid gland via the otic ganglion .

The Internal Ear, or Labyrinth
• Situated in the petrous part
of the temporal bone, medial
to the middle ear.
• It consists of:
Bony labyrinth a series of
cavities within the bone.
Membranous labyrinth a
series of membranous sacs &
ducts contained within the
bony labyrinth.

Bony Labyrinth
• Consists of three parts:
 The vestibule.
 The semicircular canals.
 The cochlea.
• These are cavities situated in
the substance of dense bone.
• They are lined by endosteum
& contain clear fluid, the
perilymph in which is
suspended the membranous
labyrinth.

The Vestibule
• The central part of the bony
labyrinth, lies posterior to
the cochlea & anterior to the
semicircular canals.
• In its lateral wall are the
fenestra vestibuli, which is
closed by the base of the
stapes & its anular ligament,
& the fenestra cochleae.
• Lodged within the vestibule
are the saccule & utricle of
the membranous labyrinth.

Semicircular Canals
• These are 3 canals, each 2/3 of a
circle, each canal has a swelling at
one end called the ampulla.
• They open into vestibule by 5 orifices
 The superior canal is vertical &
placed at right angles to long axis of
petrous bone.
 The posterior canal is also vertical
but is placed parallel with the long
axis of the petrous bone.
 The lateral canal is set in a horizontal
position & lies in the medial wall of
the aditus to the mastoid antrum,
above the facial nerve canal.

The Cochlea
• It resembles a snail shell.
• It opens into the anterior part of
the vestibule.
• It consists of a central pillar, the
modiolus, around which a
hollow bony tube makes 2.5
spiral turns.
• Each successive turn is of
decreasing radius so that the
whole structure is conical.
• The apex faces anterolaterally &
the base faces posteromedially.

Membranous Labyrinth
• Situated within the bony labyrinth
• It is filled with endolymph &
surrounded by perilymph.
• It consists of:
 The utricle & saccule which placed
in the bony vestibule.
 The 3 semicircular ducts, which lie
within the bony semicircular canals.
 The duct of the cochlea, which lies
within the bony cochlea.
• All these structures freely
communicate with one another.

• Specialized sensory receptors are located on the walls
of the utricle & saccule which are sensitive to the
orientation of the head to gravity.
• When the head begins or stop to move, or accelerates
or decelerates, the endolymph in the semicircular ducts
changes its speed relative to that of the walls of
semicircular ducts.
• This change is detected in the sensory receptors in the
ampullae of the semicircular ducts.
• The highly specialized epithelium that lies on the
basilar membrane forms the spiral Organ of Corti &
contains the sensory receptors for hearing.
Membranous Labyrinth

Vestibulocochlear Nerve (CN VIII)
• It is a sensory nerve(Special
sensory) vestibular & cochlear.
 The vestibular fibers originate
from the vestibule & the
semicircular canals &
 The cochlear fibers originate in
the organ of Corti.
• The 2 types of fibers pass the
internal acoustic meatus as one
nerve to reach the anterior
surface of the brain between
pons & medulla oblongata.

Vestibulocochlear Nerve (CN VIII)
• The vestibular nerve expanded to form vestibular ganglion
• Its branches pierce the lateral end of the internal acoustic
meatus & gain entrance to membranous labyrinth, where
they supply the utricle, the saccule, & the ampullae of the
semicircular ducts.
• Therefore, they are concerned with the sense of position &
with movement of the head.
• Cochlear Fibers: are the central processes of the nerve cells
of the spiral ganglion of the cochlea.
• Originate in the spiral organ of Corti & are therefore
concerned with hearing.
• The peripheral branches of this nerve pass from the ganglion
to the spiral organ of Corti.
29

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