ANATOMY OF THE EAR
•The organ of hearing and equilibrium
•Divided into three parts:
• External ear
• Middle ear
• Internal ear
External ear
Includes:
• The Auricle and;
• The External acoustic meatus
Middle ear
Internal ear
auricle
External acoustic meatus
External ear
External Ear
Auricle
•Collects sound waves and Directs them into the external acoustic meatus
•Formed of a thin plate of cartilage covered by skin
•Has a lateral and medial surfaces
•The lateral surface presents some elevations and depressions
Superior & inferior
crura of antihelix
Triangular fossa
Helix
Antihelix
Crus of helix
Parts of the auricle:
• Helix: the curved outer margin of the auricle
• Begins anteriorly at a ridge called the crus of helix
• Ends postero-inferiorly at the lobule of the ear
• Antihelix: a cruved ridge in front of the posterior part of helix
• Superiorly it divides into sup. & inf. crura
• The crura are separated by the triangular fossa
• Scaphoid fossa: depression between helix and antihelix
• Tragus: a projection below the crus of helix
• Antitragus: a small tubercle on the lower part of antihelix
• Concha : the central depression of the auricle
Concha
Antitragus
Lobule
Tragus
Muscles of the auricle:
Extrinsic muscles:
•Auricularis anterior
Supplied by temporal branches of facial n.
•Auricularis superior
•Auricularis posterior, supplied by post. auricular n. (from facial)
Intrinsic muscles: slips of striated muscle fibers, supplied by
temporal and posterior auricular branches of facial n.
Auricularis superior
Auricularis posterior
Arterial supply of the auricle:
Auricularis anterior
•Auricular branches of superficial temporal a.
•Auricular branch of posterior auricular a.
Sensory nerve supply of the auricle:
• Great auricular: supplies lower 1/3 of lateral surface &
lower 2/3 of medial surface
• Auriculotemporal: supplies upper 2/3 of lateral surface
• Lesser occipital: supplies upper 1/3 of medial surface
• Auricular branch of vagus: supplies skin of concha
• Facial nerve: communicates with auricular branch of vagus
External acoustic meatus
External acoustic meatus
•The passage between the concha and the outer surface of tympanic membrane
•Conducts sound waves from the auricle to the tympanic membrane
•Measures 4 cm from the tragus (2.5 cm from bottom of concha)
•The lateral 1/3 forms the cartilagenous part of the meatus
•The medial 2/3 form the bony part of the meatus
•The anterior wall and floor of the meatus are longer than the roof and post wall
(because of the obliquity of the tympanic membrane)
•The meatus is S-shaped, and has 2 constrictions:
• At the junction between the cartilagenous and bony parts
• In the bony part (5mm from the tympanic membrane) called the isthmus
External acoustic
meatus
Tympanic membrane
•The skin of the meatus is thin and firmly attached to its walls
•The outer 1/3 contains hairs and seruminous glands (secrete ear wax)
Tympanic Membrane
• An oval semitransparent membrane
• Obliquely situated at the bottom of the external acoustic meatus
• The circumference of the membrane is thickened and fitted into the
tympanic sulcus of temporal bone
• The upper part of the sulcus is deficient forming a notch
• Two fibrous bands connect the ends of the notch to the lateral
process of malleus (anterior & posterior malleolar folds)
• Three parts of the membrane can be recognized:
• Pars flaccida: the triangular area between the malleolar folds
• Pars tensa: the greater part of the membrane
• Cone of light: at the antero-inferior part of the membrane
Posterior malleolar
• The handle of malleus is attached to the center
fold
of the inner surface of the membrane leading to
projection of the membrane towards the middle ear
• The membrane is concave laterally and convex
Handle of
medially
malleus
Layers of the tympanic membrane:
• Outer cuticular layer
• Middle fibrous layer
• Inner mucous layer
Lateral process
of malleus
Pars flaccida
Handle of
malleus
anterior view
Anterior malleolar
fold
Lateral process
of malleus
Cone of
light
Lateral view
Arterial supply of the external acoustic meatus:
• Auricular branches of superficial temporal
• Auricular branch of posterior auricular
• Arterial supply of the tympanic membrane:
Outer surface:
• Deep auricular (branch of maxillary)
Inner surface:
• Anterior tympanic (maxillary)
• Posterior tympanic (stylomastoid artery)
• Carotico-tympanic (internal carotid artery)
Nerve supply of the external acoustic meatus:
• Auriculotemporal n: supplies anterior wall and roof
• Auricular branch of vagus: supplies floor and posterior wall
Nerve supply of the tympanic membrane:
• Outer surface: same nerves which supply the external meatus
• Inner surface: tympanic branch of glossopharyngeal
Summary of arterial & nerve supply of external ear
Nerve supply of the external ear:
Arterial supply of the external ear:
• Great auricular n:
-lower 1/3 of lateral surface of auricle
-lower 2/3 of medial surface of auricle
• Lesser occipital n:
-outer surface of tympanic membrane
-upper 1/3 of medial surface of auricle
• Auricular branches of superficial temporal a.
-lateral surface of auricle
-external acoustic meatus
• Auricular branch of posterior auricular a.
-medial surface of auricle
-external acoustic meatus
• Deep auricular (of maxillary)
-outer surface of tympanic membrane
• Auriculotemporal n:
-upper 2/3 of lateral wall of auricle
-anterior wall and roof of meatus
-outer surface of tympanic membrane
• Auricular branch of vagus:
-concha of auricle
-floor and posterior wall of ext. ac. meatus
Inner surface of tympanic membrane is
supplied by
• tympanic branch of glossopharyngeal
Inner surface of tympanic membrane is supplied by:
-Anterior tympanic (maxillary)
-Posterior tympanic (stylomastoid)
-Carotico-tympanic (internal carotid)
Posterior
Medial
Lateral
Anterior
An terior view
Middle Ear (Tympanic Cavity)
• A small irregular cavity inside the temporal bone, on the inner aspect of the tympanic membrane
• Contains air conveyed to it from the nasopharynx through the auditory tube
• Also contains 3 very small bones (ear ossicles), malleus, incus and stapes
• The ear ossicles transmit sound vibrations from the tympanic membrane to the internal ear
Incus
Stapes
Tympanic
membrane
Epitympanic recess
malleus
External
auditory meatus
External
auditory meatus
Tympanic membrane
Auditory tube
IJV
Auditory tube
Anterior view
• The tympanic cavity is formed of 2 parts:
-Tympanic cavity proper: the part medial to the tympanic membrane
-Epitympanic recess: the part above the level of the tympanic membrane
• The tympanic cavity communicates posteriorly with the mastoid antrum, AND
communicates anteriorly with the nasopharynx
Epitympanic recess
Malleus
Incus
Stapes
External acoustic
meatus
Medial view
Tympanic membrane
Auditory tube
Anterior view
Walls of the Middle Ear
Roof: (tegmental wall)
• Formed by the tegmen tympani: a thin plate of the petrous bone
• It separates the middle ear from the middle cranial fossa
Floor: (jugular wall)
• Formed by the jugular fossa, a thin plate of
bone which separates the tympanic cavity
from the superior bulb of IJV
Anterior view
Tegmen tympani
IJV
Anterior wall: (carotid wall)
• Its lower part is formed by the posterior wall of the carotid canal (the posterior wall of carotid canal is
perforated by the carotico-tympanic nerves and the carotico-tympanic branch of ICA)
• The upper part of the anterior wall presents two openings of two canals:
- Canal for tensor tympani: transmits the tensor tympani to be inserted into the handle of malleus
- Auditory tube: runs below the canal for tensor tympani
Mastoid antrum
Aditus to mastoid antrum
Chorda tympani
Mastoid air cells
Epitympanic recess
Tensor tympani
Auditory tube
ICA
IJV
ICA
Facial nerve
Jugular fossa
Handle of malleus
Medial view
Posterior wall: (mastoid wall)
The posterior wall shows the following features:
• Aditus to the mastoid antrum: an aperture from the epitympanic recess to the mastoid antrum
• Pyramid: a small hollowed pyramidal eminence, it contains the stapedius muscle. The base of the pyramid
is connected to the facial canal by an aperture which transmits the nerve to stapedius
• Posterior canaliculus for the chorda tympani: Lies close to the lateral side of the pyramid and transmits
the chorda tympani from the facial canal to the middle ear.
Tegmen tympani
Facial nerve
Mastoid antrum
Tensor tympani
Pyramid
Chorda tympani
Tendon of stapedius muscle
Facial nerve
Jugular fossa
Auditory tube
Lateral View (tympanic membrane removed)
Lateral wall: (membranous wall)
• Formed mainly by the tympanic membrane and partly by the lateral wall of epitympanic recess.
• Presents the following features:
-Posterior canaliculus for chorda tympani
-Anterior canaliculus for chorda tympani
-Petrotympanic fissure (through which passes the anterior tympanic branch of maxillary a)
Epitympanic recess
Anterior canaliculus
for chorda tympani
Tensor
tympani
Chorda tympani
Medial view
Medial wall: (labyrinthic wall)
• Formed by the lateral aspect of the internal ear. It presents the following features:
- Promontory: a rounded bulge formed by the basal turn of the cochlea. The surface of the promontory
presents grooves lodging the tympanic plexus of nerves.
- Oval (vestibular) window: a small opening above the promontory, it lodges the base of stapes
- Round (cochlear) window: a small opening below the promontory closed by a delicate membrane
called the secondary tympanic membrane
- Prominence of facial canal: traverses the medial wall above the oval window.
Tendon of stapedius
pyramid
Oval window closed by base of stapes
Prominence of facial canal
Chorda tympani
Tensor tympani
Lateral view
Auditory tube
Round window
Promontory showing
tympanic plexus of nerves
ICA
Facial nerve
Posterior
Medial
Lateral
Anterior
Oval window
(closed by base of stapes)
Prominence of
facial canal
Promontory formed by
the basal turn of cochlea
Base of stapes
Round window closed by
the secondary tympanic membrane
Auditory tube
Auditory Ossicles
• Three very small bones which form a bony chain that transmits sound waves
from the tympanic membrane across the tympanic cavity to the oval window
• They include: Malleus, Incus and Stapes
Malleus:
•
•
•
•
The largest of the three ossicles
Hammer-shaped, formed of a head, neck and three processes (the handle, anterior and lateral processes)
The head carries an articular facet for articulation with the body of incus
The anterior process gives attachment to the anterior ligament of malleus which connects it to the
petrotympanic fissure
• The lateral process is attached to the tympanic membrane, and to the anterior and posterior malleolar
folds which connect it to the upper notch of the tympanic sulcus.
• The handle is adherent to the tympanic membrane and receives the insertion of the tensor tympani
Head of malleus
Body of incus
Lateral process
Anterior process
Handle of malleus
Medial view
stapes
Incus:
• Formed of a body and 2 processes (a long and a short process)
• The body carries a facet for articulation with the head of malleus
• The long process is directed downwards, its lower end bends
medially to articulate with the head of stapes
• The short process is directed backwards
Head of malleus
Body of incus
incus
malleus
External acoustic meatus
stapes
Short limb of incus
Long limb of incus
Tympanic membrane
Anterior view
Head of stapes
Medial view
Stapes:
• Formed of a head, neck, two limbs and a base (footplate)
• The head is directed laterally and articulates with the lower end of the long limb of incus.
• The neck gives insertion to the tendon of stapedius
• The base is lodged in the oval window on the medial wall of the middle ear.
Long limb of incus
incus
Neck of stapes
Head of stapes
Ant & post
limbs of stapes
malleus
Base of stapes
External acoustic meatus
stapes
Tympanic membrane
Anterior view
Medial view
Auditory Muscles
Handle of malleus
Tendon of
tensor tympani
Tensor tympani
O: cartilaginous part of the auditory tube and
walls of the canal for tensor tympani
I: handle of malleus
N: mandibular nerve (through a branch from the
nerve to medial pterygoid)
External auditory
meatus
Stapedius
O: inner wall of the pyramid
I: neck of stapes
N: facial nerve (the nerve to stapedius arises in the facial canal)
Anterior view
Tendon of stapedius
Pyramid
Neck of stapes
Action of auditory muscles:
• The tensor tympani pulls the tympanic membrane inwards
• The stapedius pulls the stapes outwards
• The two muscles contract in response to sounds of high
intensity to lessen the transmission of sound waves to the
oval window
Lateral view
Mastoid antrum
An air sinus which comuunicates with the post part of epitympanic recess through an aditus
Relations of the mastoid antrum:
•
•
•
•
•
•
Anterior wall: communicates with the epitympanic recess through the aditus
Posterior wall: sigmoid sinus and mastoid air cells
Roof: tegmen tympani
Floor: mastoid air cells
Lateral: suprameatal triangle of temporal bone
Medial: posterior semicircular canal
Medial view
Superior view
Auditory (Pharyngotympanic) Tube
• A mucous lined canal (36mm long) connecting the tympanic cavity with the nasopharynx
• From the anterior wall of the tympanic cavity, the canal is directed downwards, forwards and medially
• Its lateral 1/3 is bony, while its medial 2/3 are cartilagenous
• The widest part of the tube is at its opening in the nasopharynx
• Its narrowest part is at the junction of the bony and cartilaginous parts
• The tube equalizes pressure on both sides of the tympanic membrane
Auditory tube
(cartilaginous part)
Facial Nerve
Course
• Leaves the cranial cavity by passing into the internal acoustic meatus
• Pierces the bottom of the meatus and enters into the facial canal
• Runs laterally above the vestibule of internal ear until it reaches the medial wall of the tympanic cavity
• Bends sharply backwards above the promontory forming the geniculum of the facial nerve
• Continues backwards forming a prominence in the medial wall of the middle ear.
• Reaches the posterior wall of the middle ear and descends vertically behind the pyramid to emerge from
the stylomastoid foramen
pyramid
Prominence
of facial canal
Tendon
Vestibular window
of stapedius
Chorda tympani
geniculum
Greater petrosal n
Promontory &
tympanic plexus
Superior view
Facial nerve
Lateral view
Epitympanic recess
Chorda tympani
Tensor tympani
Facial nerve
Medial view
Branches of the Facial Nerve
Communicating branches:
• In the internal acoustic meatus: With the stato-acoustic nerve
• From the geniculate ganglion:
a. external petrosal (joins the sympathetic plexus around the middle meningeal artery)
b. greater petrosal (joins the sphenopalatine ganglion)
c. a twig which joins the lesser petrosal (to the otic ganglion)
• In the facial canal: communicates with the auricular branch of vagus
Branches of distribution:
In the facial canal:
• Nerve to stapedius: arises in the facial canal, passes into the pyramid to supply the stapedius m.
• Chorda tympani:
Below the stylomastoid foramen
• Posterior auricular n: arises just below the stylomastoid foramen
• Digastric branch: arises just below the stylomastoid foramen and supplies the post belly of digastric
• Stylohyoid branch: arises just below the stylomastoid foramen and supplies the stylohyoid m.
• Terminal branches in the face:
- Temporal - Zygomatic
- Buccal - Marginal mandibular
- Cervical
Chorda tympani
Chorda tympani:
• Arises in the facial canal 6mm above the
stylomastoid foramen
• Enters the tympanic cavity through a canaliculus
in its posterior wall
• Runs forwards through the tympanic cavity
between the fibrous and mucous layers of the
tympanic membrane
• Leaves the tympanic cavity through a canaliculus
in its anterior wall (med to the spine of sphenoid)
• Reaches the infratemporal fossa and joins the
lingual nerve
• Carries taste fibers from the ant 2/3 of the tongue
and preganglionic parasympathetic fibers to the
submandibular and sublingual salivary glands
Branches of the Facial Nerve
Tympanic nerve:
• A branch from the glossopharyngeal just below the jugular foramen
• Enters the floor of the tympanic cavity through the tympanic canaliculus
• Joins the tympanic plexus on the promontory
• The tympanic plexus gives rise to the lesser petrosal nerve
• The lesser petrosal leaves the cranial cavity through the foramen ovale and joins the otic ganglion
• It carries preganglionic parasympathetic fibers to the otic ganglion
Geniculate ganglion
Greater petrosal
Tympanic plexus
Tympanic nerve
Jugular fossa
Arterial supply of the middle ear:
•
•
•
•
•
•
•
Anterior tympanic artery: from the first part of maxillary a (ECA)
Stylomastoid artery: from the post auricular or occipital a (from ECA)
Carotico-tympanic artery: from the ICA in the carotid canal
Superior tympanic artery: from the ascending pharyngeal a (ECA)
Inferior tympanic artery: from the middle meningeal artery
Petrosal branch of middle meningeal artery
A twig from the artery of pterygoid canal: from the third part of maxillary a
Venous drainage of the middle ear:
•Pterygoid plexus of veins
•Superior petrosal sinus
Nerve supply of the middle ear:
• Nerves which supply the middle ear form the tympanic plexus on the promontory
• The tympanic plexus is formed of:
- Tympanic nerve: from the glossopharyngeal nerve
- Superior caroticotympanic nerve: from the sympathetic plexus around ICA
- Inferior caroticotympanic nerve: from the sympathetic plexus around ICA
• Both carotico-tympanic nerves pierce the posterior wall of the carotid canal to enter the middle ear
• The tympanic plexus gives the following branches:
- Lesser petrosal nerve: the motor root to the otic ganglion
- Twigs to the mucosa of tympanic cavity, auditory tube, mastoid antrum and mastoid air cells
- Communicating branch to the greater petrosal nerve
Facial Nerve Paralysis:
• Upper motor neuron lesion: Only the lower half of the face on the opposite side of the lesion is
affected (the upper half of facial nucleus receives cortico-nuclear fibers from both pyramidal tracts, while
the lower half of the nucleus receives cortico-nuclear fibers from the opposite pyramidal tract only)
• Lower motor neuron lesion: affects the corresponding half of the face
Signs and symptoms of facial nerve paralysis:
A. Lesion below the stylomastoid foramen:
• Skin creases disappear, with no expressions on the affected side of the face
• Inability to close the eyelids (paralysis of orbicularis oculi) or wrinkle the forehead (paralysis of occipitofrontalis)
• Dropped angle of the mouth
• Falling of food into the vestibule of the mouth (paralysis of buccinator)
B. Lesion in the facial canal:
• All the above, in addition to:
• Loss of taste on the anterior part of the tonge on the affected side (due to involvement of chorda tympani)
• Decreased salivation, dryness of the mouth (involvement of chorda tympani)
• Hyperacusis (involvement of nerve to stapedius)
C. Lesion in the internal acoustic meatus:
• All the above, in addition to:
• Deafness (due to involvement of the vestibulo-cochlear nerve)
Internal Ear (Labyrinth)
The internal ear is formed of:
•Bony labyrinth: intercommunicating bony cavities inside the petrous bone
•Membranous labyrinth: intercommunicating membranous sacs and ducts inside the bony labyrinth.
Bony labyrinth: formed of three parts; vestibule, semicircular canals and cochlea
The vestibule:
• A small ovoid cavity medial to the
tympanic cavity, in front of the
semicircular canals and behind the
cochlea
• Its lateral wall presents an oval
opening; the vestibular (oval) window
• Its medial wall presents an opening for
the vestibular aqueduct and
perforations for the vestibular and
cochlear nerve fibers
• Posteriorly, the vestibule receives the
openings of the semicircular canals (5
openings)
• Anteriorly, it communicates with the
scala vestibuli of the cochlea
Semicircular canals
vestibule
Perforations
for vestibular n
Perforations for cochlear n
cochlea
Vestibular window
Round window
Opening for vestibular aqueduct
Semicircular canals
• Three curved canals connected to the posterior part of the vestibule by five openings
• According to their position, they are called: superior, posterior and lateral semicircular canals
• The three canals are oriented at 90 degrees to one another.
• Each canal presents a dilatation at one end forming the ampulla of the semicircular canal
Superior semicircular canal
ampullae
vestibule
lateral semicircular canal
Oval window
cochlea
posterior semicircular canal
Round window
Cochlea
• A conical bony cavity resembling a snail shell,
in front of the vestibule
• The cochlea is in the form of a bony spiral that
makes 2 ½ turns around a central bony axis (the
modiolus)
• The first turn of the cochlea produces a bulge in
the medial wall of the tympanic cavity
(promontory)
• The modiolus projects into the spiral cochlea
with a shelf of bone called the spiral lamina
• Blood veseels and the spiral ganglia pass
through the spiral lamina
• The dendritic processes of the spiral ganglion
cells perforate the spiral lamina to reach the
hair cells
• The axons of the spiral ganglion cells run
through the modiolus forming the cochlear
nerve which leaves the cochlea through the
internal acoustic meatus
Spiral ganglion
Cochlear nerve
Round window
Basal turn of cochlea (promontory)
modiolus
Spiral lamina
Bony wall of cochlea
Membranous labyrinth
• The membranous labyrinth (in the form of sacs and ducts) is
enclosed within the bony labyrinth
• It is filled with endolymph and bathed in the perilymph of
the bony labyrinth
• The membranous labyrinth is composed of:
•Utricle and saccule (enclosed within the bony vestibule)
•Semcircular ducts (within the semicircular canals)
•Cochlear duct (within the cochlea)
•Endolymphatic duct
Semicircular ducts
ampullae
Endolympatic duct & sac
Cochlear duct
Utricle:
• A small sac in the bony vestibule
• It receives the openings of the semicircular ducts
• It contains a highly specialized organ for
equilibruim (macula utriculi)
• The utricle is connected to the saccule by the
utriculo-saccular duct
Saccule:
• A small sac in the bony vestibule
• Carries a sensory organ for equilibrium
called the macula sacculi
utricle
Utriculo-saccular duct
saccule
Semicircular ducts:
•
•
•
•
Three ducts which occupy the semicircular canals
They have similar names to the enclosing bony canals
Each duct presents a dilatation (ampulla) enclosed within the corresponding bony ampulla
Each ampulla contains a sensory organ for equilibrium called the crista ampullaris
Endolymphatic duct and sac
• Arises from the utriculo-saccular duct
• Passes through the aqueduct of the vestibule
to end in a dilatation (endolymphatic sac)
• The endolymphatic sac lies under the dura
on the posterior surface of petrous bone
Vestibular membrane
Cochlear duct
• Enclosed within the bony cochlea
• Contains the sensory organ of hearing (organ
of Corti)
• The duct is triangular in cross section
• Its floor is formed by an elastic membrane
(basilar membrane)
• Its roof is formed by a delicate membrane (the
vestibular membrane)
• The organ of Corti lies on the upper surface
of the basilar membrane)
• The outer wall of the cochlear duct is adherent
to the bony cochlea and called stria vascularis
• The cochlear duct is connected to the saccule
by the ductus reuniens
• The space between the vestibular membrane
and bony cochlea is called the scala vestibuli
and is continuous with the vestibule
• The space between the basilar membrane and
bony cochlea is called the scala tympani
• The scala tympani presents the round window
at its lower end
• The two scalae are continuous at the apex of
the cochlea through an opening (the
helicotrema)
Spiral lamina
Cochlear duct
Stria vascularis
Scala vestibuli
Scala tympani
Spiral ganglion
Bony cochlea
Organ of Corti
Basilar membrane
Cochlear nerve
Scala vestibuli
Scala tympani
Round window
Mechanism of hearing:
• Sound vibrations collected by the auricle lead to vibrations in the tympanic membrane
• These vibrations are transmitted through the auditory ossicles to the base of stapes and augmented about
20 times (due to the small surface area of the base of stapes)
• The waves are then transmitted into the vestibular perilymph through the oval window
• The perilymph carries the waves into the scala vestibuli where they lead to vibrations of the vestibular
membrane
• The vibrations are transmitted into the endolymph of the cochlear duct resulting in vibrations of the
basilar membrane leading to stimulation of the hair cells in the organ of Corti
• In the organ of Corti, the vibrations are converted into nerve impulses which are carried by the peripheral
processes of the sprial ganglion cells into the spiral ganglia and cochlear nerve
• The sound vibrations in the perilymph of scala vestibuli are also carried (through the helicometra) to the
scala tympani, and continue down to the lower end of the scala tympani where they are eliminated by
outward bulging of the secondary tympanic membrane (which closes the round window)
Arterial supply of the labyrinth:
•Labyrinthine artery: from the basilar artery
•Stylomastoid artery: from the posterior auricular (or occipital a)
Venous drainage:
•Into the superior petrosal and transverse sinuses