Anatomy of the ear

Anatomy of the Ear
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Introduction
The ear is the organ of hearing and balance. It has three parts :
1. External Ear
2. Middle Ear
3. Inner Ear

External Ear
Parts of the External Ear:
 Auricle: A wrinkly
musculocutaneous tissue that is
attached to the skull and
functions to capture sound.
 External Acoustic Meatus: A
bony-cartilaginous canal that
projects from the auricle to the
middle ear, from which it is
separated by the tympanic
membrane.
 The tympanic membrane: It
separates the external acoustic
meatus from the middle ear

Auricle: Parts & Muscles
Parts of the Auricle:
 Helix: The large outside rim of the
auricle. It ends inferiorly at the fleshy
lobule, the only part of the auricle not
supported by cartilage.
 Antihelix: A smaller curved rim, parallel
and anterior to the helix.
 Concha of the auricle: The fossa that is
continuous with the external acoustic
meatus at the center of the auricle.
 Tragus & Anitragus: The tragus is an
elevation anterior to the opening of the
external acoustic meatus, in front of the
concha. Opposite the tragus, and above
the fleshy lobule, is another elevation
the antitragus.
Muscles: help in positioning auricle
(innervated by CN VII)
 Intrinsic Muscles
 Extrinsic Muscles: the anterior, superior,
and posterior auricular muscles

Auricle: Innervation, Vessels
Innervation: Sensory:
• Superficial surfaces: are supplied by the
great auricular nerve, lesser occipital
nerve, Auriculotemporal branch of
Mandibular nerve
• Deeper parts: supplied by the vagus
nerve [X] (the auricular branch) and the
facial nerve [VII]
Blood Supply:
 Arterial supply: posterior auricular
branch, superior auricular artery from
External Carotid Artery, anterior auricular
branches from superficial temporal artery
& a branch of Occipital Artery
 Venous drainage: follows arterial supply
Lymphatic drainage:
Parotid nodes anteriorly, posteriorly
into mastoid nodes and deep cervical
lymph nodes

External acoustic meatus
The external acoustic meatus extends
from the deepest part of the concha to
the tympanic membrane (eardrum), a
distance of approximately 1 inch. It
consists of:
 Membranous External Acoustic
Meatus: makes up the lateral 1/3 of this
canal. It is directed posteriorly and
superiorly
 Bony External Acoustic Meatus: makes
up the medial 2/3 of the canal. It is
directed anteriorly and inferiorly.
Throughout its length the external acoustic
meatus is covered with skin, some of
which contains hair and modified sweat
glands producing cerumen (earwax). Its
diameter varies, being wider laterally and
narrow medially.

Tympanic Membrane
The tympanic membrane is a thin, oval shaped
translucent partition between the external acoustic
meatus & middle ear. It measures 9×10mm and is
positioned at an acute angle of 55o with the floor of
external acoustic meatus.
Surfaces: It has 2 surfaces:
1) Outer Surface: Lined by skin and faces the
external ear.
2) Inner Surface: Lined by mucous membrane. At its
center, a concavity is produced by the attachment
of the lower end of the handle of the malleus.
This point of attachment is the umbo of the
tympanic membrane. Anteroinferior to the umbo
is a bright reflection of light(seen in otoscopic
examinations), referred to as the cone of light.
Subdivisions: Extending away from the elevation of the
lateral process of the malleus are the anterior
and posterior malleolar folds. These divide the
membrane into:
1. Pars flaccida (thin)- Between folds
2. Pars tensa (thick)- rest of the membrane

Tympanic Membrane
Histological Structure and Embryological origins: The tympanic membrane is composed of 3 layers:
1) Outer Cuticular layer (Ectoderm of 1st pharyngeal cleft): Lined by hairless, keratinized stratified
squamous epithelium.
2) Intermediate fibrous layer (Surrounding Mesenchyme): made up of superficial radiating fibers and
deep circulating fibers
3) Inner mucous layer (Endoderm of 1st pharyngeal pouch) : lined by simple columnar or squamous
epithelium.
Blood Supply:
 Arterial supply:
– Outer Surface: deep auricular branch of maxillary artery
– Inner Surface: Anterior tympanic branch of maxillary artery and posterior tympanic branch of
stylomastoid branch of posterior auricular artery
 Venous drainage:
– Outer Surface: External Jugular vein
– Inner Surface: Transverse sinus and into venous plexus around auditory tube
Lymphatic drainage:
Pre auricular & retro pharyngeal lymph nodes
Innervation:
Outer surface: Auriculotemporal nerve and Auricular branch of vagus
Inner Surface: Tympanic branch of Glossopharyngeal nerve

External Ear: Clinical Anatomy
+ Examination of the External ear
• The otoscopic examination begins by grasping the posterosuperior
aspect of the ear and gently retracting it to straighten the external
auditory meatus. The normal tympanic membrane is relatively
translucent and has a gray–reddish tinge.
+ Perforation of the Tympanic Membrane
• The tympanic membrane is a relatively thin and is susceptible
to perforation (usually by trauma or infection).
• An infection of the middle ear (otitis media) causes pus and fluid to
build up behind the tympanic membrane. This causes an increase in
pressure within the middle ear, and eventually the eardrum can
rupture.
• In some cases the tympanic membrane heals itself, but in larger
perforations surgical grafting may be required.
• It may be necessary to enter the middle ear through the tympanic
membrane. Because the chorda tympani runs in the upper 1/3 of the
tympanic membrane, incisions are always below this level. The
richer blood supply to the posterior aspect of the tympanic
membrane determines the standard surgical approach in the
posteroinferior aspect.

Middle Ear
Parts of the middle ear:
• Tympanic cavity immediately adjacent to the tympanic
membrane, and
• Epitympanic recess superiorly.
• Ear ossicles
Boundaries of the middle ear
• Roof – formed by a thin bone from the petrous part of
the temporal bone. It separates the middle ear from
the middle cranial fossa.
• Floor – known as the jugular wall, it consists of a thin
layer of bone, which separates the middle ear from the
internal jugular vein
• Lateral wall – made up of the tympanic membrane and
the lateral wall of the epitympanic recess.
• Medial wall – formed by the lateral wall of the internal
ear. It contains a prominent bulge, produced by
the facial nerve as it travels nearby.
• Anterior wall – a thin bony plate with 2 openings; for
the auditory tube and the tensor tympani muscle. It
separates the middle ear from the internal carotid artery.
• Posterior wall (mastoid wall) – it consists of a bony
partition between the tympanic cavity and the mastoid
air cells.

Boundaries: Medial Wall
The labyrinthine (medial) wall of the middle ear is also the lateral wall of the internal
ear. A prominent structure on this wall is a rounded bulge (the promontory) produced
by the basal coil of the cochlea. Associated with the mucous membrane covering the
promontory is a plexus of nerves (the tympanic plexus)
Tympanic Plexus primarily consists of:
• tympanic branch of the Glossopharyngeal nerve CN (IX)
• branches from the internal carotid plexus
Functions:
• supplies the mucous membrane of the middle ear, the mastoid area, and the
pharyngotympanic tube.
• Sends a branch (the lesser petrosal nerve) to otic ganglion.
Windows & structures passing through medial wall:
 The oval window is posterosuperior to the promontory, is the point of attachment for
the base of the stapes (footplate)
 The round window is posteroinferior to the promontory
 Posterior and superior to the oval window on the medial wall is the prominence of the
facial canal, which is a ridge of bone produced by the facial nerve [VII]
 Just above and posterior to the prominence of the facial canal is a broader ridge of
bone (prominence of the lateral semicircular canal) produced by the lateral
semicircular canal

Branches of the Facial Nerve
Course: The facial nerve (CN VII)enters the internal acoustic meatus along with CN VIII. CN VII
enters the facial canal and continues laterally between the internal and middle ear. It is at
this point that the sensory geniculate ganglion forms a bulge in CN VII and gives rise to the
following branches:
– Greater petrosal nerve. Provides visceral motor innervation to the lacrimal, nasal, and palatal glands.
– Nerve to the stapedius muscle (branchial motor). Provides innervation to the stapedius muscle.
– Chorda tympani nerve.

Chorda Tympani Nerve
Course: Arises from CN VII before it exits the skull , courses through the middle layer
of the tympanic membrane, continues between the malleus and stapes, and exits
the skull at the petro-tympanic fissure.
Innervation: The chorda tympani innervates the
– submandibular and sublingual salivary glands
– Conveys taste sensation (special sensory) from the anterior 2/3s of the tongue.

Mastoid Area
Location: Posterior to the epitympanic recess of the
middle ear is the aditus to the mastoid antrum,
which is the opening to the mastoid antrum
Description: The mastoid antrum is a cavity
continuous with collections of air-filled spaces
(the mastoid cells), throughout the mastoid part
of the temporal bone, including the mastoid
process.
Function: The mastoid air cells act as a ‘buffer system’
of air – releasing air into the tympanic cavity
when the pressure is too low.
+ Mastoiditis (Clinical)
Infection within the mastoid antrum and mastoid
cells is usually secondary to infection in the middle
ear because the mucous membrane lining the
mastoid air cells is continuous with that of the
middle ear. This is called Mastoiditis

Pharyngotympanic Tube
Description: The pharyngotympanic tube connects the
middle ear with the nasopharynx
Formation: Its opening in the middle ear is on the
anterior wall, and from here it extends forward,
medially, and downward to enter the nasopharynx
just posterior to the inferior meatus of the nasal
cavity
Parts: It consists of:
• bony part (the 1/3 nearest the middle ear)
• cartilaginous part (the remaining 2/3 s).
Function: Equalizes pressure on both sides of the
tympanic membrane.
Blood Supply:
 Arterial supply:
– Branches arise from the ascending pharyngeal artery
(a branch of the external carotid artery) and from 2
branches of the maxillary artery
 Venous drainage:
– pterygoid plexus of veins in the infratemporal fossa
Innervation:
Primarily from the Tympanic plexus

Auditory ossicles
Malleus
• The malleus is the largest and is attached to the tympanic
membrane.
• Its posterior surface articulates with the incus. (Saddle-
type joint)
• The anterior process is attached to the anterior wall of the
middle ear by a ligament.
• The lateral process is attached to the anterior and posterior
malleolar folds of the tympanic membrane.
• It is the smallest long bone in the body!
Incus
• The 2nd bone in the series of auditory ossicles is the incus.
• The body of the incus articulates with the head of the
malleus and is in the epitympanic recess.
• The long limb bends medially to articulate with the stapes.
• The short limb is attached by a ligament to the upper
posterior wall of the middle ear.
Stapes
• The stapes is the most medial bone in the osseous chain
and is attached to the oval window
• The head of the stapes articulates with the long process of
the incus. (Ball & Socket Joint)
• The 2 limbs separate from each other and attach to the oval
base.
• It’s the smallest bone in the body!

Muscles associated with Auditory Ossicles

Muscles associated with Auditory Ossicles
Functions:
• Tensor tympani: Tenses the tympanic membrane, reducing the
force of vibrations in response to loud noises
• Stapedius: Contraction of the stapedius muscle, usually in response
to loud noises, pulls the stapes posteriorly and prevents excessive
oscillation. It is the smallest muscle in the body!

Middle Ear: Blood Supply
Arterial supply: Numerous arteries supply the structures in the middle ear:
• The 2 largest branches are the tympanic branch of the maxillary artery and the mastoid branch of the
occipital or posterior auricular arteries;
• Smaller branches come from the middle meningeal artery, the ascending pharyngeal artery, the artery
of the pterygoid canal, and tympanic branches from the internal carotid artery.
Venous drainage: By the pterygoid plexus of veins and the superior petrosal sinus.

Middle Ear: Innervation & Origins
Innervation:
 General Sensory:
– mucosal side of the tympanic membrane via
the tympanic branches of the Glossopharyngeal
nerve (CN IX).
– tympanic cavity is also innervated by CN IX via
the tympanic plexus.
 Sympathetic:
– caroticotympanic nerves from the carotid
sympathetic plexus.
 Motor: (to muscles)
– Stapedius from a branch of the facial nerve (CN
VII)
– Tensor tympani is supplied via the medial
pterygoid branch of CN V3 (Mandibular nerve).
Embryological Origins:
 Tympanic cavity – Distal part Endoderm of the 1st
pharyngeal pouch
 Pharyngotympanic tube – Proximal part Endoderm of
the 1st pharyngeal pouch
 Ear ossicles- Mesenchyme of the 1st pharyngeal arch
(malleus & incus) and 2nd pharyngeal arch (stapes)

Middle Ear: Clinical Anatomy
+ Otitis media
• Otitis media is a viral or bacterial infection of the middle ear observed commonly in children.
• The infection may migrate along the pharyngotympanic tube. Therefore, it is common to see patients
presenting with both otitis media and pharyngitis or tonsillitis.
• This is because the position of the pharyngotympanic tube in children is more horizontal and also the
length of the pharyngotympanic tube is smaller than that of adults.
• These features may facilitate the spread of pathogenic agents to and from nasopharynx.
+ Hyperacusis
• A lesion of CN VII may cause paralysis of the stapedius muscle, resulting in wider oscillation of stapes.
• Consequentially, there is a heightened reaction of the auditory ossicles to sound vibration.
• This condition is known as hyperacusis and results in an increased sensitivity to loud sounds.

Internal Ear: Location & Components
Location: The inner ear is located within the petrous part
of the Temporal bone. It lies between the middle ear
and the internal acoustic meatus, which lie laterally
and medially respectively.
Components: The inner ear has 2 main components –
the bony labyrinth and membranous labyrinth.
– Bony labyrinth – consists of a series of bony cavities within
the petrous part of the temporal bone. It is composed of the
cochlea, vestibule and 3 semi-circular canals. All these
structures are lined internally with periosteum and contain a
fluid called perilymph.
– Membranous labyrinth – lies within the bony labyrinth. It
consists of the cochlear duct, 3 semi-circular ducts, utricle and
the saccule. The membranous labyrinth is filled with fluid called
endolymph.
Openings: The inner ear has 2 openings into the middle
ear, both covered by membranes.
– Oval window lies between the middle ear and the
vestibule, whilst
– Round window separates the middle ear from the
scala tympani (part of the cochlear duct).

Bony labyrinth: Vestibule
• The vestibule, which contains the oval window in its
lateral wall, is the central part of the bony labyrinth. It
communicates anteriorly with the cochlea and
posterosuperiorly with the 3 semicircular canals.
• A narrow canal (the vestibular aqueduct) leaves the
vestibule, and passes through the temporal bone to
open on the posterior surface of the petrous part of
the temporal bone.
• Two parts of the membranous labyrinth;
the saccule and utricle, are located within the
vestibule.

Bony labyrinth: Semi Circular Canals
• Projecting in a posterosuperior direction from the
vestibule are the anterior, posterior, and lateral
semicircular canals
• Each of these canals forms 2/3s of a circle
connected at both ends to the vestibule and with
one end dilated to form the ampulla.
• The canals are oriented so that each canal is at
right angles to the other two.

Bony labyrinth: Cochlea
Structure: The cochlea houses the cochlea duct of the
membranous labyrinth – the auditory part of the inner
ear. It twists upon itself 2.5 times around a central
portion of bone called the modiolus, producing a cone
shape which points in an anterolateral direction.
Branches from the cochlear portion of
the vestibulocochlear (CN VIII) nerve are found at the
base of the modiolus.
• Extending outwards from the modiolus is a ledge of
bone known as spiral lamina, which attaches to the
cochlear duct, holding it in position.
• The presence of the cochlear duct creates two
perilymph-filled chambers above and below:
– Scala vestibuli: Located superiorly to the cochlear duct. As its
name suggests, it is continuous with the vestibule.
– Scala tympani: Located inferiorly to the cochlear duct. It
terminates at the round window.
• The scala vestibuli and the scala tympani are
separated completely, except at the narrow apex of
the cochlea called the helicotrema, where they are
continuous.

Membranous labyrinth
Description: The membranous labyrinth is a continuous system of ducts filled
with endolymph. It lies within the bony labyrinth, surrounded by perilymph.
Arrangement: The general organization of the parts of the membranous labyrinth
places:
– cochlear duct within the cochlea of the bony labyrinth, anteriorly,
– saccule and utricle within the vestibule of the bony labyrinth, in the middle.
– 3 semicircular ducts within the 3 semicircular canals of the bony labyrinth,
posteriorly
Organs of balance :
• 5 of the 6 components of the membranous labyrinth are concerned with balance.
– Utricle
– Saccule
– 3 Semicircular ducts
Organ of hearing :
– Cochlear duct

Membranous labyrinth: Organs of balance
Utricle, saccule, and endolymphatic duct
– Utricle- The utricle is the larger of the two sacs. It is oval, elongated and irregular in
shape and is in the posterosuperior part of the vestibule of the bony labyrinth. The 3
semicircular ducts empty into the utricle.
– Saccule- A smaller, rounded sac lying in the anteroinferior part of the vestibule of the
bony labyrinth. The cochlear duct empties into it.
– Endolymphatic duct- Duct via which Endolymph from the saccule and utricle drains
into.
Function: In the utricle and saccule the sense organ of balance is the macula of the utricle
and the macula of the saccule, respectively. They respond to linear acceleration :
– Utricle responds to linear acceleration in the horizontal plane and sideways head tilts
– Saccule responds to linear acceleration in the vertical plane,
Semicircular Ducts:
The semi-circular ducts are located within the semi-circular canals, and share their
orientation. Upon movement of the head, the flow of endolymph within the ducts changes
speed and/or direction.
Function: Sense organ of balance is in the ampulla of each of the 3 semicircular ducts is the
crista. Sensory receptors in the crista respond to rotational movement in any direction

Membranous labyrinth: Organ of hearing
Cochlear duct:
Description: The cochlear duct is located within the
bony scaffolding of the cochlea. It is held in
place by the spiral lamina. The presence of the
duct creates 2 canals above and below it –
the scala vestibuli and scala
tympani respectively.
Arrangement: The cochlear duct can be described
as having a triangular shape :
– Lateral wall – Formed by thickened periosteum,
known as the spiral ligament.
– Roof – Formed by a membrane which separates the
cochlear duct from the scala vestibuli, known as the
vestibular membrane /Reissner’s membrane.
– Floor – Formed by a membrane which separates the
cochlear duct from the scala tympani, known as the
basilar membrane.
• The basilar membrane houses the epithelial
cells of hearing – the Spiral Organ/ Organ of
Corti. It projects into the enclosed, endolymph-
filled cochlear duct

Internal Ear: Blood Supply
Blood supply:
Arterial Supply:
• Bony Labyrinth: 3 arteries, which also supply
the surrounding temporal bone:
– Anterior tympanic branch (from maxillary
artery).
– Petrosal branch (from middle meningeal
artery).
– Stylomastoid branch (from posterior auricular
artery).
• Membranous Labyrinth: supplied by
the labyrinthine artery, a branch of the inferior
cerebellar artery has 3 branches:
– Cochlear branch – supplies the cochlear duct.
– Vestibular branches (x2) – supply the vestibular
apparatus.
Venous drainage:
Venous drainage of the inner ear is through
the labyrinthine vein, which empties into the
sigmoid sinus or inferior petrosal sinus.

Internal Ear: Innervation
Innervation: The inner ear is innervated by the vestibulocochlear (CN VIII) nerve. It enters the
inner ear via the internal acoustic meatus, where it divides into the vestibular
nerve (responsible for balance) and the cochlear nerve (responsible for hearing):
• Vestibular nerve – enlarges to form the vestibular ganglion, which then splits into superior
and inferior parts to supply the utricle, saccule and 3 semi-circular ducts.
• Cochlear nerve – enters at the base of the modiolus and its branches pass through the
lamina to supply the receptors of the Organ of Corti.

Internal Ear: Clinical Anatomy
+ Motion sickness
• Motion sickness is a condition characterized by nausea and vomiting due to
travelling.
• It is due to fluctuations in maculae.
+ Vertigo
• Vertigo is a condition in which a person has a false sensation that either him or
surroundings are in motion .
• It can cause nausea, dizziness, sweating and vomiting.
• This condition is associated with vestibular malfunction.
+ Meniere’s disease
• Meniere’s disease is a disorder of the inner ear, characterised by episodes of
vertigo, low-pitched tinnitus and hearing loss.
• The symptoms are thought to be caused by an excess accumulation
of endolymph within the membranous labyrinth, causing progressive distension
of the ducts.
• The resulting pressure fluctuations damage the thin membranes of the ear that
detect balance and sound.

Internal Ear: Embryological Origins
Membranous Labyrinth:
• At about 22 days, a thickening of ectoderm
on either side of the hindbrain develops; this
is the otic placode. The placode invaginates
forming a pit that later becomes separated
from the ectoderm, forming the otic vesicle.
The otic vesicle is surrounded by mesoderm
that will become the otic capsule, the
cartilaginous precursor of the bony labyrinth.
Bony Labyrinth:
• The cartilage that surrounds the
membranous labyrinth (otic capsule) is
ossified (weeks 16–24) and creates a
perilymph‐filled protective space for the
inner ear.

Transmission of Sound
A sound wave enters the external acoustic meatus and strikes the tympanic membrane.
The sound wave transfers its energy into the vibration of the tympanic membrane.
As the tympanic membrane vibrates, it causes the malleus to move medially, which in turn
causes the incus and stapes to move sequentially, amplifying the sound wave.
The stapes is attached to the oval window/vestibular window; thus, the oval window also
moves, resulting in a wave forming in the perilymph within the scala vestibuli of the
cochlea.
The fluid wave in the perilymph progresses from the scala vestibuli of the cochlea, resulting
in an outward bulging of the round window/cochlear window at the end of the scala
tympani.
This bulging causes the basilar membrane in the cochlea to vibrate, which in turn results in
stimulation of the receptor hair cells in the spiral organ (of Corti).
The receptor hair cells conduct impulses to the Brain through the cochlear division of CN
VIII, where the Brain interprets the wave as sound.

Central Auditory Pathway
 The 1st order axons entering the brainstem from the cochlea terminate
ipsilaterally on the dorsal and ventral cochlear nuclei.
 From here, 2nd order axons forming the ascending auditory pathway ascend to the
pons and project bilaterally on the superior olivary nucleus forming the trapezoid
body . (Bilateral projections are important for auditory acuity and localizing the
sound origin).

Central Auditory Pathway
 From superior olivary nucleus and the posterior nucleus of trapezoid body, fibers continue to
ascend as the lateral lemniscus and terminate in the inferior colliculus of the midbrain.
 Axons leaving the inferior colliculus then have a synaptic relay in the medial geniculate
nucleus of the thalamus.
 Those axons then reach the final synaptic target: the primary auditory cortex
 The sound is then interpreted by the secondary auditory cortex (Wernicke’s Area)

Summary of Central Auditory Pathway

Summary of Central Auditory Pathway
1st order axons from cochlea enter dorsal and ventral cochlear nuclei (in
brainstem) ipsilaterally (same side as they are situated) via cochlear nerve.
From here, 2nd order axons ascend and project bilaterally on the superior olivary
nucleus and forming the trapezoid body. (in Pons)
Axons continue to ascend as the lateral lemniscus (3rd order)
They terminate in the inferior colliculus of the midbrain.
4th order axons (leaving inferior colliculus) then have a synaptic relay in the medial
geniculate nucleus of the thalamus
Axons then reach the Primary auditory cortex in the superior temporal gyrus of
the cerebrum
Primary auditory cortex then send signals to Secondary auditory cortex to
interpret sound.

Anatomy of the ear

Anatomy of the ear

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Anatomy of the ear