Anatomy of the EarAnatomy of the Ear
Stefan SivkovStefan Sivkov
Dept. of Anatomy, Histology andDept. of Anatomy, Histology and
EmbryologyEmbryology

Major Divisions of the EarMajor Divisions of the Ear
Peripheral Mechanism Central Mechanism
OuterOuter
EarEar
MiddleMiddle
EarEar
InnerInner
EarEar
VIIIVIII
CranialCranial
NerveNerve
BrainBrain

External ear, Auris externa
Auricula
Meatus acusticus externus
Middle ear, Auris media
Cavitas tympani
Membrana tympanica
Ossicula auditus
Tuba auditiva
Inner ear, Auris interna
Labyrinthus membranaceus
- Labyrinthus vestibularis
- Labyrinthus cochlearis
Labyrinthus osseus
- Vestibulum
- Canales semicirculares ossei
- Cochlea
- Meatus acusticus internus

Outer EarOuter Ear
Pinna
External
Auditory
Meatus
Pinna
Preauricular Tags
Preauricular Pits
EAM
Cerumen
Function
EAM resonance

Function of Outer EarFunction of Outer Ear
 Collects soundCollects sound
 LocalizationLocalization
 ResonatorResonator
 ProtectionProtection
 SensitiveSensitive
(earlobe)(earlobe)

PinnaPinna
 The visible portion that isThe visible portion that is
commonly referred to ascommonly referred to as
"the ear""the ear"
 Helps localize soundHelps localize sound
sourcessources
 Directs sound into the earDirects sound into the ear
 Each individual's pinnaEach individual's pinna
creates a distinctive imprintcreates a distinctive imprint
on the acoustic waveon the acoustic wave
traveling into the auditorytraveling into the auditory
canalcanal

External Auditory MeatusExternal Auditory Meatus
 Extends from the pinna to the tympanicExtends from the pinna to the tympanic
membranemembrane
– About 26 mm in length and 7 mm in diameter inAbout 26 mm in length and 7 mm in diameter in
adult ear.adult ear.
– Size and shape vary among individuals.Size and shape vary among individuals.
 Protects the eardrumProtects the eardrum
 ResonatorResonator
– Provides about 10 decibels (dB) of gain to theProvides about 10 decibels (dB) of gain to the
eardrum at around 3,300 Hertz (Hz).eardrum at around 3,300 Hertz (Hz).
 The net effect of the head, pinna, and earThe net effect of the head, pinna, and ear
canal is that sounds in the 2,000 to 4,000 Hzcanal is that sounds in the 2,000 to 4,000 Hz
region are amplified by 10 to 15 dB.region are amplified by 10 to 15 dB.
– Sensitivity to sounds greatest in this frequencySensitivity to sounds greatest in this frequency
regionregion
– Noises in this range are the most hazardous toNoises in this range are the most hazardous to
hearinghearing

Outer earOuter ear
Tissues:Tissues: elastic cartilage covered with skinelastic cartilage covered with skin
A.A. Meatus acusticus externusMeatus acusticus externus besides the hairbesides the hair
follicles and fat glands contains:follicles and fat glands contains:
GlandulaeGlandulae ceruminosaeceruminosae –– modified sweatmodified sweat
glands on the lateral wall of the canalglands on the lateral wall of the canal..
ССerumerumееnn (ear wax) combination of wax and(ear wax) combination of wax and
fat glands secret and desquamated epithelialfat glands secret and desquamated epithelial
cellscells..

Middle EarMiddle Ear
Tympanic Cavity
Tympanic Membrane
Ossicles
Middle Ear Muscles
Eustachian Tube
Mastoid

Function of Middle EarFunction of Middle Ear
 ConductionConduction
– Conduct sound from the outer ear to the inner earConduct sound from the outer ear to the inner ear
 ProtectionProtection
– Creates a barrier that protects the middle and inner areasCreates a barrier that protects the middle and inner areas
from foreign objectsfrom foreign objects
– Middle ear muscles may provide protection from loudMiddle ear muscles may provide protection from loud
soundssounds
 TransducerTransducer
– Converts acoustic energy to mechanical energyConverts acoustic energy to mechanical energy
– Converts mechanical energy to hydraulic energyConverts mechanical energy to hydraulic energy
 AmplifierAmplifier
– Transformer action of the middle earTransformer action of the middle ear
– only about 1/1000 of the acoustic energy in air would beonly about 1/1000 of the acoustic energy in air would be
transmitted to the inner-ear fluids (about 30 dB hearing loss)transmitted to the inner-ear fluids (about 30 dB hearing loss)

Tympanic cavity
• Volume – 1.5 ml
• Form – flatten drum
• Structure – six walls:
- Lateral
- Medial
- Anterior
- Posterior
- Superior
- Inferior

Lateral wall

Tympanic MembraneTympanic Membrane
 Separates outer ear from middle earSeparates outer ear from middle ear
 Barrier from foreign objectsBarrier from foreign objects
 Cone-shaped in appearanceCone-shaped in appearance
– about 17.5 mm in diameterabout 17.5 mm in diameter
 Vibrates in response to soundVibrates in response to sound
waves.waves.
 The membrane movement isThe membrane movement is
incredibly smallincredibly small
– as little as one-billionth of aas little as one-billionth of a
centimetercentimeter

Two parts:
Pars flaccida – upper, thin, loose
Pars tensa – lower, tense
Three layers:
1. Outer, cutaneous – continuation of
the canal skin. No hairs and glands.
2. Middle, fibrous – elastic fibers.
3. Inner, mucous – tympanic cavity
lining
Tympanic membrane

Most complex.
On this wall are distinguished:
-fenestra vestibuli
-fenestra cochleae
-promontorium
-prominentia canalis semicircularis
lateralis
- prominentia canalis facialis
Superior wall, paries tegmentalis
Separates tympanic from cranial cavity.
Children less than 2 years – infections of
the middle ear can pass to the cranial
cavity.
Medial wall, paries labyrinthicus

Inferior wall, paries jugularis
Separates tympanic cavity from fossa
jugularis
Anterior wall, paries caroticus
Separates tympanic cavity from
canalis caroticus
-canalis musculotubularis
Posterior wall, paries mastoideus
Composed of:
•Styloid complex of Procter
•Antrum mastoideum
•Fossa incudis

Auditory (Eustachian) tube
Connects tympanic cavity with pharynx
Two openings:
•ostium pharyngeum tubae
•ostium tympanicum tubae.
Two parts:
•bony
•cartilagenous
Function:
• Equalizes pressure on both sides ofEqualizes pressure on both sides of
tympanic membrane for optimal hearing.tympanic membrane for optimal hearing.

OssiclesOssicles
 MalleusMalleus
(hammer)(hammer)
 IncusIncus
(anvil)(anvil)
 StapesStapes
(stirrup)(stirrup)
smallest bonesmallest bone
of the bodyof the body

Inner EarInner Ear
Auditory
Vestibular
Vestibular
semicircular canals
utricle and saccule
Cochlear
traveling wave
traveling wave
traveling wave
pathologies

Inner earInner ear
Two compartments:Two compartments:
((аа) Bony labyrinth and) Bony labyrinth and
(b) Membraneous labyrinth.(b) Membraneous labyrinth.
Bony labyrinth::
•• complex cavity in dense bonecomplex cavity in dense bone
((pars petrosapars petrosa))
Parts of the bony labyrinth:Parts of the bony labyrinth:
a.Vestibuluma.Vestibulum..
b. Semicircular canals.b. Semicircular canals.
c.Cochleac.Cochlea..

Bony labyrinth.
Labyrinthus osseus
Vestibulum and semicircular canals

Vestibulum
Two walls: External and internal.
External wall has
• Fenestra vestibuli.
Internal wall has:
•Recessus ellipticus
•Recessus sphericus
•Recessus cochlearis
•Maculae cribrosae superior,
medius, inferior

Openings into vestibulumOpenings into vestibulum
aa.. Fenestra vestibuli.Fenestra vestibuli.
b.b. Fenestra cochleae.Fenestra cochleae.
c.c. Openings (5) of the semicircular canalsOpenings (5) of the semicircular canals
d.d. Aqueductus vestibuliAqueductus vestibuli

3: anterior, posterior and lateral.
Have ampulla and crus.
Canalis semicircularis lateralis –horizontal.
- eminentia canalis semicircularis lateralis on the medial wall of
tympanic cavity.
Canalis semicircularis anterior –frontal.
- eminentia arcuata on pars petrosa of os temporale.
Canalis semicircularis posterior –sagittal
Semicircular canals

Cochlea Meatus acusticus internus
Labyrinthus osseus. Cochlea

• Cone-shaped: base and apex.
• Canalis spiralis cochleae
- promontorium, on the medial wall of
tympanic cavity.
• Modiolus
- canales longitudinales modioli.
• Lamina spiralis ossea
-hamulus
Divides canalis spiralis cochleae
into:
•Scala tympani
•Scala vestibuli
Охлюв

Labyrinthus membranaceus

Function of Inner EarFunction of Inner Ear
 Converts mechanicalConverts mechanical
sound waves to neuralsound waves to neural
impulses that can beimpulses that can be
recognized by the brainrecognized by the brain
for:for:
– HearingHearing
– BalanceBalance

•Closed system of sacs and ducts
underling the bony labyrinth.
•Filled with endolymph.
•Two parts:
vestibular & cochlear.
Membraneous labyrinth.
Labyrinthus
membranaceus

Vestibular labyrinth
Composed of :
• Two bags - sacculus et utriculus
• Three ductus semicirculares
• One ductus endolymphaticus.

Cristra ampullaris

BalanceBalance
 Linear motionLinear motion
 Rotary motionRotary motion

Sensory cells
(Epitheliocytus
pilosus)

Macula utriculi
(sacculi)
Otoliths. Statoconia

MMaculaeaculae react to gravitational forcesreact to gravitational forces andand
participate in maintaining the static balanceparticipate in maintaining the static balance ..
Static balance

CCristaeristae ampullares react to rotatory movementsampullares react to rotatory movements andand
paticipate in dynamic balancepaticipate in dynamic balance ..
Dynamic balance

CochleaCochlea
 The cochlea resembles aThe cochlea resembles a
snail shell and spirals forsnail shell and spirals for
about 2 3/4 turns around aabout 2 3/4 turns around a
bony columnbony column
 Within the cochlea areWithin the cochlea are
three canals:three canals:
– Scala VestibuliScala Vestibuli
– Scala TympaniScala Tympani
– Scala MediaScala Media

Spiral canal - ductus cochlearis.
Occupies scala media of the spiral canal.
Has two blind ends - cecum vestibulare and cecum
cupulare.
Has three walls:
• paries vestibularis
• paries externus
• paries tympanicus- organ of Corti, basal membrane
Cochlear labyrinth

Organ of CortiOrgan of Corti
 End organ ofEnd organ of
hearinghearing

Organ of CortiOrgan of Corti

Sensory cells of
the organ of Corti