ANATOMY OF THE
EAR
M.Rogha M.D
Isfahan university of medical sciences
MAJOR DIVISIONS OF THE EAR
Peripheral Mechanism
Outer
Ear
Middle
Ear
VIII
Inner
Cranial
Ear
Nerve
Central Mechanism
Brain
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 EAR
Pinna
Preauricular Tags
Pinna
Preauricular Pits
EAM
Cerumen
External
Auditory
Meatus
Function
EAM resonance
FUNCTION OF OUTER EAR
• Collects sound
• Localization
• Resonator
• Protection
PINNA
• The visible portion that is
commonly referred to as "the
ear"
• Helps localize sound sources
• Directs sound into the ear
• Each individual's pinna
creates a distinctive imprint
on the acoustic wave traveling
into the auditory canal
EXTERNAL AUDITORY
MEATUS
• Extends from the pinna to the tympanic
membrane
• About 26 mm in length and 7 mm in diameter in adult
ear.
• Size and shape vary among individuals.
• Protects the eardrum
• Resonator
• Provides about 10 decibels (dB) of gain to the eardrum
at around 3,300 Hertz (Hz).
• The net effect of the head, pinna, and ear canal is
that sounds in the 2,000 to 4,000 Hz region are
amplified by 10 to 15 dB.
• Sensitivity to sounds greatest in this frequency region
• Noises in this range are the most hazardous to hearing
OUTER EAR
Tissues: elastic cartilage covered with skin
A. Meatus acusticus externus besides the hair
follicles and fat glands contains:
Glandulae ceruminosae – modified sweat
glands on the lateral wall of the canal.
Сerumеn (ear wax) combination of wax and fat
glands secret and desquamated epithelial cells.
MIDDLE EAR
Tympanic Cavity
Tympanic Membrane
Ossicles
Middle Ear Muscles
Eustachian Tube
Mastoid
FUNCTION OF MIDDLE EAR
• Conduction
• Conduct sound from the outer ear to the inner ear
• Protection
• Creates a barrier that protects the middle and inner areas
from foreign objects
• Middle ear muscles may provide protection from loud
sounds
• Transducer
• Converts acoustic energy to mechanical energy
• Converts mechanical energy to hydraulic energy
• Amplifier
• Transformer action of the middle ear
• only about 1/1000 of the acoustic energy in air would be
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 MEMBRANE
• Separates outer ear from middle ear
• Barrier from foreign objects
• Cone-shaped in appearance
• about 17.5 mm in diameter
• Vibrates in response to sound waves.
• The membrane movement is incredibly
small
• as little as one-billionth of a
centimeter
TYMPANIC MEMBRANE
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
MEDIAL WALL, PARIES LABYRINTHICUS
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.
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 of
tympanic membrane for optimal hearing.
OSSICLES
• Malleus
(hammer)
• Incus
(anvil)
• Stapes
(stirrup)
smallest bone
of the body
INNER EAR
Vestibular
semicircular canals
utricle and saccule
Auditory
Cochlear
traveling wave
traveling wave
Vestibular
traveling wave
pathologies
INNER EAR
Two compartments:
(а) Bony labyrinth and
(b) Membraneous labyrinth.
Bony labyrinth:
 complex cavity in dense bone
(pars petrosa)
Parts of the bony labyrinth:
a.Vestibulum.
b. Semicircular canals.
c.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 VESTIBULUM
a. Fenestra vestibuli.
b.
Fenestra cochleae.
c.
Openings (5) of the semicircular canals
d.
Aqueductus vestibuli
SEMICIRCULAR
CANALS
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
Labyrinthus osseus. Cochlea
Cochlea
Meatus acusticus internus
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
Labyrinthus membranaceus
FUNCTION OF INNER EAR
• Converts mechanical
sound waves to neural
impulses that can be
recognized by the brain
for:
• Hearing
• Balance
Membraneous labyrinth.
Labyrinthus membranaceus
•Closed system of sacs and ducts
underling the bony labyrinth.
•Filled with endolymph.
•Two parts:
vestibular & cochlear.
Vestibular labyrinth
Composed of :
• Two bags - sacculus et utriculus
• Three ductus semicirculares
• One ductus endolymphaticus.
Cristra ampullaris
BALANCE
• Linear motion
• Rotary motion
Sensory cells
(Epitheliocytus
pilosus)
Macula utriculi
(sacculi)
Otoliths. Statoconia
Static balance
Maculae react to gravitational forces and participate
in maintaining the static balance.
Dynamic balance
Cristae ampullares react to rotatory movements
and paticipate in dynamic balance.
COCHLEA
• The cochlea resembles a
snail shell and spirals for
about 2 3/4 turns around a
bony column
• Within the cochlea are
three canals:
• Scala Vestibuli
• Scala Tympani
• Scala Media
Cochlear labyrinth
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
ORGAN OF CORTI
• End organ of hearing
ORGAN OF CORTI
Sensory cells of
the organ of Corti