Anatomy of the EarAnatomy of the Ear

Stefan SivkovStefan Sivkov

Dept. of Anatomy, Histology and Dept. of Anatomy, Histology and EmbryologyEmbryology

Major Divisions of the EarMajor Divisions of the Ear

Peripheral Mechanism Central Mechanism

Outer Outer EarEar

Middle Middle EarEar

Inner Inner EarEar

VIII VIII CraniaCrania

l l NerveNerve

BrainBrain

External ear, Auris externaAuriculaMeatus acusticus externus

Middle ear, Auris mediaCavitas tympaniMembrana tympanicaOssicula auditusTuba auditiva

Inner ear, Auris internaLabyrinthus membranaceus - Labyrinthus vestibularis

- Labyrinthus cochlearis

Labyrinthus osseus

- Vestibulum

- Canales semicirculares ossei

- Cochlea

- Meatus acusticus internus

External ear, Auris externaAuriculaMeatus acusticus externus

Middle ear, Auris mediaCavitas tympaniMembrana tympanicaOssicula auditusTuba auditiva

Inner ear, Auris internaLabyrinthus 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 Sensitive Sensitive

(earlobe)(earlobe)

PinnaPinna

The visible portion that is The visible portion that is commonly referred to as commonly referred to as "the ear" "the ear"

Helps localize sound Helps localize sound sourcessources

Directs sound into the Directs sound into the earear

Each individual's pinna Each individual's pinna creates a distinctive creates a distinctive imprint on the acoustic imprint on the acoustic wave traveling into the wave traveling into the auditory canal auditory canal

External Auditory External Auditory MeatusMeatus

Extends from the pinna to the tympanic Extends from the pinna to the tympanic membranemembrane– About 26 mm in length and 7 mm in diameter About 26 mm in length and 7 mm in diameter

in adult ear. in 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 the Provides 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 ear The net effect of the head, pinna, and ear canal is that sounds in the 2,000 to 4,000 canal is that sounds in the 2,000 to 4,000 Hz region are amplified by 10 to 15 dB. Hz region are amplified by 10 to 15 dB. – Sensitivity to sounds greatest in this frequency Sensitivity to sounds greatest in this frequency

regionregion– Noises in this range are the most hazardous to Noises 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 hair besides the hair follicles and fat glands contains:follicles and fat glands contains:

GlandulaeGlandulae ceruminosaeceruminosae – – modified sweat modified 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 epithelial fat glands secret and desquamated epithelial cellscells..

Middle EarMiddle Ear

Tympanic CavityTympanic Membrane

OssiclesMiddle Ear Muscles

Eustachian TubeMastoid

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 areas Creates a barrier that protects the middle and inner areas

from foreign objectsfrom foreign objects– Middle ear muscles may provide protection from loud Middle 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 be only 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 sound Vibrates in response to sound waves. waves.

The membrane movement is The membrane movement is incredibly smallincredibly small– as little as one-billionth of a as little as one-billionth of a

centimetercentimeter

Two parts:Pars flaccida – upper, thin, loosePars 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 tegmentalisSeparates 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 jugularisSeparates tympanic cavity from fossa jugularis

Anterior wall, paries caroticusSeparates tympanic cavity from

canalis caroticus-canalis musculotubularis

Posterior wall, paries mastoideusComposed 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 Equalizes pressure on both sides of tympanic membrane for optimal hearing.tympanic membrane for optimal hearing.

OssiclesOssicles

Malleus Malleus (hammer)(hammer)

Incus Incus (anvil)(anvil)

Stapes Stapes (stirrup) (stirrup) smallest bone smallest 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 canals Openings (5) of the semicircular canals

d.d. Aqueductus vestibuli Aqueductus 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

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Labyrinthus membranaceus

Function of Inner EarFunction of Inner Ear

Converts mechanical Converts mechanical sound waves to neural sound waves to neural impulses that can be impulses that can be recognized by the brain recognized 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

MMaculae aculae react to gravitational forcesreact to gravitational forces and and participate in maintaining the static balanceparticipate in maintaining the static balance. .

Static balance

CCristae ristae ampullares react to rotatory movementsampullares react to rotatory movements and paticipate in dynamic balanceand paticipate in dynamic balance..

Dynamic balance

CochleaCochlea

The cochlea resembles a The cochlea resembles a snail shell and spirals for snail shell and spirals for about 2 3/4 turns around a about 2 3/4 turns around a bony columnbony column

Within the cochlea are Within the cochlea are three canals:three canals:– Scala Vestibuli Scala 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 of End organ of hearinghearing

Organ of CortiOrgan of Corti

Sensory cells of the organ of Corti