EXTERNAL EAR, MIDDLE EAR, INTERNAL EAR

DR PRATIK MISTRY

INTRODUCTIONOrgan of hearing and maintaining the balance (equilibrium) of the body

Human ear sensitive to sound frequency between 1500 Hz to 3000 Hz

Consist of 3 parts:1. External ear2. Middle ear3. Internal ear

Note: Reading a loud is a quicker way of memorizing

FUNCTIONS OF EAR External ear collects and conducts sound from air to tympanic membrane which vibrate according to sound frequencies

Middle ear intensifies the vibration of sound 15 to 20 times more by chain of ear ossicles

Internal ear convert sound energy into nerve impulse and convey sense of hearing by cochlear nerve and sense of equilibrium by vestibular nerve

External earCollect and Conduct sound from air to tmConsists of auricle (pinna) and external acoustic meatus

The auricleMammalian featureConsists of yellow elastic cartilage

Skin of auricle. Hairy pinnaParts of auricleMuscles of auricle1. Extrinsic 2. intrinsicNerve supplyblood supplyApplied boils, perichondritis, anotia, microtia, cauliflower ear

EXTERNAL ACOUSTIC MEATUS

EXTENT, 24 MM LONG LATERAL 1/3 CARTILAGINOUS (8

MM) AND MEDIAL 2/3 BONY (16 MM)

3 PARTS: OUTER, MIDDLE, INNER COURSE: ‘S’ SHAPED. OUTER PART: UPWARD,

FORWARD MIDDLE PART: UPWaRD,

BACKWARD INNER PART: DOWNWARD,

FORWARDEAR EXMINATION IN ADULT

AND CHILD ANT. WALL AND FLOOR LONGER CONSTRICTIONS AT THE junction

of two partsForeign bodies trapping Ceruminous glandsEar wax and aural syringing

Blood supplyNerve supplyLymphatic drainageApplied: earache cough reflex, diagnosis of leprosy, for grafting

Middle ear (tympanic cavity)

introduction Within petrous temporal contain Air and lined by

mucous membrane Adult size at birth Communicate in front

and behind Biconcave disc shape

like shape of rbc Measurements Total outline like pistol Subdivisions:Epitympanum Mesotympanumhypotympanum

boundariesRoughly cuboidalSix wallsRoofFloorAnterior wallPosterior wallMedial wallLateral wall

roof Tegmen tympany

Lessor petrosal n. & Greater petrosal n. Spread infection from middle ear to meninges

floorJugular fossaSuperior bulb of ijvTympanic branch of ix nerve enter from floor

Anterior wallLower part, carotid canal with ICA with sympathetic nerves

This wall pierced by sup. And inf. Caroticotympanic nerves

Upper part 2 bony canals

Upper - for tensor tympany muscle

Lower – auditory tube

Posterior wallWider above than below

Aditus to mastoid antrum

Fossa incudisFacial canalPyramidal eminence with stapedius muscle and its nerve

Medial wallFace towards bony labyrinth & presents:

Promontory & tympanic plexus

Fenestra vestibuli (oval window)

Fenestra cochleae (round window)

Sinus tympanyOblique part of facial canal

Processus cochleariformis

Lateral wallFormed by mucous covered medial surface of tympanic membrane

Chorda tympany nerve

Upper part of wall is formed by squamous temporal bone which contain head of malleus & body of incus

Tympanic membrane (ear drum) Oval, semi-transparent,

pearly grey trilaminar membrane 9-10 mm in diameter peripherally attached to tympanic sulcus

Position of t.m. & its difference in new born child

Medial surface is convex. Most prominent part – umbo

Subdivisions: Structure: On exanimation:

Blood supply:Nerve supply

Applied:MyringotomyMyringoplastyretracted tympanic membrane

Contents of the middle earThree ear ossicles-malleus, incus &stapes

movementsTwo muscles- tensor tympany & stapedius

Arteriesnerves

Clinical anatomy Throat infections Otitis media- acute or

chronic, leads to otorrhoea Mastoiditis and mastoid

abscess Otoscelorosis Stapedectomy Conductive deafness Clinical tests for hearing:Rinne’s testWeber’s testAudiometry Hyperacusis earache

Internal ear

introductionSeries of inter-communicating bony cavities within petrous temporal bone

Consists of outer bony labyrinth and inner membranous labyrinth

Perilymph is filled between two labyrinth and membranous labyrinth contains endolymph

Bony labyrinth Consists of 3 parts from before backwards:

1. Cochlea2. Vestibule3. Semi-circular canals Membranous labyrinth consists

of closed system of inter-communicating membranous sacs and ducts within bony labyrinth filled with endolymph

Consists of 3 parts:1. Cochlear duct within cochlea-

contain organ of corti for hearing

2. Saccule & utricle in the vestibule- contain maculae for static equilibrium and linear acceleration

3. Three semi-circular ducts in the canal- contain crista ampullaris for kinetic equilibrium and angular acceleration

From the base of cochlea, rootlets of cochlear nerve emerge

From vestibule and semi-circular canals rootlets of vestibular nerve emerge

Both the divisions pass through the internal acoustic meatus and end in the pons.

Internal ear is supplied by the labyrinthine artery

Applied anatomyTinnitus- ringing sound, sign of cochlear diseaseVertigo- sense of rotation, sign of labyrinthine dysfunction

Motion sickness due to stimulation of utricle & SacculeSensori-neural deafnessMeniere’s disease: classical triad vertigo, tinnitus, deafness

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