Date post: | 14-Feb-2017 |
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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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