The ear. auditory pathway and olfactory pathway
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Transcript of The ear. auditory pathway and olfactory pathway
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EAR AND AUDITORY PATHWAY
Maj Rishi PokhrelDept of Anatomy
NAIHSwww.slideshare.net
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• One structure of human body 0.1 mm thick
and derived from all 3 germ layers?
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3Cochlea Sec tympanic membrane
Promontory
Middle ear
Stapes
Semicircular canal
Vestibule of inner ear
THREE PARTS OF EAR
Ext auditory meatusTympanic membrane
External ear
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EXTERNAL EAR
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• Pinna• External auditory meatus
PINNA• Concha• Helix• Antihelix• Scaphoid fossa & triangular
fossa• Tragus• Antitragus• Intertragic notch• Lobule
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EXTERNAL EAR
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EXTERNAL AUDITORY MEATUS
Extends from bottom of concha to TM (Length: 25 mm)
Parts– Cartilaginous: lateral 1/3rd
– Bony: medial 2/3rd
Bends– B/T lateral 1/3rd & medial 2/3rd
– 5 mm from tympanic membrane
Direction – Backwards & medially
Epithelium (skin)– Adherent to bone & cartilage
– Ceruminous glands
– Secretions prevent entry of bacteria6
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Nerve supply• ATN (V3)
• Great auricular (C2,3)
•Lesser occipital (C2)
•Facial
•Vagus
•Motor- Facial
Blood supply•Post auricular
•Superficial temporal
•Ant tympanic
•Deep auricular
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TYMPANIC MEMBRANE
Size
Diameter – 1cm
Thickness – 0.1 mm
Position– Lie obliquely 55 deg to EAM
– Faces downward, forward & laterally
Umbo– Concavity due to attachment of
handle of malleus
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TYMPANIC MEMBRANESubdivisions
– Pars flaccida (Shrapnel’s membrane)
• between folds
• lax area
– Pars tensa• Rest of the membrane
• tense due to
– attachment of handle of malleus
– radiating fibres of intermediate layer
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PF
Pars Tensa
AMF
PMF
Line of attach of handle of malleuson medial surface
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TYMPANIC MEMBRANE
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SurfacesLateral surface
• Concave, directed down, forward & laterally
Medial surface• Convex, maximum at umbo
• Handle of malleus attached here
• Chorda tympani is medial to handle of malleus
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TYMPANIC MEMBRANEStructure
From lateral to medial– Outer cuticular layer: stratified squamous nonkeratinized epithelium
– Intermediate fibrous layer: Outer radiating, inner circular fibres
– Inner mucous layer: columnar epithelium; patchy ciliated
Handle of malleus & chorda tympani lie b/t mucous & intermediate fibrous layer
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Outer cuticular layer
Middle fibrous layerInner mucous layer
Deep circularfibres
SuperficialRadiating fibres
Pars flaccida
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Tegmen tympani
Tensor tympani
Petrotympanic fissure
Anterior canaliculus
Chorda tympani
Tympanic membrane
Handle of malleus
Processuscochleariformis
Aditus
LATERAL WALL OF LT MIDDLE EAR WITH CONTENTS
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TYMPANIC MEMBRANENerve supply
– Lateral surface
• ATN
• Vagus (auricular br)
– Medial surface
• IX CN (tympanic br)
• Chorda tympani
Blood supply– Deep auricular
– Anterior tympanic
– Posterior auricular: stylomastoid br 13
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CLINICAL ANATOMY
• ASOM– Pus discharged laterally
• Myringotomy• Incision at posteroinferior quadrant
–Prevent damage to chorda tympani–Rich blood supply: healing faster
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MIDDLE EAR
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Canal for T T
Auditory tube
Aditus to antrum
Mastoid antrum
Mastoid cells
Mastoid process
A P
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Left ear: TM removed
Roof
Floor
Medial wall
Antwall
Postwall
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ROOF
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Petrous temporal
Formation – Tegmen tympani: thin bony plate of petrous temporal
• Separates tympanic cavity from MCF
• Pierced by lesser & greater petrosal nerves
Applied – If unossified: spread of infection to meninges
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FLOORFormation
– Floor of jugular fossa (posteriorly)– Posterior wall of ascending part of carotid canal (anteriorly)- Tympanic Canaliculus for tympanic br of IX CN
Applied– Spread of infection to IJV: thrombosis
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Epitympanicrecess
Aditus
Auditory tube
ICA
Sup bulb of IJV
VII CN
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ANTERIOR WALL
• Shortened by approximation of roof & floor
• Anteriorly shows posterior wall of carotid canal
• Canal for • Tensor tympani (above)
• Auditory tube (below)
• Processus trochleariformis• Bony shelf extends back on
medial wall & turns laterally; pulley for tensor tympani
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POSTERIOR WALL• Wider above than below
• Aditus to mastoid antrum
• Facial canal
• Pyramid: tendon emerges from apex
• Posterior Canaliculus of chorda tympani
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MEDIAL WALL
Promontory: due to basal turn of cochlea
– Tympanic plexus (IX CN) lies over promontory
Oval window (fenestra vestibuli )
– behind & above promontory
– closed by base of stapes & annular ligament
Round window (fenestra cochleae )
– below & behind promontory
– closed by secondary TM
Facial canal: above & behind promontory
– oblique part, run back & down above oval window
Prominence of lateral semicircular canal– above facial canal
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Left ear: TM removed
Medial wall
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MEDIAL WALL
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LATERAL WALL• Tympanic Membrane
• Epitympanic recess
– Part above tympanic cavity
– Upper half of malleus
– Greater part of incus
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MIDDLE EAR: COMMUNICATIONS
• Anterior wall : auditory tube
• Posterior wall: mastoid antrum
• Medial wall : inner ear
• Lateral wall shows : tympanic membrane
• Roof and floor: none
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EAR OSICLES
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MALLEUSHead
In epitympanic recess
Post surface: facet for incus- Incudomalleal joint (saddle)
NeckAgainst pars flaccida
Chorda tympani cross medial to neck
• HandleProject down & back till umbo
Processes:
lateral pr: Upper end, handle & lat pr attached to fibrous layer of TM, malleolar folds
Anterior pr: attachment of ant lig of malleus
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INCUS
Body• In epitympanic recess
• Articulates anteriorly with head of malleus
Short process• Lig attached to fossa incudis (post wall of TC)
Long process• Hook medially, articulate with stapes
• Incudostapedial joint: ball & socket
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STAPES• Head
– Articulates with lenticular nodule of incus• Neck
– Stapedius attached to back of neck• Ant & post limbs• Foot plate
– anchored to fenestra vestibuli by annular lig– syndesmosis
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TENSOR TYMPANIOrigin
• Bony & cart part of AT, becomes tendon, hooks around processus trochleariformis
Insertion• Handle of malleus: upper part
Nerve supply• Nerve to medial pterygoid
Actions• Pull handle of malleus, TM concave,
makes tense• Increase tight adhesion of footplate to
fenestra vestibuli– dampens sound
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STAPEDIUSOrigin
• Interior of hollow pyramidInsertion
• Back of neck of stapesNerve supply
• Facial nerveActions
• Retract neck of stapes from fenestra vestibuli• Paralysis: hyperacusis
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CLINICAL ANATOMY
Normal TM Wax
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PERFORATION OF TM
Perforation
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MYRINGOTOMY
MYRINGOTOMY & SYRINGING
EAR SYRINGING
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OTITIS MEDIA
Serous otitis mediaASOM
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OTITIS EXTERNA
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TYMPANOSCLEROSIS
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Internal ear
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Auditory pathway
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Auditory pathway
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Olfactory pathway
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Olfactory reflexes
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