EAR AND AUDITORY PATHWAY

Maj Rishi PokhrelDept of Anatomy

NAIHSwww.slideshare.net

• One structure of human body 0.1 mm thick

and derived from all 3 germ layers?

2

3Cochlea Sec tympanic membrane

Promontory

Middle ear

Stapes

Semicircular canal

Vestibule of inner ear

THREE PARTS OF EAR

Ext auditory meatusTympanic membrane

External ear

EXTERNAL EAR

4

• Pinna• External auditory meatus

PINNA• Concha• Helix• Antihelix• Scaphoid fossa & triangular

fossa• Tragus• Antitragus• Intertragic notch• Lobule

5

EXTERNAL EAR

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

7

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

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

8

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

9

PF

Pars Tensa

AMF

PMF

Line of attach of handle of malleuson medial surface

TYMPANIC MEMBRANE

10

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

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

11

Outer cuticular layer

Middle fibrous layerInner mucous layer

Deep circularfibres

SuperficialRadiating fibres

Pars flaccida

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

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

CLINICAL ANATOMY

• ASOM– Pus discharged laterally

• Myringotomy• Incision at posteroinferior quadrant

–Prevent damage to chorda tympani–Rich blood supply: healing faster

15

MIDDLE EAR

16

Canal for T T

Auditory tube

Aditus to antrum

Mastoid antrum

Mastoid cells

Mastoid process

A P

17

Left ear: TM removed

Roof

Floor

Medial wall

Antwall

Postwall

18

ROOF

19

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

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

20

Epitympanicrecess

Aditus

Auditory tube

ICA

Sup bulb of IJV

VII CN

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

21

22

POSTERIOR WALL• Wider above than below

• Aditus to mastoid antrum

• Facial canal

• Pyramid: tendon emerges from apex

• Posterior Canaliculus of chorda tympani

23

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

24

25

Left ear: TM removed

Medial wall

26

MEDIAL WALL

LATERAL WALL• Tympanic Membrane

• Epitympanic recess

– Part above tympanic cavity

– Upper half of malleus

– Greater part of incus

27

MIDDLE EAR: COMMUNICATIONS

• Anterior wall : auditory tube

• Posterior wall: mastoid antrum

• Medial wall : inner ear

• Lateral wall shows : tympanic membrane

• Roof and floor: none

28

EAR OSICLES

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

30

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

31

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

32

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

33

STAPEDIUSOrigin

• Interior of hollow pyramidInsertion

• Back of neck of stapesNerve supply

• Facial nerveActions

• Retract neck of stapes from fenestra vestibuli• Paralysis: hyperacusis

34

35

36

CLINICAL ANATOMY

Normal TM Wax

37

PERFORATION OF TM

Perforation

MYRINGOTOMY

MYRINGOTOMY & SYRINGING

EAR SYRINGING

39

OTITIS MEDIA

Serous otitis mediaASOM

40

OTITIS EXTERNA

TYMPANOSCLEROSIS

Internal ear

42

43

44

Auditory pathway

45

Auditory pathway

46

47

Olfactory pathway

48

49

50

51

52

53

54

Olfactory reflexes

?55