middle and inner ear 15416

EAR

1st part ……………external ear

2nd part….................middle ear

3rd part……………..inner ear

EXTERNAL EAR

ANATOMY OF MIDDLE EAR CLEFT

THE MIDDLE EAR CLEFT

The middle ear cleft consists of the

tympanic cavity,

Eustachian tube and

mastoid air cell system.

THE TYMPANIC CAVITY

Divided into threecompartments

Epitympanum

Mesotympanum

Hypotympanum

Walls of the Tympanic Cavity

It has 6 walls,

I. Membranous wall (lateral wall)

II. Tegmental wall (roof)

III. Jugular wall (floor)

IV. Carotid wall (anterior wall)

V. Labyrinthine wall (medial wall)

VI. Mastoid wall (posterior wall)

THE ROOF

Tegment tympani

It is formed by both the petrous and squamous portions ofthe temporal bone

The petrosquamous suture line, which does not closeuntil adult life, can provide a route of access for infectioninto the extradural space in children

Veins from the tympanic cavity running to the superiorpetrosal sinus pass through this suture line

THE FLOOR

The dome of thejugular bulb

Tympanicbranch of theglossopharyngealnerve

THE ANTERIOR WALL

Lower-third

carotid artery

Middle-third

A)tympanic orifice of the

Eustachian tube

B)canal for the tensor

tympani muscle

Upper-third

pneumatized

THE POSTERIOR WALL

The aditus of mastoid antrum

Fossa incudis

Pyramid

Bony facial canal(vertical part)

THE LATERAL WALL

Formed by the

Bony lateral wall ofepitympanum

Tympanic membrane

Bony lateral wall ofhypotympanum

THE MEDIAL WALL

The promontory

Oval window

Round window

Oblique part offacial canal

THE CONTENTS OF THE TYMPANIC CAVITY

The tympanic cavity contains the

Ear ossicles – malleus, incus and stapes

Muscles – Stapedius, Tensor tympani

The chorda tympani and

The tympanic plexus

EAR OSSICLES

THE MALLEUS (the hammer)

Largest, 9 mm in length

The head lies in theepitympanum

The head of the malleusarticulate with the bodyof the incus by a synovialjoint

The lateral processprominent landmark onthe tympanic membrane

Body

THE INCUS (the anvil)

Has a body and two processes

The body lies in the epitympanum

The short process lie in the fossaincudes

The long process descends intothe mesotympanum

Lenticular process articulates withthe head of the stapes.

THE STAPES (the stirrup)

Shaped like a stirrup

Consists of a head, neck, theanterior and posterior crura and afootplate.

The stapedius tendon inserts intoneck

The two crura arise from lower partof the neck

Footplate lies in the oval windowwhere it is attached to the bonymargins by the annular ligament

THE STAPEDIUS MUSCLE

Arises from wall of conical cavity within pyramid

Attaches to neck of stapes

Helps to dampen loud sound,

Preventing noise trauma

Supplied by branch of Facial Nerve

TENSOR TYMPANI MUSCLE

● Arises from a)bony canal above ET b)cartilagenous part of ET c) greater wing of sphenoid

● Attaches to neck of malleus

● Tenses tympanic membrane

● Supplied by branch of Mandibular Nerve

THE MASTOID AIR CELL SYSTEM

The mastoid antrum air-filled sinus in the petrous part oftemporal bone.

It communicates with the middle ear by the aditus.

Antrum is well developed at birth.

Volume = 2 ml (adult).

The medial wall relates to the posterior semicircular canal.

More deeply and inferiorly is the dura of the posterior cranialfossa and the endolymphatic sac.

The roof of the mastoid antrum and mastoid air cell spaceform the floor of the middle cranial fossa.

MacEwen's triangle

– Temporal line

– Posterosuperior segment of bony EAC

– a tangent through the posterior border of EAC

Normally lining of the mastoid is a flattened, nonciliatedepithelium without goblet cells or mucus glands.

THE BLOOD SUPPLY OF THE TYMPANIC CAVITY

Arise from both the internal and external carotid system.

The overlap is extensive and great variability is present.

Anterior tympanic

Stylomastoid

Maxillary

Posterior auricular

Middle meningeal

Ascending pharyngeal

Artery of pterygoid canal and internal carotid arteries.

The anterior tympanic and stylomastoid arteries arethe biggest.

Venous drainage

Pterygoid plexus

Superior petrosal sinus

Lymphatic

Retropharyngeal

Parotid lymph node

Applied anatomy

Facial nerve injury

Hyperacusis

Eustachian catarrh

Encephalitis

Facial nerve injury

Hyperacusis

Eustachian catarrh

Encephalitis

Applied anatomy

Otitis Media Otitis media is an infection

or inflammation of the

middle ear

This inflammation often

begins when infections that

cause sore throats, colds, or

other respiratory or

breathing problems spread

to the middle ear

Otosclerosis

Otosclerosis is the abnormal

growth of bone of the middle

ear. This bone prevents

structures within the ear from

working properly and causes

hearing loss

Symptoms: Severe tinnitus,

recurring auditory memories,

and frequent vertigo

The inner ear is called as labyrinth, from the complexity of its shape.

It consists of two parts:

1. The osseous labyrinth

2. The membranous labyrinth

The Osseous Labyrinth (labyrinthus osseous)

Consists of three parts:

The vestibule,

semicircular canals

cochlea.

lined by periosteum.

Contain a clear fluid, perilymph, in which the membranous labyrinth is situated

The Vestibule (vestibulum)

38

The Bony Semicircular Canals 3 in number

superior, posterior, and lateral,

Above and behind the vestibule.

Unequal in length

They open into the vestibule by five orifices, one of the apertures being common to two of the canals

THE COCHLEA

Resemblance to a common snail-shell

Anterior part of the labyrinth

It is conical in form, and placed almost horizontally in front of the vestibule

Apex

Base

Membranous labyrinth consists of

Cochlear duct,

Two sacs, utricle and saccule

Three semicircular ducts

Endolymphatic duct & sac

4/15/2016 41

Blood supply of labyrinth Mainly by internal auditory a. (branch of AICA - branch of

basilar a.)

Internal auditory artery divides into

1. Anterior vestibular artery

Supplies utricle ,superior & lateral SCC

2. Common cochlear artery

Main cochlear artery(80%)-supplies cochlea

Vestibulocochlear artery

1. Post vestibular A.-supplies saccule & post SCC

2. Cochlear branch –supplies to cochlea4/15/2016 43

4/15/2016 44

Venous drainage Mainly by:

Internal auditory vein

Vein of cochlear aqueduct

Vein of vestibular aqueduct

These Drain into inferior petrosal and sigmoid sinuses.

4/15/2016 45

Conductive Hearing Loss

Sensorineural Hearing Loss

LabyrinthitisInflammation of the semi-circular canals give you a

sense of motion when you’re not moving = VERTIGO

(dizziness) or LABYRINTHITIS

Meniere’s Disease Vertigo, balance problems,

Loss of low pitches

Tinnitus

Fluctuating hearing loss

THANK YOU