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EAR

Lecture for BDS students onlyByProf. Ansari04/21/23

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Objectives

Gross anatomy of External ear. Gross anatomy of Middle ear. Gross anatomy of Internal ear. Applied anatomy

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EAR

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Objectives

Parts of external ear, Middle ear cavity, & contents. Internal ear Applied anatomy.

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The external ear has Pinna & external acoustic meatus.

The external ear and external acoustic meatus

Is made up of elastic cartilage. The extrinsic muscles of ear are

auricularis anterior, auricularis superior and auricularis posterior.

These muscles are non functional and are supplied by facial nerve.

In lower animals these muscles carry the pinna in the respective directions to collect the sound waves.

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The external acoustic meatus

It is partly cartilagenous and partly bony.

At the medial end it has tympanic membrane closing the canal.

The meatus is lined by stratified squamous epithelium with wax glands.

Developmentally it is from the first cleft.

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THE NORMAL TYMPANIC MEMBRANE

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The middle ear It is a six sided chamber, it has a roof,

floor, ant.wall, post. Wall, medial wall & lateral wall.

Roof is formed by tegmen tympani. Floor is formed by jugular bulb&

carotid canal. Ant. Wall has two tubes, canal for

tensor tympani muscle & auditory tube.

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Walls of middle ear The posterior wall has aditus ad-

antrum, canal that communicates with the mastoid air cells, which are present in mastoid process.

Medial wall has round window and oval window, the foot plate of stapes fits into the oval window.

The lateral wall is formed by tympanic membrane.

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Middle ear contents seen through the tympanic membrane

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Contents of middle ear

Muscles are:- 1. Tensor tympani, 2. Stapedeus. Nerves are:- 1. Tympanic plexus, 2. chorda tympani nerve, 3. facial nerve. Bones are:- 1. Malleus, 2. Incus, 3. Stapes.

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The middle ear cavity

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Walls of the middle earTegmen tympani

Mastoid Air cells

Jugular bulb

Tensor tympani

Auditory tube

Carotid canal

Oval window

THE EAR OSSICLES

MALEUS INCUS AND STAPES

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The contents of middle ear after opening from roof

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Internal ear

It is in the petrous part of temporal bone.

It lodges cochlea, vestibule and semicircular canals.

It communicates with the middle ear through two windows, oval and round.

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Parts of internal ear

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Development of external ear Six ear hillocks develop around the

first pharyngeal cleft. They coalesce with each other and

form the pinna. The external acoustic meatus

develops from first pharyngeal cleft. The lateral surface of tympanic

membrane develops from the ectoderm of first cleft.

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Development of middle ear The tympanic cavity develops from

the first pharyngeal pouch, endoderm.

The malleus, incus ossicles develop from the first pharyngeal arch.

The tensor tympani is also from first arch derivative.

The stapes and stapedius muscle develops from second arch mesoderm

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The internal ear development

It is ectodermal, from otic placode. Ear is an example of organ

developing from all three germ layers.

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Applied anatomy

There are two functions done by ear, Hearing and balancing/equilibrium. Acoustic neuroma is a tumour of

auditory nerve, which causes nerve deafness.

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Review of ear

References

Essential Clinical AnatomyKeith L. Moore4th editionPage nos. 578-588.

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A 36 year old person develops ipsilateral sensorineural hearing loss/deafness, disturbed sense of balance and altered gait, vertigo with associated nausea and vomiting.

His CT of head region showed the following picture.

Acoustic neuroma was diagnosed.

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