By –Mr. ASHOK BISHNOILecturer, JINR

ANATOMY AND PHYSIOLOGY OF THE

EAR

Divided into “3” parts:-

1. Outer Ear

2. Middle Ear (Tympanic cavity)

3. Inner Ear

Major Divisions of the EarPeripheral Mechanism Central Mechanism

Outer Ear

Middle Ear

Inner Ear

VIII Cranial Nerve

Brain

It consist of the auricle (Pinna) & External acoustic meatus ( Auditory canal)

Pinna Landmarks Helix Antihelix Concha Tragus Intertragal Notch Antitragus

Auricle (Pinna):-

It is visible part of ear It composed of fibro elastic cartilage

convered with skin. Helix- it is outer ridge part Lobule (Ear lobe) –Soft pliable part

External acoustic meatus ( Auditory canal)

Slightly “S” Shaped tube About 2.5 cm long ( 1 inch ) External from auricle to tympanic

membrane There numerous ceruminous gland &

hair follicles Numerous gland are modified sweat

gland that secret cerumen (Earwax)

Tympanic membrane (Eardrum):- Thin membrane

It is Oval shaped

Forms boundary between outer and middle ear

Vibrates in response to sound waves

Changes acoustical energy into mechanical energy

Mastoid Process of Temporal Bone

Bony ridge behind the auricle.

Hardest bone in body, protects cochlea and vestibular system.

Provides support to the external ear and posterior wall of the middle ear cavity.

Contains air cavities which can be reservoir for infection

Collect sound

Localization

Resonator

Protection

Sensitive (earlobe)

This is irregular shaped air filled cavity.

1- Malleus2- Incus 3- Stapes 6- Eustachian Tube

The Ossicles

Ossicular chain = malleus, incus & stapes

Malleus (It is Hammer shaped bone) TM attaches

Incus (It is Anvil shaped bone) Connector function

Stapes ( It is a Stirrup shaped bone) Smallest bone in the body Footplate inserts in oval window on

medial wallFocus/amplify vibration of TM to smaller

area, enables vibration of cochlear fluids

Eustachian Tube (Pharyngotympanic tube) ( “The Equalizer”)

Mucous-lined, connects middle ear cavity to nasopharynx

“Equalizes” air pressure in middle ear

Normally closed, opens under certain conditions

Closing of the Eustachian tube protects the middle ear from unwanted pressure fluctuations and loud sounds.

Conduction Conduct sound from the outer ear to the inner ear

Protection Creates a barrier that protects the middle and inner areas

from foreign objects Transducer

Converts acoustic energy to mechanical energy Converts mechanical energy to hydraulic energy

Amplifier Transformer action of the middle ear

The inner ear contain the organ of hearing & balance

It consist of – Vestibule (Balance) Cochlea Semicircular canalCochlea - Snail-shaped organ with a series of fluid-filled

tunnels; converts mechanical energy into electr ical energy

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� Oval Window – located at the footplate of the stapes; when the footplate vibrates, the cochlear fluid is set into motion

� Round Window – functions as the pressure relief port for the fluid set into motion initially by the movement of the stapes in the oval window

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Organ of Corti

The end organ of hearing; contains stereocil ia and hair cells.

Convert mechanical sound waves to neural impulses that can be recognized by the brain for:

Hearing

Balance

Pathway of Sound:-

Sound waves enter pinna travel through auditory canal Sound waves strike tympanic membrane causing vibrations

(mechanical energy) Vibrating TM causes ossicles to vibrate Vibrating stapes bone at oval window generates movement of

cochlear fluid (Hydralics) Fluid movement stimulates cilia- lined cochlea Cilia sends electrical impulses along auditory nerve to brain

for interpretation

Flow of ear:-

Hearing

Sound Conduction and Transmission

Balance and Equilibrium