ANATOMY OF EAR: THE HEARING

PATHWAYBY

Ph.D. Alsayed Ali Mahran

MAHRAN S.A

3-Sense of hearing Hearing; is the ability to perceive sound by detecting vibrations through an ear.

Hearing: is mental process that requires concentrating on sound, deriving meaning from it, and reacting to it.

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With our ears we can hear…

People singing

Bells ringing

Babies cryingMAHRAN S.A

Anatomy of the earThe ear is a sensory organ with dual functions—hearing and balance.

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The sense of hearing is essential for normal development and maintenance of speech as well as the ability to communicate with others

Balance, or equilibrium, is essential for maintaining body movement, position, and coordination

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• The ear is divided into three parts:

External ear transmits sound to the tympanic membrane.

Middle ear conduct sound from the tympanic membrane to the inner ear.

Internal ear changes the sound vibration into nervous impulses

External ear consisting of :

Auricle External acoustic meatus

Tympanic membrane

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Anatomy of the ear (coronal section).MAHRAN S.A

Auricle - (also called the pinna); the visible part of the external ear and consists of cartilage covered by skin.. It collects sound and directs it into the external auditory tube.

External earMAHRAN S.A

External acoustic meatus; is a canal about 2.5 cm long and extends to the tympanic membrane (eardrum). The lateral third is an elastic fibrocartilage and the medial two thirds is bone .It is lined with thin skin contains hair, sebaceous glands, and ceruminous glands, which secrete a brown, wax like substance called cerumen (ear wax ).

Tympanic membrane - (also called the eardrum)about 1 cm in diameter and very thin, lies between the external acoustic meatus and middle ear .It vibrates when sound waves reach it, then transfers sound waves to the bones of the middle ear.

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2-The middle ear; is an air-filled space about 2

cubic cm in volume and lined by mucous

membrane .It lies in the temporal bone between

the tympanic membrane and the internal ear .it is

separated from the inner ear by two

windows, the oval window and the round

window. It contains

Ear ossicles (malleus, incus, and stapes).

Eustachian tube

Two muscles (tensor tympani and stapedius muscles) MAHRAN S.A

Middle earMAHRAN S.A

Ear Ossicles:

Three tiny bones (the ossicles) in the middle ear(the malleus, incus, and stapes).

Form a chain suspended by ligaments and joined by synovial joints

Transmit sound

waves from the

tympanic

membrane

(outer ear)

to the oval window

(inner ear).

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Eustachian tube - (also called the pharyngotympanic or auditory tube)—is approximately 1 mm wide and 35 mm long, connects the middle ear to the nasopharynx

-It equalizes pressure in the middle ear cavity

with the external air pressure .i.e. equalizes

the pressure on both sides of the tympanic

membrane.

Muscles of middle ear- Tensor tympani and

stapedius muscles. These muscles contract to protect

the inner ear by reducing the intensity of sound

transmission to the inner ear. MAHRAN S.A

•3-The inner ear; is small (about the size of a pea)lies in temporal bone and consists of a groups of ntercommunicatedintercommunicated tubules which are :

The COCHLEA, responsible for hearing; converting sound waves from the outer ear into electrochemical impulses which are transmitted to the brain by he auditory nerve.

The VESTIBULAR SYSTEM(vestibule and semicircular canals)which responsible for sense of balance

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The cochlea and semicircularcanals are surrounded by bony wall (bony labyrinth) filled by fluid called perilymph.The bony wall surrounds and protects

the membranous wall (membranous labyrinth), which is filled by fluid called endolymph.

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Anatomy of the internal ear .(a) semicircular canal, and (b) cross section in semicircular canal.

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Cochlea:

The cochlea is the site of the sense organs for hearing (organ of Corti). The cochlea consists of a bony, snail-like shell that contains three ducts or canals.

The vestibular duct (upper canal), which begins at the oval window,

The tympanic canal (lower canal) , that begins at the round window.

The cochlear duct (between the two other canals), which contain the organ of Corti.

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(a). Cross section of cochlea and (b).Structure of organ of corti MAHRAN S.A

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Cross section in the cochleaMAHRAN S.A

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(a).Cross section of cochlea and (b). Structure of organ of Corti.MAHRAN S.A

VestibuleThe vestibule is like a chamber that lies in between the cochlea and the semicircular canals . Internally Contains two membranous sacs;

• The saccule and utricle contain mass of tiny hair cells called maculae ("macula" means "spot“) covered by a gelatinous otolithic membrane containing in which embedded a tiny particles of calcium and carbonate called otoliths ("earstones" or "earsand").

Utricle is continuous with the semicircular canals

Saccule is continuous with the cochlear duct

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•Macula is responds to changes in head position or linear movements (forward-backward movement, left-right movement, or a combination thereof).

• bending of hairs results in generation of nerve impulse

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Semicircular Canals:

•Semicircular Canals; are three canals at right angles (anterior ,posterior and lateral)

•Each has a swelling called ampulla which contain sensory organ of balance called crista ampularis of membranous labyrinth that communicates with the vestibule

•Crista ampularis responds to rotatory movements of the head

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In summary the functions of the ear

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1-Hearing is sensed by the organ of Cortiwithin the cochlear ductof the cochlea

2-Balance: •Head position (i.e., gravity; also linear movements) is sensed by the otolith organsof the vestibule . •Head rotation (i.e., angular movements) is sensed by the cristae ampularis of the semicircular canalsMAHRAN S.A

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THANK YOU ANY QUESTION

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