Anatomy and physiology of middle ear

     ANATOMY AND PHYSIOLOGY OF MIDDLE EAR 

The middle ear is and air filled cavity connected to the back of the Nose bt along , thin tube called Eustachian tube . The middle ear space three bones , The HAMMER , ANVIL and STAPES. The outer wall of the middle ear is the TYMPANIC MEMBRANE  , and inner ear wall is the COCHLEA.

TYMPANIC MEMBRANE : 

The external audiotary meatus ends at the TM or ear drum , which angled at 55 degree to the canal. Tympanic membrane is firmly attached to the tympanic sulcus. Almost tranpsrent membrane with average thickness of only about 0.074 mm. It is slightly taller (about 0.9 to 1.0 cm ) , than it is wide about 0.8 to 0.9 cm . The tympanic membrane is connected to the malleus which is the first [art of the middle ear bones.

OSSICULAR CHAIN:

Three tiny bones known as Ossicles ot the Ossicular chain transmit the sound induced vibration of the Tympanic membrane to the cochlea via the oval window . The ossicles are the smallest bones of the body and include MALLECUS , INCUS , STAPES   .

MALLEUS : 

The malleus ( Hammer or Mace ) is approx 8 to 9 mm long and weight about 25mg . Its manubrium ( Handle ) is firmly embedded between the fibrous and mucous membrane layer of the eardrum . The neck of the malleus is a narrowing between its Mamubrium and Head.

INCUS : 

Incus which is 7mm long and weight roughly 30mg is commonly called "ANVIL" .Its look like tooth with two roots . The short process descends from the body of the incus , parallel wirth the manubrium of the body of malleus.

STAPES: 

The Stapes resemblance to the Stirrup which is its common name. Its Head is connected via the Neck to two strut like process called Anterior and Prosterior Crura . The stapes is about 3 to 4 mg. It is about 3.2 m long.

MIDDLE EAR MUSCLES :

The TENSOR TYMPANI  muscle is the innervated by the trigeminal ( 5th cranial ) nerve . This muscle is about 25 mm long and aries from the cartilage of the Eustachian tube . Contraction of the Tensor tympani pulls the malleus in the Anteromedial direction , thereby stiffining in the ossicular chain.

The STAPEDIAL MUSCLE is the smallest muscle in the sketal muscle of the body with lenght of 6.3mm and is innervated by the facial (7th cranial ) nerve. Contraction of the stapedial pulls the stapes posterioly. The normal mottion of the ossicles and their contraction has the effect of stiffning the osscular chain, thereby reducing the amount of the energy that is delivered to the inner .

EUSTACHIAN TUBE :

Eustachian ( Auditory) tube provides for the Aeration and Drainage of the middle ear system and make it possible for the air pressue to the same on the both side of the ear drum . Eustachian tube is almost Horizontal in infants and young children . In adults the Eustachian is 3.5 to 3.8 cm long tittling down an angle of about 45 degree.

                       Function of Middle Ear

CONDUCTION: Conduct sound from the outer ear to the inner ear .

PROTECTION: Creates a barrier that protect the middle and inner areas from foregin objects.

Middle ear mmuscles may provides protection from loud sounds.

TRANSDUCER:  Convetrs acoustic energy to mechanical energy.

Convets mechanical energy to Hydraulic energy.

AMPLIFIER : Transformer action of the middle ear.

The acoustic energy in the air would be transmitted to the inner ear fluid.