STRUCTURE OF EAR IN ENGLISH

                                                  

                                          STRUCTURE OF  EAR IN ENGLISH

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Ø  THE EAR

Ø  The ear is the organ of hearing and is also involved in balance. The ear consists of three parts-

Ø  The outer ear,

Ø  The middle ear, and

Ø  The inner ear

Ø  The outer ear- The outer ear consists of two structures. these are-

Ø  The auricle (pinna) and

Ø  The external acoustic meatus (auditory canal).

Ø  The auricle (pinna) - The auricle or pinna is the visible part of the ear.  It is composed of fibro-elastic cartilage and covered with skin. It is deeply grooved and ridged. the most prominent outer ridge is the helix

Ø    The lower end of the ear is made of soft tissue and is known as ear lobe. the auricle may act as a funnel for sound waves. Sound waves coming from outside are directed into the ear canal towards the ear drum.

Ø  The Auditory canal (ear canal) - This is a slightly ‘S’ shaped tube and is about 2.5 cm long. It starts from the auricle and ends at the tympanic membrane (eardrum). The canal is lined with skin containing cerumiuous glands and hair follicles.

Ø  Ceruminous glands are modified sweat glands that secrete cerumen (earwax). It a sticky material containing protective substances including the enzyme lysozyme and immunoglobulins.

Ø  Special features of ear canal protects our ear from external hazards.

Ø  Foreign materials such as dust, insects and microbes, are prevented from reaching the tympanic membrane by wax, hairs and the curvature of the meatus. 

Ø  Movements of the temporo-mandibular joint during chewing and speaking ‘massage’ the cartilaginous canal and help in moving the ear wax towards the exterior.

Ø  The Tympanic membrane- The eardrum, or tympanic membrane is formed by three types of tissue. the outer covering of hairless skin, the middle layer of fibrous tissue and the inner lining of mucous membrane, is stretched across the end of the ear canal and vibrates when sound waves strike it.

Ø  The middle ear-This is an irregular-shaped air-filled cavity within the petrous portion of the temporal bone. It is also known as tympanic cavity. There are three auditory bones: the malleus, incus, and stapes arranged across the cavity.

Ø  They form a series of movable joints with each other and with the medial wall of the cavity at the oval window. They are named according to their shapes. The vibrations of ear drum are transmitted through the three auditory bones to oval window of inner ear.

Ø  The eustachian tube (auditory tube) extends from the middle ear to the nasopharynx and permits air to enter or leave the middle ear cavity. The air pressure in the middle ear must be the same as the external atmospheric pressure in order for the eardrum to vibrate properly.

Ø  The inner ear -Inner ear is situated within the temporal bone.  the inner ear is a cavity called the bony labyrinth.  which is lined with membrane having same structure called the membranous labyrinth.

Ø  The bony labyrinth and membranous labyrinth consists of three structures:

Ø  The vestibule

Ø  The cochlea

Ø  Three semicircular canals.

Ø  The vestibule-  This is the expanded part nearest the middle ear. The oval and round windows are located in its lateral wall. It contains two membranous sacs, the utricle and the saccule, which are important for balance.

Ø  The cochlea- This resembles a snail’s shell. It has a broad base  and a narrow apex, and it spirals round a central bony column.

Ø  The semicircular canals- These are three tubes arranged so that one is situated in each of the three planes of space. 

Ø  Between the bony and membranous labyrinth there is a layer of watery fluid called perilymph and within the membranous labyrinth there is a similarly watery fluid, endolymph.

Ø  The cochlear duct is part of the membranous labyrinth and is triangular in shape. On the basilar membrane, or base of the triangle, are supporting cells and specialised cochlear hair cells containing auditory receptors. These cells form the spiral organ  of Corti , the sensory organ that responds to vibration by initiating nerve impulses that are then perceived as hearing within the brain.

PHYSILOGY OF HEARING

Ø  the process of hearing involves the transmission of vibrations and the generation of nerve impulses. When sound waves enter the ear canal, vibrations are transmitted by the following sequence of structures: eardrum, malleus, incus, stapes, oval window of the inner ear, and perilymph and endolymph within the cochlea.

Ø  the vibrations produces fluid waves in perilymph and endolymph. The basilar membrane ripples and pushes the hair cells of the organ of Corti against the tectorial membrane. When the haircells bend, they generate impulses that are carried by the 8th cranial nerve to the brain in the temporal lobes of the cerebral cortex. It is here that sounds are heard and interpreted.

PHYSILOGY OF BALANCE

Ø  The semicircular canals and vestibule are associated with posture and balance. There are three semicircular canals, one lying in each of the three planes of space. They are situated above, beside and behind the vestibule of the inner ear and open into it.

Ø  Any change of position of the head causes movement in the perilymph and endolymph, which bends the hair cells and stimulates the sensory receptors in the utricle, saccule and ampullae. The resultant nerve impulses are transmitted by the vestibular nerve to the brain and balance and position of our body is interpreted by the brain.