Structure and functions of the mammalian ear


The ear is the sense organ for hearing and balancing. The ear is located in bony boxe fixed on each side of the skull. The ear is made up of three main parts: the outer ear, which is composed of pinna (plural: pinnae) and the external auditory meatus or canal which leads to the tympanic membrane, tympanum or eardrum; the middle ear, Which contains the small bones or ear ossicles; and the inner ear which consists of the vestibular apparatus, the cochlea and the nerve endings of the auditory nerve.

OUTER EAR 

The pinna contains cartilage and collects sound waves, channeling them down the external auditow meatus or ear canal. Many mammals have the ability to move their pinnae, which help to pinpoint the direction of sound. At the end of the ear canal is the ear drum, tympanic membrane or tympana (singular: tympanum); which vibrate to transmit the sound waves to the ossicles or bones in the middle ear. Vibration of . the ear drum multiplies the amplitude of the sound waves by about 20 times as it moves into the inner ear. The ear drum separates the outer ear from the middle ear.



Middle Ear

This is air-filled and contains three small bones called ear ossicles. These include: malleus or hammer, incus or anvil and stapes or stirrup. The ossicles are connected end to end and are held in position by slender ligaments and muscles. The malleus is connected to outer ear by the ear drum whilst the stapes connects the middle ear to the inner ear by the oval window. The Eustachian tube connects the middle ear to the pharynx. The Eustachian tube equalizes the pressure on both sides of the ear drum. Hearing is impaired if this tube is blocked, for instance, by mucus, as in the case of a cold.


lnner Ear 

The inner ear is fluid-tilled and contains the cochlea and vestibular apparatus, which is made up of three semicircular canals, arranged at right angles to each other on an oval or spherically-shaped utriculus, which is also connected to the cochlea by the sacculus. The end of each semi-circular canal is swollen to form an ampulla (plural: ampullae), which contain sensory nerve endings. The cochlea detects sound vibrations whereas vestibular apparatus, i.e. the semi-circular canals, sacculus and utriculus control balance and posture.

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