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The Ear

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The Ear - Lesson Summary



The ear is an important organ for hearing and to maintain balance. It is divided into– the outer ear, the middle ear and the inner ear. The outer and middle ear assist only in hearing, while the inner ear also helps in equilibrium.
The outer ear has pinna and external auditory meatus. Very fine hairs and wax-secreting sebaceous glands are present on the skin of the pinna and the meatus, which prevent dust and small insects. The pinna directs the sound into the meatus.
 
The tympanic cavity is bound externally by the tympanic membrane and internally by an auditory capsule. The auditory capsule has two membrane bound apertures called the oval window and the round window. The middle ear has three ossicles called the malleus, incus and stapes, these are attached like a chain. They increase the efficiency of transmission.
Air pressure maintained by the Eustachian tube.
 
The inner ear consists of labyrinth, which consists of two functional parts – the cochlea, for hearing and the vestibular apparatus, for balance. The labyrinth is of two types – bony and membranous.
 
The cochlea, has two membranes, namely Reissner’s membrane and the basilar membrane which divide the bony labyrinth into scala vestibuli and scala tympani. The fluids in the labyrinth cushion the soft structures and conduct waves from the middle ear to the organ of Corti. Which, is the actual receptor of sound. It is composed of hair cells, which are in contact with tectorial membrane.
 
The inner ear contains vestibular apparatus that helps maintain the body’s balance. It consists of three semi-circular canals and the otolith organ which consists of the saccule and utricle, responsible for maintaining the body’s balance and posture.
 
The external ear receives sound waves and directs them to the eardrum. The eardrum vibrates and transmits them through the malleus, incus and stapes – to the oval window. The ossicles, in turn, amplify the sound and pass the vibrations through the oval window to the fluid of the cochlea. This generates waves which induces a ripple in the basilar membrane, then bend the hair cells, pressing them against the tectorial membrane. This in turn stimulates the hair cells, to  generate nerve impulses, which are transmitted to the auditory cortex of the brain. The brain then interprets these nerve impulses and sound is recognised. 

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