The outer ear collects sounds, the middle ear amplifies it and the inner ear transduces it. We shall now discuss each of these three parts in brief.
(i) External Ear:
The external or outer ear consists of three parts, the pinna, the auditory canal or meatus, and the ear drum. The pinna collects the sound waves which travel through a small air-filled duct, called the auditory canal to the eardrum.
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The ear-drum is a thin membrane located at the end of the canal and it makes the inner boundary of the external ear.
(ii) Middle Ear:
The middle ear consists of three tiny bones called the ossicles. These bones are connected like a series of levers. Hence, the energy is mechanically transmitted and the amplification takes place through the middle ear. The three bones of the middle ear which are collectively called ossicles are Malleus (hammer), Incus (anvil) and Stapes (stirrup). The malleus, or hammer, is connected to the eardrum. It moves the incus or anvil, which in turn, moves the stapes or stirrup. The stakes are attached to the oval window. Also attached to the middle ear is a thin tube, known as the Eustachian tube, which connects it with the mouth cavity.
(iii) Inner Ear:
The inner ear is the most complicated of the three major parts of the ear. It consists of two kinds of sense organs. One is concerned with the sense of balance and the other with hearing. The organs for the balance are called vestibular sense organs.
The sense organs for hearing are located in a bony structure which is spiraled like a snail (Kokhlos or land snail is a Greek word) and thus called the cochlea. Cochlea contains three liquid- filled canals lying one on top of the other. These three canals are the vestibular canal, the cochlea canal and the tympanic canal.
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The cochlea is the organ of hearing. One of the membranes of cochlea is called as basilar which are the real receptors for hearing. The nerve impulses generated as a result of the stimulation of hair cells eventually reaches the temporal lobe after which we hear.
