. The bony labyrinth has three semi- circular canals at right angle to each other, a cavity, called vestibule , and a coiled structure, called cochlea . The semicircular canals have fine hair cells, which are highly sensitive to postural changes as well as changes in the body orientation. Inside the bony cochlea, there is a membranous cochlea, which is also known as scala media .
It is filled with endolymph, and has a spirally coiled membrane, called basilar membrane . It has got fine hair cells arranged in a series to form the organ of corti . This is the main organ for hearing. Working of the Ear Pinna collects the sound vibrations and serves them to the tympanum through the auditory meatus.
From the tympanic cavity the vibrations are transferred to the three ossicles, which increase their strength and transmit them to the inner ear. In the inner ear the cochlea receives the sound waves. Through vibrations the endolymph is set in motion, which also vibrates the organ of corti. Finally, the impulses are sent to the auditory nerve, which emerges at the base of cochlea and reaches the auditory cortex where the impulse is interpreted.
Sound as a Stimulus We all know that sound is the stimulus for ears. It results from pressure variations in the external environment. Any physical movement disturbs the surrounding medium (i.e. air), and pushes the air molecules back and forth.
This results in changes in pressure that spread outward in the form of sound waves, travelling at a rate of about , ft/sec. These changes travel in waves much like the ripples set up by a stone thrown into a pond. When these sound waves strike our ears, they initiate a set of mechanical pressure changes that ultimately trigger the auditory receptors. The simplest kind of sound wave is one that causes successive pressure changes over time in the form of a single repeating sine wave (Fig.
. ). Sound waves vary in amplitude as well as in wavelength. Amplitude is a general measure of stimulus magnitude.
It is the amount of change