Sense of Hearing

                                  

Hearing (or audition) is an organism’s ability to receive mechanical energy in the form of sound waves. Sound wave is thus the stimulus for auditory sensation. Receptor cells of the ear are excited by the sound waves. Frequency and intensity of sound determines the nature of sound. 20 – 20,000 per second sound frequency is possible to denote and distinct.

When an object makes a noise, it sends vibrations (known as sound waves) speeding through the air. Such sound waves from external environment at first reach to outer ear (or pinna). These vibrations are then funneled into ear canal by outer ear. As the vibrations move into middle ear, they hit the eardrum and cause it to vibrate as well. This sets off a chain reaction of   vibrations. Eardrum, which is smaller and thinner than he nail on the pinky finger, vibrates the three smallest bones: hammer, anvil, and the stirrup consecutively. These structure transfer vibrations from eardrum to oval window. The vibration then passes into a coiled tube in the inner ear called the cochlea. The fluid-filled cochlea contains thousands of hair-like nerve endings called cilia. When the stirrup causes the fluid in the cochlea to vibrate, the cilia move. The cilia change the vibrations into message that are sent to the brain through the auditory nerve. The auditory nerve carries message from 25,000 receptors in ear to the brain. The brain then makes sense of the messages and tells what sounds you are hearing.