How sound is heard...
The outer, middle, and inner ear together are known as the peripheral auditory system and function by receiving sounds from the environment. Generally, there are two processes in hearing: (1) getting sounds to the brain through the outer, middle, and inner ear; and (2) learning the meaning of those sounds once they are in the brain. Obviously, sounds must first be heard before making sense of those sounds (learning) can take place. Hearing involves the gathering and interpreting of sounds. Each part of the ear serves a purpose in translating sound waves from the environment into meaningful information to the brain. Here is what happens when sound is perceived:
As sound waves funnel down the auditory ear canal, they push up against the eardrum (tympanic membrane), causing it to vibrate. These vibrations are conducted to the inner ear through the middle ear by the three smallest bones in the body, the ossicles. The ossicles, also known as the ossicular chain, are interconnected and are attached to the eardrum and a membrane called the oval window, which serves as the gateway to the inner ear. As the eardrum vibrates, it jiggles the first of the three ossicles, the malleus, starting it to move. The malleus jiggles the second ossicle, the incus, which jiggles the third ossicle, the stapes. Meanwhile the stapes plunges up against the entrance to the fluid-filled inner ear swooshing the fluid with every movement it makes. It is here, within the snail-like organ (cochlea) where the real action of hearing takes place.
The cochlea is considered to be the main sensory organ for hearing. The fluid in the ducts of the cochlea moves in response to the mechanical energy sent by the ossicles. Tiny hair cells within the cochlea convert the mechanical energy into electrical impulses that are transmitted by neurons along the auditory nerve to the brain. These hair cells allow our brains to sense and distinguish different sounds. Each region responds to a different frequency of sound. Think of your cochlea as a piano keyboard, each section or "note" is responsible for a different frequency of sound.
