Hearing is a complex and intricate process, during which sound waves in the air are transformed into electrical signals that the auditory nerve carries to the brain. The mechanism of hearing is a chain reaction among the external ear, middle ear, inner ear and nerve pathways.
The External Ear
- The auricle/pinna and the external ear canal.
- The purpose of the external ear is to collect sound waves and transmit them to the eardrum.
The Middle Ear
- The air-filled space between the eardrum and the inner ear that contains three ossicles, or bones called the malleus, the incus and the stapes.
- The purpose of the middle ear is to transmit vibrations of the eardrum into fluid waves in the inner ear. As this chain reaction occurs, a secondary effect is amplification of sound.
- The middle ear space is connected to the back of the nose by a small channel called the Eustachian tube. The tube serves to maintain equalization of pressure between the middle ear and the outside atmosphere.
- The cochlea, or inner ear, is a fluid filled structure enclosed in dense bone and lined with thousands of hair cells.
- The purpose of the inner ear is to transmit the motion of fluid, initiated by the lever action of the middle ear ossicles, into electrical signals along the auditory nerve. Electrical signals are created, specifically, when the motion of inner ear fluid deflects hair cells.
- The nerve pathways leading to the brain are enclosed in a small bony canal along with the nerve of balance and the nerve that stimulates movement of the facial muscle.
- The purpose of neural pathways is to transmit electrical impulses, created in the inner ear, to the brain, where sounds are processed and where speech understanding occurs.