How We Hear
- Sound is transmitted as sound waves from the environment. The sound waves are gathered by the outer ear and sent down the ear canal to the eardrum.
- The sound waves cause the eardrum to vibrate, which sets the three tiny bones in the middle ear into motion.
- The motion of the bones causes the fluid in the inner ear or cochlea to move.
- The movement of the inner ear fluid causes the hair cells in the cochlea to bend. The hair cells change the movement into electrical pulses.
- These electrical impulses are transmitted to the hearing (auditory) nerve and up to the brain, where they are interpreted as sound.
The Outer Ear
The part of the outer ear that we see is called the pinna, or auricle. The pinna provides a natural boost for sounds in the 2000 to 3000 Hz frequency range. The ear canal, also called the external auditory meatus, is the other important outer ear landmark. The ear canal is lined with only a few layers of skin and it is a highly vascularized area. This means that there is an abundant flow of blood to the ear canal.
The Middle Ear
The eardrum, or tympanic membrane (abbreviated TM) is the dividing line between the outer and middle ears. The ossicles are the three tiny bones of the middle ear that are fully developed at birth. They serve as a mechanical link between the tympanic membrane and the inner ear. The Eustachian tube is the middle ear’s air pressure equalizing system. The middle ear is encased in bone and does not communicate with the outside atmosphere except through the Eustachian tube.
The Inner Ear
The inner ear is a series of channels and chambers embedded deep within the temporal bone. The inner ear is called the cochlea. The cochlea transduces (changes from one form to another) the mechanical stimulus of sound, via the tympanic membrane and the ossicular chain, into a sequence of electrical discharges that is the language of the auditory nervous system.