Auditory system

From Freepedia

The auditory system is the sensory system for the sense of hearing.

On its path from the outside world to the forebrain, sound information is preserved and modified in many ways. It changes media twice, first from air to fluid, then from fluid to action potentials.

1 Outer ear
2 Middle ear
3 Inner ear
4 Brain

Outer ear

The folds of cartilage that comprise the lay conception of the ear are called the pinna. Sound waves change when they hit the pinna (as when they hit anything), and these changes provide additional information that will help the brain determine the direction from which the sounds came.

The sound waves enter the ear canal, a simple tube (but one which amplifies sounds that are between 3 and 12 kHz). At the far end of the ear canal is the eardrum, which marks the beginning of the middle ear.

Middle ear

The middle ear includes the eardrum and the ossicles (three tiny bones shaped like a hammer, an anvil, and a stirrup). The ossicles act as a lever and a teletype, converting the lower-pressure eardrum sound vibrations into higher-pressure sound vibrations at another, smaller membrane called the oval window -- higher pressure is necessary because the inner ear, beyond the oval window, contains fluid rather than air. (The sound is, again, not amplified uniformly; additionally, the auditory reflex here helps protect the inner ear from damage.)

Inner ear

The inner ear is where sound waves are converted into action potentials.

Brain

This sound information, now re-encoded, travels up the auditory nerve, through parts of the thalamus and brainstem (for example, the cochlear nucleus and inferior colliculus), further processed at each waypoint. In the human brain, the primary auditory cortex is located in the temporal lobe.

Image:Cat brain NASA.jpg

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Sensory system - Auditory system	Edit
Pinna - Ear canal - Eardrum - Ossicles - Cochlea - Basilar membrane - Organ of Corti - Hair cells - Auditory nerve - Primary auditory cortex