How does does your ear hear sound?

Answer 1

Your ear may be considered to have three major parts, the external ear, the middle ear, and the innerear.

The external ear comprises the parts that are exposed to the outside air, up to the ear drum. Attached to the innerpart of the eardrum are three tiny bones (the smallest bones in your body - grain sized.), and these in turn connect to an oval window, which is one of the boundaries of the inner ear. The inner ear is a tapering tube, arranged compactly as a spiral, and with a membrane dividing the tube into two lengthwise. Arranged along this dividing membrane, are numerous sensory hairs, each connected to its hair cell, and these to our auditory nerves.

The ear drum vibrates in response to a sound, and this moves the series of three middle ear bones. Their arrangement helps the ear to deal with the huge range of sounds we encounter. The third of these is the stapes, which in turn vibrates the oval window, and passes the sound wave (now a vibration) to the fluid-filled cochlea. The vibrations in the cochlea, in turn activate the many thousands of hair cells (grouped according to frequency), and these send an electrical signal to the brain for interpretation.

[Mammals have a 3-bone middle ear, and a 1-bone jaw. Earlier species in evolution have a 2-bone middle ear, and a 2-bone jaw.] The middle ear is ventilated to the atmosphere via your Eustachian tube, and when this becomes blocked by an infection, (or by rapid change in altitude e.g. air travel), we experience pain due to the ear drum being pressurized.

[Located in the general vicinity of your ear are your balance organs, but these are not part of the hearing process. Birds have a magnificent 3-axis set of balance tubes, land animals have a good set, and fish have rather inferior set of balance tubes. [It doesn't matter so much if a fish falls over!]]

Answer 2

When something makes a noise, it sends vibrations, or sound waves, through the air.

The human eardrum is a stretched membrane, like the skin of a drum. When the sound waves hit your eardrum, it vibrates and the brain interprets these vibrations as sound.

Actually, as most things having to do with the human body, it is a little more complicated than that.

After the vibrations hit your eardrum, a chain reaction is set off. Your eardrum, which is smaller and thinner than the nail on your pinky finger, sends the vibrations to the three smallest bones in your body. First the hammer, then the anvil, and finally, the stirrup. The stirrup passes those vibrations along a coiled tub in the inner ear called the cochlea.

Inside the cochlea there are thousands of hair-like nerve endings, cilia. When the Cochlea vibrates, the cilia move. Your brain is sent these messages (translated from vibrations by the cilia) through the auditory nerve.

Your brain then translates all that and tells you what you are hearing. Neurologists don't yet fully understand how we process raw sound data once it enters the cerebral cortex in the brain.