Hearing

  
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The Ear
There are three main sections to the ear - external, middle, and internal. Most of the organ is housed within the temporal bone, and located within the head.

The external ear is the part you can see protruding from the head. That particular part, the external flap, is called the auricle, or pinna. But the external ear also consists of the external auditory canal, a short tube from the auricle measuring about 3 cm (1.25 in) long.

The middle ear contains the mechanism that conducts, or moves, sound waves to the internal ear. This narrow tube, called the cleft, is about 3 cm (1.25 in long), and travels vertically, then horizontally. To allow air in and out of the middle ear, it is directly connected to the nose and throat through the eustachian tube. The middle ear contains the three smallest bones in the body, the malleus, incus and stapes (commonly known as hammer handle, anvil and stirrup, respectively). These three movable bones are called the ossicles, which aurally connect the eardrum to the inner ear.

The internal ear, also called the labyrinth, is separated from the middle ear by the fenestra ovalis (oval window), and is part of the temporal bone containing the hearing organ which receives filaments of the auditory nerve. This section consists of membranous canals located in a temporal bone. It is divided into the cochlea (Greek for "snail shell"), the vestibule, and three semicircular canals filled with a gel-like liquid called endolymph.

Hearing Process
To hear, sound waves travel through the external auditory canal (which together with the auricle form a cone-like structure that increases sound reception, like a satellite dish does electromagnetic waves). The waves hit the eardrum, causing it to vibrate. The vibrations travel up the ossicular chain in the middle ear, through the oval window, and into the inner ear. This causes the endolymph to move, stimulating the fine hair cells, or collectively Corti, that protrude from the inner surface of the cochlea. These hairs send signals, which contain unique information about the sound, to the auditory nerve, which then passes the signals on to the brain. The information is then interpretable by the auditory centres of the brain.

Equilibrium
The components of the ear, particularly the semicircular canals and the vestibule, have one other important bodily function: they help control your balance, or equilibrium. The canals have hairs, similar to those in the Corti organ, which respond to changes in your head’s position.

From the vestibule, the canals extend at right angles. Each canal can monitor their respective directions - up and down, forward and backward, and left and right. This is accomplished when the otoliths (calcium carbonate crystals known as ear sand), which rest onto of the hairs, shift, forcing the hairs to shift in response to the pressure change. While not the only organs involved in the equilibrium process - the eyes, sensory cells in the skin and other internal tissues play a major role - by if a person’s ear labyrinth is damaged, they may not be able to stand still without swaying or falling, especially when their eyes are closed.