Physiology: The Special SensesFitness Gear & Equipment
External ear: This is the only visible part. It is mostly cartilage, shaped to receive sounds, with the small end opening into a tube, the auditory canal (meatus). This canal ends at a thin wall, called the ear drum (typanic membrane). The lining of the auditory canal is covered with tiny hairs and secretes a waxy substance, called cerumen. This aids the transmission of sound and the taste of it causes entering insects to hurriedly exit.
Middle ear: This is a small cavity, behind the ear drum, in the temporal bone of the skull. It has two openings: one into the mastoid cells behind it and the other into the eustachian tube that goes down to the back of the nose (nasopharynx). If the eustachian tube was not there, your ear drum would be destroyed as soon as you climbed or descended a few thousand feet. Because it is there, the ear drum can vibrate freely, transmitting sound. The tube only opens during swallowing. Infection can travel from the throat to the middle ear through that tube.
Three small bones (the ossicles) hang between the ear drum and the cavity side wall, which are named for their strange shapes: the hammer (malleus), the anvil (incus), and the stirrup (stapes). Sound waves start vibrations of the ear drum that set these bones in motion, and they carry the sound across the middle ear.
Inner ear: The internal ear has two parts: the cochlea and the semicircular canals. The cochlea looks like a snail shell. Its coils are filled with fluid that carries the sound waves that enter from the middle ear. The base of the stirrup bone fits into the opening between the middle ear and the inner ear. When the stirrup sets the fluid in the cochlea in motion, the tiny receptive nerve endings pass the vibrations on to the auditory nerve, which carries them to the brain. The brain interprets these vibrations as sounds.
Semicircular canals: The three semicircular canals in each ear, shaped like horseshoes, lie beside the cochlea. They are partly filled with fluid that is set in motion by head or body movements. Because this fluid also has communication with the brain, we are able to sense and maintain proper balance.
Smell: The sense of smell is obtained through the olfactory smells, which are nerve receptors in the walls of the nasal activity. Tiny particles of odorous substances in the air, in these cells, are dissolved in a special secretion. A message is then sent to the brain, where they are interpreted as a particular odor.
Taste: The taste receptor nerves are called taste buds. Buds on the sides sense sour (which is acid). Those on top sense sweet (organic products, especially carbohydrates). Those on the tip and sides sense salty (chlorides). Those at the back of the tongue sense bitter (alkaloids and bile).
Touch: You have sensory organs in your skin, so you know when you touch or are touched. You can sense pressure, heat, cold, and pain. These receptors vary from 16,000 for heat to 4 million for pain.
Kinesthetic: This is the sense of position (proprioceptive sense). You are able to sense your position, erect posture, muscle tonus, weight, pressure, and coordinated body movements. You have sense organs in certain skeletal muscles (interfusal fibers and neuromuscular spindles). You also have sense organs in your tendons (neurotendinous spindles). And of course, you have the semicircular canals in your ears which, by locating the pull of gravity, help you maintain balance.