Equilibrioception or sense of balance is one of the physiological
senses. It helps prevent humans and animals from falling over when walkingor standing still.
In humans, equilibrioception is mainly sensed by the detection of acceleration, which occurs in the
vestibular system. Other senses play roles as well, e.g. the visual systemand proprioception. The importance of visual input for balance is illustrated by its being harder to stand on one foot with eyes closed than with eyes open.
In the vestibular system, equilibrioception is determined by the level of
fluidproperly called endolymphin the labyrinth - a complex set of tubing in the inner ear.
When the sense of balance is interrupted it causes dizziness,
disorientationand nausea. Balance can be upset by Meniere's disease, superior canal dehiscence syndrome, an inner ear infection, by a bad common coldaffecting the head or a number of other medical conditions. It can also be temporarily disturbed by rapid and vigorous movement, for example riding on a merry-go-round. See also vertigo.
astronauts find that their sense of balance is impaired when in orbit, because they are in a constant state of free-fallwhile their rockets are off. This causes a form of motion sicknesscalled space sickness.
Some animals have better equilibrioception than humans, for example a
catuses its inner earand tail to walk on a thin fence. [http://www.sciencedaily.com/articles/e/equilibrioception.htm]
Equilibrioception in many marine animals is done with an entirely different organ, the
statocyst, which detects the position of tiny calcareous stones to determine which way is "up".
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