| What makes people dizzy when they spin? |
EasyNews, UseNet made Ea .. |
| ::darkshadows:: (blood@thirsty.net) |
2008/05/30 08:08 |
What makes people dizzy when they spin?
Rolling down a hill or spinning around in endless circles causes
dizziness or vertigo because hair-like sensory nerve cells in our ears
send wrong messages to our brain.
The motions of our bodies are detected by the vestibular system found
in the upper part of our inner ear. The vestibular system senses
whether we are standing up or lying down.
When we spin in circles or get up too fast from the couch, we feel
dizzy and lightheaded due to the vestibular system's nerve reactions
to these unusual motions.
Here's how our vestibular system reacts to a slight change in
direction when we bend our heads: The vestibular system senses
motion through three semicircular canals that are at right angles to
one another. Not only do these canals have hair-like sensory nerve
cells, but they also contain a fluid called endolymph.
Following the principle of inertia, endolymph resists changes in
motion. As a result of this resistance, the endolymph lags behind and
stimulates hair cells to send nerve signals to the brain. Our brain
interprets the nerve messages and knows which direction the head
moved.
However, when we spin, our brain receives mixed messages. The
endolymph slowly begins to move in the same direction we are spinning.
As time goes by, the endolymph catches up to the rate of speed we are
spinning and no longer stimulates the hair-like nerve cells. This
causes our brain to quickly adapt to the nerve signals. However, when
we stop spinning, the endolymph continues to move and stimulates hair
cells in the opposite direction.
These hair cells send wrong messages to the brain making it think that
the head is still spinning although it actually has stopped. As a
result of this inaccurate signal, we experience dizziness. Eventually,
the endolymph stops moving and no more signals are sent to the brain.
The brain interprets that the spinning motion has ceased and the
dizziness disappears.
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