We've all felt it; the sharp, tingling
sensation in our forearm or legs. Most people know this sensation as "pins
and needles" or they say their foot has "fallen asleep." Science calls it
temporary paresthesia and it occurs when some sort of exterior pressure
compresses the nerve and cuts off localized blood flow in a specific part of
the body, which messes with that part's ability to send signals to the brain. Image Credit
When your legs are caught against a hard surface, such as
from sitting on a chair or crossing your legs, it also puts pressure on the nerves
and blood vessels. With those tiny blood vessels impaired, your nerves sense
something's not right; they send the tingling sensation as a pain response,
which tells you to move the extremity. The peripheral nerves send information back
to the brain and spinal cord. When a sensory nerve is pressed it begins to stop
working. In time, the affected extremity "falls asleep," which means the
sensory messages are blocked.
Removing the pressure often results
in return of function. But we all know your leg, arm, or foot keeps hurting
even after adjusting your position. This is because your nerves need to restart
and return to their normal state. The sensations range from feeling hot to cold
to numb. The feeling depends on which nerves are affected. If it's the nerves
used for sensing that are compressed, then the area will feel numb. If it's the
nerves that tell your muscles to move, then you won't be able to move that
part. The nerves may stop firing or fire hyperactively, and the mixed signals
are interpreted as burning, prickling, or tingling. Image Credits
Since there is no rule for how quickly the extremity will fall
asleep it's important to pay attention to when the sensation starts to occur.
For example, if you notice that your leg starts to tingle ten minutes into a
movie, start massaging, stretching or readjusting your legs just before that to
bring blood to the area
People with poor circulation are more prone to having
extremities fall asleep and should avoid sitting cross-legged or readjust
frequently to avoid putting pressure on the blood vessels. In general,
temporary paresthesia is nothing to worry about. If you have constant pins
and needles it could be a sign of chronic paresthesia, which often requires
medical attention.
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