MadSci Network: General Biology
Query:

Re: why do our hands and legs fall asleep?

Date: Thu Apr 19 06:47:46 2001
Posted By: Benoit A. Bacon, Post-doc/Fellow, Psychology, University of Glasgow
Area of science: General Biology
ID: 987617846.Gb
Message:

Dear Meturek,
 Thank you for your very interesting question. As I’m sure you have 
noticed, arms or legs usually "fall asleep" when they are squeezed 
under your body. Typical examples include sitting on the floor with 
your leg under you, or sleeping on your arm.
 When you squeeze your arm or leg like this, you temporarily 
compress, or squash, the nerves in that part of the body. Nerves are 
like little wires that allow your brain to communicate with the rest of 
your body. When they are squashed, the brain "loses 
communication" and the result is that you don’t feel anything in the 
part that is squashed. 
 After a while, you will feel a little "tingling sensation", that appears to 
protect your nerves from damage! Sitting on your nerves for 10 
minutes is not a problem, but imagine squashing them for 8 hours! 
When you finally change your position and release the nerves, they 
"wake up", and sensation comes back gradually with an annoying 
"needles and pins" sensation.
 It is possible that you also cut blood circulation in your arm and leg. 
Although this is not the main cause of the "falling asleep", it can 
contribute to the problem because your nerves need blood, or more 
precisely the oxygen that the blood carries, to function properly.
 Don’t be worried about your arms and legs falling asleep. It happens 
to everyone and it’s not dangerous. If you don’t like that weird, tingling 
feeling or even worse the needles and pins, just avoid squashing 
your nerves!
 I hope this answers your question.
 Cheers !
 Benoit



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