Re: Why can't you feel anything when a limb falls asleep?

When you lie on your arm, causing it to go numb, you have cut down the supply of blood to the arm, causing it to become ischaemic. The lack of blood supply to the nerves of the ischaemic limb result in reduced impulses along the nerve, thus feeling becomes dulled, and the limb appears to go to sleep. Once the constriction on the blood supply is removed, then the nerve imulses return to normal and so feeling is restored.

Added by Rob West, 3-31-97

2 studies from the 30's and 40's (references below) have conclusively shown that the "pins and needles" feeling is caused by an abnormal "excitability" in the nerve trunk after the blood dupply is returned to normal. The effect is not caused by the reperfusion of the limb or the reactivation of the sensory endings.

Rob West

Robert West, Ph.D.

Research Service 151-S

VA Medical Center

westr@vax.cs.hscsyr.edu