It’s been a while since I last woke up from a deep sleep and realized that my arm felt like a big lump of wood attached to my body that I could neither move nor feel. I have, however, been suffering increasing problems with numbness and tingling in my hands, most likely because my work has my fingers perpetually connected to a keyboard and I am starting to get carpel tunnel.
It got me thinking about what exactly causes my extremities to fall asleep. I had heard the common explanation that it is caused by lack of blood flow, but this always seemed unlikely to me because my limbs have never turned blue, and such a lack of proper oxygenation to cells would most certainly cause permanent damage.
I did some research, and discovered that an extremity will begin to “fall asleep” when pressure is applied to nerve pathways, causing them to loose their electrochemical connection with the brain. This interruption in signal causes the impulses coming into the brain from the extremity to become garbled and random, resulting in the tingling sensation we are used to feeling when our body part begins to go numb. Interestingly, this can also be caused when pressure is applied to an artery, restricting blood flow to the extremity and depriving nerve cells of nutrients. The initial tingling serves as an early warning system to tell us that we should adjust our position so that we can avoid the serious nerve damage that could result should the blood flow be restricted for an extended period of time.
The random signals interpreted by our brains as tingling are usually all it takes to get us to adjust position and solve the problem, but occasionally, we are so sound asleep that we don’t notice it and the extended pressure causes a total loss in nerve connectivity. When this happens the extremity goes completely numb and our brain is unable to move or feel it at all. Since we have passed the early warning system at this point, I am unsure what exactly stirs in our brain to alert us to the situation, but I can attest that the sensation of having a totally dead feeling arm attached to my body is disturbing to say the least. As is the extended period of tingling when the limb comes back to life.
At least I now know why it happens.