Science Questions

What is pins and needles?

Sun, 16th Dec 2007

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I just noticed when I crouched down or if Iím sleeping on my arms at work that when I wake up I have this pins and needles sensation. Apparently itís quite normal and many other people have it. I wanted to know what the basis of it is and why does it happen?


The nerves in your body have an incredibly high energy requirement so they have a big supply of blood and sugar to keep themselves going. If you lie on you arm when you go to sleep then the common place for this to happen is in your forearm or under your armpit. There is a condition called Saturday Night Palsy. This is where people go up the boozer and have a few. They come home and they fall asleep with their arm over the back of the chair. The arm of the chair pushing up under the arm compresses the nerves supplying their arm against their humerus (the upper arm bone). It squashes the nerve flat and you can actually get a nerve palsy because of it. Normally when you go to sleep at night, when you squash a nerve flat, you squash the arm but reduce the blood flow down the nerve. This means the brain doesnít get signals back into the spinal cord from the nerve because the interruption of the blood flow because of laying on your arm or just physically pushing on the nerve stops the flow of information. The brain starts wondering where the signal has gone from that bit of the body and so it increases sensitivity to whatever that nerve was supplying. You start to get spurious signals as though you could really feel that bit of your body. Itís a bit like phantom limb pain you get when you have apart of the body amputated. When you restore the blood flow by moving in your sleep or rubbing or elevating the bit of the body thatís starved of blood such as your leg then all the blood rushes back in. The pressureís taken off the nerve as well and it starts to work again. So you get your sensation restored. Thankfully, itís not harmful. But, it can also be assign in people who have other diseases like diabetes that the nerve is deteriorating. As long as youíre getting pins and needles thatís good news. If you had it all the time then that might be a sign that something bad is happening. If youíre just going to bed and laying on your arm itís nothing.


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