pins and needles in a sleeping limb

[gib65]

When one's foot or hand falls asleep, one usually experiences what is commonly called "pins and needles". Does this sensation come directly from the epidermis, or does it originate in the brain. If I didn't know that the "falling asleep" of the hand or foot consisted of the local nerves becoming non-responsive, I'd assume it originated from the epidermis of the hand or foot. However, if all sensation from the hand or foot is cut off due to the non-responsiveness of the nerves, then how could these pins and needles come from the hand or foot. I've heard of phantom limb phenomena, where an amputated limb is still felt because the brain centers for tactile sensation of that limb become active. Is it a similar phenomenon for "pins and needles"?

[ecoli]

It originates in the epidermis, I believe, because of a pinched nerve. But technically, all feeling is "felt" in the brain.

[Helix]

Rather, the pinched nerves send the info to the brain where it is "felt".

[Glider]

When one's foot or hand falls asleep, one usually experiences what is commonly called "pins and needles". Does this sensation come directly from the epidermis, or does it originate in the brain.

It comes from random firing of the affected nerve. If the nerve feeds an area of epidermis then the signals will be interpreted by the brain as having originated in the epidermis.

If I didn't know that the "falling asleep" of the hand or foot consisted of the local nerves becoming non-responsive, I'd assume it originated from the epidermis of the hand or foot.

Nerves are very sensitive to oxygen deprivation. If the blood flow is restricted, the nerves will very quickly become non-responsive. When blood flow is restablished, the nerves begin to function again and begin to fire randomly, resulting in parasthesia (pins and needles). It doesn't really matter where along their length the activity occurs. If a nerve innervates your little finger, activity in that nerve at any point along its length will 'feel' like it's coming from your little finger. A good example of this is when you bang your 'funny bone'. This is sudden compression of the ulnar nerve and the site of compression (the elbow) is the origin of the activity in response to the insult, but this nerve innervates your little finger (and ring finger) and that's why you feel the tingling there.

However, if all sensation from the hand or foot is cut off due to the non-responsiveness of the nerves, then how could these pins and needles come from the hand or foot.

See above

I've heard of phantom limb phenomena, where an amputated limb is still felt because the brain centers for tactile sensation of that limb become active. Is it a similar phenomenon for "pins and needles"?

Not really. In phantom limb pain, the nerve endings no longer exists. The parasthesias associated with the phantom limb could originate anywhere along the sensory pathway, from the terminated nerve ending, the dorsal horn of the spine or even in the primary somatosensory cortex.

 

There is a surgical procedure designed to alleviate phantom limb pain called a 'Drezotomy'. This involves isolating the afferent nerves from the missing limb at the dorsal root, and cutting them. However, this is not always successful, and even when it is, the sensation sometimes returns and is often worse, resulting in a really painful burning sensation.

 

Tghis would suggest that the sensation does not (in these cases) originate in the nerve itself, but higher up, possibly in the thalamus.