If you put extended pressure on your arm, by leaning or sleeping on it, it might go numb and then give you a tingling feeling. Your arm falls asleep like this because prolonged pressure on a nerve, or on a nerve's blood supply, can temporarily damage it.

Sensory Input

Nerves allow you to sense feeling by sending messages to the brain describing sensory input. If you touch a hot burner, you pull your hand back because the nerves in your hand have sent the message to your brain that your hand is in pain.

When a nerve is compressed or when the blood supply to a nerve is compromised, the normal messages nerves send to the brain are stopped or altered. At this point, when the nerve is no longer functioning appropriately, numbness occurs.

Nerve Recovery

When the nerve begins to recover, you may feel a tingling sensation. This feeling of pins and needles is due to the fact that at the early stages of the nerves' recovery, it functions inappropriately, giving your brain misinformation.

To understand why nerves work this way, we need to think about the anatomy of a nerve. Every nerve is filled with thousands of nerve fibers, each carrying specific information to the brain.

False Signals

Some of these fibers are large, others are small, and all recover at different rates. Because the thousands of fibers that make up a damaged nerve recover at different speeds, the message they collectively send the brain as they are recovering is inaccurate.

So though your arm isn't actually tingling at all, the way it would if you received a mild electric shock, your brain believes that it's tingling because the brain always believes messages that nerves send-whether those messages are accurate or not.