Why Do Body Parts Fall Asleep?

Position

Oftentimes a body part will fall asleep as the person sleeps or sits in a certain way, since he may be unintentionally positioning a body part in a way that applies pressure to the nerves, thus cutting off their communication with the rest of the body, primarily the brain. The nerves can also be cut off if blood is restricted from the body part from an awkward positioning of limbs, since the nerves need blood in order to function.

Sleeping Nerves

The nerves themselves are made up of fibers of differing thickness and sensitivity. When a body part is asleep, the messages from the nerves to the brain are inhibited. When a body part is shifted so that the nerves can regain their functionality, they "wake up," either by a lack of pressure or resurgence of blood, and begin sending their messages to the brain in different orders depending on their size.

Waking Up

The smallest nerves awake first and the more sensitive, larger nerves awake last. The first nerves to awake are the ones controlling pain and temperature, thus the tingly sensation. Next, the touch nerves awake, and the limb is no longer numb. Finally, the motor neurons are able to communicate with the brain, and control over limb movement is restored.

References

• Why do parts of our bodies "fall asleep"?
• Why Do Limbs "Fall Asleep"?

Resources

• "Sleeping" limbs