Ouch!

Ouch! You know the feeling. Stub your toe or bite into your tongue, and the sensation of pain shoots through your body. But what exactly is pain? To understand, we'll have to look just under the surface of your skin. Don't worry ... it won't hurt.

You have four distinctly different types of receptors beneath your skin - for pain, pressure, heat, and cold. (You also have chemical receptors in your tongue and inside your nose, and photoreceptors in the eye. Some animals can also sense electrical and magnetic fields.) Each receptor has dendrites that receive input and change it to an electrical message.

Here's how they work. Imagine you prick your skin with a pin. Cells are damaged. They release chemicals into their surroundings, and those chemicals cause changes in the membranes of dendrites. Within your brain, the injury message is sorted out from other messages and interpreted as pain.

What happens if you rub your injured skin, or warm it? These messages stimulate other receptors, but their signals travel the same pathway as the pain signals, masking them. Doctors use this technique to help those who suffer from chronic pain. They implant a device that sends a constant tingle along the path to the brain, muffling the pain signal for the patient.

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