Why Do We Feel Pain?

Ever wonder how your body processes that painful whack of your toe against the table leg? Find out how your body and brain let you know that you've been hurt.

Everyone has felt the ache of a stubbed toe, the twinge of a pulled muscle, or the pounding pain of a bad headache. The pain response we take for granted is actually a sophisticated and instantaneous chain reaction.

Pain happens for one simple reason: to protect you. If your brain registers pain, you typically stop doing what caused it. It goes back to the "fight or flight" instinct, says Sujittra Tongprasert, MD, an anesthesiologist with the University of Louisville Hospital in Kentucky. Pain is the body's way of letting you know that what you are doing is harmful, and that you need to stop.

The Pain Process

Pain starts at the source of an injury or inflammation, whether it's your toe or your lower back. When you injure yourself, the body's automatic response is to stimulate pain receptors, which in turn release chemicals, says Dr. Tongprasert.

These chemicals, carrying the message “Ouch, that hurts,” go directly to the spinal cord. The spinal cord carries the pain message from its receptors all the way up to the brain, where it is received by the thalamus and sent to the cerebral cortex, the part of the brain that processes the message.

In other words, the physical message from the injury travels from where you're hurt directly to your brain, where it registers the sensation known as pain. Your brain perceives that pain, and sends the pain message back to the area of your body that hurts — and it all goes very quickly. You don't stub your toe and notice that it hurts five minutes later; you know right away.

The Difference Between Acute and Chronic Pain

There are different types of pain — more than just mild and severe — that can affect the way that you feel and perceive pain.

Acute pain is short-term pain, usually what you experience after some sort of accident or injury — you break your arm or drop a can of soup on your foot. Once that injury has healed, your pain disappears and doesn't require further treatment.

Chronic pain is persistent pain, generally caused by a condition like fibromyalgia or arthritis. People with chronic pain need long-term treatment and therapy to manage their pain. They feel pain differently and process those pain messages differently from an acute, stub-your-toe or paper-cut pain because of their long experience with pain.

How Pain Can Change the Nervous System

The chemicals released by the body when an injury occurs or when the body has other abnormal processes taking place actually make changes to the nervous system. The types of changes they make are related to the type of pain you feel.

"In chronic pain patients, there is an abnormal functioning of pain processing," says Tongprasert. Normally, the central nervous system automatically inhibits unpleasant sensations like pain. But with chronic pain, the nervous system's function is altered and becomes more sensitive to pain. The nerve cells in people with chronic pain may become so sensitive that the brain perceives even a gentle touch as pain.

There is physical evidence, based on magnetic resonance imaging (MRI) scans, that shows an abnormal amount of stimulation in the brains of chronic pain patients, says Tongprasert. That means people with chronic pain physically perceive and feel pain differently — more intensely — than others.

"Memory also is a part of pain perception," notes Tongprasert. When the brain is stimulated, the brain recognizes that pain stimulus, but also relies on past experiences to help determine what that stimulus is. When the brain has "memory" of chronic and persistent pain, it changes the way that it "feels" every new pain, and feels it more strongly. "That is why even with the same type and amount of stimulation, pain perception is unique," Tongprasert says.

What we know now about pain and how to treat it is only the beginning of what we will eventually understand about pain. There's still much that we need to learn about chronic pain and effective pain management, says Tongprasert.

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