PAIN

1 Detection

Acute pain begins with nociceptors—long neurons that originate in the spinal cord and end as thin fibers in the skin. Those fibers are tipped with receptors that respond to pain-inducing stimuli. When a stimulus is strong enough, these receptors generate an electrical current—the pain signal.

2 Transmission

The pain signal travels along the neurons through a series of channels that allow sodium ions back and forth across cell membranes. These channels, like Nav1.7, allow those charged particles across a membrane if the pain signal is strong enough. (If it isn’t, the person feels no pain.)

3 Perception

When a pain signal reaches the spinal cord, it continues up to the brain, where the somatosensory cortex is primarily responsible for translating information about the intensity of the pain signal. The brain’s motor cortex then generates the body’s response—a shout of surprise, a jerk of a hand.

4 Aftermath

After an injury, even an innocuous stimulus—like a warm bath or a pat on the back—can generate a pain signal at the site of the original injury.