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When something in the body is not working properly, the body's nerve cells sense pain at the site of the damage or injury and send a signal to the brain, which triggers a response.
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This "pain transmission" involves several bodily structures:
- Nerve endings. Located throughout the body, externally in the skin and internally in the body's organs. They pick up the painful stimuli and convey them to the brain.
- Nerve fibers. These connect the nerve endings, the spinal cord and the brain. Their job is to carry nerve impulses over long distances.
- The brain. Interprets the stimuli and reacts to them.
Nerve endings sensitive to stimuli are called receptors. The receptors sensitive to pain are called nocireceptors, and the human body has over 3 million of them. They are found in the skin, muscles, bones, blood vessels and in certain organs. These cells are sensitive to pain and react to particular stimuli. They can pick up sensations and carry the signals to the nerve cells, and then to the brain.
Pain is caused by various stimuli, both internal and external. The three main types of stimuli are:
- Mechanical: a blow or a fall.
- Thermal: hot and cold.
- Chemical: certain chemical substances (e.g. histamines) that can stimulate pain receptors.
When the stimuli are intensified and exceed a certain threshold, they stimulate the receptors. In turn, the receptors respond to specific types of stimulus. They transform the stimulus into a nerve signal, then increase the signal and transmit it to the brain.
The neural transmission of the pain message is regulated by substances called mediators and hormones. The mediators make the receptors more sensitive to pain, while the hormones (prostaglandins) can trigger or increase the painful sensation. They bring on inflammation and fever.
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