What Causes Pain?
Pain receptors on the skin, synovium, joint space etc, trigger an electrical impulse that travels from the pain receptor to the spinal cord. The spinal cord acts as a relay terminal where the pain signal can be blocked, enhanced, or modified before it is transmitted to the brain for processing.
The most common destination in the brain for pain signals is the thalamus and from there to the cortex, the main center for complex thoughts. The thalamus also serves as a key role in relaying messages between the brain and various parts of the body.
In addition, pain is a complicated process that involves an intricate relationship between important chemicals found naturally in the brain and spinal cord. These chemicals, called neurotransmitters, transmit nerve impulses from one cell to another. Some chemicals govern mild pain sensations while others control intense or severe pain.
The body's chemicals act in the transmission of pain messages by stimulating neurotransmitter receptors found on the surface of cells. Each receptor has a corresponding neurotransmitter. Receptors function much like gates enabling pain messages to pass through to the neighboring cells. Other important receptors in pain transmission are opiate-like receptors. Morphine and other opioid drugs work by attaching onto opioid receptors, switching on pain-inhibiting pathways or circuits, and thereby blocking pain.
Another type of receptor that responds to painful stimuli is called a nociceptor. Nociceptors are thin nerve fibers in the skin, muscle, and other body tissues, that, when stimulated, carry pain signals to the spinal cord and brain. Nociceptors only respond to strong stimuli such as a pinch. However, when tissues become injured or irritated, they release chemicals that make nociceptors more sensitive, causing them to transmit pain signals in response to even milder stimuli. This condition is called allodynia where pain is produced by innocuous stimuli.
Neuropathic pain is a complex, chronic pain state that usually is accompanied by tissue injury. With neuropathic pain, the nerve fibers themselves may be damaged or they may become dysfunctional. Damaged nerve fibers send incorrect signals to other pain centers. The impact of nerve fiber injury includes a change in nerve function both at the site of injury and areas around the injury.
Neuropathic pain often seems to have no obvious cause; but, some common causes of neuropathic pain include alcoholism, amputation, back, leg, and hip problems, chemotherapy, diabetes, nerve problems, HIV infection or AIDS, Multiple Sclerosis, Shingles, spine and joint surgery.
Symptoms may include: shooting and burning pain, tingling and numbness.