Everyone knows pain. Its inconvenience can take many forms, whether it’s a burn, the daily ache of arthritis or a nagging headache. But what you may not know is the mechanism behind the pain that explains why you are in pain.
Pain involves a complex interaction between specialized nerves, your spinal cord and your brain. Imagine a complicated traffic system, with ramps, different speeds, traffic lights, varying weather and road conditions, a traffic control center, an emergency response system, and more. And the vehicle you’re in also makes a difference, because the experience of pain varies from person to person.
The pain is both physical and emotional. It’s about learning and memory. How you feel and react to pain depends on what’s causing it, as well as many personal factors.
Acute pain versus chronic pain
There are two broad categories of pain. Pain can be short-term (acute) or long-term (chronic):
Acute pain is severe or sudden pain that resolves within a certain period of time. You may experience severe pain when you have an illness, injury, or surgery.
Chronic pain is persistent, lasting for months or even longer. Chronic pain is considered a health problem in itself.
With acute pain, you usually know exactly where and why it hurts. Your elbow burns after a scratch or you feel pain at the site of a surgical incision. Acute pain is triggered by tissue damage. Its purpose is to alert you to injuries and protect you from further damage.
With chronic pain, you might not know the reason for the pain. For example, a wound has healed, but the pain remains and may even become more intense. Chronic pain can also occur without any indication of injury or disease.
Causes of pain
At the most basic level, pain begins when particular nerve endings are stimulated. This could result from damage to your body tissues, such as when you cut yourself. Pain can also result from damage or disruption if inflicted on the nerves themselves. Sometimes the pain occurs without any known cause, or long after an injury has healed.
Pain can affect any part of your body. Some of the most common forms of pain are back and neck pain, joint pain, headache, pain caused by nerve damage, pain caused by injury, pain related to cancer, and related conditions. to pain such as fibromyalgia (a disorder that causes widespread musculoskeletal pain).
Pain caused by tissue damage
Pain is your body’s way of warning you of danger and letting you know what is going on in your body. You perceive pain through sensory nerve cells. These are the same types of cells that transmit information from your senses, allowing you to smell, see, hear, taste and touch.
The nerve cells that respond to pain are part of the peripheral nervous system, which includes all the nerves in the body except those in the spinal cord and the brain (the central nervous system). Peripheral nerve cells line up in a network of fibers that carry messages from skin, muscles, and internal organs to your spinal cord and brain. The messages take the form of electrical currents and chemical interactions.
Illustration of how nerves run through the body
The peripheral nervous system brings together all the nerves in your body, apart from those in your brain and spinal cord. It acts as a communication relay between your brain and your extremities. For example, if you touch a hot stove, pain signals travel from your finger to your brain in a fraction of a second. In that short time, your brain is telling the muscles in your arm and hand to rip your finger off the hot stove.
Peripheral nerve fibers have special endings that can sense different types of noxious stimuli, anything that damages or threatens to damage your body’s tissues. It could be a cut, pressure, heat, inflammation, or even chemical changes. Injuries, disease, and surgery can all cause tissue damage.
These specialized nerve endings are called nociceptors. You have millions of them in your skin, bones, joints, muscles, and connective tissues, as well as in the protective membranes around your internal organs.
In response to tissue damage, nociceptors, the source of pain messages, relay information from the injury in the form of electrical impulses. These pain messages travel along a peripheral nerve to your spinal cord.
This type of pain is called nociceptive pain. It can be mild or severe. It can be sharp, stabbing, throbbing, burning, tingling, dull or very sharp. Ouch!
The way of pain
In your spinal cord, specialized nerve cells filter and prioritize messages from peripheral nerves. These nerve cells act as gates, controlling what messages pass through your brain and how quickly and with what force. The severe pain, like from a burn, is treated as an urgent warning, triggering your muscles to pull your hand away from the stove. Some pain messages, such as a scratch or an upset stomach, are relayed more slowly or with less force.
From the spinal cord, pain messages travel to the brain. Your brain responds by sending messages that promote the healing process. For example, the brain can signal your autonomic nervous system, which controls blood flow, to send extra white blood cells and platelets to help repair tissue at the site of an injury. Your brain can also trigger the release of pain-relieving chemicals.
The way of pain
Pain results from a series of complex electrical and chemical changes involving your peripheral nerves, spinal cord and brain.
Pain caused by nerve damage
Sometimes the pain results from damage to one or more peripheral or spinal nerves. This can happen as a result of an accident, infection, surgery or illness. Damaged nerves contort and send pain signals spontaneously, rather than in response to injury.
This type of pain, called neuropathic pain, is often described as burning, numbness, or tingling. It can also create a “pins and needles” feeling. A common form of neuropathic pain occurs when diabetes damages small nerves in the hands and feet, producing a painful burning sensation.
Another form of neuropathic pain occurs when pain pathways in peripheral nerves and the spinal cord become persistently activated. This process, called sensitization, amplifies the message of pain. It is out of proportion to or even disconnected from the original illness or injury. This is what happens in what is called phantom limb pain, even though an injured limb is gone, the pain transmission pathways along the nerves are still activated, as if the limb is still there.
Other influences on pain
An injury or illness that is extremely painful for one person might be only mildly embarrassing for another. A person’s response to pain is strongly influenced by many individual traits, as well as psychological, emotional, and social factors.
When pain messages reach your brain, they pass through the emotional and thinking regions, as well as the region of physical sensation. A person’s experience of pain is shaped by the complex emotional and cognitive processing that accompanies physical damage or sensation. So the pain is really in your head as much as it is in your body.
Factors that can influence your sensitivity to pain and how you react to it include:
Genetic. Your genetic makeup affects your body’s sensitivity to pain signals and how you perceive pain. Some evidence suggests that the tendency to develop neuropathic pain after nerve injury may also have a strong genetic component. Genetic factors will also influence your response to painkillers.
Sex. Women report more frequent pain, more severe levels of pain, and longer lasting pain than men. It is unclear whether this is due to biological differences or psychological and social factors.
Long-term health issues. Many chronic diseases and conditions, such as fibromyalgia, migraines, and irritable bowel syndrome, are associated with pain.
Psychological factors. The pain is more common in people with depression, anxiety, or low self-esteem. Exaggerated pessimism or “catastrophizing” the pain can also make it worse.
Social factors. Stress and social isolation add to the pain experience. Research also suggests that lower levels of education, low income and unemployment are linked to a higher prevalence of pain.
Past experiences. Your memories of past painful experiences can influence your current experiences. If you have had a bad experience with a dentist or have never been to a dentist you may be very nervous about this. Even a minor probe can produce a strong pain response. And pain itself can predispose you to more pain: The most consistent risk factor for developing a painful condition is a previous episode of pain.
Other individual factors. Your upbringing, coping strategies, and general attitude can affect how you interpret pain messages and how well you tolerate pain. The same goes for your expectations of how you “think” you should feel or react.
The impact of pain
Common and complex pain is a burden. The pain interferes with your ability to take part in your daily activities. It can negatively affect your relationships and interactions with others. It can sap your energy and make you feel less healthy overall. The more intense the pain, the more it weighs on your well-being.
Fortunately, many different treatment options are available to help manage both acute pain and chronic pain. Your attitude and lifestyle will also play a key role.