Understanding pain

You know what it's like to feel pain. Its unpleasantness can take many forms, whether it's the smart of a burn, the daily ache of arthritis or a throbbing headache. What you might not be aware of is the science behind why you hurt.

Pain involves a complex interaction between specialized nerves, your spinal cord and your brain. Imagine a complicated traffic system, with on-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 one person to another.

Pain is both physical and emotional. It involves learning and memory. How you feel and react to pain depends on what's causing it, as well as many personal factors.

Acute versus chronic pain

There are two major categories of pain. Pain can be short term (acute) or long term (chronic):

  • Acute pain is a severe or sudden pain that resolves within a certain amount of time. You might feel acute 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 condition in itself.

With acute pain, you typically know exactly where and why it hurts. Your elbow burns after a scrape 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 injury and protect you from further harm.

With chronic pain, you might not know the reason for the pain. For example, an injury has healed, yet the pain remains — and might even become more intense. Chronic pain can also occur without any indication of an injury or illness.

Causes of pain

At the most basic level, pain begins when particular nerve endings are stimulated. This might result from damage to your body tissues, such as when you cut yourself. Pain can also result from damage or disruption to the nerves themselves. Sometimes pain occurs for no 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, headaches, pain from nerve damage, pain from an injury, cancer pain, and pain-related conditions such as fibromyalgia (a disorder that causes widespread musculoskeletal pain).

Pain from tissue damage

Pain is your body's way of alerting you to danger and letting you know what's happening in your body. You perceive pain through sensory nerve cells. These are the same type 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 of the body's nerves except those in the spinal cord and brain (the central nervous system). Peripheral nerve cells align into 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 is all the nerves in your body, aside from the ones 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, the pain signals travel from your finger to your brain in a split second. In just as short a time, your brain tells the muscles in your arm and hand to snatch your finger off the hot stove.

The peripheral nerve fibers have special endings that can sense different types of harmful stimuli — anything that damages or threatens to damage tissues in your body. It could be a cut, pressure, heat, inflammation, even chemical changes. Injuries, illnesses and surgery all can cause tissue damage.

These specialized nerve endings are called nociceptors (no-sih-SEP-turs). 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 at the source of the injury relay pain messages in the form of electrical impulses. These pain messages travel along a peripheral nerve to your spinal cord.

This type of pain is referred to as nociceptive pain. It may be mild or severe. It may be sharp, stabbing, throbbing, burning, stinging, tingling, nagging, dull or aching. Ouch!

The pain pathway

In your spinal cord, specialized nerve cells filter and prioritize messages from the peripheral nerves. These nerve cells act like gates, controlling which messages get through to your brain — and at what speed and strength. Severe pain, as from a burn, is processed as an urgent warning, triggering your muscles to pull your hand away from the stove. Some pain messages, such as from a scratch or an upset stomach, are relayed more slowly or with less strength.

From the spinal cord, pain messages travel to the brain. Your brain responds by sending back messages that promote the healing process. For example, the brain can signal your autonomic nervous system, which controls blood flow, to send additional white blood cells and platelets to help repair tissue at an injury site. Your brain can also signal the release of pain-suppressing chemicals.

The pain pathway

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 pain results from damage to one or more peripheral or spinal nerves. This can happen as a result of an accident, infection, surgery or disease. The damaged nerves will misfire and send pain signals spontaneously, rather than in response to an injury.

This type of pain, called neuropathic pain, is often described as burning, freezing, numbing or tingling. It can also create a "pins and needles" sensation. A common form of neuropathic pain occurs when diabetes damages the small nerves in the hands and feet, producing a painful burning sensation.

Another form of neuropathic pain happens when pain pathways in the peripheral nerves and spinal cord become persistently activated. This process, called sensitization, amplifies the pain message. It's out of proportion to or even disconnected from the original disease or injury. This is what happens in so-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 slightly bothersome for another. Why is this? A person's response to pain is heavily 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 physical sensation region. A person's experience of pain is shaped by the complex emotional and cognitive processing that accompanies the physical damage or sensation. So pain really is in your head as well as your body.

Factors that can influence how sensitive you are to pain and how you respond to it include:

  • Genetics. Your genetic makeup affects how sensitive your body is to pain signals and how you perceive pain. Some evidence suggests that the tendency to develop neuropathic pain after a nerve injury also can have a strong genetic component. Genetic factors will also influence your response to pain medications.
  • Gender. Women report more frequent pain, more severe levels of pain and longer-lasting pain than men do. It's not known whether this is due to biological differences or psychological and social factors.
  • Long-term health problems. Many chronic illnesses and conditions, such as fibromyalgia, migraine headaches and irritable bowel syndrome, are associated with pain.
  • Psychological factors. Pain is more prevalent in individuals with depression, anxiety or low self-esteem. An exaggerated pessimism or "catastrophizing" of pain can also make it worse.
  • Social factors. Stress and social isolation add to the experience of pain. Research also suggests that lower education levels, lower income and being unemployed are linked to a higher prevalence of pain.
  • Past experiences. Your memories of past painful experiences can influence your current experiences. If you had a bad experience with a dentist or have never been to a dentist and are very nervous about it, 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 you tolerate pain. So can your expectations as to how you "think" you should feel or react.

The impact of pain

Pain is common and complex — and a burden. 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 severe the pain, the heavier a toll it takes 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. If you approach any painful condition with a positive attitude and a willingness to change, you're likely to be successful in coping with your pain.

July 02, 2019

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