Pain

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Pain

Psychological factors in the individual experience of pain

Pain is an unpleasant feeling that is carried to the brain by the nervous system. Injury is a major cause, but pain may also arise from an illness. It may accompany a psychological condition, such as depression, or may even occur for no obvious reason. Pain, in its most basic form, results from a variety of outside stimuli such as a pinprick or a serious burn. However, pain is a complex experience that eludes simple definitions. Not only does the central nervous system play a crucial role in the experience of pain, but psychological factors can also affect how an individual perceives pain. Most pain results from the intense stimulation of nerve endings beneath the skin that serve as the body’s alarm system for detecting injury.

Pain can be classified as acute (brief) or chronic (long-lasting). Acute pain often results from tissue damage, such as a skin burn or broken bone. Acute pain can also be associated with headaches or muscle cramps. This type of pain usually goes away as the injury heals or the cause of the pain is removed.

Chronic pain is pain that lingers after an injury heals, or is related to a disease, or has no known cause but will not go away. It is estimated that one in three people in the United States will experience chronic pain at some time in their lives.

For the majority of people, pain is immediate and intense. However, in certain situations, the feeling of pain may be delayed or may fail to occur altogether (as sometimes happens with soldiers in the midst of battle). Another baffling aspect of pain is its persistence after the source of pain is gone, such as phantom limb pain that continues even after the injured limb has been amputated. Although people usually seek to avoid pain, some people, called sadomasochists, can derive pleasure from pain.

Everyone experiences and describes pain in their own way, so it can be difficult to communicate precisely about its quality and intensity. There are no tests that can show what type of pain a person is having or how severe it is. This is the reason why doctors ask patients many questions about their pain, including where it is located and what type of pain it is—burning, shooting, stinging, stabbing, throbbing, or aching, for example. Doctors also ask what kinds of things increase or relieve the pain, how long it has lasted, and whether there are any variations in it. Sometimes patients are asked to rate their pain on a scale of zero (no pain) to ten (the worst pain ever experienced).

The physical origins of pain

Despite the advances made in the study of pain over the past 50 years and the evolution of several pain theories—such as the specificity, pattern, and gate-control theories—many questions remain about the physiological and psychological components of this enigmatic but common experience. Most scientists agree, however, that the physiology of pain is a complex biochemical process that begins with pain receptors on nerve fibers that lie beneath the skin. An outside stimulus, such as intense heat, a cut, or even an exceptionally strong handshake, causes biochemicals on the nerve endings to produce a series of electrical nerve impulses. These impulses pass a pain message through the spinal cord to the brain’s thalamus, which is located on top of the brain stem and processes the signals to the cerebral cortex. It is the cerebral cortex that interprets the feeling of pain and produces the appropriate reaction, such as pulling the hand away from a hot surface.

A number of biochemicals are involved in the experience of pain. Prostaglandins are biochemicals that are released where the injury occurs. These prostaglandins increase blood circulation in the injured area in order to battle infection and promote healing by increasing the supply of white blood cells, antibodies, and oxygen. Prostaglandins also work in concert with other biochemicals, like bradykinin, to increase nerve-ending sensitivity and transmit electrical impulses to the brain. The speed at which these electrical impulses travel will vary according to the type of pain. For example, a pinprick may cause only a slight pain, but the impulse it triggers travels at the astonishing rate of 98 ft/sec (30 m/sec). In contrast, the pain impulse of a slight burn or ache travels at approximately 6.5 ft/sec (2 m/sec). As a result, some types of pain may cause immediate flinching whereas other kinds of pain produce a delayed response.

As scientists continue to study pain, they are uncovering more detailed information concerning its physiological intricacies. For example, they have identified certain receptors in the brain’s neurons, called the NMDA (N-methyl-D-aspartic acid) receptors, that may amplify pain messages in the spinal cord, causing an individual to feel pain after touching an area that has been burned. Scientists are also locating with increased precision the areas of the brain that process pain information. One study has indicated that three specific structures in the cerebral cortex interpret pain messages, including where the pain is located. One structure, the anterior cingulate gyrus (which is thought to control emotions), may also play a crucial role in an individual’s response to pain. Another group of researchers have found that a complex network of nerves in the brain may control the various responses that different people will have to the identical amount of pain.

Types of pain

Pain occurs in various degrees, from dull and aching to piercing and intense. Acute pain is usually associated with tissue injury and, for the most part, occurs for only a short amount of time. Chronic pain, however, persists for long periods of time, even years after the injury that originally caused the pain has gone away. For example, severe burns can create scar tissue that can continue to cause excruciating discomfort. Certain disorders, such as arthritis or cancer, may also cause persistent pain. In the case of phantom limb pain, an individual may continue to perceive pain in an arm or leg that has been amputated as though the appendage was still there. The precise cause of phantom limb pain is unknown. One theory is that the nerve endings remaining after the amputation continue to process the electrical pain impulses. Other theories focus on the firing of spinal cord neurons and the intricate neuronal circuitry of the brain.

Specific types of pain include causalgia (caused by severe burning that injures the nerve fibers under the skin) and neuralgia (caused by factors like viral infections and nerve degeneration that damages peripheral nerves). Headaches are the most common of all pain and may be chronic or acute in nature. Vascular headaches, like migraines, are caused by the constriction and dilation of the blood vessels in the area around the brain. Tension headaches have their origin in muscular contractions and are usually associated with psychological factors such as stress and depression. Traction or inflammatory headaches, which account for approximately 2% of all headaches, are caused by diseases.

KEY TERMS

Anterior cingulate gyrus —A part of the brain that may play a critical role in controlling emotions and response to pain.

Biochemical —The biological or physiological chemicals of living organisms.

Bradykinin —A biochemical present in the blood that acts as a vasodilator (which causes the dilation of blood vessels).

Causalgia —A type of pain caused by severe burning of the skin.

Central nervous system —The brain and spinal cord components of the nervous system that control the activities of internal organs, movements, perceptions, thoughts, and emotions.

Cerebral cortex —The external gray matter surrounding the brain and made up of layers of nerve cells and fibers; it is thought to process sensory information and impulses.

Endorphins —Biochemicals produced by the brain that act as opiates and reduce pain.

Neuralgia —Severe throbbing or stabbing pain that originates in the nerve fibers. Neurons—Nervous system unit that includes the nerve cell, dendrites, and axons.

NMDA receptors —Specific neuron receptors that strengthen neural connections and may play a role in pain perception.

Prostaglandins —A biochemical substance, present in many tissues, that plays an important role in healing injured areas and relaying pain messages to the brain.

Thalamus —A structure at the top of the brain stem that acts as the primary relay station for biochemical messages from the spinal cord to the brain.

Psychological factors in the individual experience of pain

The psychology of pain is a complex area of study. Although pain is universal, in that every human being experiences it in one form or another, individual feelings of and responses to pain vary greatly. Each individual has a unique pain threshold (the point at which they first begin to experience pain) and tolerance to pain. Cultural heritage, tension, emotions, fears, and expectations all play a role in the experience of pain.

For example, in certain cultures specific rites and rituals may involve a pain that is readily accepted by the people within that particular society. Scientists believe that people in these cultures experience that pain to a far lesser degree than others from different cultures would if they underwent the same experience. In such cases, the ability to focus on other aspects of the ritual, such as its social or religious ramifications, may act as a psychological sedative that helps the individual better tolerate the pain or, perhaps, feel no pain at all. The expectation of pain also determines how much pain is felt. Two people, for example, may go to the dentist; the person who has greater anxiety about the experience is likely to feel a greater amount of pain. Tension and emotional states may also cause biochemical changes that lower the amount of endorphins (naturally occurring opiates) produced by the brain.

Pain control

Many drugs are available for preventing or treating pain. Drugs from different classes may be combined to handle certain types of pain.

Nonopioid analgesics, such as aspirin, acetaminophen (Tylenol^®), and ibuprofen (Advil^®) are most often used for minor pain. These drugs are available without a doctor’s prescription, but there are also some prescription-strength medications in this class.

Narcotic analgesics are available only with a doctor’s prescription and are used for more severe pain, such as cancer pain. These drugs include codeine, morphine, and methadone. Contrary to earlier beliefs, physiological addiction to these painkillers when used therapeutically is not common.

Anticonvulsants as well as antidepressant drugs, initially developed to treat seizures and depression, respectively, also can be used as pain-killers. Furthermore, it is not unusual for people with chronic or extreme pain to experience some depression, so treatment with anti-depressants may serve a dual role. Commonly prescribed anticonvulsants for pain include phenytoin, carbamazepine, and clonazepam. Antidepressants used for this purpose include doxepin, amitriptyline, and imipramine.

Pain that cannot be relieved with the drugs discussed above may be treated by injections of local anesthetics directly into or near the nerve that is transmitting the pain signal. These root blocks may also be useful in determining the source of pain.

Drugs are not always effective in controlling pain. Surgical methods are used as a last resort if drugs and local anesthetics fail.

Alternative treatments are sometimes used to help patients deal with both the physical and psychological aspects of pain. Some of the most popular treatment options include acupressure and acupuncture, massage, chiropractic, and relaxation techniques, such as yoga, hypnosis, and meditation. Herbal therapies are gaining increased recognition as viable options. For example, capsaicin, the component that makes cayenne peppers spicy, is used in ointments to relieve the joint pain associated with arthritis. Contrast hydro-therapy can also be very beneficial for pain relief.

Psychological approaches to reduce pain by increasing an individual’s pain threshold and tolerance were largely developed for chronic pain sufferers, but may also work in cases of acute pain. One such method involves focusing the attention on something other than the pain, such as a past pleasant experience, music, or even a complex mathematical problem. Relaxation and meditation techniques are used to reduce stress and muscle tension that may increase feelings of pain. Exercise can also help reduce pain because it causes the brain to produce more endorphins, the body’s natural painkillers.

See also Analgesia; Anesthesia.