addiction. An illness in which a person seeks and consumes a substance, such as alcohol, tobacco or a drug, despite the fact that it causes harm.

aerobic (are-O-bik) exercise. Aerobic means "with oxygen." In reference to exercise, the term refers to the intensity and duration of activity and the energy fuel being used.

allodynia (al-o-DIN-e-uh). An altered sensation in which normally nonpainful events are felt as pain.

analgesic (an-ul-JE-zik). A medication or agent that reduces pain.

anesthetic. A substance used to abolish sensation.

anticonvulsant. A drug used to prevent seizures, which also may be useful for treating pain.

autonomic nervous system. The portion of the nervous system that regulates involuntary body functions, including those of the heart and intestine. Controls blood flow, digestion and temperature regulation.

bursa. A fluid-containing sac near or involving a joint or bony prominence that reduces friction between a tendon and a bone, or between a bone and skin during movement.

celiac plexus (SE-le-ak PLEK-sus). A network of nerve fibers in the abdomen that's controlled by the autonomic nervous system. This group of nerves also conducts pain sensation from the abdominal organs, such as the liver, spleen, stomach and pancreas.

corticosteroids. Anti-inflammatory drugs created from or based on a naturally occurring hormone (cortisone) produced by the cortex of the adrenal glands.

cortisone. A naturally occurring hormone produced by the cortex of the adrenal glands. It decreases inflammation.

COX-2 inhibitor. A nonsteroidal anti-inflammatory drug (NSAID) that specifically inhibits an enzyme known as cyclooxygenase-2 (COX-2). These drugs are used to treat pain and may be less likely to cause gastrointestinal bleeding than other NSAIDs.

dysthesia. An unpleasant, abnormal sensation, often described as burning or crawling. May be spontaneous or evoked.

endorphins. Naturally occurring molecules made up of amino acids. Endorphins attach to special receptors in the brain and spinal cord to stop pain messages. These are the same receptors that respond to morphine.

enkephalins (en-KEF-uh-lins). Naturally occurring molecules in the brain. Enkephalins attach to special receptors in your brain and spinal cord to stop pain messages. They also affect other functions within the brain and nervous system.

epidural anesthesia. A procedure used to provide anesthesia during labor and some surgery. Medication is given through a catheter placed in the back. Also called an epidural block.

ergonomics. The science of designing the job to fit the worker, rather than physically forcing the worker's body to fit the job.

facet joint (FAS-ut joint). A joint between two adjacent vertebrae. Each vertebra is connected at the intervertebral disk in the front and the two facet joints in the back.

field block injection. A procedure used to relax a muscle or to reduce muscle pain and inflammation. The targeted muscle is injected with a local anesthetic and corticosteroid. Also called trigger point injection.

frontal cortex. The portion of the brain that's involved with reasoning, planning, abstract thought and other complex cognitive functions in addition to motor function.

hyperalgesia. Abnormally increased pain sensation.

inflammation. The protective response of body tissues to irritation or injury. Inflammation may be acute or chronic. Signs and symptoms are redness, heat, swelling and pain, often accompanied by loss of function.

intraspinal. Within or into the vertebral column, which contains the spinal cord and cerebrospinal fluid.

limbic system. The portion of the brain that produces emotions.

local anesthetic. A medication that blocks electrical signals in nerves. It eliminates pain in a specific part of the body and causes intended, temporary paralysis.

myofascial pain. Pain and tenderness in the muscles and adjacent fibrous tissues (fascia).

narcotics. A group of drugs that relieves pain by preventing transmission of pain messages to the brain. Also referred to as opioids.

nerve block. A local anesthetic that is injected around a nerve, preventing pain messages traveling along that nerve pathway from reaching the brain. Used most often to relieve pain for a short period, such as during a surgery.

neuralgia. Pain that extends along one or more nerve pathways.

neurobiology. A branch of biology that is concerned with the anatomy and physiology of the nervous system.

neurolytic. A substance or procedure that destroys nerves.

neuromodulation. Electrical stimulation of a peripheral nerve, the spinal cord or the brain for relief of pain. It may be done transcutaneously or with an implanted stimulator.

neuropathic pain. Pain that originates from a damaged nerve or nervous system.

neurotransmitters. Chemicals in the brain, such as acetylcholine, serotonin and norepinephrine, that facilitate communication between nerve cells (neurons).

nociceptors (no-sih-SEP-turs). Nerve endings attached to peripheral nerves that detect potential or actual tissue damage. They sense unpleasant situations such as extreme heat, cold, a cut or pressure.

nonsteroidal anti-inflammatory drugs (NSAIDS). (en-SAYDS). Medications used to reduce inflammation that aren't corticosteroid based.

occupational therapy. Skilled treatment that helps people return to ordinary tasks around home and at work by maximizing physical potential through lifestyle adaptations and possible use of assistive devices.

pain behaviors. Responses to pain that include talking about pain, rubbing or protecting an affected part of the body, or avoiding routine activities because of pain.

pain scale. A system of rating pain. Often based on a scale of 0 to 10, with 0 being no pain and 10 being the worst pain imaginable.

pain threshold. The point at which pain is noticeable.

pain tolerance level. The peak amount of pain that a person can endure.

palliative care. Care given to people with chronic, often life-threatening illnesses. Care focuses on symptom management, such as relieving pain or stopping nausea, enhancing quality of life and psychosocial needs.

patient controlled analgesia (PCA). A system that allows people to control the amount of pain medication that they receive. The person pushes a button and a machine delivers a dose of pain medicine into the bloodstream through a vein.

peripheral nerves. Nerves that run from your spinal cord to all other parts of your body. Peripheral nerves transmit messages from the spinal cord and the brain to and from other parts of your body, and send sensory signals back to the spinal cord and brain.

phantom pain. Pain or discomfort following amputation that feels as if it comes from the missing limb.

physiatrist. A doctor who specializes in physical medicine and rehabilitation. A physiatrist evaluates and recommends treatments that restore function in people with chronic disease.

physical dependence. The physical condition in which rapid discontinuation of a substance, such as alcohol, tobacco or a drug, causes a withdrawal reaction.

physical therapist. A trained professional who teaches exercises and other physical activities to aid in rehabilitation and maximize physical ability with less pain.

rebound pain. When regular use of a pain medication makes a person's pain worse instead of better.

receptors. Located on the outer side of a receiving nerve cell, receptors bind the neurotransmitter to the receiving nerve cell and change the activity of this cell.

reflex sympathetic dystrophy (RSD). A chronic and painful condition that usually affects an arm or leg. Signs and symptoms include intense burning or aching pain along with swelling, abnormal sweating and hypersensitivity of the area.

regional anesthesia. Medications used to block pain in a certain region of the body without altering consciousness.

sciatica. Achiness that may include tingling, numbness or muscle weakness along the sciatic nerve. This major nerve runs through the buttock muscles into the back of the thigh and divides into two nerves behind the knee that run down into the foot.

selective serotonin reuptake inhibitors (SSRIs). Medications used to relieve depression. May work by increasing the availability of a brain chemical that helps to regulate mood (serotonin).

serotonin (ser-o-TOE-nin). A brain chemical (neurotransmitter) that helps to regulate your mood. A lack of it may lead to depression.

somatosensory cortex. A part of the brain responsible for processing stimulation coming from the skin, body wall, muscles, bones, tendons and joints. It plays a part in determining pain intensity.

spinal nerve block. A procedure that's used to relieve pain affecting a broad area, such as the abdomen or the legs. A local anesthetic is injected in or near the spinal column, preventing pain messages traveling along that nerve pathway from reaching the brain.

stellate ganglion block. A procedure designed to relieve pain caused by overactivity of the sympathetic nervous system in the upper extremities, the head or the neck. A local anesthetic is injected into the front of the neck to block sympathetic nerves without blocking sensory pathways.

substance P. A protein substance that stimulates nerve endings at an injury site and within the spinal cord, increasing pain messages.

sympathetic block. An injection of an anesthetic to relieve pain resulting from abnormal activity of the sympathetic nervous system. The sympathetic nerves control circulation and perspiration and are part of your autonomic nervous system.

syndrome. A collection of symptoms that characterize a specific disease or condition.

thalamus. A portion of the brain that relays impulses from the sensory nerves. Sensory nerves enable people to feel objects that they touch, and they allow people to feel pain.

tolerance. The point at which a person adapts to a specific substance, so larger amounts of the prescribed medication or a new medication is needed to achieve the same results.

topical agents. Medications that are applied to the skin rather than ingested or injected. They can come in the form of a cream or a gel. Also called ointments.

transdermal. Entering via the skin, such as a medicated cream being absorbed through the skin.

tricyclic antidepressants. A group of drugs used to relieve symptoms of depression. These drugs may also help relieve pain.

trigger point. Places on the body where muscles and adjacent fibrous tissue (fascia) are sensitive to touch. These areas are generally in the upper and lower back muscles, but they may occur elsewhere.

withdrawal. The physical or psychological state experienced when certain substances or medications are discontinued rapidly.

© 2002 Mayo Foundation for Medical Education and Research. All rights reserved. Reprinted with permission from Mayo Clinic on Chronic Pain. For more information, visit www.healthe-store.com