pain الدفعة التانية

Definition
Pain is an unpleasant feeling that is conveyed to the brain by sensory neurons. The discomfort signals actual or potential injury to the body. However, pain is more than a sensation, or the physical awareness of pain; it also includes perception, the subjective interpretation of the discomfort. Perception gives information on the pain's location, intensity, and something about its nature. The various conscious and unconscious responses to both sensation and perception, including the emotional response, add further definition to the overall concept of pain.

Description
Pain arises from any number of situations. 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 in the absence of a recognizable trigger.Acute pain
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 (stimulus) is removed.
To understand acute pain, it is necessary to understand the nerves that support it. Nerve cells, or neurons, perform many functions in the body. Although their general purpose, providing an interface between the brain and the body, remains constant, their capabilities vary widely. Certain types of neurons are capable of transmitting a pain signal to the brain.
As a group, these pain-sensing neurons are called nociceptors, and virtually every surface and organ of the body is wired with them. The central part of these cells is located in the spine, and they send threadlike projections to every part of the body. Nociceptors are classified according to the stimulus that prompts them to transmit a pain signal. Thermoreceptive nociceptors are stimulated by temperatures that are potentially tissue damaging. Mechanoreceptive nociceptors respond to a pressure stimulus that may cause injury. Polymodal nociceptors are the most sensitive and can respond to temperature and pressure. Polymodal nociceptors also respond to chemicals released by the cells in the area from which the pain originates.
Nerve cell endings, or receptors, are at the front end of pain sensation. A stimulus at this part of the nociceptor unleashes a cascade of neurotransmitters (chemicals that transmit information within the nervous system) in the spine. Each neurotransmitter has a purpose. For example, substance P relays the pain message to nerves leading to the spinal cord and brain. These neurotransmitters may also stimulate nerves leading back to the site of the injury. This response prompts cells in the injured area to release chemicals that not only trigger an immune response, but also influence the intensity and duration of the pain.Chronic and abnormal pain
Chronic pain refers to pain that persists after an injury heals, cancer pain, pain related to a persistent or degenerative disease, and long-term pain from an unidentifiable cause. It is estimated that one in three people in the United States will experience chronic pain at some point in their lives. Of these people, approximately 50 million are either partially or completely disabled.
Chronic pain may be caused by the body's response to acute pain. In the presence of continued stimulation of nociceptors, changes occur within the nervous system. Changes at the molecular level are dramatic and may include alterations in genetic transcription of neurotransmitters and receptors. These changes may also occur in the absence of an identifiable cause; one of the frustrating aspects of chronic pain is that the stimulus may be unknown. For example, the stimulus cannot be identified in as many as 85% of individuals suffering lower back pain.
Other types of abnormal pain include allodynia, hyperalgesia, and phantom limb pain. These types of pain often arise from some damage to the nervous system (neuropathic). Allodynia refers to a feeling of pain in response to a normally harmless stimulus. For example, some individuals who have suffered nerve damage as a result of viral infection experience unbearable pain from just the light weight of their clothing. Hyperalgesia is somewhat related to allodynia in that the response to a painful stimulus is extreme. In this case, a mild pain stimulus, such as a pin prick, causes a maximum pain response. Phantom limb pain occurs after a limb is amputated; although an individual may be missing the limb, the nervous system continues to perceive pain originating from the area.How the body feels pain

A person begins to feel pain when nociceptors in the skin, muscles, or internal organs detect pressure, inflammation, a toxic substance, or another harmful stimulus. The pain message travels along peripheral nerve fibers in the form of electrical impulses until it reaches the spinal cord. At this point, the pain message is filtered by specialized nerve cells that act as gatekeepers. Depending on the cause and severity of the pain, the nerve cells in the spinal cord may either activate motor nerves, which govern the ability to move away from the painful stimulus; block out the painful message; or release chemicals that increase or lower the strength of the original pain message on its way to the brain. The part of the spinal cord that receives and "processes" the pain messages from the peripheral nerves is known as the dorsal horn.
After the pain message reaches the brain, it is relayed to an egg-shaped central structure called the thalamus, which transmits the information to three specialized areas within the brain: the somatosensory cortex, which interprets physical sensations; the limbic system, which forms a border around the brain stem and governs emotional responses to physical stimuli; and the frontal cortex, which handles thinking. The activation of these three regions explains why human perception of pain is a complex combination of sensation, emotional arousal, and conscious thought.
In addition to receiving and interpreting pain signals, the brain responds to pain by activating parts of the nervous system that send additional blood to the injured part of the body or that release natural pain-relieving chemicals, including serotonin, endorphins, and enkephalins.

Factors that affect pain perception
LOCATION AND SEVERITY OF PAIN Pain varies in intensity and quality. It may be mild, moderate, or severe. In terms of quality, it may vary from a dull ache to sharp, piercing, burning, pulsating, tingling, or throbbing sensations; for example, the pain from jabbing one's finger on a needle feels different from the pain of touching a hot iron, even though both injuries involve the same part of the body. If the pain is severe, the nerve cells in the dorsal horn transmit the pain message rapidly; if the pain is relatively mild, the pain signals are transmitted along a different set of nerve fibers at a slower rate.
The location of the pain often affects a person's emotional and cognitive response, in that pain related to the head or other vital organs is usually more disturbing than pain of equal severity in a toe or finger.

• timing (time of day; continuous or intermittent)
  
• location in the body
  
• quality (piercing, burning, aching, etc.)
  
• factors that relieve the pain or make it worse (temperature or humidity; body position or level of activity; foods or medications; emotional stress, etc.)
  
• its relationship to mood swings, anxiety, or depression
  

The doctor will then take the patient's medical history, including past illnesses, injuries, and operations as well as a family history. In some cases, the doctor may need to ask about experiences of emotional, physical, or sexual abuse. The doctor will also make a list of all the medications that the patient takes on a regular basis. Other information that may help the doctor evaluate the pain includes the patient's occupation and level of functioning at work; marriage and family relationships; social contacts and hobbies; and whether the patient is involved in a lawsuit for injury or seeking workers' compensation. This information may be helpful in understanding what the patient means by "pain" as well as what may have caused the pain, particularly because many people find it easier to discuss physical pain than anxiety, anger, depression, or sexual problems.
Some doctors may give the patient a brief written pain questionnaire to fill out in the office. There are a number of different instruments of this type, some of which are designed to measure pain associated with cancer, arthritis, HIV infection, or other specific diseases. Most of these rating questionnaires ask the patient to mark their pain level on a scale from zero to 10 or zero to 100 with zero representing "no pain" and the higher number representing "worst pain imaginable" or "unbearable pain." The patient then answers a few multiple-choice questions regarding the impact of the pain on his or her employment, relationships, and overall quality of life.

Physical examination
A thorough physical examination is essential in identifying the specific disorders or injuries that are causing the pain. The most important part of pain management is removing the underlying cause(s) whenever possible, even when there is a psychological component to the pain.

Special tests
Although there are no laboratory tests or imaging studies that can demonstrate the existence of pain as such or measure its intensity directly, the doctor may order special tests to help determine the cause(s) of the pain. These studies may include one or more of the following:

• Treatment
  

Treatment of either acute or chronic pain may involve several different approaches to therapy.

Medications
Medications to relieve pain are known as analgesics. Aspirin and other nonsteroidal anti-inflammatory drugs, or NSAIDs, are commonly used analgesics. NSAIDs include such medications as ibuprofen (Motrin, Advil), ketoprofen (Orudis), diclofenac (Voltaren, Cataflam), naproxen (Aleve, Naprosyn), and nabumetone (Relafen). These medications are effective in treating mild or moderate pain. A newer group of NSAIDs, which are sometimes called "superaspirins" because they can be given in higher doses than aspirin without causing stomach upset or bleeding, are known as COX-2 inhibitors. The COX-2 inhibitors include celecoxib (Celebrex), rofecoxib (Vioxx), and valdecoxib (Bextra).
For more severe pain, the doctor may prescribe an NSAID combined with an opioid, usually codeine or hydrocodone. Opioids, which are also called narcotics, are strong painkillers derived either from the opium poppy Papaver somniferum or from synthetic compounds that have similar effects. Opioids include such drugs as codeine, fentanyl (Duragesic), hydromorphone (Dilaudid), meperidine (Demerol), morphine, oxycodone (OxyContin), and propoxyphene (Darvon). They are defined as Schedule II controlled substances by the Controlled Substances Act of 1970, which means that they have a high potential for abuse in addition to legitimate medical uses. A doctor must have a special license in order to prescribe opioids. In addition to the risk of abuse, opioids cause potentially serious side effects in some patients, including cognitive impairment (more common in the elderly), disorientation, constipation, nausea, heavy sweating, and skin rashes.
If the patient's pain is severe and persistent, the doctor will give separate dosages of opioids and NSAIDs in order to minimize the risk of side effects from high doses of aspirin or acetaminophen. In addition, the doctor may prescribe opioids that are stronger than codeine—usually morphine, fentanyl, or levorphanol.
The "WHO Ladder" for the treatment of cancer pain is based on the three levels of analgesic medication. Patients with mild pain from cancer are given nonopioid medications with or without an adjuvant (helping) medication. For example, the doctor may prescribe a tranquilizer to relieve the patient's anxiety as well as the pain medication. Patients on the second "step" of the ladder are given a milder opioid and a nonopioid analgesic with or without an adjuvant drug. Patients with severe cancer pain are given stronger opioids at higher dosage levels with or without an adjuvant drug.
Acute pain following surgery is usually managed with opioid medications, most commonly morphine sulfate (Astromorph, Duramorph) or meperidine (Demerol). In some cases, NSAIDs that are available in injectable form (such as ketorolac) are also used. Patient-controlled analgesia, or PCA, allows patients to control the timing and amount of pain medication they receive. Although there are oral forms of PCA, the most common form of administration involves an infusion pump that delivers a small dose of medication through an intravenous line when the patient pushes a button. The PCA pump is pre-programmed to deliver no more than an hourly maximum amount of the drug.
Some types of chronic pain are treated by injections in specific areas of the body rather than by drugs administered by mouth or intravenously. There are three basic categories of injections for pain management:

• Joint injections. Joint injections are given to treat chronic pain associated with arthritis. The most common medications used are corticosteroids, which suppress inflammation in arthritic joints, and hyaluronic acid, which is a compound found in the joint fluid of healthy joints.
  
• Soft tissue injections. These are given to reduce pain in trigger points (areas of muscle that are hypersensitive to touch) and bursae, which are small pouches or sacs containing tissue fluid that cushions pressure points between tendons and bones. When a bursa becomes inflamed—a condition called bursitis—the person experiences pain in the nearby joint. Corticosteroids are the drugs most often used in soft tissue injections, although the doctor may also inject an anesthetic into a trigger point in order to relax the muscle.
  
• Nerve blocks. Nerve blocks are injections of anesthetic around the fibers of a nerve to prevent pain messages relayed along the nerve from reaching the brain. They may be used to relieve pain in specific parts of the body for a short period; a common example of this type of nerve block is the lidocaine injections given by dentists before drilling or extracting a tooth. Some nerve blocks are injected in or near the spinal column to control pain that affects a larger area of the body; an example is the epidural injection given to women in labor or to patients with sciatica. A third type of nerve block is administered to block the sympathetic nervous system as part of pain management in patients with complex chronic pain syndromes. amaged nerves to control neuropathic pain