The sensation of pain is triggered by the nervous system, usually in response to an injury or illness. The pain sensation hurts, causing discomfort, distress and perhaps agony, depending on its severity.
Pain can be felt in a variety of forms; it can be dull and constant, or short and sharp. Pain may be experienced in one area of the body, such as the back or abdomen, or it can be felt all over, like when your muscles ache during the flu. Pain can be very useful for helping to diagnose a problem. Without pain, trauma may occur without someone even realising it. Alternatively, a medical condition may remain hidden without the associated pain to help identify it. Once the instigating injury or illness has been treated, the pain will usually subside. In these instances, the pain can be classified as being acute.
However, sometimes pain can continue for weeks, months or even years. This is known as chronic pain. Chronic pain can be the result of a long-term condition, such as arthritis or cancer. In other cases, the cause can remain unknown. The most common types of pain include:
- Back pain – most cases of back pain aren't caused by anything too serious. In most cases, back pain is caused by minor sprains or injuries. These injuries can be incurred by bending or twisting awkwardly, lifting heavy objects, overstretching, slouching or hunching, and overusing muscles. Some cases of back pain can be the result of a more serious medical condition, such as sciatica, arthritis or a slipped or prolapsed disc. On rare occasions, back pain can be the sign of something more serious, such as a spinal fracture or cancer.
- Headache – headaches can be divided into two categories; primary and secondary. Primary headaches are, in most cases, caused by a dysfunction or an over activity in the pain- sensitive structures in the head. Examples of primary headaches include; migraine, tension headache and cluster headaches. Secondary headaches are a symptom of another condition that stimulates the pain-sensitive nerves in the head. An example of a secondary headache is an alcohol-induced hangover.
- Joint pain – is the result of damage to the joints, either through disease or injury. A variety of conditions can lead to joint pain, including; osteoarthritis, rheumatoid arthritis, gout, bursitis, sprains, strains and other injuries.
- Period pain – is the result of muscular contractions of the womb. These contractions constantly pass through the womb, however, they are usually so mild that they pass unnoticed. During menstruation, these contractions can become more vigorous. This is to encourage the wombs lining to shed away as part of the monthly cycle. These more intense contractions can compress the blood vessels in the womb, temporarily cutting off the blood supply. Without blood, the tissues in the womb become deprived of oxygen, which causes them to release chemicals that trigger pain in the body.
- Muscular pain – also known as myalgia, is often the result of too much stress, tension, or physical activity. However, in some cases, myalgia can be related to a medical condition, such as; viral or bacterial infections, fibromyalgia, thyroid problems, hypokalemia (low potassium), autoimmune disorders, and certain medicines, such as ACE inhibitors.
- Dental pain – toothache is usually the result of the tooths innermost layer becoming inflamed. This layer is known as the dental pulp and is made up of sensitive nerves and blood vessels. The dental pulp can become inflamed as a result of; tooth decay, receding gums, a cracked tooth, loose or broken fillings, and a periapical abscess. Other conditions that can cause dental pain, without the dental pulp being affected, include; sore and swollen gums, sinusitis, ulcers, periodontal abscess, and injury to the temporomandibular joint, which connects the jaw to the skull. Babies can always experience dental pain when their teeth begin to develop. This is called teething.
Pain can be further classified as being; nociceptive, non-nociceptive, somatic, neuropathic, sympathetic, visceral, and referred.
Nociceptive pain occurs when specific pain receptors are stimulated. These receptors sense vibrations, temperature, inflammation, stretching and the chemicals released by damaged cells.
Non-nociceptive pain isn't caused by specific pain receptors. Instead, it is a response to a nerve(s) becoming injured or unstable, causing its signalling system to become confused. The brain (central nervous system) interprets these abnormal signals as pain.
Somatic pain is a type of nociceptive pain that is experienced on the skin, or in the muscles, joints, ligaments and bones. Somatic pain tends to be sharp and localised at the cause.
Neuropathic pain is a type of non-nociceptive pain. It occurs inside the nervous system itself and is often referred to as a trapped or pinched nerve. This type of pain originates from the peripheral or central nervous system. Causes of neuropathic pain include; nerve degeneration, nerve inflammation, pressure on the nerves or nerve infection.
Sympathetic pain (non-nociceptive) occurs in the sympathetic nervous system. This system controls blood flow, perspiration and the speed at which the peripheral nervous system works. Sympathetic pain usually occurs after bone fractures or soft tissue damage. As with neuropathic pain, sympathetic pain is the result of a nerve becoming injured or unstable, causing it to send abnormal signals to the brain, which then interprets them as pain.
Visceral pain is a type of nociceptive pain. It is usually experienced in the internal organs and main body cavities, such as the thorax, abdomen and pelvis. Visceral pain is harder to localise compared with somatic pain. The sensation will usually resemble a deep ache or cramping.
Visceral pain commonly refers to some type of back pain: Upper back = thoracic, mid-back = abdominal, and lower back = pelvic.
Referred pain is sometimes called reflective pain. This form of pain is experienced next to, or at a distance from the origin of the injury. For example, a person suffering a heart attack may feel pain around the shoulders, back or neck, instead of the chest. The origin and causes of referred pain are still unknown.