Pain provides the body with a protective mechanism, alerting it to potential or actual damage to the body’s tissues. In the example of a bee sting, the pain receptors in the skin detect tissue damage from the bee sting. Then, the peripheral nerves send a pain signal to the brain. The brain analyzes the pain signal. In turn, the brain delivers a message back to the muscles of the arm to react. Pain and how you sense it. Scientists are gradually unravelling the processes within the body that lead to the unpleasant sensation of pain. Here’s a simple explanation of what happens when you feel one type of pain.
You prick your finger on something sharp. This causes tissue damage, which is registered by microscopic pain receptors (nociceptors) in your skin. Each pain receptor forms one end of a nerve cell (neuron). It is connected to the other end in the spinal cord by a long nerve fibre or axon. When the pain receptor is activated, it sends an electrical signal up the nerve fibre.
The nerve fibre is bundled with many others to form a peripheral nerve. The electrical signal passes up the neurone within the peripheral nerve to reach the spinal cord in the neck.
Within an area of the spinal cord called the dorsal horn, the electrical signals are transmitted from one neurone to another across junctions (synapses) by means of chemical messengers (neurotransmitters). Signals are then passed up the spinal cord to the brain.
In the brain, the signals pass to the thalamus. This is a sorting station that relays the signals on to different parts of the brain. Signals are sent to the somatosensory cortex (responsible for physical sensation), the frontal cortex (in charge of thinking), and the limbic system (linked to emotions).
The end result is that you feel a sensation of pain in your finger, think ‘Ouch! What was that?’ or something similar, and react emotionally to the pain; e.g. you feel annoyed or irritated.
However, you will probably have reacted involuntarily even before you were consciously aware of the injury. In sudden strong pain like that generated by pricking your finger, a reflex response occurs within the spinal cord. Motor neurones are activated and the muscles of your arm contract, moving your hand away from the sharp object. This occurs in a fraction of a second — before the signal has been relayed on to the brain — so you will have pulled your arm away before even becoming conscious of the pain.
Pain is a distressing feeling often caused by intense or damaging stimuli. Because it is a complex, subjective phenomenon, defining pain has been a challenge. The International Association for the Study of Pain's widely used definition states: "Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." In medical diagnosis, pain is regarded as a symptom of an underlying condition.
Pain motivates the individual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Most pain resolves once the noxious stimulus is removed and the body has healed, but it may persist despite removal of the stimulus and apparent healing of the body. Sometimes pain arises in the absence of any detectable stimulus, damage or disease.
Pain is the most common reason for physician consultation in most developed countries. It is a major symptom in many medical conditions, and can interfere with a person's quality of life and general functioning. Simple pain medications are useful in 20% to 70% of cases. Psychological factors such as social support, hypnotic suggestion, excitement, or distraction can significantly affect pain's intensity or unpleasantness. In some arguments put forth in physician-assisted suicide or euthanasia debates, pain has been used as an argument to permit people who are terminally ill to end their lives.
Classification: In 1994, responding to the need for a more useful system for describing chronic pain, the International Association for the Study of Pain (IASP) classified pain according to specific characteristics:
region of the body involved (e.g. abdomen, lower limbs),
system whose dysfunction may be causing the pain (e.g., nervous, gastrointestinal),
duration and pattern of occurrence,
intensity and time since onset, and
cause
However, this system has been criticized by Clifford J. Woolf and others as inadequate for guiding research and treatment. Woolf suggests three classes of pain:
nociceptive pain,
inflammatory pain which is associated with tissue damage and the infiltration of immune cells, and
pathological pain which is a disease state caused by damage to the nervous system or by its abnormal function (e.g. fibromyalgia, peripheral neuropathy, tension type headache, etc.).
