Pain is an unpleasant feeling which may be associated with actual or potential tissue damage. Despite causing suffering, pain is a critical component of the body’s defence system. It is part of a rapid warning relay instructing the motor neurons of the central nervous system to minimise detected physical harm. Pain can be classified as acute or chronic.
- Acute pain: short-term pain or pain with an easily identifiable cause. Acute pain is the body’s warning of present damage to tissue or disease. It is often fast and sharp followed by aching pain. Acute pain is centralised in one area before becoming somewhat spread out. This type of pain responds well to medications.
- Chronic pain: pain that has lasted 6 months or longer. This constant or intermittent pain has often outlived its purpose, as it does not help the body to prevent injury. It is often more difficult to treat than acute pain. The experience of physiological pain can be grouped according to the source and related nociceptors (pain detecting neurons):
- Somatic pain originates from ligaments, tendons, bones, blood vessels, and is detected with somatic nociceptors. The scarcity of pain receptors in these areas produces a dull, poorly-localised pain of longer duration than cutaneous pain: examples include sprains.
- Visceral pain originates from body’s viscera, or organs. Visceral nociceptors are located within body organs and internal cavities. Visceral pain is extremely difficult to localise, and several injuries to visceral tissue exhibit “referred” pain, where the sensation is localised to an area completely unrelated to the site of injury.
- Neuropathic pain or neuralgia, can occur as a result of injury or disease to the nerve tissue itself. This can disrupt the ability of the sensory nerves to transmit correct information to the thalamus, and hence the brain interprets painful stimuli even though there is no obvious or known physiologic cause for the pain.