Pain is a subjective sensation that has no objective correlates.
Pain has many forms, and the perception of pain is affected by many factors including actual circumstances expectation, stress, and the emotional state of the person.
Many forms of pain are best described as suffering.
Pain may be divided into two large groups: pain that is caused by direct stimulation (physical or chemical) of specific receptors (nociceptors) and pain that is not caused by stimulation of nociceptors. There is also a third kind of pain in which activation of neural plasticity plays an important role.
Stimulation of nociceptors that are located in the skin, the cornea, tooth pulp, muscles, joints, peripheral nerves, the respiratory system, and viscera causes acute pain that has both a fast and a slow component.
Pain can also be caused by trauma or inflammatory processes generated in nerves or in the nervous system and not from activation of specific pain receptors.
Expression of neural plasticity can create pain (central neuropathic pain) that is caused by neural activity in the brain without peripheral input.
Transmission of pain in the dorsal horn of the spinal cord (and the trigeminal nucleus) can be modulated by input from skin receptors (Aβ fibers) and descending activity from supraspinal sources.
The sympathetic nervous system can modulate the sensitivity of nociceptors and the transmission of pain signals in the spinal cord and the trigeminal nucleus.
Activation of neural plasticity can also cause change in processing of nociceptor-elicited pain signals causing hyperpathia (exaggerated and prolonged response to painful stimuli) and allodynia (painful sensation from light touch of the skin).
The vagus nerve is involved in some forms of pain, and electrical stimulation may reduce pain.
KeywordsSomatic pain Visceral pain Neuropathic pain Central neuropathic pain Neural plasticity
Central nervous system
Dorsolateral pontomesencephalic tegmentum
International Association for the Study of Pain
Nucleus of the solitary tract
Rostral ventromedial medulla
Primary somatosensory cortex
Ventral posterior inferior (thalamus)
Ventral posterior lateral (thalamus)
Ventral posterior medial (thalamus)
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