Pain experienced at a place distant from the origin.
The area of the pain is supplied by the same spinal segment as the actual pain location.
Dermatomal rule: example: the heart and the arm have the same segmental origin.
Convergence theory: the number of peripheral pain impulses exceed the number of lateral spinothalamic fibers. This means that both somatic and visceral afferent convergence upon the same spinothalamic tract neurons, the individual gets the feeling that the pain originates from the somatic area.
Facilitation theory: visceral and somatic pain afferents connect with adjoining spinothalamic neurons and there may be some overlap of the neurons, visceral afferents have collaterals connecting to the spinothalamic neurons receiving somatic pain afferents. This can cause impulses to travel up the somatic spinothalamic path and causes the sensation of pain in the skin.
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