At least four physiological mechanisms have been proposed to explain pain:
Latter, two involve primarily central nervous system mechanisms.
1 - Sympathetic nerves
Cause pain by releasing substances that sensitize primary afferent nerve endings in the region of pain (Procacci and Zoppi, 1981), or possibly by restricting the flow of blood in the vessels that nourish the sensory nerve fiber itself.
2 - Peripheral branching of primary afferent nociceptors,
A nerve to separate parts of the body causes the brain to misinterpret messages originating from nerve endings in one part of the body as coming from the nerve branch supplying the other part of the body.
3 - Convergence-projection
Is a hypothesis, defines as single nerve cell in the spinal cord receives nociceptive input both from the internal organs and from nociceptors coming from the skin and muscles.
The brain has no way of distinguishing whether the excitation arose from the somatic structures or from the visceral organs. It is proposed that the brain interprets any such messages as coming from skin and muscle nerves rather than from an internal organ.
The convergence of visceral and somatic sensory inputs onto pain projection neurons in the spinal cord has been demonstrated (Milne et al., 1981; Foreman et al., 1979).
4 - Convergence-facilitation
Is also hypothesis, defines as the background (resting) activity of pain projection neurons in the spinal cord that receive input from one somatic region is amplified (facilitated) in the spinal cord by activity arising in nociceptors originating in another region of the body.
In this model, nociceptors producing the background activity originate in the region of perceived pain and tenderness; the nerve activity producing the facilitation originates elsewhere, for example, at a myofascial trigger point.
This convergence-facilitation mechanism is of clinical interest because one would expect that blocking sensory input in the reference zone with cold or a local anesthetic should provide temporary pain relief. One would not expect such relief according to the convergence-projection theory.
Clinical experiments have demonstrated both kinds of responses.
Mechanism of Pain - Post RN BSN Nursing ACN – I Course | POST RN BSN Nursing Resources
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