Central Mechanisms of transfer and sensitization of pain

Central Mechanisms of transfer and sensitization of pain »  Health Generation IndiaPain is transferred through various pathways in the body. Of the several pathways the first and the most important is the Spinal cord, which also raises the sensation of referred pain.The nociceptors are the ends of the nerves which feel the pain causing stimulus and in turn generate an electrical impulse which is carried forward by the nerve of the nociceptors towards the central nervous system which is made up of brain and the spinal cord. The dorsal (back) side of the spinal cord is the entry point of the nerve carrying the electrical impulse ends here in the gray mater of the spinal cord. The terminals of the primary afferent axons of the pain impulse carrying  nerve contact the spinal cord neurons through which the pain is transmitted to specific sites in the brain which understand the pain stimulus.Upon stimulus of the nociceptors by pain stimulus, chemicals known as neurotransmitters are released from their end terminals which excite the spinal cord neurons. Some of the important neurotransmitters are glutamate which aids in rapidly exciting the neurons of the dorsal horn of the spinal cord. Along with neurotransmitter chemicals which are released at the nerve endings, peptides, substance P and calcitonin are also released. These substances also produce excitation of the dorsal horns of the neurons of the spinal cord which produce a slower and longer lasting excitation. Thus every axon contacts many spinal nerves and because of this, each spinal neuron receives several convergent inputs.This hypothesis of convergence of signals to the spinal cord and vice versa shows us that the visceral afferent nociceptors converge on one similar point of neurons which project the pain. Because of this the projection of pain happens in those parts of the body too, where the nerves from the neurons on which the pain is projected; are present.The importance of the inputs from the sensory system to the pain transmitting single spinal neuron is high because of the fundamental logic of referred pain. All spinal neurons receive dual signals of a single type and area of pain. One is from the viscera and the deep lying musculoskeletal structures and and secondly from the overlying skin.Thus, the pattern of convergence are determined by the spinal segment of the dorsal root ganglion which gives nerve supply to the afferent entry of the nerves to the specific structure. and because of this convergence of the supply from the spinal neurons which are generally activated by the inputs from the skin to the nerves, the sensation of the pain from the deep structures are many a times mislocalized to a structure which is in the same supply of either the afferent supply or the efferent supply and is roughly co-extensive to the same spinal segment.