ABSTRACT
Simplistically, nociceptive pathways can be considered as a three neuron-chain, with the first order neuron originating in the periphery and projecting to the spinal cord, the second order neuron ascending the spinal cord, and the third order neuron projecting into the cerebral cortex and other supraspinal structures. On a more complex level, the pathway involves a network of branches and communications with other sensory neurons and descending inhibitory neurons from the midbrain which modulate afferent transmission of painful stimuli. The first process of pain recognition involves encoding mechanical, chemical, or thermal energy into electrical impulses by specialized nerve endings termed nociceptors. Nociception is the transduction, conduction, and central nervous system processing of signals generated by the stimulation of nociceptors. Transduction is the translation of physical energy into electrical activity at the peripheral nociceptor. Transmission is the propagation of nerve impulses through the nervous system. Modulation occurs through the endogenous descending analgesic systems, which modify nociceptive transmission.
