Functions of the nociceptive primary neurons.

The functions of nociceptive primary neurons are reviewed in brief, with special reference to the polymodal receptor. The polymodal receptor is considered to be a primitive sensory receptor that is not well differentiated and that plays important roles in signaling pain especially from tissues in pathological states, and in causing reflex modulations of a wide variety of bodily functions. This sensory receptor is characterized by the existence of neuropeptides in its neuron. The wide distribution of the central axon branchings of this neuron and the long-lasting effects of the neuropeptides released from the axon terminals provide an "analogue-like" action of the nervous system, which had hitherto been considered to be "digital-like," point-to-point connections in the central neuron network. Neuropeptides released from the peripheral endings of this neuron, on the other hand, play important roles in local regulation of such functions as inflammation, visceral tract motility, trophic effects, immune system functioning and so on. The functions of nociceptive primary neurons are, therefore, not limited to sensory function but should be understood as a component related to the regulation of fundamental functions of the entire organism.