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Neuroscience & Karma
but the disordered activity of other sense-organs. To a large extent this is what in fact has been found by recent studies of the physiology of pain. E. Internal Pains
Though there is no known cortical centre for pain, it must, in some way, become connected with the cortical analysers, otherwise we should never be able to learn to avoid external events that are likely to be painful. What is the physiological basis of pain ? Pain, probably, results from disordered nerve discharges, especially if they involve impulses in certain of the thin nerve-fibres called free nerve endings. These are the simplest of all sensory nerve-terminals and they occur not only in the skin but also in some internal organs, especially in the walls of arteries and in the heart. This raises the question of how we feel intemal pains. The answer is paradoxically that to a large extent we don't. For instance, cutting or pricking the stomach or intestine does not give pain. What does burt is dragging or pressing them. The pains that we feel as headaches are probably in the blood vessels of the brain. F. Regulation of Pais — Reticular Formation
If pain is not felt in the cortex, is there any other part of the brain in which it can be said to be located ? From the spinal cord, three main pathways lead upwards to the brain. One of these three pathways consists not of long straight-through fibres but of a series of little neurons with axons that are small and short and therefore called 'reticular' or 'net-like'. This reticular system is a very complicated set of cells. These can send signals to many different areas. The reticular system is thus not only central in position but also in the fact that it communicates information very widely. It is also central in its functions in the sense that it regulates the whole state of activity of the brain, for example, in sleeping and waking. The nerve-cells of the reticular formation can prod
uce the substance enkephalin injection of which kills pain in the same way as does morphia. Enkephalin is probably the neurotransmitter involved in synaptic transmission in these reticular brain centres. Morphine thus acts
1. See chapter 7.
