Читать книгу Reflexology: The Definitive Practitioner's Manual: Recommended by the International Therapy Examination Council for Students and Practitoners - Beryl Crane - Страница 26

An essential part of the working of the nervous system is a group of chemicals known as neurotransmitters. There are excitatory and inhibitory neurotransmitters in the parasympathetic and sympathetic nervous systems. Excitatory transmitters stimulate action; inhibitory neurotransmitters inhibit it. When an impulse passes down a parasympathetic nerve, acetylcholine appears at nerve endings and then it transmits the effects of the parasympathetic impulse. This system is involved in maintaining normal levels of activity. The same happens with the sympathetic nervous system, which works in conjunction with the former. At the nerve endings the chemical noradrenaline (a hormone closely related to adrenaline) is released as a neurotransmitter by sympathetic nerve endings. Among its many actions are constriction of swollen blood vessels, often leading to an increase in blood pressure. Increasing the blood flow through the coronary arteries and slowing of the heart rate increases the rate and depth of breathing and complete relaxation to the smooth muscle of the intestinal walls.

Even today there is still a lot to learn about their different types and what each individual chemical does. Most nervous disorders are linked to the homeostatic imbalance of these substances. Many of the 50 or so neurotransmitters of the nervous system are thought to be neuromodulators; the largest group is known as the neuropeptides, which are thought to include both excitatory and inhibitory factors. One particular neuropeptide found within the sensory nerves, the spinal cord pathways and certain portions of the brain is known as substance P; it is thought to stimulate the perception of pain. It is also thought to be involved in the spinal cord pathways and certain portions of the brain that are associated in pain transmission. Conversely, it is known that substances called encephalins have their powerful analgesic effects on the body by inhibiting pain impulses; the endorphins also possess strong analgesic and behavioural effects. The analgesic compounds are concentrated in the thalamus, the hypothalamus and the pituitary gland. This correlates with what Fitzgerald said in those early years, that stimulation to the pituitary gland reflex point is thought to block or suppress pain. He also elaborated: ‘these functions were carried out by the pituitary body and multiple nerve pathways from it’. It may be that stimulation of the pituitary reflex causes the pituitary body to release adrenocorticotrophic hormone (ACTH), which is released in response to stress, and which controls the release of corticosteroid hormone from the adrenal cortex, a powerful anti-inflammatory substance that helps many of the disorders of the body.