交感神经和副交感神经（Sympathetic and parasympathetic nerves）Sympathetic nervous system1., the sympathetic nervous system of the circulatory organ can stimulate the heart activity, accelerate the heartbeat frequency and accelerate the heartbeat strength. To the blood vessel, it mainly promotes the contraction of the arteriole, thus increasing the peripheral resistance of the blood flow and increasing the arterial blood pressure. But the actual situation is quite complex and must be treated differently. Most human organs only accept vascular sympathetic innervation of sympathetic nerve on the abdominal viscera, blood vessels and skin blood vessels have significant effect on contraction; skeletal muscle blood vessels, both sympathetic vasoconstrictor, and sympathetic vasodilator, on the coronary circulation of the blood vessels, the direct effect of sympathetic nerve is vasoconstriction, but its indirect effect is vasodilatation. The vessels of external genital organs take the action of contraction. The blood vessels of the brain and lungs, although sympathetic, are weak.2. of the digestive organs of sympathetic nerve has inhibitory effect on gastrointestinal motility, which reduce the tension and the frequency of gastrointestinal motility of gastrointestinal smooth muscle, and weaken the creep strength; but when gastrointestinal smooth muscle tension is too low or the activity is very weak, sympathetic nerve activity can also cause the increase. Yes, the salivary glands promote the secretion of sticky saliva.3., the respiratory organs and sweat glands sympathetic nerve can inhibit the smooth muscle of bronchioles, which can dilatebronchioles and help ventilation. The sweat gland receives sympathetic innervation only, sympathetic nerve excitation causes sweat gland secretion.4., the sympathetic nerve of the eyeball smooth the iris radiation muscle and causes the pupil to expand.5. pairs of endocrine glands and adrenal medulla are innervated by sympathetic preganglionic fibers. When the sympathetic nerve is excited, the secretion of epinephrine and norepinephrine increases. Because the effect of the adrenal medulla hormone is largely consistent with the sympathetic nervous system, it is physiologically referred to as the sympathetic adrenal medulla system.6., the function of sympathetic nerve in urogenital organs is to inhibit the activity of detrusor and promote the contraction of internal sphincter, so as to prevent urination. To the genital organs, the sympathetic nerve can promote the contraction of the pregnant uterus, but make the nonpregnant uterus relax. Sympathetic nerve also can promote male seminal vesicle and ejaculation tube smooth muscle contractive, cause ejaculation motion thereby.7., the glucose metabolism and sympathetic nerve can directly act on the liver cells, and promote the decomposition of liver glycogen, thereby increasing blood sugar. But in whole, the effect of ascending blood glucose of sympathetic nerve is mainly realized by the increase of adrenaline secretion.Parasympathetic nervous systemThe main function of parasympathetic nerve is to reduce the pupil, slow heartbeat, skin and internal vascular relaxation, small bronchial contraction, gastrointestinal motility enhanced, sphincter relaxation, saliva secretion increased.The parasympathetic nervous system acts contrary to the sympathetic nervous system, although it is not as consistent as the sympathetic nervous system, but it is also related. Its fibers are not distributed in the limbs, while the sweat glands, vertical rectus, adrenal glands, thyroid, uterus and so on, have parasympathetic nerve distribution.Parasympathetic nervous system can keep the body in a quiet state of physiological balance, and its role in three aspects: first, to promote the activities of the gastrointestinal tract, digestive gland secretion, promote excretion of feces and urine, to maintain the body's energy. Reduce the pupil to reduce the stimulation and promote the production of liver glycogen, so as to save energy. Slow heartbeat, lower blood pressure, reduce the size of the bronchus, to save unnecessary consumption, and assist in reproductive activities, such as the expansion of the genital vessels and the increase of the secretion of sex organs.The difference between parasympathetic and sympathetic nervesThe difference between the sympathetic and parasympathetic nerves are: central position is different, the lower center of sympathetic nerve in the spinal cord to the first thoracic segment third lumbar section of the side angle, the lower center of parasympathetic nerve in the brainstem and spinal cord ofthe sacrum.The location of the surrounding ganglia is different, and the preganglionic fibers in the sympathetic nerve, along with the anterior root of the spinal nerve and the spinal nerve, emerge out of the spinal nerve,Sympathetic trunk ganglia. The part of neurons in the section, the sympathetic postganglionic fibers leave return spinal nerve and spinal nerve distribution with limbs and body wall of blood vessels, sweat and arrectores pilorum. Most preganglionic fibers change neurons in the sympathetic trunk, and the postganglionic fibers no longer join the spinal nerve, forming a nerve plexus around the arteries, with the arteries distributed to the head, neck and chest, and organs and glands of the abdominal cavity. The parasympathetic preganglionic fibers in a self central neurons in parasympathetic ganglia, postganglionic fibers distributed to smooth muscle, myocardium and glands, parasympathetic ganglia are generally in organs or organs near the wall, short postganglionic fiber.The effect of the two on the same organ is different. When the sympathetic nerve is excited, the abdominal visceral and peripheral vessels contract, the heart rate increases; the bronchial smooth muscle expands; the gastrointestinal movement and the stomach secretion are suppressed; the metabolism hyperfunction; the pupil disperses big and so on. Parasympathetic nervous stimulation, cardiac slowing down; bronchial smooth muscle contraction; gastrointestinal movement to strengthen the secretion of digestive juices; such as shrinking the pupil.The general visceral organs have both sympathetic and parasympathetic innervation, and the two nerves are antagonistic to the same organ, but in the whole, the activities of the two nerves are antagonistic, unified and coordinated. The sympathetic activity is relatively wide, relatively limited parasympathetic activity, when the body is in a state of calm, parasympathetic nerve excitement is dominant, is conducive to digestion and absorption of energy and nutrition, is conducive to the protection of the body. When strenuous exercise or adverse environment, sympathetic activities strengthen, mobilize the potential of many organs of the body, improve the ability to adapt to cope with the rapid changes in the environment, and maintain the relative stability of the internal environment.。
