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The sympathetic nervous system is described as being antagonistic to the parasympathetic nervous system. The latter stimulates the body to "feed and breed" and to (then) "rest-and-digest". The SNS has a major role in various physiological processes such as blood glucose levels, body temperature, cardiac output, and immune system function.
The two parts are, however, closely connected. The sympathetic component of the cardiac plexus comes from cardiac nerves, which originate from the sympathetic trunk. The parasympathetic component of the cardiac plexus originates from the cardiac branches of the vagus nerve.
The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. [1] [2] The autonomic nervous system is responsible for regulating the body's unconscious actions.
Polyvagal theory views the parasympathetic nervous system as being split into two distinct branches: a "ventral vagal system" which supports social engagement, and a "dorsal vagal system" which supports immobilisation behaviours, both "rest and digest" and defensive immobilisation or "shutdown". [14]
Autonomic nervous system, showing splanchnic nerves in middle, and the vagus nerve as "X" in blue. The heart and organs below in list to right are regarded as viscera. The autonomic nervous system has been classically divided into the sympathetic nervous system and parasympathetic nervous system only (i.e., exclusively motor).
postganglionic sympathetic neurons (e.g. blood vessels) enhance vasoconstrictor action of noradrenaline; noradrenaline release inhibitor; VIP: peptide: parasympathetic nerves to salivary glands; NANC innervation to smooth muscle of airways; parasympathetic ganglia in sphincters, gallbladder and small intestine; vasodilation; acetylcholine ...
Paroxysmal sympathetic hyperactivity (PSH) is a syndrome that causes episodes of increased activity of the sympathetic nervous system. Hyperactivity of the sympathetic nervous system can manifest as increased heart rate, increased respiration, increased blood pressure, diaphoresis , and hyperthermia . [ 1 ]
Parasympathetic innervation of the heart is partially controlled by the vagus nerve and is shared by the thoracic ganglia. Vagal and spinal ganglionic nerves mediate the lowering of the heart rate. The right vagus branch innervates the sinoatrial node. In healthy people, parasympathetic tone from these sources is well-matched to sympathetic tone.