In contrast, the parasympathetic nervous system is more active during "rest-and-digest" periods, promoting homeostatic processes including immune system regulation, organ repair and maintenance, and the digestion of food. The sympathetic system activates the "fight-or-flight" response by enabling the body to rise to emergency demands encountered in flight, combat, pursuit, and pain. In general, the sympathetic and parasympathetic branches of the autonomic nervous system mediate opposite effects on internal organs, maintaining a dynamic balance of function. See also: Brain Cranial nerve Ganglion Parasympathetic nervous system Spinal cord Sympathetic nervous system The enteric nervous system is sometimes considered a branch of the autonomic nervous system but can also be understood as a distinct nervous system dedicated to digestion. Within the brainstem, the hypothalamus is an important autonomic nervous system control center. Groups of nerve cell bodies, called ganglia, that are located in various parts of the body outside of the CNS (brain and spinal cord) serve as the localized control centers for the autonomic nervous system. The parasympathetic system is defined by the autonomic fibers that either exit the brainstem via the cranial nerves or exit the sacral segments of the spinal cord. The sympathetic system is defined by the autonomic fibers that exit thoracic and lumbar segments of the spinal cord. The autonomic nervous system is traditionally partitioned into the sympathetic system and the parasympathetic system, based on the region of the brain or spinal cord in which the autonomic nerves have their origin (see illustration). See also: Cardiovascular system Central nervous system Digestion Gland Metabolism Muscle Muscular system Nervous system (vertebrate) Thermoregulation The system regulates visceral processes involuntarily including those associated with cardiovascular activity, digestion, metabolism, and thermoregulation (bodily temperature). As a distinct system, the autonomic nervous system functions primarily at a subconscious level to innervate smooth muscle, cardiac muscle, and glands. The PNS is further divided into the somatic nervous system and the autonomic nervous system. The autonomic nervous system is a component of the peripheral nervous system, or PNS, which, along with the central nervous system, or CNS, represents the two main divisions of the nervous system. The part of the nervous system that controls visceral (internal organ) functions of the body. The autonomic nervous system is traditionally partitioned into the sympathetic system and the parasympathetic system, based on the region of the brain or spinal cord in which the autonomic nerves have their origin. A component of the peripheral nervous system, the autonomic nervous system controls visceral functions of the body, including those associated with cardiovascular activity, digestion, metabolism, and thermoregulation.įunctioning primarily at a subconscious level, the autonomic nervous system innervates smooth muscle, cardiac muscle, and glands.
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