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Autonomic nervous system
(section)
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== Function == The ANS is split into two main divisions: the [[sympathetic nervous system]] (SNS) and [[parasympathetic nervous system]] (PNS). The PNS and SNS serve the same organs, but one system will activate a bodily function while the other will inhibit it.<ref name="NBK539845" /> This opposition is operated by two main chemical messengers: [[norepinephrine]], which activates (excitatory) and [[acetylcholine]], which inhibits (inhibitory).<ref name="McCorry2007" /> The two divisions complement each other to regulate the body’s responses.<ref name="NBK539845" /> Functions regulated by the ANS include: * [[Blood pressure]] * [[Body temperature]] * [[Gastrointestinal system|Digestion]] and [[hunger]] * [[Emotional response]]s * [[Heart rate]] * [[Metabolism]] * Production of [[sweating episode|sweat]], [[dry mouth|saliva]] * [[Respiratory rate]] * [[Sexual response]] * [[Urination]]<ref name="McCorry2007" /><ref name="merck" /> === Sympathetic nervous system === The [[sympathetic nervous system]] (SNS) regulates what is referred to as the “fight-or-flight” response, which prepares the body against a perceived stress or threat. Stimulation of the SNS activates an internal alarm response. This causes an increase in: * Heart rate (more blood pumped throughout the body) * [[Muscle strength]] * Width of airways (maximizing the intake of [[oxygen]]/elimination of [[carbon dioxide]]) * The release of stored [[energy]] During perceived physiological or emotional stress, the SNS is activated while the PNS is less predominant. This redirects the body’s resources toward processes that are important in an emergency situation, resulting in a decrease in bodily functions controlled by the PNS, which are less important in an emergency situation.<ref name="McCorry2007" /> === Parasympathetic nervous system === The [[parasympathetic nervous system]] (PNS) is dominant in conditions referred to as “rest and digest”. It controls body processes during ordinary situations. This division of the ANS helps return the body to resting state after confronting a stressor, helping to conserve energy.<ref name="McCorry2007" /> Functions of the PNS include: * Contraction of the [[bladder]] * Reducing blood pressure<ref name="McCorry2007" /><ref name="merck" /> * Slowing heart rate * Stimulating the digestive tract, including [[gland secretion]]
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