The autonomic nervous system is a component of the peripheral nervous system that regulates involuntary physiologic processes. It functions without conscious control throughout the lifespan of an organism to control cardiac muscle, smooth muscle, and exocrine and endocrine glands, which in turn regulate blood pressure, urination, bowel movements, and thermoregulation.. The ANS does this by using many diverse chemicals and signals to maintain homeostasis. Show
It contains three anatomically distinct divisions: sympathetic, parasympathetic, and enteric.See links The autonomic nervous system operates by receiving information from the environment and from other parts of the body. The sympathetic system is viewed as a quickly responding system that mobilizes the body for action where the parasympathetic system is believed to act much more slowly to dampen responses.
Although most of the autonomic nervous system responses are involuntary, they can integrate with the somatic nervous system, which is responsible for the voluntary movements. eg in the case of defecation, there is an interplay between voluntary and involuntary movements.
Hand of a person with POTS and dysautonomia exhibiting blood pooling When the parasympathetic and sympathetic components of the autonomic nervous systems become out of sync, people can experience an autonomic disorder, also called dysautonomia. Dysautonomia is an umbrella term used to describe several different medical conditions that cause a malfunction of the Autonomic Nervous System. The Autonomic Nervous System controls functions of the body that we do not consciously think about. People living with various forms of dysautonomia have trouble regulating these systems, which can result in lightheadedness, fainting, unstable blood pressure, abnormal heart rates, malnutrition, and in severe cases, death. Over 70 million people worldwide live with various forms of dysautonomia. People of any age, gender or race can be impacted. There is no cure for any form of dysautonomia at this time. There are numerous types of autonomic disorders including: Postural Tachycardia Syndrome (POTS); Idiopathic orthostatic hypotension; Multiple system atrophy; Orthostatic hypotension; Postprandial hypotension. The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response. The autonomic nervous system is regulated by integrated reflexes through the brainstem to the spinal cord and organs. Autonomic functions include control of respiration, cardiac regulation (the cardiac control center), vasomotor activity (the vasomotor center), and certain reflex actions such as coughing, sneezing, swallowing and vomiting. Those are then subdivided into other areas and are also linked to autonomic subsystems and the peripheral nervous system. The hypothalamus, just above the brain stem, acts as an integrator for autonomic functions, receiving autonomic regulatory input from the limbic system. Although conflicting reports about its subdivisions exist in the literature, the autonomic nervous system has four branches: the sympathetic nervous system, the parasympathetic nervous system, the visceral sensory nervous system and the enteric nervous system. Some textbooks do not include the enteric nervous system as part of this system. The sympathetic nervous system is often considered the "fight or flight" system, while the parasympathetic nervous system is often considered the "rest and digest" or "feed and breed" system. In many cases, both of these systems have "opposite" actions where one system activates a physiological response and the other inhibits it. An older simplification of the sympathetic and parasympathetic nervous systems as "excitatory" and "inhibitory" was overturned due to the many exceptions found. A more modern characterization is that the sympathetic nervous system is a "quick response mobilizing system" and the parasympathetic is a "more slowly activated dampening system", but even this has exceptions, such as in sexual arousal and orgasm, wherein both play a role. There are inhibitory and excitatory synapses between neurons. A third subsystem of neurons has been named as non-noradrenergic, non-cholinergic transmitters (because they use nitric oxide as a neurotransmitter) and are integral in autonomic function, in particular in the gut and the lungs. Interestingly, although the ANS is also known as the visceral nervous system and although most of its fibers carry non-somatic information to the CNS, many authors still consider it only connected with the motor side. Most autonomous functions are involuntary but they can often work in conjunction with the somatic nervous system which provides voluntary control. Structure[edit]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 is divided into the sympathetic nervous system and parasympathetic nervous system. The sympathetic division emerges from the spinal cord in the thoracic and lumbar areas, terminating around L2-3. The parasympathetic division has craniosacral “outflow”, meaning that the neurons begin at the cranial nerves (specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve and vagus nerve) and sacral (S2-S4) spinal cord. The autonomic nervous system is unique in that it requires a sequential two-neuron efferent pathway; the preganglionic neuron must first synapse onto a postganglionic neuron before innervating the target organ. The preganglionic, or first, neuron will begin at the “outflow” and will synapse at the postganglionic, or second, neuron's cell body. The postganglionic neuron will then synapse at the target organ. Sympathetic division[edit]The sympathetic nervous system consists of cells with bodies in the lateral grey column from T1 to L2/3. These cell bodies are "GVE" (general visceral efferent) neurons and are the preganglionic neurons. There are several locations upon which preganglionic neurons can synapse for their postganglionic neurons:
These ganglia provide the postganglionic neurons from which innervation of target organs follows. Examples of splanchnic (visceral) nerves are: These all contain afferent (sensory) nerves as well, known as GVA (general visceral afferent) neurons. Parasympathetic division[edit]The parasympathetic nervous system consists of cells with bodies in one of two locations: the brainstem (Cranial Nerves III, VII, IX, X) or the sacral spinal cord (S2, S3, S4). These are the preganglionic neurons, which synapse with postganglionic neurons in these locations: These ganglia provide the postganglionic neurons from which innervations of target organs follows. Examples are:
Sensory neurons[edit]The sensory arm is composed of primary visceral sensory neurons found in the peripheral nervous system (PNS), in cranial sensory ganglia: the geniculate, petrosal and nodose ganglia, appended respectively to cranial nerves VII, IX and X. These sensory neurons monitor the levels of carbon dioxide, oxygen and sugar in the blood, arterial pressure and the chemical composition of the stomach and gut content. They also convey the sense of taste and smell, which, unlike most functions of the ANS, is a conscious perception. Blood oxygen and carbon dioxide are in fact directly sensed by the carotid body, a small collection of chemosensors at the bifurcation of the carotid artery, innervated by the petrosal (IXth) ganglion. Primary sensory neurons project (synapse) onto “second order” visceral sensory neurons located in the medulla oblongata, forming the nucleus of the solitary tract (nTS), that integrates all visceral information. The nTS also receives input from a nearby chemosensory center, the area postrema, that detects toxins in the blood and the cerebrospinal fluid and is essential for chemically induced vomiting or conditional taste aversion (the memory that ensures that an animal that has been poisoned by a food never touches it again). All this visceral sensory information constantly and unconsciously modulates the activity of the motor neurons of the ANS. Innervation[edit]Autonomic nerves travel to organs throughout the body. Most organs receive parasympathetic supply by the vagus nerve and sympathetic supply by splanchnic nerves. The sensory part of the latter reaches the spinal column at certain spinal segments. Pain in any internal organ is perceived as referred pain, more specifically as pain from the dermatome corresponding to the spinal segment. Motor neurons[edit]Motor neurons of the autonomic nervous system are found in ‘’autonomic ganglia’’. Those of the parasympathetic branch are located close to the target organ whilst the ganglia of the sympathetic branch are located close to the spinal cord. The sympathetic ganglia here, are found in two chains: the pre-vertebral and pre-aortic chains. The activity of autonomic ganglionic neurons is modulated by “preganglionic neurons” located in the central nervous system. Preganglionic sympathetic neurons are located in the spinal cord, at the thorax and upper lumbar levels. Preganglionic parasympathetic neurons are found in the medulla oblongata where they form visceral motor nuclei; the dorsal motor nucleus of the vagus nerve; the nucleus ambiguus, the salivatory nuclei, and in the sacral region of the spinal cord. Function[edit]Function of the autonomic nervous system Sympathetic and parasympathetic divisions typically function in opposition to each other. But this opposition is better termed complementary in nature rather than antagonistic. For an analogy, one may think of the sympathetic division as the accelerator and the parasympathetic division as the brake. The sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with actions that do not require immediate reaction. The sympathetic system is often considered the "fight or flight" system, while the parasympathetic system is often considered the "rest and digest" or "feed and breed" system. However, many instances of sympathetic and parasympathetic activity cannot be ascribed to "fight" or "rest" situations. For example, standing up from a reclining or sitting position would entail an unsustainable drop in blood pressure if not for a compensatory increase in the arterial sympathetic tonus. Another example is the constant, second-to-second, modulation of heart rate by sympathetic and parasympathetic influences, as a function of the respiratory cycles. In general, these two systems should be seen as permanently modulating vital functions, in a usually antagonistic fashion, to achieve . Higher organisms maintain their integrity via homeostasis which relies on negative feedback regulation which, in turn, typically depends on the autonomic nervous system. Some typical actions of the sympathetic and parasympathetic nervous systems are listed below. Target organ/systemParasympatheticSympatheticDigestive systemIncrease peristalsis and amount of secretion by digestive glandsDecrease activity of digestive systemLiverNo effectCauses glucose to be released to bloodLungsConstricts bronchiolesDilates bronchiolesUrinary bladder/ UrethraRelaxes sphincterConstricts sphincterKidneysNo effectsDecrease urine outputHeartDecreases rateIncrease rateBlood vesselsNo effect on most blood vesselsConstricts blood vessels in viscera; increase BPSalivary and Lacrimal glandsStimulates; increases production of saliva and tearsInhibits; result in dry mouth and dry eyesEye (iris)Stimulates constrictor muscles; constrict pupilsStimulate dilator muscle; dilates pupilsEye (ciliary muscles)Stimulates to increase bulging of lens for close visionInhibits; decrease bulging of lens; prepares for distant visionAdrenal MedullaNo effectStimulate medulla cells to secrete epinephrine and norepinephrineSweat gland of skinNo effectStimulate sudomotor function to produce perspirationSympathetic nervous system[edit]Promotes a fight-or-flight response, corresponds with arousal and energy generation, and inhibits digestion The pattern of innervation of the sweat gland—namely, the postganglionic sympathetic nerve fibers—allows clinicians and researchers to use sudomotor function testing to assess dysfunction of the autonomic nervous systems, through electrochemical skin conductance. Parasympathetic nervous system[edit]The parasympathetic nervous system has been said to promote a "rest and digest" response, promotes calming of the nerves return to regular function, and enhancing digestion. Functions of nerves within the parasympathetic nervous system include:[citation needed]
Enteric nervous system[edit]The enteric nervous system is the intrinsic nervous system of the gastrointestinal system. It has been described as "the Second Brain of the Human Body". Its functions include:
Neurotransmitters[edit]A flow diagram showing the process of stimulation of adrenal medulla that makes it release adrenaline, that further acts on adrenoreceptors, indirectly mediating or mimicking sympathetic activity.  At the effector organs, sympathetic ganglionic neurons release noradrenaline (norepinephrine), along with other cotransmitters such as ATP, to act on adrenergic receptors, with the exception of the sweat glands and the adrenal medulla:
A full table is found at Table of neurotransmitter actions in the ANS. Autonomic nervous system and the immune system[edit]Recent studies indicate that ANS activation is critical for regulating the local and systemic immune-inflammatory responses and may influence acute stroke outcomes. Therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response could promote neurologic recovery after stroke. History[edit]The specialised system of the autonomic nervous system was recognised by Galen.[citation needed] In 1665, Thomas Willis used the terminology, and in 1900, John Newport Langley used the term, defining the two divisions as the sympathetic and parasympathetic nervous systems. Caffeine effects[edit]Caffeine is a bioactive ingredient found in commonly consumed beverages such as coffee, tea, and sodas. Short-term physiological effects of caffeine include increased blood pressure and sympathetic nerve outflow. Habitual consumption of caffeine may inhibit physiological short-term effects. Consumption of caffeinated espresso increases parasympathetic activity in habitual caffeine consumers; however, decaffeinated espresso inhibits parasympathetic activity in habitual caffeine consumers. It is possible that other bioactive ingredients in decaffeinated espresso may also contribute to the inhibition of parasympathetic activity in habitual caffeine consumers. Caffeine is capable of increasing work capacity while individuals perform strenuous tasks. In one study, caffeine provoked a greater maximum heart rate while a strenuous task was being performed compared to a placebo. This tendency is likely due to caffeine's ability to increase sympathetic nerve outflow. Furthermore, this study found that recovery after intense exercise was slower when caffeine was consumed prior to exercise. This finding is indicative of caffeine's tendency to inhibit parasympathetic activity in non-habitual consumers. The caffeine-stimulated increase in nerve activity is likely to evoke other physiological effects as the body attempts to maintain homeostasis. The effects of caffeine on parasympathetic activity may vary depending on the position of the individual when autonomic responses are measured. One study found that the seated position inhibited autonomic activity after caffeine consumption (75 mg); however, parasympathetic activity increased in the supine position. This finding may explain why some habitual caffeine consumers (75 mg or less) do not experience short-term effects of caffeine if their routine requires many hours in a seated position. It is important to note that the data supporting increased parasympathetic activity in the supine position was derived from an experiment involving participants between the ages of 25 and 30 who were considered healthy and sedentary. Caffeine may influence autonomic activity differently for individuals who are more active or elderly. Which of the following regulates the autonomic nervous system?So, the correct answer is 'Hypothalamus'.
Which of the following is a function of the autonomic nervous system quizlet?What is the function of the autonomic nervous system? a control system that acts largely unconsciously and regulates bodily functions such as the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal.
What are three functions of the autonomic nervous system?Definition, Divisions and Function
The autonomic nervous system (ANS) is part of the peripheral nervous system, and is responsible for the control of vital functions such as heart beat, breathing and digestion.
Which of the following are controlled by the autonomic nervous system quizlet?Autonomic nervous system controls smooth muscle, cardiac muscle, and glands.
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