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The sympathetic nervous system (SNS) is one of two divisions of the
autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The autonomic nervous ...

autonomic nervous system
, along with the
parasympathetic nervous system The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies s ...
. The
enteric nervous system The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system ...
is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system. The autonomic nervous system functions to regulate the body's unconscious actions. The sympathetic nervous system's primary process is to stimulate the body's
fight or flight response The fight-or-flight response (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first described by Walter Bradford Cann ...
. It is, however, constantly active at a basic level to maintain
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
. The sympathetic nervous system is described as being antagonistic to the parasympathetic nervous system which stimulates the body to "feed and breed" and to (then) "rest-and-digest".


Structure

There are two kinds of
neurons A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

neurons
involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic. The shorter
preganglionic neurons A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In Biology, biology, the nervous system is a Complex system, high ...
originate in the
thoracolumbar division The vertebral column, also known as the backbone or spine, is part of the axial skeleton Axial may refer to: * one of the anatomical directions describing relationships in an animal body * Axial Seamount and submarine volcano off Oregon, USA ...
of the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord, which contain ...

spinal cord
specifically at
T1
T1
to
L2~L3
L2~L3
, and travel to a
ganglion A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In biology Biology is the natural science that studies li ...

ganglion
, often one of the
paravertebral ganglia The sympathetic ganglia, or paravertebral ganglia are autonomic ganglia An autonomic ganglion is a cluster of nerve cell A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connection ...
, where they synapse with a postganglionic neuron. From there, the long postganglionic neurons extend across most of the body. At the synapses within the ganglia, preganglionic neurons release
acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter—a chemical message released by nerve cells to send signals to other cells, such as neurons, musc ...

acetylcholine
, a
neurotransmitter A neurotransmitter is a signaling molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cells and coordinates multiple-cell actions. A signal is an entity that ...
that activates
nicotinic acetylcholine receptors Image:Nicotine-2D-skeletal.png">Nicotine Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine Nico ...
on postganglionic neurons. In response to this stimulus, the postganglionic neurons release
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and ...

norepinephrine
, which activates
adrenergic receptors (yellow) on its extracellular site. β2 stimulates cells to increase energy production and utilization. The membrane the receptor is bound to in cells is shown with a gray stripe.The adrenergic receptors or adrenoceptors are a class of G protein- ...
that are present on the peripheral target tissues. The activation of target tissue receptors causes the effects associated with the sympathetic system. However, there are three important exceptions: # Postganglionic neurons of
sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of an ...
s release acetylcholine for the activation of
muscarinic receptors Muscarinic acetylcholine receptors, or mAChRs, are acetylcholine receptor Acetylcholine An acetylcholine receptor (abbreviated AChR) is an integral membrane protein that responds to the binding of acetylcholine, a neurotransmitter. Class ...
, except for areas of thick skin, the palms and the plantar surfaces of the feet, where norepinephrine is released and acts on adrenergic receptors. This leads to the activation of sudomotor function which is assessed by elctrochemical skin conductance. #
Chromaffin cells Chromaffin cells, also pheochromocytes, are neuroendocrine cell Neuroendocrine cells are cells that receive neuronal input (neurotransmitter A neurotransmitter is a secreted by a to affect another cell across a . The cell receiving the sign ...
of the
adrenal medulla The adrenal medulla ( la, medulla glandulae suprarenalis) is part of the adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldostero ...
are analogous to post-ganglionic neurons; the adrenal medulla develops in tandem with the sympathetic nervous system and acts as a modified sympathetic ganglion. Within this
endocrine gland Endocrine glands are ductless gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or rela ...
, pre-ganglionic neurons synapse with chromaffin cells, triggering the release of two transmitters: a small proportion of
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and ...

norepinephrine
, and more substantially,
epinephrine Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a co ...

epinephrine
. The synthesis and release of epinephrine as opposed to norepinephrine is another distinguishing feature of chromaffin cells compared to postganglionic sympathetic neurons. # Postganglionic sympathetic nerves terminating in the
kidney The kidneys are two reddish-brown bean-shaped organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized ...

kidney
release
dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is t ...

dopamine
, which acts on
dopamine D1 receptor Dopamine receptor D1, also known as DRD1, is a protein that in humans is encoded by the ''DRD1'' gene. Tissue distribution Based upon Northern blot and in situ hybridization, DRD1 gene expression, mRNA expression in the central nervous system is ...
s of blood vessels to control how much blood the kidney filters.
Dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is t ...

Dopamine
is the immediate metabolic precursor to
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and ...

norepinephrine
, but is nonetheless a distinct signaling molecule.


Organization

Sympathetic nerves arise from near the middle of the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord, which contain ...

spinal cord
in the
intermediolateral nucleus The intermediolateral nucleus (IML) is a region of grey matter Grey matter (or gray matter) is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil ( dendrites and unmyelinated axon An axon (from Gr ...
of the
lateral grey column The lateral grey column (lateral column, lateral cornu, lateral horn of spinal cord, intermediolateral column) is one of the three grey columns of the spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, w ...
, beginning at the first
thoracic The thorax or chest is a part of the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανι ...
vertebra In the vertebrate spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform c ...
of the
vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton Axial may refer to: * one of the describing relationships in an animal body * and submarine volcano off Oregon, USA * , a ghost town * In geometry: :* ...

vertebral column
and are thought to extend to the second or third
lumbar In tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon ...

lumbar
vertebra. Because its cells begin in the thoracolumbar division – the thoracic and lumbar regions of the spinal cord – the sympathetic nervous system is said to have a ''thoracolumbar outflow''.
Axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from ...
s of these nerves leave the spinal cord through the
anterior root In anatomy and neurology, the ventral root or anterior root is the efferent nerve, efferent motoneuron, motor root of a spinal nerve. At its distal end, the ventral root joins with the dorsal root to form a mixed spinal nerve. Additional images ...
. They pass near the spinal (sensory) ganglion, where they enter the anterior rami of the spinal nerves. However, unlike somatic innervation, they quickly separate out through white rami connectors (so called from the shiny white sheaths of
myelin Myelin is a lipid-rich (fatty) substance that surrounds nerve cell axons (the nervous system's "wires") to Insulator (electricity), insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the a ...
around each axon) that connect to either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation)
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In biology Biology is the natural science that studies li ...

ganglia
extending alongside the spinal column. To reach target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through
synaptic transmission Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitter A neurotransmitter is a signaling molecule In biology, cell signal ...
. The ends of the axons link across a space, the
synapse In the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiol ...

synapse
, to the
dendrites Dendrites (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approx ...

dendrites
of the second cell. The first cell (the presynaptic cell) sends a
neurotransmitter A neurotransmitter is a signaling molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cells and coordinates multiple-cell actions. A signal is an entity that ...
across the synaptic cleft where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination. Presynaptic nerves' axons terminate in either the
paravertebral ganglia The sympathetic ganglia, or paravertebral ganglia are autonomic ganglia An autonomic ganglion is a cluster of nerve cell A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connection ...
or
prevertebral ganglia Prevertebral ganglia (or collateral ganglia, or preaortic ganglia) are sympathetic ganglia which lie between the paravertebral ganglia and the target organ. Function Similar to the paravertebral ganglia, the prevertebral ganglia are the nodules ...
. There are four different paths an axon can take before reaching its terminal. In all cases, the axon enters the paravertebral ganglion at the level of its originating spinal nerve. After this, it can then either synapse in this ganglion, ascend to a more superior or descend to a more inferior paravertebral ganglion and synapse there, or it can descend to a prevertebral ganglion and synapse there with the postsynaptic cell. The postsynaptic cell then goes on to innervate the targeted end effector (i.e. gland, smooth muscle, etc.). Because paravertebral and prevertebral ganglia are close to the spinal cord, presynaptic neurons are much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations. A notable exception to the routes mentioned above is the sympathetic innervation of the suprarenal (adrenal) medulla. In this case, presynaptic neurons pass through paravertebral ganglia, on through prevertebral ganglia and then synapse directly with suprarenal tissue. This tissue consists of cells that have pseudo-neuron like qualities in that when activated by the presynaptic neuron, they will release their neurotransmitter (epinephrine) directly into the bloodstream. In the sympathetic nervous system and other components of the peripheral nervous system, these synapses are made at sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell whose fiber leaves the ganglion is called a
postganglionic In the autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, ...
cell. As mentioned previously, the preganglionic cells of the sympathetic nervous system are located between the first thoracic segment and third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands. The ganglia include not just the sympathetic trunks but also the
cervical ganglia The cervical ganglia are paravertebral ganglia of the sympathetic nervous system. Preganglionic nerve fibers, Preganglionic nerves from the thoracic spinal cord enter into the cervical ganglions and synapse with its Postganglionic nerve fibers, post ...
(
superior Superior may refer to: *Superior (hierarchy) In a hierarchy A hierarchy (from the Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) in which the items are represented as being "ab ...

superior
, middle and inferior), which send sympathetic nerve fibers to the head and thorax organs, and the
celiac
celiac
and mesenteric ganglia, which send sympathetic fibers to the gut.


Information transmission

Messages A message is a discrete unit of communication Communication (from Latin ''communicare'', meaning "to share") is the act of developing Semantics, meaning among Subject (philosophy), entities or Organization, groups through the use of suffi ...
travel through the sympathetic nervous system in a bi-directional flow. Efferent messages can trigger changes in different parts of the body simultaneously. For example, the sympathetic nervous system can accelerate
heart rate Heart rate is the speed of the heartbeat Heartbeat or heartbeats may refer to: Physiology *Cardiac cycle, of the heart *Contraction of the cardiac muscle, muscles of the heart, or a perceived effect of it, such as: **Heart sounds, the noises gene ...

heart rate
; widen
bronchial A bronchus is a passage or airway in the respiratory tract, respiratory system that conducts Atmosphere of Earth, air into the lungs. The first bronchi to branch from the trachea are the right main bronchus and the left main bronchus, also known as ...
passages; decrease
motility Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with Sessility (motility), sessility, the ...

motility
(movement) of the
large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human dig ...

large intestine
; constrict blood vessels; increase
peristalsis Peristalsis is a radially symmetrical Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take ...

peristalsis
in the
oesophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United State ...

oesophagus
; cause
pupillary dilation Pupillary response is a physiological Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A ...
, piloerection (
goose bumps Goose bumps, goosebumps or goose-pimples are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold , a common physiological response to cold, aiming to reduce the loss of bo ...

goose bumps
) and perspiration (
sweating Perspiration, also known as sweating, is the production of fluids secreted by the sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin Skin is the layer of usually soft, f ...

sweating
); and raise blood pressure. One exception is with certain blood vessels such as those in the cerebral and coronary arteries, which dilate (rather than constrict) with an increase in sympathetic tone. This is because of a proportional increase in the presence of β2 adrenergic receptors rather than α1 receptors. β2 receptors promote vessel dilation instead of constriction like α1 receptors. An alternative explanation is that the primary (and direct) effect of sympathetic stimulation on coronary arteries is vasoconstriction followed by a secondary vasodilation caused by the release of vasodilatory metabolites due to the sympathetically increased cardiac inotropy and heart rate. This secondary vasodilation caused by the primary vasoconstriction is termed functional sympatholysis, the overall effect of which on coronary arteries is dilation. The target synapse of the postganglionic neuron is mediated by
adrenergic receptors (yellow) on its extracellular site. β2 stimulates cells to increase energy production and utilization. The membrane the receptor is bound to in cells is shown with a gray stripe.The adrenergic receptors or adrenoceptors are a class of G protein- ...
and is activated by either
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and ...

norepinephrine
(noradrenaline) or
epinephrine Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a co ...

epinephrine
(adrenaline).


Function

The sympathetic nervous system is responsible for up- and down-regulating many homeostatic mechanisms in living organisms. Fibers from the SNS innervate tissues in almost every organ system, providing at least some regulation of functions as diverse as
pupil The pupil is a black hole located in the center of the iris of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo ...

pupil
diameter, gut motility, and
urinary system The urinary system, also known as the renal system or urinary tract, consists of the kidneys The kidneys are two reddish-brown bean-shaped organs found in vertebrate Vertebrates () comprise all species of animal Animals (also ca ...

urinary system
output and function. It is perhaps best known for mediating the neuronal and hormonal stress response commonly known as the ''fight-or-flight response''. This response is also known as ''sympatho-adrenal response'' of the body, as the
preganglionic In the autonomic nervous system, fibers from the central nervous system, CNS to the autonomic ganglion, ganglion are known as preganglionic fibers. All preganglionic fibers, whether they are in the sympathetic nervous system, sympathetic division ...
sympathetic fibers that end in the
adrenal medulla The adrenal medulla ( la, medulla glandulae suprarenalis) is part of the adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldostero ...
(but also all other sympathetic fibers) secrete acetylcholine, which activates the great secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline (norepinephrine) from it. Therefore, this response that acts primarily on the
cardiovascular system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and bloo ...
is mediated directly via impulses transmitted through the sympathetic nervous system and indirectly via
catecholamines A catecholamine (; abbreviated CA) is a monoamine neurotransmitter, an organic compound that has a catechol (benzene with two hydroxyl side groups next to each other) and a Side chain, side-chain amine. Catechol can be either a free molecule ...
secreted from the adrenal medulla. The sympathetic nervous system is responsible for priming the body for action, particularly in situations threatening survival. One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for action. Sympathetic nervous system stimulation causes vasoconstriction of most blood vessels, including many of those in the skin, the digestive tract, and the kidneys. This occurs as a result of activation of alpha-1 adrenergic receptors by norepinephrine released by post-ganglionic sympathetic neurons. These receptors exist throughout the vasculature of the body but are inhibited and counterbalanced by beta-2 adrenergic receptors (stimulated by epinephrine release from the adrenal glands) in the skeletal muscles, the heart, the lungs, and the brain during a sympathoadrenal response. The net effect of this is a shunting of blood away from the organs not necessary to the immediate survival of the organism and an increase in blood flow to those organs involved in intense physical activity.


Sensation

The afferent fibers of the
autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The autonomic nervous ...

autonomic nervous system
, which transmit sensory information from the internal organs of the body back to the central nervous system (or CNS), are not divided into parasympathetic and sympathetic fibers as the efferent fibers are.Moore, K.L., & Agur, A.M. (2007). ''Essential Clinical Anatomy: Third Edition.'' Baltimore: Lippincott Williams & Wilkins. 34–35. Instead, autonomic sensory information is conducted by
general visceral afferent fibers The general visceral afferent (GVA) fibers conduct sensory impulses (usually pain or reflex sensations) from the internal organs An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many org ...
. General visceral afferent sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the
CNS
CNS
. While the unconscious reflex arcs normally are undetectable, in certain instances they may send
pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society A learned societ ...
sensations to the CNS masked as
referred pain Referred pain, also called reflective pain, is pain perceived at a location other than the site of the painful stimulus. An example is the case of angina pectoris brought on by a myocardial infarction (heart attack), where pain is often felt in the ...
. If the
peritoneal cavity The peritoneal cavity is a potential space between the parietal peritoneum (the peritoneum that surrounds the abdominal wall) and visceral peritoneum (the peritoneum that surrounds the internal organs). The parietal and visceral peritonea are laye ...
becomes inflamed or if the bowel is suddenly distended, the body will interpret the afferent pain stimulus as
somatic Somatic may refer to: * Somatic (biology), referring to the cells of the body in contrast to the germ line cells ** Somatic cell, a non-gametic cell in a multicellular organism * Somatic nervous system, the portion of the vertebrate nervous syste ...
in origin. This pain is usually non-localized. The pain is also usually referred to
dermatomes A dermatome is an area of skin that is mainly supplied by afferent nerve fibres from the dorsal root of spinal nerve, dorsal root of any given spinal nerve. There are 8 cervical nerves (C1 being an exception with no dermatome), 12 thoracic nerves ...
that are at the same spinal nerve level as the visceral afferent
synapse In the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiol ...

synapse
.


Relationship with the parasympathetic nervous system

Together with the other component of the
autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The autonomic nervous ...

autonomic nervous system
, the parasympathetic nervous system, the sympathetic nervous system aids in the control of most of the body's internal organs. Reaction to stress—as in the flight-or-fight response—is thought to be elicited by the sympathetic nervous system and to counteract the parasympathetic system, which works to promote maintenance of the body at rest. The comprehensive functions of both the parasympathetic and sympathetic nervous systems are not so straightforward, but this is a useful rule of thumb.


Disorders

In
heart failure Heart failure (HF), also known as congestive heart failure (CHF) and (congestive) cardiac failure (CCF), is a set of manifestations caused by the failure of the heart The heart is a cardiac muscle, muscular Organ (biology), organ in mo ...
, the sympathetic nervous system increases its activity, leading to increased force of muscular contractions that in turn increases the
stroke volume In cardiovascular physiology Cardiovascular physiology is the study of the cardiovascular system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a group of organs ...
, as well as peripheral
vasoconstriction Vasoconstriction is the narrowing of the blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits bl ...

vasoconstriction
to maintain
blood pressure Blood pressure (BP) is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mas ...

blood pressure
. However, these effects accelerate disease progression, eventually increasing mortality in heart failure. Sympathicotonia is a stimulated condition of the sympathetic nervous system, marked by
vascular spasm Vasospasm refers to a condition in which an arterial spasm leads to vasoconstriction. This can lead to tissue ischemia and tissue death (necrosis). Cerebral vasospasm may arise in the context of subarachnoid hemorrhage. Symptomatic vasospasm or del ...
,thefreedictionary.com
Citing: The American Heritage Medical Dictionary Copyright © 2007
, and
goose bumps Goose bumps, goosebumps or goose-pimples are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold , a common physiological response to cold, aiming to reduce the loss of bo ...

goose bumps
.


History and etymology

The name of this system can be traced to the concept of
sympathy Sympathy is the perception, understanding, and reaction to the distress or need of another life form. According to David Hume, this sympathetic concern is driven by a switch in viewpoint from a personal perspective to the perspective of another g ...
, in the sense of "connection between parts", first used medically by
Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized Linguistic anglicisation (or anglicization, occasionally anglification, anglifying, or Englishing) is the practice of modi ...
. In the 18th century, Jacob B. Winslow applied the term specifically to nerves.


See also

*
Cremaster muscle The cremaster muscle is a muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given ...
*
Cremasteric reflex Cremasteric Reflex The cremasteric reflex is a superficial (i.e., close to the skin's surface) reflex observed in human males. This reflex is elicited by lightly stroking or poking the superior and medial (inner) part of the thigh—regardless of ...

Cremasteric reflex
*
Epinephrine Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a co ...

Epinephrine
*
History of catecholamine research The catecholamines comprise the endogenous substances dopamine, noradrenaline (norepinephrine) and adrenaline (epinephrine) as well as numerous artificially synthesized compounds such as isoprenaline. Their investigation constitutes a prominent cha ...
*
Limbic system The limbic system, also known as the paleomammalian cortex, is a set of brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and anim ...
*
Norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and ...

Norepinephrine
*
Sympathetic ganglia The sympathetic ganglia, or paravertebral ganglia are autonomic ganglia An autonomic ganglion is a cluster of nerve cell A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connection ...
*
Sympathetic trunk The sympathetic trunks (sympathetic chain, gangliated cord) are a paired bundle of nerve fibers that run from the base of the skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemb ...

Sympathetic trunk


References

{{DEFAULTSORT:Sympathetic Nervous System