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University of Ottawa
Anatomy and Physiology
Jacqueline Carnegie

The Autonomic Nervous System ANSAlso called involuntary nervous system or general visceral motor systemRegulates for optimal homeostasisIs a system of motor neurons that innervates smoothcardiac musclesglands make adjustments to ensure optimal support for body activities operates via subconscious controlComparison of SomaticAutonomic NSEffectorsSNS stimulates skeletal musclesANS innervates cardiacsmooth musclesglandsEfferent PathwaysGangliaSNS motor neuron cell body in CNS its thick myelinated group A fibers that conduct nerve impulses quicklyextend in spinalcranial nerve to skeletal muscle does not contain gangliaANS uses 2neuron chain pathway1 Preganglionic Neuron in CNS has thin lightly myelinated preganglionic axon2 Postganglionic ganglionic neuron in autonomic ganglion gangliamotor ganglia outside CNS has nonmyelinated postganglionic axon that extends to effector organNeurotransmitter EffectsSNS all somatic motor neurons release ACh acetylcholine has excitatorystimulatory effectANS preganglionic fibers release ACh postganglionic fibers release norepinephrine effects either excitatory or inhibitory depends on receptor typeANS DivisionDuel Innervation all visceral organs served by both divisions but cause opposite effects maintains homeostasisParasympatheticPromotes maintenance functions conserves body energyDigestion defecation diuresis urination D DivisionRestdigest person relaxing after mealregulateslowers blood pressure heartrespiratory rate gastrointestinal tract activity high constricts pupils discards waste SympatheticMobilizes body during activityFight or flight excitement exercise emergency embarrassment E Division inc heart rate dry mouth coldsweaty skin dilated pupils inhibits digestionelimination During rigorous physical activity shunts blood to muscles heart dilates bronchioles causes glucose release in liverANS AnatomyParasympathetic Craniosacral DivisionLong preganglionic fibers from brain stemsacrum opposite ends of CNS extend from CNS almost to target organs where axon synapses w postganglionic neurons in terminal ganglia close to within target organsShort postganglionic fibers synapse w effectorsCranial PartCell bodies lie in brain stemPreganglionic fibers run inOculomotor Nerves smooth muscle of eyeFacial Nerves stimulate large glands in headGlossopharyngeal Nerves parotid salivary glandsVagus Nerves necknerve plexuses for all thoracicabdominal visceraSacral PartServes pelvic organsdistil half of large intestine Comes from neurons in lateral gray matter of S2S4Axons travel in ventral root of spinal nerves Synapse w ganglia in pelvic floor intramural ganglia in walls of distil half of large intestine urinary bladder uterusreproductive organsSympathetic Thoracolumbar DivisionMore complex as it innervates more organsPreganglionic neurons are in spinal cord segments T1L2 in gray matter form lateral horns of spinal cordPreganglionic fibers pass thru white rami communicantesenter sympathetic trunk chain or paravertebral ganglia Sympathetic TrunksPathwaysOnce preganglionic axon reaches trunk ganglion preganglionicpostganglionic neurons can1 Synapse at same level synapse is in same trunk ganglion2 Synapse at higher or lower level ascend or descend sympathetic trunk to another trunk ganglion3 Synapse in distant collateral ganglion pass thru trunk ganglionemerge wout synapsing only in abdomen pelvisPathways w Synapses in Trunk GangliaPostganglionic axons enter ventral rami via grey rami communicantes effectorssweat glands arrector pili musclesinnervates vascular smooth musclesWhite ramimyelinated carry preganglionic axons to sympathetic trunksGrey raminonmyelinated carry postganglionic axons from cervical to sacral region but never carry parasympathetic fibers Pathways to HeadPreganglionic fibers emerge from spinal cord T1T4synapses w postganglionic neurons Serves skinblood vessels of head stimulates dilator muscles of irises of eyes innervates nasal salivary glandssmooth muscle on upper eyelidPathways to ThoraxPreganglionic fibers emerge from T1T6synapse in cervical trunk gangliaPostganglionic fibers emerge from middleinferior cervical gangliaenter nerves C4C8Fibers innervate heart via cardiac plexus thyroid gland skin lungs esophagusPathways w Synapses in Collateral GangliaMost fibers from T5L2 synapse in collateral gangliaFrom thoracic lumbarsacral splanchnic nervesGanglia include celiacsuperiorinferior mesenteric Pathways to AbdomenPreganglionic fibers from T5L2 travel thru thoracic splanchnic nerves to synapse at superior mesenteric gangliaceliacPostganglionic fibers serve stomach intestines liver spleen kidneysPathways to PelvisPreganglionic fibers from T10L2 travel via lumbarsacral splanchnic nerves Postganglionic fibers serve distil half of large intestine bladderreproductive organsInhibit activity of musclesglands in abdominopelvic visceral organs Pathways w Synapses in Adrenal MedullaSome preganglionic fibers pass directly to adrenal medulla wout synapsingWhen stimulated medullary cells secrete noepinephrine into bloodSympathetic gangliaadrenal medulla misplaced SG arise from same tissueVisceral ReflexesstVisceral Sensory Neurons 1 link in autonomic reflexes send info concerning chemical changes stretchirritation of visceralVisceral Reflex Arcs have same components as somatic reflex arcs diffvisceral has 2 neurons in motor pathwaysVisceral pain afferents travel along same pathways as somatic pain fibers contributes to referred pain ANS PhysiologyNeurotransmitters NTCholinergic Fibersrelease NT ACh all ANS preganglionic axonsall parasympathetic postganglionic axons at effector synapsesAdrenergic Fibersrelease NT NE most sympathetic postganglionic axons exceptionsympathetic postganglionic fibers that secrete ACh onto sweat glandsReceptorsCholinergic Receptorsbind ACh named after drugs Nicotinicrespond to nicotine always excitatory opens ion channels depolarizing postsynaptic cellFound on sarcolemma of skeletal muscle cells at NMJ all postganglionic neurons sympapara hormone producing cells of adrenal medulla Muscarinicactivated by mushroom poison muscarine G protein coupled receptoreither inhibitory or excitatory depends on receptor type of target organ
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