BIOL 2457 1st Edition Lecture 32Outline of Last Lecture The Brain and Cranial NervesOutline of Current LectureThe Autonomic Nervous SystemANS Coordinates cardiovascular, respiratory, digestive, urinary and reproductive functions Preganglionic neurons in the CNS send axons to synapse on ganglionic neurons in autonomic ganglia outside the CNSDivisions of the ANS Sympathetic division (thoracolumbar, “fight or flight”)Thoracic and lumbar segments Parasympathetic division (craniosacral, “rest and repose”)Preganglionic fibers leaving the brain and sacral segmentsOverview of Autonomic Motor Pathways Anatomical componentsPreganglionic neuron – meylinatedPostganglionic neuron – non-myelinated DivisionsSympathetic (thoracolumbar) (short pre/long post)* [cholinergic/adenergic] Parasympathetic (craniosacral) (long pre/short post) [cholinergic/cholinergic] *adrenal exceptionSympathetic Division Thoracolumbar division Preganglionic neurons originate from the thoracic and lumbar levels of the spinal cord (T1-L2) Sympathetic gangliaSympathetic trunk (vertebral chain) gangliaPrevertebral (collateral) ganglia Celiac, superior mesenteric, inferior mesenteric, aorticorenal and renal Organization and anatomy of the sympathetic division Segments T1-L2, ventral roots give rise to myelinated white ramus Leads to sympathetic chain gangliaSympathetic ganglia  Sympathetic chain ganglia (paravertebral ganglia) Collateral ganglia (prevertebral ganglia) Both the above have short preganglionic fibers &long postganglionic fibers The adrenal medulla is the exception… with long preganglionic & short postganglionic fibersSympathetic Division A single sympathetic preganglionic fiber has many axon collaterals and may synapse with 20 or more postganglionic neurons.  The postganglionic axons typically terminate in several visceral effectors and therefore the effects of sympathetic stimulation are more widespread than the effects of parasympathetic stimulation.Cephalic Periarterial Nerves Some sympathetic preganglionic neurons that enter the sympathetic trunk ascend to the superior cervical ganglion where they synapse with postganglionic neurons. Some of these leave the sympathetic trunk by forming cephalic periarterial nerves. Serve visceral effectors in the skin of the face and headPathway from Spinal Cord to Sympathetic Trunk Ganglia Preganglionic axons → anterior root of a spinal nerve → white ramus → sympathetic trunk ganglion White rami communicantes: structures containing sympathetic preganglionicaxons that connect the anterior ramus of the spinal nerve with the ganglia of the sympathetic trunkSpinal Nerves Gray ramus: Axons of some postganglionic neurons leave the sympathetic trunk by entering a short pathway called a gray ramus and merge with the anterior ramus of a spinal nerve. Gray rami communicantes: structures containing sympathetic postganglionic axons that connect the ganglia of the sympathetic trunk to spinal nerves.Organization of Sympathetic Trunk Ganglia Sympathetic trunk ganglia: 3 cervical, 11 or 12 thoracic, 4 or 5 lumbar, 4 or 5 sacral and 1 coccygeal Postganglionic neurons from the superior cervical region-head and heartmiddle cervical ganglion and the inferior cervical ganglion-heart Thoracic sympathetic trunk- heart, lungs, and bronchiPostganglionic Neurons in the Sympathetic Division An axon may synapse  With postganglionic neurons in the ganglion it first reaches or... Sympathetic chains (short preganglionic) or…  Continue, without synapsing, through the sympathetic trunk ganglion to end at a prevertebral ganglion and synapse with postganglionic neurons there (short preglanglionic) Through the sympathetic trunk ganglion and a prevertebral ganglion and then to the adrenal medulla. (long pre exception) Postganglionic fibers Rejoin spinal nerves and reach their destination by way of the dorsal and ventral rami Those targeting structures in the thoracic cavity form sympathetic nerves Go directly to their destinationPathways from Sympathetic Trunk Ganglia to Visceral Effectors Axons leave the sympathetic trunk in 4 possible ways Spinal nerves Cephalic periarterial nerves Sympathetic nerves Splanchnic nervesAbdominopelvic viscera Sympathetic innervation via preganglionic fibers that synapse within collateral ganglia SplanchicnervesAbdominopelvic viscera Celiac ganglion Innervates stomach, liver, gall bladder, pancreas, spleen Superior mesenteric ganglion Innervates small intestine and initial portion of large intestine Inferior mesenteric ganglion Innervates kidney, urinary bladder, sex organs, and final portion of large intestineSympathetic Nerves Some axons of the postganglionic neurons leave the trunk by forming sympathetic nerves. Innervate the heart and lungs Splanchnic Nerves Some sympathetic preganglionic axons pass through the sympathetic trunk without terminating in it. Beyond the trunk they form nerves called splanchnic nerves which extend to prevertebral ganglia. T5-T9 or T10- Greater splanchnic nerve T10-T11- Lesser splanchnic nerve L1-L4- Lumbar splanchnic nerveSplanchnic Nerves to the Adrenal Medulla Some sympathetic preganglionic axons pass, without synapsing, through the sympathetic trunk, greater splanchnic nerves and celiac ganglion into the adrenal medulla (modified sympathetic ganglia). Release hormones into blood- 80% epinephrine, 20% norepinephrineSympathetic activation In crises, the entire sympathetic division responds Sympathetic activation Affects include increased alertness, energy and euphoria, increased cardiovascular and respiratory activities, elevation in muscle tone, mobilization of energy resourcesNeurotransmitters & sympathetic function Stimulation of sympathetic division has two distinct results Release of ACh or NE at specific locations Secretion of E and NE into general circulation Most postganglionic fibers are adrenergic, a few are cholinergic or nitroxidergic Two types of receptors are alpha receptors and beta receptors Sympathetic ganglionic neurons end in telodendria studded with varicosities filled with