Autonomic Nervous System PDF

The Autonomic Nervous System Dr. A. Aktar Divisions of the Nervous System Functional Divisions of the Nervous System • Somatic & Visceral • Visceral: Autonomic Motor innervation of organs & glands Involuntary responses, such as those related to homeostasis Sensory • Somatic: Nerves carrying...

The Autonomic Nervous System Dr. A. Aktar Divisions of the Nervous System Functional Divisions of the Nervous System • Somatic & Visceral • Visceral: Autonomic Motor innervation of organs & glands Involuntary responses, such as those related to homeostasis Sensory • Somatic: Nerves carrying conscious sensation from periphery back to CNS, nerves innervating voluntary muscles Autonomic Nervous System • 2 divisions: Sympathetic division Parasympathetic division • Sympathetic activity: Fight-or-flight response • Parasympathetic activity: Rest and digest • Homeostasis: The balance between the two systems • At each target effector, dual innervation determines activity Autonomic Nervous System • The PS & S sets of neurons constitute an integrated system for the coordination of neural regulation of visceral & homeostatic functions • Widespread activation of the S nervous system may ocur with emotions such as rage or fear • S nervous system may also be activated discretely In general: Sympathetic activity results in: -constriction of cutaneous arteries, thereby increasing blood supply to heart, muscle & brain tissue -increase in heart rate & blood pressure - constriction of sphincters & decrease in peristalsis ➔ mobilize body energy stores for dealing with increased activity Parasympathetic activity results in: - increase in intestinal peristalsis & glandular activities - decrease in heart rate Autonomic Nervous System General Organization Ganglion PNS Central Nervous System Preganglionic nerve fiber 2 neurons: Preganglionic neuron w/ cell body in CNS Postganglionic neuron w/cell body in a ganglion in the PNS Preganglionic neuron: Postganglionic neuron: Cell body in CNS Cell body in ganglia in PNS Autonomic Nervous System - Sympathetic Central Nervous System Preganglionic neuron Postganglionic neuron ACh ACh ACh NN Various Organs NE NN ACh M Epi α or β Neurohumoral transmission NN α or β Heart Smooth muscle Glands Sweat glands Piloerector muscles Various organs Transported via blood Adrenal Medulla Sympathetic: Short preganglionic, long postganglionic (except adrenal medulla) Autonomic Nervous System - Parasympathetic Central Nervous System Preganglionic neuron Various Organs Postganglionic neuron Preganglionic nerve fiber Parasympathetic: ACh NN ACh M Heart Smooth muscle Glands Long preganglionic, short postganglionic Pre-ganglionic neuron: Cell body in CNS Post-ganglionic neuron: Cell body in ganglia in PNS NN ACh M Neuronal nictotinic receptor Acetylcholine Muscarinic receptor Parasympathetic Outflow = Craniosacral outflow Origin Site of Synapse Innervation Cranial nerves III, VII, IX 4 cranial ganglia Glands & smooth muscle of the head Cranial nerve X Terminal ganglia in or near walls of viscera Viscera of neck, thorax, foregut, midgut Pelvic splanchnic nerves Terminal ganglia in or near walls of viscera (S2, S3, S4) Hindgut & pelvic viscera including urinary bladder & erectile tissue Parasympathetics • Neuron cell bodies located in medulla (cranial half of the system) & sacral segment of spinal cord (sacral half of system) • 75% of all parasympathetic fibres are in vagus nerve • Preganglionic fibres from medulla and spinal cord project to ganglia very close, or attached to target organ and make a synapse • The preganglionic neurons synapse with postganglionic neurons within terminal ganglia which are close to or embedded within effector tissues • Axons of parasympathetic postganglionic neurons are very short & usually unmyelinated due to their proximity to the cells of the effector tissue Parasympathetic Outflow • Cranial nerves III, VII, IX, X have a parasympathetic component • Oculomotor n. : Constrictor pupillae of the iris & the cilliary muscles (lens) • Facial n: Submandibular, sublingual, lacrimal glands, nasal mucosa • Glossopharyngeal n.: Parotid gland • Vagus n.: Viscera of neck, thorax, foregut, midgut gag reflex Sympathetic Outflow = Thoracolumbar outflow Origin Site of Synapse Innervation Spinal cord levels T1 – L2 Sympathetic chain ganglia (paravertebral ganglia) Smooth muscle & glands of body wall & limbs, head & thoracic viscera Thoracic splanchnic nerves T5 – T12 Prevertebral ganglia (collateral ganglia) E.g. Celiac, aorticorenal, sup. mesenteric, inf. mesenteric Smooth muscle & glands of foregut & midgut Lumbar splanchnic nerves L1 L2 Prevertebral ganglia (collateral) Smooth muscle & glands of pelvic viscera & hindgut E.g. inferior mesenteric Foregut Oesophagus Stomach Duodeonum Liver Pancreas Midgut Jejunum Ileum Prox. transverse colon Hindgut Distal transverse colon Descending colon Sigmoid colon Rectum Coeliac trunk Sup mesenteric a Inf mesenteric a Great splanchnic n T 5-9 Lesser splanchnic n T 10-11 Least and lumbal splanchnic nn T12-L3 N vagus Nervi Erigentes S 2-4 Sympathetic Outflow = Thoracolumbar outflow Lateral horn T1 – L2 Sympathetic Outflow • Cell bodies of preganglionic neurons are in lateral horns of gray matter of T1 – L2 segments of spinal cord • Fibers (Preganglionic) leave spinal cord within spinal nerves through the ventral roots (together with the PNS motor neurons) • White rami → enter sympathetic chain/trunk • Sympathetic chain contains paravertebral ganglia • 2 chains, 1 on either side of vertebral column along entire length • Some sympathetic fibers synapse w/these ganglia • Post ganglionic branches continue into head & neck • Prevertebral ganglia (splanchnic) lie around origin of large branches of abdominal aorta • Some preganglionic sympathetic fibers pass through sympathetic trunk (chain) w/o forming a synapse then synapse at prevertebral (collateral) ganglia Sympathetic Trunk Sympathetic Chain Sympathetic Outflow - Course & Synpasing of Fibers • Pass briefly through ant. rami → preganglionic fibers enter sympathetic trunk via white rami communicantes • Inside trunk, preganglionic fibers can follow 1 of 4 courses: (1) Ascend & synapse in a higher level paravertebral ganglion Usually from T1-5 . Nerves other than T1-L2/3 can participate in the synapse (2 Descend & synapse in a lower paravertebral ganglion Usually involves fibers from T5-L2(3) (3) Synapse directly in a paravertebral ganglion at same level Postganglionic fibers leave through a gray ramus communicans Fibers distributed to effector tissues w/peripheral branches of ant. & post. rami of the same spinal nerve. Fibers can also combine with fibers from other levels to form splanchnic nerves (4) Travel w/o synapsing to prevertebral ganglia Usually derived from T5 to L2(3). Synapse on a prevertebral ganglia. Postsynaptic fibers pass onto abdomen & pelvic viscera via a visceral motor nerve plexus Sympathetic Outflow Superior cervical ganglion • Post-ganglionic nerves travel in the internal & ext carotid nerves • They innervate the dilator pupillae, smooth muscle of arteries, head sweat glands Middle cervical ganglion • Heart, trachea, bronchi, lungs • Sometimes absent Inferior cervical ganglion • Subclavian & vertebral arteries, heart Sympathetic Outflow - Splanchnic Nerves • Greater splanchnic nn • Lesser splanchnic nn • Least splanchnic nn • Lumbar splanchnic nn • Sacral splanchnic nn • Collectively called abdominopelvic splanchnic nerves • Synapse happens in prevertebral ganglia (not paravertebral ganglia) • Postganglionic fibers follow main branches of the aorta & project onto all the organs in abdominal & pelvic cavities • Exception: adrenal glands Sympathetic Outflow Adrenal Medulla – Exception • Neurohumoral transmission • Stimulated to release epinephrine (adrenalin) & norepinephrine (noradrenalin) • In turn increases metabolic rate of cells & stimulates liver to release glucose • Nerves project directly onto medullary cells without synapsing • Medullary cells play role of postganglionic neurons by releasing neurotransmitters (epinephrine & norepinephrine) directly into the bloodstream • Results in widespread sympathetic response Horner’s Syndrome • a clinical syndrome caused by damage to the sup cervical symp.gang./the fibers arising from that gang. • Signs found in all patients on affected side of face include • • • • • pseudoptosis (drooping upper eyelid from loss of sympathetic innervation to the ciliary muscle), Miosis (constricted pupil-dilator pupilla m. Not functioning) Enophthalmos (the impression that the eye is sunk in) Anhidrosis (decreased sweating) on the affected side of the face Flushing of face (vasodilation) Sympathetic Outflow White & Gray Ramus Communicans • Ramus communicans (plural rami communicantes) Latin: a nerve which conects two other nerves, "communicating branch". • Difference in coloration due to differences in myelination • More myelinated than unmyelinated fibres in white rami communicantes, converse is true for grey rami communicantes. Gray ramus communicans • Exists at every level • Each spinal nerve receives a branch from the adjacent paravertebral ganglion of the sympathetic trunk • Carries postganglionic fibres from paravertebral ganglia to their destination • Also carries preganglionic fibres which enter paravertebral ganglia but do not synapse White ramus communicans • Exist only at levels where intermediolateral cell column is present (T1-L2) • Carries preganglionic fibres from spinal cord to paravertebral ganglia • Preganglionic sympathetic outflow tract from spinal cord Sympathetic Trunk ( paravertebral ganglia form this trunk) • • • • • • 3C 12 T 4L 4S Total 22-23 ganglia Gangion impar - note: numbers 1,2,3,4 show the patterns of synapsing of symp fibers (preganglionic) 2 1 3 4 How Do Sympathetic Fibers Reach the End Organ? • Joining spinal nn (to erector pili, sweat gl, vess) • Joining cranial nn • Around arteries • Independent fibers directly to organs (pre syn) • To large autonomic plexuses and prevertebral ganglia (pre or postsynaptic) • Neurons of symp. Nervous system: at Intermedio-lateral cell coloumn (nucleus) T1L3(2) of spinal cord • Paravertebral gangliasympathetic trunk • By: White ramus communicans (15 pairs) • Back to spinal n. By:Gray ramus communicans (31 pairs) Prevertebral Ganglia (coeliac,superior and inferior mesenteric ganglia) How do symp. reach the prevertebral ganglia? Without synapsing at paravert. gang. symp.ganglia at cervical region 1.Superior Cervical Symp. Ganglion • 1-4 C • (Gray rami to C 1-4) • Sup cardiac n 2- Middle Cervical Symp. Ganglion • 5-6 C • (Gray rami to C 5-6) • Middle cardiac n 3- Inferior Cervical Symp. Ganglion • 7-8 C + T1 = Stellate • Gray rami to C 7-8 • Inferior cardiac n • Postgang.fibers arising from these 3 gang. innervate head&neck area’s structures Thoracic sympathetic ganglia • Gray rami • Cardiac, pulmonary, esophageal plexuses • Greater (5-9), lesser (10-11), least (12) splanchnic nn Lumbar Sympathetic Ganglia • Some:Gray rami of spinal nn • Some:Lumbar splanchnic nn • Visceral branches • Coeliac g • Aorticorenal g • Sup mesenteric g Sacral Sympathetic Ganglia • Gray rami • İnf.hypogastric plexus Foregut Oesophagus Stomach Duodeonum Liver Pancreas Midgut Jejunum Ileum Prox. transverse colon Hindgut Distal transverse colon Descending colon Sigmoid colon Rectum Coeliac trunk Sup mesenteric a Inf mesenteric a Great splanchnic n T 5-9 Lesser splanchnic n T 10-11 Least and lumbal splanchnic nn T12-L3 N vagus Nervi Erigentes S 2-4 Note :Thus, to know which artery supplies which organ gives a clue about the sympathetic innervation of that organ Horner’s Syndrome • a clinical syndrome caused by damage to the sup cervical symp.gang./the fibers arising from that gang. • Signs found in all patients on affected side of face include • pseudoptosis (drooping upper eyelid from loss of sympathetic innervation to the ciliary muscle), • miosis (constricted pupil-dilator pupilla m. Not functioning) • Enophthalmos (the impression that the eye is sunk in) • anhidrosis (decreased sweating) on the affected side of the face • Flushing of face (vasodilation) Spinal Nerves - Overview a spinal cord segment Ant (ventral) root (radix) – efferent motor Spinal nerve Post (dorsal) root Afferent sensory ant branch (ramus) Cervical, brachial & lumbosacral plexus Intercostal nerves post branch (ramus) Every spinal nerve is mixed, i.e. contains motor & sensory fibers Deep back muscles & back skin sensation PARASYMPATHETIC NERVOUS SYSTEM (PNS) • Named bcs its central neurons are located on either side of thoracolumbar region of the spinal cord (para- = “beside” or “near”). • Named according to where the preganglionic neuron cell bodies are in the CNS: Cranial part Craniosacral system Sacral (pelvic) part Cranial nerves III, VII, IX, X Sacral 2, 3, 4 parasympathetic nuclei Lateral horn of sacral spinal cord PARASYMPATHETIC NERVOUS SYSTEM (PNS) • Connections similar to sympathetic system w/few differences: • Preganglionic fibers from cranial region travel in cranial n.n. • Preganglionic fibers from sacral region travel in spinal n.n. • Targets of these fibers are terminal ganglia, located near—or even within—the target effector • Intramural ganglia: Found within walls of the target organ • Postganglionic fiber projects from terminal ganglia a short distance to target effector, or to specific target tissue within the organ • Comparing relative lengths of axons: In PSS preganglionic fibers are long & postganglionic fibers are short bcs the ganglia are close to—and sometimes within—the target effectors PARASYMPATHETIC NERVOUS SYSTEM (PNS) Vagus Nerve ( CN X) • Constitutes ~ 75% of the PNS • Provides PS input to most of thoracic & abdominal viscera • Sacral PS fibers innervate the descending & sigmoid colon & rectum • Has 4 nuclei in the medulla oblongata & 2 sensory ganglia PARASYMPATHETIC NERVOUS SYSTEM (PNS) Vagus Nerve ( CN X) • Dorsal nucleus of vagus n. • Presynaptic fibers from nucleus synapse with: - ganglia on walls of target effector organ (intrinsic ganglia) - regional plexus • Postsynaptic fibers regulate: - peristalsis - gastrointestinal secretions - gastrointestinal blood flow PARASYMPATHETIC NERVOUS SYSTEM (PNS) Vagus Nerve ( CN X) • Efferent preganglionic parasympathetic fibers traverse vagus n. → to the prevertebral ganglion, pass through it → synapse in an intramural ganglion within wall of target organ PARASYMPATHETIC NERVOUS SYSTEM (PNS) Vagus Nerve ( CN X) – Stress Response • Up to 80% of vagal fibers are sensory and innervate nearly all major organs • Parasympathetic ganglia express receptors for interleukin-1, (key cytokine in the inflammatory immune response) • Interleukin-1 activates the hypothalamic-pituitary-adrenal axis and SNS ➔ leads to release of glucocorticoids and NE • Inhibited vagal action through vagotomy & cholinergic inhibitors ➔ significantly reduced, if not eliminated, allergic, asthmatic, & inflammatory responses PARASYMPATHETIC NERVOUS SYSTEM (PNS) Sacral Parasympathetic Nuclei • S 2,3,4 PS nuclei • Presynaptic fibers called pelvic splanchnic nerves • Lower abodomen & pelvis • Join autonomic plexus • Synaps either on autonomic plexuses or in walls of target organs Autonomic Plexuses • Formed from sympathetic & parasympathetic fibers • Include sympathetic postganglionic axons, parasympathetic preganglionic axons, some visceral sensory axons • cardiac plexus • pulmonary plexus • esophageal plexus Primary plexuses Secondary plexuses • abdominal aortic plexus – caeliac plexus in & around walls of target organs • superior & inferior hypogastric plexuses reach organ w/vessels Autonomic Plexuses Secondary Autonomic Plexuses • Formed close to target organs by fibers exiting the primary plexuses • Hepatic plexus • Phrenic plexus • Gastric plexus • Superior mesenteric plexus • Inferior mesenteric plexus