Autonomic Nervous System, Lutfi, Post Bacc Anatomy II

BRAIN AND NERVOUS SYSTEM I – Autonomic Nervous System Dr. KIRAN C. PATEL COLLEGE OF OSTEOPATHIC MEDICINE Nicholas Lutfi, MD, MS, DPM OBJECTIVES Objectives 1. Describe the structures of the autonomic nervous system 2. Identify the structures of the parasympathetic nervous system 3. Identify the struc...

BRAIN AND NERVOUS SYSTEM I – Autonomic Nervous System Dr. KIRAN C. PATEL COLLEGE OF OSTEOPATHIC MEDICINE Nicholas Lutfi, MD, MS, DPM OBJECTIVES Objectives 1. Describe the structures of the autonomic nervous system 2. Identify the structures of the parasympathetic nervous system 3. Identify the structures of the sympathetic nervous system: output and thoracolumbar flow, hypothalamus as the output driver and Horner’s syndrome LECTURIO AND READING ASSIGNMENTS Lecturio Videos 1. Overview of the Autonomic Nervous System (ANS) 2. Parasympathetic Nervous System (PNS) 3. Sympathetic Nervous System (SNS): Output and Thoracolumbar Outflow 4. Sympathetic Nervous System (SNS): Hypothalamus as Sympathetic Output Driver and Horner’s Syndrome Readings 1. Structure, Functions, and Diseases of the Autonomic Nervous System 2. Meninges: An Overview of the Structure of the Individual Layers Visual/Technology Resources 1. Complete Anatomy (3D4Medical) INTRODUCTION INTRODUCTION ØThe Autonomic Nervous System (ANS), classically described as the visceral motor system, consists of fibers that innervate involuntary (smooth) muscle, modified cardiac muscle (the intrinsic stimulating and conducting tissue of the heart), and glands. https://nova.lecturio.com/ - /lecture/c/7140/24446 General Visceral Afferent Fibers General Visceral Efferent Fibers General Visceral Efferent Fibers INTRODUCTION The visceral efferent fibers of the ANS are accompanied by visceral afferent fibers. These fibers also play an important role in the regulation of visceral function as they conduct visceral pain impulses, and therefore are part of the ANS. INTRODUCTION ØThe efferent nerves and ganglia of the ANS are organized into two systems or divisions: ØSympathetic (thoracolumbar) division ØParasympathetic (craniosacral) division Conduction of impulses from the CNS to the effector tissues or organs involves a series of two neurons in both systems. INTRODUCTION The cell body of the 1st presynaptic, or preganglionic neuron is in the gray matter of the CNS. Its axon synapses only on the cell bodies of postsynaptic, or postganglionic neurons, the 2nd neurons in the series. INTRODUCTION ØThe cell bodies of the 2nd neurons are located in autonomic ganglia outside the CNS, with fibers terminating on the effector organ. INTRODUCTION Ø The anatomical distinction between the two divisions of the ANS is based primarily on the location of the presynaptic neurons. Ø A functional distinction, clinically important, is that the postsynaptic neurons of the two systems generally liberate different neurotransmitters: Ø Norepinephrine by the sympathetic division (except in the case of sweat glands) and acetylcholine by the parasympathetic division. OVERVIEW OF THE ANS The ANS involves two neurons between the CNS and effector. Neuron #1 is presynaptic. Neuron #2 is postsynaptic. Since synapses occur in the ANS ganglia, neuron #1 is preganglionic, and neuron #2 is postganglionic. ØNeuron #1 is always myelinated, and neuron #2 is always unmyelinated. ØNeuron #1 always produces Ach as its neurotransmitter, and neuron #2 usually produces Ach or NE. OVERVIEW OF THE ANS ØSubdivisions of the ANS: ØSympathetic - neuron #1 is short relative to neuron #2. ØParasympathetic - neuron #1 is long and neuron #2 is short. ØTheir actions are usually antagonistic to each other. OVERVIEW OF THE ANS ØFunctions: ØSympathetic “fight or flight” ØParasympathetic - “rest and digest” SYMPATHETIC AND PARASYMPATHETIC PATHWAYS SYMPATHETIC NERVOUS SYSTEM The cell bodies of the preganglionic neurons of the sympathetic division of the ANS are located in the intermediolateral cell columns (IML) of the spinal cord. SYMPATHETIC NERVOUS SYSTEM These columns are a part of the gray matter extending between T1 and L2 or L3 segments of the spinal cord. They are also referred to as lateral horns. SYMPATHETIC NERVOUS SYSTEM ØThe cell bodies of postganglionic neurons of the SNS can be found in two locations: ØThe paravertebral ganglia ØThe prevertebral ganglia https://nova.lecturio.com/ - /lecture/c/7140/24450 https://nova.lecturio.com/ - /lecture/c/7140/24454 SYMPATHETIC NERVOUS SYSTEM ØParavertebral ganglia ØLinked by trunks to form the right and left sympathetic chains on each side of the vertebral column extending its length. ØThe superior paravertebral ganglion - the superior cervical ganglion lies at the base of the skull. ØThe ganglion impar forms inferiorly where the two (right and left) trunks unite at the level of the coccyx. ØPrevertebral ganglia ØLocated at the level of the plexuses that surround the origins of the main branches of the abdominal aorta. SYMPATHETIC NERVOUS SYSTEM ØCeliac ganglion - associated with the celiac trunk ØSuperior Mesenteric Ganglion associated with the superior mesenteric artery ØInferior Mesenteric ganglion related to the inferior mesenteric artery SYMPATHETIC NERVOUS SYSTEM ØThe axons of preganglionic neurons leave the spinal cord through ventral roots and enter ventral rami of spinal nerves T1 through L2 or L3. ØImmediately after entering the ventral rami, all the preganglionic sympathetic fibers leave the ventral primary rami and pass to the sympathetic trunks to white communicating branches (white rami communicantes). SYMPATHETIC NERVOUS SYSTEM Ø Within the sympathetic trunks, preganglionic fibers follow one of three possible paths: 1. Enter and synapse immediately with a postsynaptic neuron of the paravertebral ganglion at the same level. 2. Ascend or descend in the sympathetic chain to synapse with a postsynaptic neuron of a higher or lower paravertebral ganglion. 3. Pass through the sympathetic trunk without synapsing, continuing to an abdominopelvic splanchnic nerve to reach the prevertebral ganglion. SYMPATHETIC NERVOUS SYSTEM ØPreganglionic sympathetic nerve fibers from T5-T9 form the greater splanchnic nerve. ØIts fibers synapse on the celiac ganglion. SYMPATHETIC NERVOUS SYSTEM Ø Preganglionic nerve fibers from T10-T11 form the lesser splanchnic nerve and they synapse on the superior mesenteric ganglion. Ø Preganglionic fibers from T12 form the lowest splanchnic nerve and they synapse on the aorticorenal ganglion. Ø Preganglionic fibers for L1-L2 form the lumbar splanchnic nerve and synapse on the inferior mesenteric ganglion. SYMPATHETIC NERVOUS SYSTEM ØPreganglionic sympathetic fibers that provide autonomic innervation to the head, neck, body walls, limbs, and thoracic cavity will either synapse with postsynaptic neurons of the paravertebral ganglia at the same level or ascend or descend up the chain to synapse with sympathetic postsynaptic neurons of a higher or lower paravertebral ganglion. SYMPATHETIC NERVOUS SYSTEM ØPostganglionic sympathetic fibers destined to supply the neck, body wall, and limbs pass from the paravertebral ganglia to adjacent ventral rami of spinal nerves. SYMPATHETIC NERVOUS SYSTEM ØPreganglionic fibers innervating the viscera within the abdominopelvic cavity will pass through the sympathetic trunk without synapsing, continue through an abdominopelvic splanchnic nerve to reach the prevertebral ganglia. SYMPATHETIC NERVOUS SYSTEM ØPostganglionic sympathetic fibers responsible for innervating the head, and the dilator muscle of the iris, have their cell bodies in the superior cervical ganglion. ØThey pass through a cephalic arterial branch to form the periarterial carotid plexus, and from there reach their destination. SYMPATHETIC NERVOUS SYSTEM ØPostganglionic sympathetic fibers responsible for supplying the viscera of the thoracic cavity (e.g. heart, lungs, and esophagus) pass through cardiopulmonary splanchnic nerves to enter the cardiac, pulmonary, and esophageal plexuses. SYMPATHETIC NERVOUS SYSTEM ØThe preganglionic fibers involved in the innervation of the contents of the abdominopelvic cavity (e. g. stomach, and intestines) pass to the prevertebral ganglia via the abdominopelvic splanchnic nerves (greater, lesser, least, and lumbar). Sympathetic Supply to the Head and Neck ØThe preganglionic fibers, which supply the head and neck, arise from the spinal segments T1-T2. ØThey enter the sympathetic chain (white communicating branches or gray rami communicantes) and travel upward to synapse on the three cervical ganglia: Sympathetic Supply to the Head and Neck ØThe superior cervical ganglion (C1-C2) ØThe middle cervical ganglion (small, often absent, anterior to C6) ØThe inferior cervical ganglion (or stelate) – located at C7; often fused with the first thoracic ganglion Sympathetic Supply to the Head and Neck ØEach of these ganglia give rise to (postganglionic/postsynaptic): ØBranches to target organs. ØThe superior cervical ganglion sends branches to spinal nerves C1-C4 to reach the orbit, face nasal and oral cavities, and pharynx ØThe middle ganglion to nerves C5-C6 to reach the larynx, trachea and upper esophagus ØThe inferior ganglion to nerves C7, C8, T1. Sympathetic Supply to the Head and Neck Ø Some branches (postganglionic/postsynaptic) “hitch-hike” along arteries and their branches to reach target organs: Ø The superior ganglion sends branches along the ICA and ECA to reach the orbit, face, nasal and oral cavities and pharynx. Ø The middle ganglion sends branches along the inferior thyroid artery to reach the larynx, trachea and upper esophagus. Ø The inferior ganglion sends branches to the subclavian and vertebral arteries. SYMPATHETIC NERVOUS SYSTEM Effects SYMPATHETIC NERVOUS SYSTEM Effects SYMPATHETIC NERVOUS SYSTEM Effects Neuron #1 (preganglionic) is short, neuron #2 (postganglionic) is long SYMPATHETIC NERVOUS SYSTEM Summary Synapses occurs in paravertebral chain ganglia or prevertebral collateral ganglia Neuron #1 releases Ach, usually neuron #2 releases NE Prepares for emergency action, excitatory to many organs, inhibitory to others (digestive for example) Effects very widespread and somewhat persistent PARASYMPATHETIC NERVOUS SYSTEM PARASYMPATHETIC NERVOUS SYSTEM ØPreganglionic (presynaptic) parasympathetic neuron cell bodies are located in two sites within the CNS, and their fibers exit by two routes: Ø In the gray matter of the brainstem, the fibers exit the CNS within cranial nerves III, VII, IX, and X. These fibers constitute the cranial parasympathetic outflow. https://nova.lecturio.com/ - /lecture/c/7140/24448 ØIn the gray matter of the sacral segments of the spinal cord (S2 through S4), the fibers exit the CNS through the ventral roots of spinal nerves S2 through S4 and the pelvic splanchnic nerves that arise from their ventral rami. These fibers constitute the sacral parasympathetic outflow. (postganglionic) PARASYMPATHETIC NERVOUS SYSTEM ØThe cranial outflow provides parasympathetic innervation to the head, thorax and abdomen. ØThe sacral outflow provides parasympathetic innervation to the distal gastrointestinal tract and pelvic viscera. PARASYMPATHETIC NERVOUS SYSTEM ØIn terms of innervation of the thoracic and abdominal viscera, the cranial outflow through the vagus nerve (CN X) is dominant. ØIt provides innervation to all the thoracic viscera and most of the gastrointestinal tract from esophagus through the left colic flexure. ØThe sacral outflow supplies only the descending, sigmoid colon, and rectum. PARASYMPATHETIC NERVOUS SYSTEM ØThe parasympathetic nervous system is much more restricted than the sympathetic system in its distribution. ØThe parasympathetic nervous system distributes only to the head, visceral cavities, and erectile tissues of the external genitalia. ØIt does not reach the body wall (except the external genitalia) or the limbs. TQ TQ PARASYMPATHETIC NERVOUS SYSTEM ØGeneral Functions: ØExcitatory to digestive organs ØDepresses heart rate and blood pressure ØConstricts pupils of the eyes ØSexual arousal ØSlows breathing ØConstricts urinary bladder PARASYMPATHETIC NERVOUS SYSTEM Summary ØNeuron #1(preganglionic) ØNeuron #2 (postganglionic) ØLong ØShort ØComes from the brain stem or sacral spinal cord ØProduces and releases Ach: may be either excitatory or inhibitory. ØRuns with the spinal or pelvic nerves ØProduces and releases Ach (excitatory) COMPARISON OF THE SYMPATHETIC AND PARASYMPATHETIC NERVOUS SYSTEMS TQ FUNCTIONS OF THE AUTONOMIC NERVOUS SYSTEM FUNCTIONS OF THE SNS AND PNS ØAlthough both sympathetic and parasympathetic systems innervate involuntary muscles and glands and often affect the same structures, they have different, and usually opposing, but coordinated effects. FUNCTIONS OF THE SNS AND PNS In general, the SNS is a catabolic, (energy-expending) system that enables the body to deal with stresses, such as when preparing the body to “flee or fight”. The PNS is primarily a homeostatic or anabolic (energy-conserving) system promoting the quiet and orderly processes of the body, such as those that allow the body the “feed and assimilate”. Sympathetic nervous system 1.Promotes a "fight or flight" response, corresponds with arousal and energy generation, and inhibits digestion. 2.Diverts blood flow away from the gastro-intestinal (GI) tract and skin via vasoconstriction. 3.Blood flow to skeletal muscles and the lungs is enhanced (by as much as 1200% in the case of skeletal muscles). 3.Dilates bronchioles of the lung, which allows for greater alveolar oxygen exchange. 4.Increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for the enhanced blood flow to skeletal muscles. 5.Dilates pupils and relaxes the ciliary muscle to the lens, allowing more light to enter the eye and far vision. 6.Provides vasodilation for the coronary vessels of the heart. 7.Constricts all the intestinal sphincters and the urinary sphincter. 8.Inhibits peristalsis. 9.Stimulates orgasm. Parasympathetic nervous system 1.Promotes a "rest and digest" response and enhances digestion. 2.Dilates blood vessels leading to the GI tract, increasing blood flow. This is important following the consumption of food, due to the greater metabolic demands placed on the body by the gut. 3.The parasympathetic nervous system can also constrict the bronchiolar diameter when the need for oxygen has diminished. 4.Dedicated cardiac branches of the vagus nerves impart parasympathetic control of the heart or myocardium. 5.During accommodation, the parasympathetic nervous system causes constriction of the pupil and contraction of the ciliary muscle to the lens, allowing for closer vision. 6.The parasympathetic nervous system stimulates salivary gland secretion, and accelerates peristalsis, so, in keeping with the “rest and digest” functions, appropriate PNS activity mediates digestion of food and indirectly, the absorption of nutrients. 7. It is also involved in erection of genitals, via the pelvic splanchnic nerves 2–4. CLINICAL CORRELATIONS CLINICAL CORRELATIONS - Horner’s Syndrome ØResults from the interruption of the sympathetic supply to the eye: interruption of sympathetic supply to the middle or superior cervical ganglion. ØThis leads to: (S & S) Ø Miosis Ø Ptosis Ø Anhidrosis Ø Enopthalmus Ø Vasodilation – skin redness and increased local temperature ØETIOLOGY Ø Brain stem lesions Ø Cervical spinal cord lesions (C8-T1) Ø Sympathetic chain lesions NOTE: *The S & S are ipsilateral. *Damage to the CN III also causes ptosis, but this is not related to Horner’s syndrome THANK YOU!...