Autonomics - Visceral Motor System PDF

Autonomics – Visceral Motor System Dr. Michael Mutehart WSC Bio 220 References: Content (including visual images) primarily comes from your required textbook – Human Anatomy 9th Ed., Marieb, Brady and Mallatt (2020), Pearson, New York. Images from other sources (such as other texts) ge...

Autonomics – Visceral Motor System Dr. Michael Mutehart WSC Bio 220 References: Content (including visual images) primarily comes from your required textbook – Human Anatomy 9th Ed., Marieb, Brady and Mallatt (2020), Pearson, New York. Images from other sources (such as other texts) generally contain a citation on the individual slide. Definitions, examples and content presented in lecture therefore refer back to your required textbook. You are not required to purchase the online materials that come with the text, however, they may be an excellent option for additional resources. The use of external, online compendiums (such as Wikipedia) is discouraged. Simply, the accuracy of other sources cannot be guaranteed. Dr. Mutehart has no financial disclosures at this time.  Somatic and Autonomic Nervous Systems In the somatic motor system, a single motor neuron extends from the CNS to the skeletal muscle. In the autonomic nervous system, by contrast, a chain of two motor neurons – presynaptic (or preganglionic) and postsynaptic (postganglionic) – runs between the CNS and the target structure (smooth muscle or gland).  Somatic Motor Figure 14.9a The brachial plexus, anterior view. A xillary nerve Humerus Radial nerve Musc uloc utaneous nerve Ulna Radius U lnar nerve Median nerve Radial nerve (superficial branch) Dorsal branch of ulnar nerve Superficial branch of ulnar nerve Digital branch of ulnar nerve Muscular branch (a) T he major nerves Median nerve Digital branch of the upper limb Copyright © 2011 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Visceral Motor Somatic and Autonomic Nervous Systems: Comparison Autonomic nervous system Somatic nervous system  Introduction to the Autonomic Nervous System (ANS) Definition: the general visceral motor component of the PNS. Functions: innervates smooth, cardiac muscle, and glands; regulates visceral body functions (e.g. heart rate, blood pressure, digestion, urination). 9 Marieb et al. 6th Edition, p. 463  Two Divisions of the ANS Both innervate mostly the same structures, but have opposite coordinated effects. Sympathetic division o “Fight, flight, or fright” o Originates from thoracic and lumbar spinal cord regions of CNS o long postganglionic axons Parasympathetic division o “Rest and digest” o Originates from brain and sacral spinal cord of CNS. o postganglionic axons very short, localized effect 10 Marieb et al. 6th Edition, p. 465  Sympathetic Division Sympathetic responses help address dangerous situations. – Increases heart rate and breathing rate. – Increases blood and oxygen flow to skeletal muscles. – Dilates pupils and airways. – Motility of the digestive and urinary tracts is inhibited. 11  Parasympathetic Division – Active when the body is at rest. – Concerned with conserving energy. – Directs “housekeeping” activities:  heart rate and breathing are at low-normal levels.  gastrointestinal tract digests food.  pupils are constricted. 12  Parasympathetic Division 1st neuron cell bodies found in cranial (brain) and sacral regions of CNS = craniosacral outflow Ganglia containing cell bodies of 2nd neurons are located in or near the target organs. Does NOT innervate body wall or limbs. 13 Marieb et al. 4th Edition, p. 433 Cranial Outflow Originates in the brain, innervates organs of the head, neck, thorax, and most of abdomen. Pre-ganglionic fibers run via CNs III, VII, IX, X (Oculomotor, Facial, Glossopharyngeal and Vagus. Synapse with 2nd motor neuron in 1 of 4 head ganglia or in ganglia located in walls of target organ. Pre-ganglionic fibers traveling with CN X also pass through several autonomic plexuses (e.g. cardiac, pulmonary, celiac) to reach thoracic and abdominal organs. 14 Marieb et al. 6th Edition, p. 467  Sacral Outflow Originates in the sacral spinal cord and innervates the lower abdominal and pelvic organs. Pre-ganglionic fibers exit from the visceral motor region of gray matter of the spinal cord (S2-S4) and form the pelvic splanchnic nerves that arise from ventral rami. These nerves run through the inferior hypogastric plexus to reach the pelvic organs. 15 Marieb et al. 6th Edition, p. 467  Distribution of Parasympathetic Nerve Fibers ECA – Moore, Agur and Dalley (2015) pg. 38 16  Parasympathetic Pathways CN III, VII and IX -> Synapse in one of 4 head ganglia and innervate portions of the eye, lacrimal gland, nasal mucosa and salivary glands. CN X -> through one of many autonomic plexi, synapse in an intramural ganglion in the wall of the target organ (heart, lungs and/or digestive tract). Sacral Outflow (S2, S3 and S4) -> through the inferior hypogastric plexus and synapse in an intramural ganglia in the wall of the target organ. Autonomic Plexuses Networks of parasympathetic and sympathetic nerve fibers. All autonomic plexuses contain both parasympathetic and sympathetic fibers. The ganglia found in these networks are almost exclusively sympathetic. 18 Marieb et al. 6th Edition, p. 468  Sympathetic Division Issues from thoracic and lumbar regions of CNS (spinal cord:T1-L2). Pre-ganglionic fibers form the lateral gray horn. Supplies visceral organs and structures of superficial body regions without parasympathetic innervation (sweat glands, arrector pili muscles, smooth muscles in blood vessel walls). Contains more ganglia than the parasympathetic division. 1 Marieb et al. 4th Edition, p. 433  Sympathetic Division Thoraco-lumbar outflow: o pre-ganglionic cell Eye Lacrimal gland bodies in spinal cord: Pons 1. Sympathetic trunk (chain) ganglia Nasal mucosa lateral gray horn Blood vessels; skin (arrector pili Superior muscles and Bodies of 2nd neurons are cervical sweat glands) ganglion Middle Salivary glands located in two places: cervical ganglion Heart Inferior 1. sympathetic trunk cervical ganglion Cardiac and Lung T1 pulmonary plexuses 2. Greater splanchnic nerve 2. prevertebral or collateral ganglia Lesser splanchnic nerve Liver and gallbladder Celiac ganglion L2 Stomach White rami Superior mesenteric Spleen communicantes ganglion Adrenal medulla Sacral Kidney splanchnic nerves Lumbar Inferior Small splanchnic mesenteric intestine nerves ganglion Large intestine Rectum Preganglionic Postganglionic Genitalia (uterus, vagina, and penis) and urinary bladder 20 Marieb et al. 6th Edition, p. 472 Sympathetic Trunk Ganglia Paired ganglia that run along sides of vertebrae, contain motor neuron cell bodies. Linked together by short nerves to form long sympathetic trunks or chains. Connected to ventral rami of spinal nerves by white and gray communicating rami. Also called “chain” and “paravertebral” ganglia. 21 Marieb et al. 6th Edition, p. 470  Sympathetic vs. Dorsal Root Ganglia Dorsal root ganglia contain sensory neuron cell bodies. Sympathetic chain ganglia contain motor neuron cell bodies. 22 Marieb et al. 6th Edition, p. 411 Collateral (Prevertebral, Preaortic) Ganglia Unpaired and not segmentally arranged Located anterior to the vertebral column in the abdomen and pelvis only, usually on the surface of the aorta. The main collateral ganglia (celiac, superior mesenteric, inferior mesenteric, and inferior hypogastric) lie within the autonomic nerve plexuses of the same names. 23  White and Gray Rami Communicantes – White rami — contain preganglionic fibers traveling to sympathetic trunk ganglia. – Gray rami — contain only postganglionic fibers traveling to peripheral structures. 24 Marieb et al. 6th Edition, p. 470  Sympathetic Pathways Every preganglionic sympathetic fiber leaves the lateral gray horn of the thoracolumbar spinal cord through: – an adjacent ventral root into: a spinal nerve, followed by – a white ramus communicans » to reach the associated sympathetic trunk ganglion or collateral ganglion where it synapses with the postganglionic neuron that extends to the effector. 25 Sympathetic Pathways 26 Marieb et al. 6th Edition, p. 470  Sympathetic Pathway #1 Preganglionic axons follow one of three pathways: 1) synapse with a postganglionic neuron at the same level and exit on the spinal nerve at that level. 27 Marieb et al. 6th Edition, p. 470  Sympathetic Pathway # 2 2) Axon ascends or descends in the sympathetic trunk to synapse in another ganglion. Skin (arrector pili muscles and sweat glands) To effector 2 Synapse at a higher or lower level Blood vessels 28 Marieb et al. 6th Edition, p. 470  Sympathetic Pathway #3 3) Axon passes through the sympathetic trunk, exits on a splanchnic nerve (thoracic or lumbar), and synapses in a collateral ganglion. Do not confuse pelvic splanchnic nerves, Splanchnic nerve which are Collateral ganglion PARASYMPATHETIC, (such as the celiac) with the thoracic and lumbar splanchnic Target organ in abdomen nerves that are (e.g., intestine) SYMPATHETIC. 3 Synapse in a distant collateral ganglion anterior to the vertebral column (b) Three pathways of sympathetic innervation 29 Marieb et al. 6th Edition, p. 470  Visceral Reflexes Generalized similarities between somatic reflex and visceral reflex. Comparison: Sympathetic vs. Parasympathetic Important Consideration Remember that the sympathetic division of the ANS innervates superficial structures, along with all structures in the inner tube of the body. This means that there are sympathetic fibers in the limbs. Arrector pili muscles Sweat Glands Smooth muscle in the walls of the arteries and veins When you become nervous, excited or scared your body reacts in different ways this is often manifested by profuse sweating and more blood being diverted (vasoconstriction).