Chapter 16 APR Enhanced Lecture Slides See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes and animations. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 16 Autonomic Nervous System 16-2
16.1 Contrasting the Somatic and Autonomic Nervous Systems Peripheral nerves contain both motor and sensory neurons Among the motor neurons, some of these are somatic and innervate skeletal muscles while some are autonomic and innervate smooth muscle, cardiac muscle, and glands Sensory neurons are not subdivided into somatic and autonomic since there is overlap in function; e.g., pain receptors can stimulate both somatic and autonomic reflexes 16-3
Contrasting the Somatic and Autonomic Nervous Systems Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Spinal nerve Spinal nerve Autonomic ganglion (b) Spinal cord Preganglionic neuron (a) Spinal cord Somatic motor neuron Skeletal muscle Postganglionic neuron Effector (e.g., smooth muscle of colon) 16-4
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Somatic and Autonomic Nervous Systems Somatic Skeletal muscle Conscious and unconscious movement Skeletal muscle contracts One synapse Acetylcholine Receptor molecules: nicotinic Autonomic Smooth and cardiac muscle and glands Unconscious regulation Target tissues stimulated or inhibited Two synapses Acetylcholine by preganglionic neurons and ACh or norepinephrine by postganglionic neurons Receptor molecules: varies with synapse and neurotransmitter 16-6
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TABLE 16.1 Comparison of the Somatic and Autonomic Nervous Systems Effector Regulation Response to Stimulation Neuron Arrangement Neuron Cell Body Location Number of Synapses Axon Sheaths Neurotransmitter Substance Receptor Molecules Somatic Nervous System Skeletal muscle Controls all conscious and unconscious movements of skeletal muscle Skeletal muscle contracts. One neuron extends from the central nervous system (CNS) to skeletal muscle. Neuron cell bodies are in motor nuclei of the cranial nerves and in the ventral horn of the spinal cord. One synapse between the somatic motor neuron and the skeletal muscle Myelinated Acetylcholine Receptor molecules for acetylcholine are nicotinic. Autonomic Nervous System Smooth muscle, cardiac muscle, and glands Unconscious regulation, although influenced by conscious mental funtions Target tissues are stimulated or inhibited. There are two neurons in series; the preganglionic neuron extends from the CNS to an autonomic ganglion, and the postganglionic neuron extends from the autonomic ganglion to the target tissue. Preganglionic neuron cell bodies are in autonomic nuclei of the cranial nerves and in the lateral part of the spinal cord; postganglionic neuron cell bodies are in autonomic ganglia. Two synapses; first is in the autonomic ganglia, and second is at the target tissue Preganglionic axons are myelinated; postganglionic axons are unmyelinated. Acetylcholine is released by preganglionic neurons; either acetylcholine or norepinephrine is released by postganglionic neurons. In autonomic ganglia, receptor molecules for acetylcholine are nicotinic; in target tissues, receptor molecules for acetylcholine are muscarinic, whereas receptor molecules for norepinephrine are either α- or β-adrenergic. 16-7
16.2 Anatomy of the Autonomic Nervous System Divided into sympathetic and parasympathetic divisions as well as the enteric nervous system Sympathetic and parasympathetic divisions often supply the same organs but differ in a number of features The enteric nervous system Nerve plexuses within the wall of the digestive tract. Contributions from: sensory neurons between digestive tract and CNS, ANS motor neurons between the CNS and the digestive tract, and enteric neurons confined within the plexuses Functions Stimulate/inhibit smooth muscle contraction Stimulate/inhibit gland secretions Detect changes in content of lumen Interneurons connect sensory and motor aspects of enteric 16-8
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TABLE 16.2 Comparison of the Sympathetic and Parasympathetic Divisions Location of Preganglionic Cell Body Outflow from the CNS Sympathetic Division Lateral horns of spinal cord gray matter (T1 L2) Spinal nerves Sympathetic nerves Splanchnic nerves Parasympathetic Division Brainstem and lateral parts of spinal cord gray matter (S2 S4) Cranial nerves Pelvic splanchnic nerves Ganglia Number of Postganglionic Neurons For Each Preganglionic Neuron Sympathetic chain ganglia along spinal cord for spinal and sympathetic nerves; collateral ganglia for splanchnic nerves Many (much divergence) Terminal ganglia near or one fector organ Few (less divergence) Relative Length of Neurons Shortpreganglionic Longpostganglionic Longpreganglionic Shortpostganglionic 16-9
Sympathetic (Thoracolumbar) Division T1 L2 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Preganglionic neuron Postganglionic neuron Preganglionic cell body in lateral horn of gray matter Preganglionic neuron to sympathetic chain ganglion Postganglionic neurons Preganglionic neuron to collateral ganglion Postganglionic neurons Preganglionic cell bodies in lateral horns of spinal cord T1-L2: thoracolumbar Preganglionic axons pass through ventral roots to white rami communicantes to the retroperitoneal sympathetic chain ganglia. Collateral ganglia Sympathetic chain ganglia 16-10
Sympathetic Division
Routes of Sympathetic Axons 1. Spinal nerves: preganglionic axons synapse (at the same or different level) with postganglionic neurons within the sympathetic chain. These postganglion neurons exit the ganglia through the gray rami communicantes and re-enter spinal nerves. 2. Sympathetic nerves: preganglionic axons synapse (at the same or different level) with postganglionic neurons, which exit the ganglia through sympathetic nerves Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Preganglionic neuron Postganglionic neuron Preganglionic axon in a spinal nerve Dorsal root ganglion Preganglionic axon in a spinal nerve White ramus communicans Sympathetic chain ganglion Gray ramus communicans Postganglionic axon in a spinal nerve Postganglionic axon in a spinal nerve Ventral root Heart White ramus communicans Sympathetic chain ganglion Sympathetic nerve Postganglionic axon (a) Preganglionic axons from a spinal nerve pass through a white ramus communicans into a sympathetic chain ganglion. Some axons synapse with a postganglionic neuron at the level of entry; others ascend or descend to other levels before synapsing. Each postganglionic axon exits the sympathetic chain through a gray ramus communicans and enters a spinal nerve. (b) Part (b) is like part (a), except that each postganglionic neuron exits a sympathetic chain ganglion through a sympathetic nerve. 16-12
Routes of Sympathetic Axons 3. Splanchnic nerves: preganglionic axons pass through the chain ganglia without synapsing to form splanchnic nerves. Preganglionic axons then synapse with postganglionic neurons in collateral ganglia. Postganglionic neurons then send fibers to target organs (viscera). 4. Innervation to the adrenal gland: preganglionic axons synapse with the cells of the adrenal medulla. Embryologically, adrenal medulla is derived from same cells as postganglionic ANS cells. Medullary cells secrete epinephrine and norepinephrine; act as hormones promoting physical activity. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Preganglionic axon in a spinal nerve Preganglionic axon in a spinal nerve White ramus communicans Sympathetic chain ganglion Splanchnic nerve Preganglionic axon Collateral ganglion Postganglionic axon Adrenal gland White ramus communicans Sympathetic chain ganglion Splanchnic nerve Collateral ganglion Preganglionic axon Viscera (c) Preganglionic neurons do not synapse in the sympathetic chain ganglia, but exit in splanchnic nerves and extend to a collateral ganglion, where they synapse with postganglionic neurons. (d) Part (d) is like part (c), except that the preganglionic axons extend to the adrenal medulla, where they synapse with specialized adrenal medullary cells. 16-13
Parasympathetic (Craniosacral) Division Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cranial nerves Pelvic splanchnic nerves Postganglionic neurons Terminal ganglia Preganglionic neurons Preganglionic neuron Postganglionic neuron Midbrain Pons Medulla Sacral region of spinalcord (S2 S4) Brainstem Preganglionic cell bodies in nuclei of brainstem or lateral parts of spinal cord gray matter from S2-S4 Preganglionic axons from brain pass to terminal ganglia through cranial nerves III, VII, IX and X Preganglionic axons from sacral region pass through pelvic splanchnic nerves to terminal ganglia Terminal ganglia located near organ innervated or embedded in wall of organ 16-14
Parasympathetic Division
Enteric Nervous System Consists of nerve plexuses within wall of digestive tract Sources of neurons Sensory neurons that connect the digestive tract to CNS ANS motor neurons that connect CNS to digestive tract Enteric neurons that are confined to enteric plexuses 16-16
Distribution of ANS Fibers: Sympathetic Sympathetic axons reach organs through 1. Spinal nerves: innervate sweat glands, smooth muscle of blood vessels to skeletal muscle and skin, and arrector pili 2. Head and neck nerve plexuses: innervate sweat glands, smooth muscle of blood vessels to skeletal muscle and skin, and arrector pili 3. Thoracic nerve plexuses: cardiac and pulmonary; heart and lungs 4. Abdominopelvic nerve plexuses: celiac, superior mesenteric, inferior mesenteric, hypogastric plexuses. Organs of abdominopelvic cavity 16-17
Distribution of ANS Fibers: Parasympathetic Parasympathetic axons reach organs through 1. Cranial nerves Oculomotor (III) through ciliary ganglion. Ciliary muscles and iris Facial (VII) through pterygopalatine ganglion and submandibular ganglion. Lacrimal glands, mucosal glands of nasal cavity and palate, some salivary glands Glossopharyngeal (IX) through otic ganglion. Parotid salivary gland 2. Vagus nerve and thoracic nerve plexuses. Heart, lungs, esophagus through esophageal plexus 3. Abdominopelvic nerve plexuses. Parts of vagus nerve supply stomach and other viscera 4. Pelvic splanchnic nerves and nerve plexuses. Colon, urinary bladder, reproductive organs 16-18
Distribution of Autonomic Nerve Fibers Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Facial nerve Glossopharyngeal nerve Internal carotid plexus Superior cervical sympathetic chain ganglion Sympathetic nerves Cervicothoracic ganglion Oculomotor nerve Ciliary ganglion Pterygopalatine ganglion Otic ganglion Submandibular ganglion Vagus nerve Pulmonary plexus Cardiac plexus Sympathetic nerves Fifth thoracic sympathetic chain ganglion Greater splanchnic nerve Spinal nerve White ramus communicans Gray ramus communicans Lesser splanchnic nerve Kidney Second lumbar sympathetic chain ganglion Lumbar splanchnic nerves Esophagus and esophageal plexus Heart Aorta and thoracic aortic plexus Stomach Celiac ganglion and plexus Superior mesenteric ganglion and plexus Aorta and abdominal aortic plexus Small intestine Inferior mesenteric ganglion and plexus Superior hypogastric plexus Sacral splanchnic nerves Pelvic splanchnic nerves Sacral plexus Colon Inferior hypogastric plexus Urinary bladder Rectum Prostate gland Sympathetic Parasympathetic 16-19
Sensory Neurons in Autonomic Nerve Plexuses Parts of reflex arcs regulating organ activities Transmit pain and pressure sensations from organs to the CNS 16-20
16.3 Physiology of the ANS Neurotransmitters: primary substances produced by neurons of ANS Acetylcholine released by cholinergic neurons Norepinephrine released by adrenergic neurons Certain cells have receptors that combine with neurotransmitters causing a response in the cell Cholinergic: bind acetylcholine. Have two different forms: nicotinic and muscarinic Nicotinic: all receptors on postganglionic neurons, all skeletal muscles, adrenal glands Muscarinic: all receptors on parasympathetic effectors, receptors of some sweat glands Adrenergic receptors bind norepinephrine/epinephrine Alpha and beta receptors.these are further subdivided into categories. α 1 and β 1 usually have opposite affects than α 2 and β 2 16-21
Location of ANS Receptors Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Nicotinic receptors, which respond to acetylcholine (ACh), are located on the cell bodies of both sympathetic and parasympathetic postganglionic neurons in autonomic ganglia. Binding of ACh to nicotinic receptors has an excitatory effect. ACh released Location of nicotinic receptors Preganglionic neuron Postganglionic neuron (b) Muscarinic receptors, which respond to ACh, are located on the cells of all parasympathetic effectors and some sympathetic effectors, such as sweat glands. Binding of ACh to muscarinic receptors may be excitatory or inhibitory, depending on the specific Preganglionic neuron Location of nicotinic receptors ACh released ACh released Postganglionic neuron Location of muscarinic receptors Cell of effector (c) Adrenergic receptors, which respond to norepinephrine (NE), are located on most sympathetic effectors. Binding of NE to adrenergic receptors may be excitatory or inhibitory, depending on the specific effector. Location of nicotinic receptors Location of adrenergic receptors Cell of effector ACh released NE released Preganglionic neuron Postganglionic neuron 16-22
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16.4 Regulation of the ANS Autonomic reflexes control most of activity of visceral organs, glands, and blood vessels. Autonomic reflex activity influenced by hypothalamus and higher brain centers, but it is the hypothalamus that has overall control of the ANS. Sympathetic and parasympathetic divisions influence activities of enteric nervous system through autonomic reflexes. These involve the CNS. But, the enteric nervous system can function independently of CNS through local reflexes. E.g., when wall of digestive tract is stretched, sensory neurons send information to enteric plexus and then motor responses sent to smooth muscle of gut wall and the muscle contracts. 16-25
Autonomic Reflexes Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Integration in medulla oblongata Glossopharyngeal nerve Increase in blood pressure detected by carotid baroreceptors Common carotid artery a) Parasympathetic reflex via vagus lowers heart rate. Vagus nerve Terminal ganglion Heart rate decreases, causing blood pressure to decrease. Heart Spinal cord Sympathetic chain ganglia Integration in medulla oblongata Sympathetic nerve Heart rate increases, causing blood pressure to increase. Glossopharyngeal nerve Decrease in blood pressure detected by carotid baroreceptors Common carotid artery b) Sympathetic reflex via cardiac accelerator nerves (sympathetic) cause heart rate to increase. 16-26
Enteric Nervous System: Autonomic and Local Reflexes Regulation of activity of digestive tract Sensory neurons of enteric plexuses supply CNS with information Autonomic neurons affect responses of smooth muscle and glands Local reflex: does not involve CNS. Produces involuntary, unconscious, stereotypical response to stimulus. E.g., stretch of wall of digestive tract causes contraction of smooth muscle of the wall. 16-27
Influence of Brain on Autonomic Functions 16-28
Control of Autonomic Function Cerebral Cortex
Control of Autonomic Function Hypothalamus
Control of Autonomic Function Midbrain, Pons, Medulla
Control of Autonomic Function Spinal Cord Reflexes
16.5 Functional Generalizations Dual innervation to most organs with sympathetic and parasympathetic having the opposite effects. Either division alone or both working together can coordinate activities of different structures. Sympathetic prepares body for physical activity or flight-or-fight response. But also important at rest. Blood vessel walls receive only sympathetic stimulation, so at rest, sympathetic is responsible for maintenance of blood pressure. In general, parasympathetic more important for resting conditions: SLUDD: salivation, lacrimation, urination, digestion, defecation 16-33
Innervation of Organs by ANS Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Preganglionic neuron Postganglionic neuron Eye Lacrimal gland Ciliary ganglion III Nasal mucosa Pterygopalatine ganglion Spinal cord T1 Sublingual and submandibular glands Parotid gland Sympathetic nerves Submandibular ganglion Otic ganglion Trachea VII IX X Medulla Lung L2 Sympathetic chain Greater splanchnic nerve Lesser splanchnic nerve Lumbar splanchnic Inferior nerves mesenteric ganglion Sacral splanchnic Hypogastric nerves ganglion Celiac ganglion Superior mesenteric ganglion Adrenal gland Urinary system and genitalia Heart Liver Stomach Spleen Pancreas Small intestine Kidney Large intestine Pelvic splanchnic nerve Preganglionic neuron Postganglionic neuron Sympathetic (thoracolumbar ) Parasympathetic (craniosacral ) S2 S3 S4 16-34
Sympathetics & Parasympathetics Slows and Speeds Function
Functions at Rest vs. Activity 1. Increased heart rate and force of contraction 2. Blood vessel dilation in skeletal and cardiac muscles 3. Dilation of air passageways 4. Energy sources availability increased Glycogen to glucose Fat cells break down triglycerides 5. Muscles generate heat, body temperature increases 6. Sweat gland activity increases 7. Decrease in nonessential organ activities 16-36
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