The Autonomic Nervous System and Visceral Sensory Neurons The
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C HAPT E R 15 The Autonomic Nervous System and Visceral Sensory Neurons The ANS and Visceral Sensory Neurons • • The ANS—a system of motor neurons Innervates • Smooth muscle • Cardiac muscle • Glands Gl d The ANS and Visceral Sensory Neurons • The ANS—a system of motor neurons • Regulates visceral functions • Heart rate • Blood pressure • Digestion • Urination • The ANS is the • General visceral motor division of the PNS 1 The Autonomic Nervous System and Visceral Sensory Neurons Figure 15.1 Comparison of Autonomic and Somatic Motor Systems • Somatic motor system • One motor neuron extends from the CNS to skeletal muscle • Axons are well myelinated, conduct impulses rapidly Comparison of Autonomic and Somatic Motor Systems • Autonomic nervous system • Chain of two motor neurons • Preganglionic neuron • Ganglionic neuron • Conduction C d ti is i slower l due d to t thinly thi l or unmyelinated li t d axons 2 Autonomic and Somatic Motor Systems SOMATIC NERVOUS SYSTEM Cell bodies in central nervous system Peripheral nervous system Neurotransmitter Effector at effector organs Effect Single neuron from CNS to effector organs ACh Stimulatory Heavily myelinated axon Skeletal muscle SYMPATH HETIC NE ACh Unmyelinated postganglionic axon Lightly myelinated Ganglion preganglionic axons Epinephrine and ACh norepinephrine Adrenal medulla PARASYMPATHETIC AUTONOMIC NERVOUS SYS STEM Two-neuron chain from CNS to effector organs Blood vessel ACh Lightly myelinated preganglionic axon ACh Unmyelinated Ganglion postganglionic axon Smooth muscle (e.g., in gut), glands, cardiac muscle Stimulatory or inhibitory, depending on neurotransmitter and receptors on effector organs Figure 15.2 Divisions of the Autonomic Nervous System • Sympathetic and parasympathetic divisions • Chains of two motor neurons • Innervate mostly the same structures • Cause opposite effects 3 Divisions of the Autonomic Nervous System • Sympathetic – “fight, flight, or fright” • Activated during exercise, excitement, and emergencies • Parasympathetic – “rest and digest” • Concerned C d with i h conserving i energy Anatomical Differences in Sympathetic and Parasympathetic Divisions • Parasympathetic Issue from different regions of the CNS • Sympathetic—also • called the thoracolumbar division Parasympathetic—also called the craniosacral division Sympathetic Eye Brain stem Salivary glands Heart Eye Skin* Cranial Cervical Sympathetic ganglia Salivary glands Lungs Lungs T1 Heart Stomach Thoracic Pancreas Stomach L1 Liver and gallbladder Lumbar Adrenal gland Pancreas Liver and gallbladder Bladder Bladder Genitals Genitals Sacral Figure 15.3 Anatomical Differences in Sympathetic and Parasympathetic Divisions • Length of postganglionic fibers • Sympathetic – long postganglionic fibers • Parasympathetic – short postganglionic fibers • Branching of axons • Sympathetic axons – highly branched • Influences many organs • Parasympathetic axons – few branches • Localized effect 4 Anatomical Differences in Sympathetic and Parasympathetic Divisions • Neurotransmitter released by postganglionic axons • Sympathetic – most release norepinephrine (adrenergic) • Parasympathetic – release acetylcholine Parasympathetic division • • Preganglionic neurons in the brainstem and sacral segments of spinal cord Ganglionic neurons in peripheral ganglia located within or near target organs The Parasympathetic Division • Cranial outflow • Comes from the brain • Innervates organs of the head, neck, thorax, and abdomen • S Sacral l outflow tfl • Supplies remaining abdominal and pelvic organs 5 The Parasympathetic Division Ciliary ganglion CN III CN VII CN IX CN X Eye Lacrimal gland Nasal mucosa Pterygopalatine ganglion Submandibular ganglion Otic ganglion Submandibular and sublingual glands Parotid gland Heart Cardiac and pulmonary plexuses Lung Celiac plexus Liver and gallbladder Stomach Pancreas S2 Large intestine S4 Small intestine Pelvic splanchnic nerves Inferior hypogastric plexus Rectum Urinary bladder and ureters Genitalia (penis, clitoris, and vagina) Preganglionic Postganglionic CN Cranial nerve Figure 15.4 Cranial Outflow • Preganglionic fibers run via: • • • • • Oculomotor nerve (III) Facial nerve (VII) Glossopharyngeal nerve (IX) Vagus nerve (X) Cell bodies located in cranial nerve nuclei in the brain stem Sacral Outflow • • • Emerges from S2-S4 Innervates organs of the pelvis and lower abdomen Preganglionic cell bodies • Axons run in ventral roots to ventral rami • Located in visceral motor region of spinal gray matter • Form splanchnic nerves • Run through the inferior hypogastric plexus 6 Sympathetic Pathways to Thoracic Organs Eye Lacrimal gland Nasal mucosa Pons Sympathetic trunk (chain) ganglia Blood vessels; skin (arrector pili muscles and sweat glands) Superior cervical ganglion Middle cervical ganglion T1 Salivary glands Heart Inferior cervical ganglion Cardiac and pulmonary plexuses Lung Greater splanchnic nerve Lesser splanchnic nerve Celiac ganglion L2 Liver and gallbladder Stomach White rami communicantes Superior mesenteric ganglion Spleen Adrenal medulla Kidney Sacral splanchnic nerves Lumbar splanchnic nerves Inferior mesenteric ganglion Small intestine Large intestine Rectum Preganglionic Postganglionic Genitalia (uterus, vagina, and penis) and urinary bladder Figure 15.7 The Sympathetic Division • Basic organization • Issues from T1-L2 • Preganglionic fibers form the lateral gray horn • Supplies visceral organs and structures of superficial body regions • Contains C t i more ganglia li than th the th parasympathetic th ti division di i i Sympathetic ganglia • • Sympathetic chain ganglia (paravertebral ganglia) Collateral ganglia (prevertebral ganglia) 7 Sympathetic Trunk Ganglia Spinal cord Lateral horn (visceral motor zone) Dorsal root Dorsal root Ventral root Dorsal root ganglion Rib Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Gray ramus communicans White ramus communicans Sympathetic trunk ganglion Sympathetic trunk Ventral ramus of spinal nerve Skin (arrector pili muscles and sweat glands) Gray ramus communicans White ramus communicans Thoracic splanchnic nerves (a) Location of the sympathetic trunk Ventral root Sympathetic trunk ganglion Sympathetic trunk 1 Synapse at the same level To effector Blood vessels Splanchnic nerve Collateral ganglion (such as the celiac) Skin (arrector pili muscles and sweat glands) Target organ in abdomen (e.g., intestine) To effector 3Synapse in a distant collateral ganglion anterior to the vertebral column 2 Synapse at a higher or lower level Blood vessels (b) Three pathways of sympathetic innervation Figure 15.6 Sympathetic Trunk Ganglia • • • • Located on both sides of the vertebral column Linked by short nerves into sympathetic trunks Joined to ventral rami by white and gray rami communicantes Fusion of ganglia fewer ganglia than spinal nerves Sympathetic Pathways to Thoracic Organs Eye Lacrimal gland Nasal mucosa Pons Sympathetic trunk (chain) ganglia Blood vessels; skin (arrector pili muscles and sweat glands) Superior cervical ganglion Middle cervical ganglion T1 Inferior cervical ganglion Salivary glands Heart Cardiac and pulmonary plexuses Lung Greater splanchnic nerve Lesser splanchnic nerve Celiac ganglion L2 Liver and gallbladder Stomach White rami communicantes Superior mesenteric ganglion Spleen Adrenal medulla Kidney Sacral splanchnic nerves Lumbar splanchnic nerves Inferior mesenteric ganglion Small intestine Large intestine Rectum Preganglionic Postganglionic Genitalia (uterus, vagina, and penis) and urinary bladder Figure 15.7 8 Prevertebral Ganglia • • • • Unpaired, not segmentally arranged Occur only in abdomen and pelvis Lie anterior to the vertebral column Main ganglia • Celiac, superior mesenteric, inferior mesenteric, inferior hypogastric ganglia Sympathetic Pathways to the Body Periphery • Innervate • Sweat glands • Arrector pili muscles • Peripheral blood vessels Sympathetic Pathways to Thoracic Organs • • Sympathetic fibers to heart have a less direct route Function – increase heart rate, dilate bronchioles, dilate blood vessels to the heart wall, inhibit the muscle and glands in the esophagus 9 Sympathetic Pathways to the Abdominal Organs • • Preganglionic fibers originate in spinal cord (T5-L2) Pass through adjacent sympathetic trunk ganglia • Then travel in thoracic splanchnic nerves • Synapse in prevertebral ganglia on the abdominal aorta • Celiac and superior mesenteric ganglia • Inhibit activity of muscles and glands in visceral organs Sympathetic Pathways to the Pelvic Organs • • • • Preganglionic fibers originate in spinal cord (T10 –L2) Some fibers synapse in sympathetic trunk Other preganglionic fibers synapse in prevertebral ganglia Postganglionic fibers proceed from plexuses to pelvic organs The Role of the Adrenal Medulla in the Sympathetic Division • • • • Major organ of the sympathetic nervous system Constitutes largest sympathetic ganglia Secretes great quantities of norepinephrine and adrenaline Stimulated to secrete by preganglionic sympathetic fibers 10 The Adrenal Medulla Sympathetic trunk Spinal cord: Ventral T8–L1 root Thoracic splanchnic nerves Kidney Adrenal medulla Adrenal gland Epinephrine and norepinephrine Adrenal medulla cells Capillary Figure 15.8 Table 15.2 (1 of 3) Table 15.2 (2 of 3) 11 Table 15.2 (3 of 3) Visceral Sensory Neurons • General visceral sensory neurons monitor • • Cell bodies are located in the dorsal root ganglion Visceral pain • Stretch, temperature, chemical changes, and irritation • No pain results when visceral organs are cut • Visceral pain results from chemical irritation or inflammation • Visceral pain often perceived to be of somatic origin • Phenomenon of referred pain A Map of Referred Pain Heart Lungs and diaphragm Liver Gallbladder Appendix Heart Liver Stomach Pancreas Small intestine Ovaries Colon Kidneys Urinary bladder Ureters Figure 15.9 12 Visceral Reflexes • Visceral sensory and autonomic neurons • Participate in visceral reflex arcs • Defecation reflex • Micturition reflex • • Some are simple S i l spinal i l reflexes fl Others do not involve the CNS • Strictly peripheral reflexes Visceral Reflex Arc Stimulus 1 Sensory receptor in viscera 2 Visceral sensory neuron 3 Integration center •May be preganglionic neuron (as shown) •May M b be a dorsal d l horn h interneuron •May be within walls of gastrointestinal tract Dorsal root ganglion Spinal cord Autonomic ganglion 4 Efferent pathway (two-neuron chain) •Preganglionic neuron •Postganglionic neuron 5 Visceral effector Response Figure 15.10 Central Control of the ANS • Control by the brain stem and spinal cord • Reticular formation exerts most direct influence • Medulla oblongata • Periaqueductal gray matter • Control C t l by b the th hypothalamus h th l andd amygdala d l • Hypothalamus—the main integration center of the ANS • Amygdala—main limbic region for emotions • Control by the cerebral cortex 13 Central Control of the ANS Communication at subconscious level Cerebral cortex (frontal lobe) Limbic system (emotional input) Hypothalamus Overall integration of ANS, the boss Brain stem (reticular formation, etc.) Regulation of pupil size, respiration, heart, blood pressure, swallowing, etc. Spinal cord Urination, defecation, erection, and ejaculation reflexes Figure 15.12 14
