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The Autonomic Nervous System: Modified by Dr. Par Mohammadian
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Autonomic Nervous System (ANS)
ANS consists of motor neurons that Innervate smooth and cardiac muscle, and glands Make adjustments to ensure optimal support for body activities Operate via subconscious control Also called involuntary nervous system or general visceral motor system © 2013 Pearson Education, Inc.
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Central nervous system (CNS) Peripheral nervous system (PNS)
Figure Place of the ANS in the structural organization of the nervous system. Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division © 2013 Pearson Education, Inc.
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Somatic vs Autonomic Nervous Systems
Both have motor fibers Differ in Effectors Efferent pathways and ganglia Target organ responses to neurotransmitters © 2013 Pearson Education, Inc.
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Somatic nervous system
Effectors Somatic nervous system Skeletal muscles ANS Cardiac muscle Smooth muscle Glands © 2013 Pearson Education, Inc.
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Efferent Pathways and Ganglia
Somatic nervous system Cell body in CNS; thick, myelinated, group A fiber extends in spinal or cranial nerve to skeletal muscle ANS pathway uses two-neuron chain 1. Preganglionic neuron (in CNS) has a thin, lightly myelinated preganglionic axon. 2. Postganglionic (ganglionic) neuron in autonomic ganglion outside CNS has nonmyelinated postganglionic axon that extends to effector organ
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Neurotransmitter Effects
Somatic nervous system All somatic motor neurons release acetylcholine (ACh) Effects always stimulatory ANS Preganglionic fibers release ACh Postganglionic fibers release norepinephrine or ACh at effectors Effect is either stimulatory or inhibitory, depending on type of receptors © 2013 Pearson Education, Inc.
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Figure 14.2 Comparison of motor neurons in the somatic and autonomic nervous systems.
Cell bodies in central nervous system Neurotransmitter at effector Effector organs Peripheral nervous system Effect Single neuron from CNS to effector organs ACh SOMATIC NERVOUS SYSTEM + Stimulatory Heavily myelinated axon Skeletal muscle Two-neuron chain from CNS to effector organs ACh NE Nonmyelinated postganglionic axon SYMPATHETIC Lightly myelinated preganglionic axons Ganglion Epinephrine and norepinephrine + – ACh Stimulatory or inhibitory, depending on neuro- transmitter and receptors on effector organs AUTONOMIC NERVOUS SYSTEM Adrenal medulla Blood vessel ACh ACh Smooth muscle (e.g., in gut), glands, cardiac muscle PARASYMPATHETIC Lightly myelinated preganglionic axon Nonmyelinated postganglionic axon Ganglion Acetylcholine (ACh) Norepinephrine (NE) © 2013 Pearson Education, Inc.
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Parasympathetic division Dual innervation
Divisions of the ANS Sympathetic division Parasympathetic division Dual innervation ~ All visceral organs served by both divisions, but cause opposite effects Dynamic antagonism between two divisions maintains homeostasis © 2013 Pearson Education, Inc.
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Role of the Parasympathetic Division
Promotes maintenance activities and conserves body energy Directs digestion, diuresis, defecation As in person relaxing and reading after a meal Blood pressure, heart rate, and respiratory rates are low Gastrointestinal tract activity high Pupils constricted; lenses accommodated for close vision © 2013 Pearson Education, Inc.
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Role of the Sympathetic Division
Mobilizes body during activity; "fight-or-flight" system Exercise, excitement, emergency, embarrassment Increased heart rate; dry mouth; cold, sweaty skin; dilated pupils During vigorous physical activity Shunts blood to skeletal muscles and heart Dilates bronchioles Causes liver to release glucose
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Long preganglionic & short postganglionic
Parasympathetic Sympathetic Eye Eye Brain stem Origin: Craniosacral part: Brain stem nuclei of cranial nerves oculomotor III, facial VII, glossopharyngeal IX, vagus X & spinal cord segments S2-S4 Salivary glands Skin* Cranial Sympathetic ganglia Salivary glands Heart Cervical Lungs Lungs T1 Heart Stomach Thoracic Stomach Pancreas Length of Fibers: Long preganglionic & short postganglionic Liver and gall- bladder Pancreas L1 Liver and gall- bladder Adrenal gland Lumbar Location of Ganglia: In the visceral effector organs Bladder Bladder Genitals Genitals Sacral
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Origin: Thoracolumbar, lateral gray horn of spinal cord segments T1-L2
Parasympathetic Sympathetic Eye Eye Brain stem Origin: Thoracolumbar, lateral gray horn of spinal cord segments T1-L2 Salivary glands Skin* Cranial Sympathetic ganglia Salivary glands Heart Cervical Lungs Lungs T1 Heart Stomach Length of Fibers: Thoracic Short preganglionic & long postganglionic Stomach Pancreas Liver and gall- bladder Pancreas L1 Liver and gall- bladder Adrenal gland Lumbar Location of Ganglia: Close to the spinal cord Bladder Bladder Genitals Genitals Sacral
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Parasympathetic Ganglia
CN III Ciliary ganglion Eye Lacrimal gland CN VII Pterygopalatine ganglion CN IX Nasal mucosa CN X 1. ciliary ganglion smooth muscle of the eye 2. pterygopalatine ganglion nasal mucosa, palate, pharynx, lacrimal gland 3. submandibular and otic ganglia salivary glands 4. cardiac and pulmonary plexuses to the heart and lungs Submandibular ganglion Submandibular and sublingual glands Otic ganglion Parotid gland Heart Cardiac and pulmonary plexuses Lung Liver and gallbladder Celiac plexus Stomach Pancreas S2 Large intestine S4 Pelvic splanchnic nerves Small intestine Inferior hypogastric plexus Rectum Urinary bladder and ureters Genitalia (penis, clitoris, and vagina) Preganglionic Postganglionic CN Cranial nerve S Sacral nerve
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Sympathetic (Thoracolumbar) Division
Preganglionic neurons are in spinal cord segments T1 – L2 Form lateral horns of spinal cord Preganglionic fibers pass through white rami communicantes and enter sympathetic trunk (chain or paravertebral) ganglia © 2013 Pearson Education, Inc.
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Figure 14.6 Sympathetic division of the ANS.
Eye Lacrimal gland Pons Nasal mucosa *Sympathetic trunk (chain) ganglia Blood vessels; skin (arrector pili muscles & sweat glands) Superior cervical ganglion Salivary glands (dry mouth during fight & flight!! Middle cervical ganglion *Sympathetic trunk: ganglia & fibers Heart Inferior cervical ganglion Cardiac and pulmonary plexuses Lung T1 Greater splanchnic nerve Lesser splanchnic nerve Celiac ganglion Liver and gallbladder L2 Stomach Superior mesenteric ganglion White rami Communicantes (pathway) White: myelinated Spleen Inferior mesenteric ganglion Adrenal medulla Kidney Sacral splanchnic nerves Lumbar splanchnic nerves Small intestine Large intestine Rectum Preganglionic Postganglionic Genitalia (uterus, vagina, and penis) and urinary bladder © 2013 Pearson Education, Inc.
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Sympathetic Ganglia 1. superior cervical ganglion
sweat glands, eye, face vessels and glands 2. middle cervical ganglion heart 3. inferior cervical ganglion 4. thoracic ganglia heart, lungs, bronchi, thoracic viscera 5. lumbar and sacral ganglia viscera of abdominopelvic cavity
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Visceral reflexes have the same elements as somatic reflexes
They are always polysynaptic pathways Afferent fibers are found in spinal and autonomic nerves © 2013 Pearson Education, Inc.
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1 2 3 4 5 Stimulus Dorsal root ganglion Receptor in viscera
Figure Visceral reflexes. Stimulus Dorsal root ganglion 1 Receptor in viscera Visceral sensory neuron 2 Spinal cord Integration center • May be preganglionic neuron (as shown) • May be a dorsal horn interneuron • May be within walls of gastrointestinal tract 3 Autonomic ganglion Motor neuron (two-neuron chain) • Preganglionic neuron • Postganglionic neuron 4 5 Visceral effector Response © 2013 Pearson Education, Inc.
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Levels of ANS Control The hypothalamus is the main integration center of ANS activity Subconscious cerebral input via limbic lobe connections influences hypothalamic function Other controls come from the cerebral cortex, the reticular formation, and the spinal cord
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Levels of ANS Control
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Hypothalamic Control Centers of the hypothalamus control:
Heart activity and blood pressure Body temperature, water balance, and endocrine activity Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex) Reactions to fear and the “fight-or-flight” system
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