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Autonomic Nervous System
Organization Comparison of peripheral nervous system Components of the ANS Receptors/neurotransmitters Hypothalamic control Visceral function
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Homeostasis & Organization
Maintenance of the internal environment – what else? Visceral efferent division of the human nervous system respond via contraction/relaxation or secretion conduction of sensory impulses back to NTS feedback loop: visceral efferent & afferent system Parasympathetic & sympathetic branches exit the spinal cord in different regions - craniosacral & thoracolumbar
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Distribution of PNS: cranial nerve nuclei in brainstem
Oculomotor (III) Facial (VII) Glossopharyngeal (IX) Vagus (X) Sacral spinal nerves (S2-S4)
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SNS arises from thoracic & lumbar spinal cord levels – forming sympathetic trunk
intermediolateral (IML) cell column (prevertebral)
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Autonomic sympathetic & parasympathetic pathways
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Organization of Efferent Divisions of the ANS
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Key questions for understanding organization & function of the ANS
1. How do the 2 autonomic branches differ anatomically? 2. The autonomic divisions are distinguished biochemically by their neurotransmitters & receptors explain?
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Cholinergic Receptors
Nicotinic receptors: preganglionic receptor for both PSN & SNS, at NMJ & in the adrenal medulla responds to ACh; produce excitation ® binding opens ion channels influx of Na+ & efflux of K+ Muscarinic receptors (M1 & M2): postganglionic for PSN; located in heart, smooth muscle & glands; respond to ACh M1 receptor: IP3 is second messenger and IC [Ca2+] M2 receptor: inhibits adenylate cyclase result is ¯ [cAMP] & slows rate of depolarization
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Adrenergic Receptors receptor activation mechanism location produces of action a1 skin & splanchnic excitation formation of IP3 vascular SM, GI & IC [Ca2+] & bladder sphincters a2 walls of GI tract inhibition inhibit adenylate fat cells & platelets cyclase, ¯ [cAMP] b1 heart excitation produce cAMP, activate adenylate b2 GI tract & bladder relaxation same as b1 vascular & bronchial SM
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Synapses in Autonomic Nerves
Varicosities NT released to ECF No cleft Effect: large area slow acting long duration Synapses in Autonomic Nerves
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Summary of two branches of the ANS
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Comparison of the Somatic & Autonomic Nervous Systems
ANS: is a two-neuron system: preganglionic fibers & postganglionic fibers self-governed exclusively a reflex system innervates smooth muscle, viscera & glands ACh & norepinephrine (NE) -- neurotransmitters Somatic nervous system: cell bodies in the CNS – axons extend to skeletal muscle: lack ganglia (single-neuron system) voluntary/reflex system innervate skeletal muscle ACh is excitatory neurotransmitter
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Adrenal Medulla: an extension of the SN S
acts like a combined autonomic ganglion & postsynaptic sympathetic nerve releases epinephrine & norepinephrine (E = 80% & NE = 20%) action of adrenals are under control of the hypothalamus
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Hypothalamus Has Central Control of the ANS
Integrates autonomic & neuro- endocrine functions; serves as a homeostatic center Coordinates visceral activities in response to changes in environment Final common pathway is located in brainstem
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ANS & Visceral Function
Structure SNS Stimulation PNS Stimulation iris pupil dilation pupil constriction salivary glands saliva production saliva production heart HR, conduction/force ¯ HR & conduction blood vessels vasoconstrict/dilatate lung relax SM SM contraction GI tract ¯ motility peristalsis, motility digestion liver glycogenolysis conserve glucose kidney ¯ GFR urine secretion sweat glands sweating bladder wall relaxed, sphincter wall contracted closed sphincter relaxed
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