Autonomic Nervous System Organization Comparison of peripheral nervous system Components of the ANS Receptors/neurotransmitters Hypothalamic control Visceral function
Homeostasis & Organization Maintenance of the internal environment – what else? http://itc.gsw.edu/faculty/gfisk/anim/autonomicns.swf 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
Distribution of PNS: cranial nerve nuclei in brainstem Oculomotor (III) Facial (VII) Glossopharyngeal (IX) Vagus (X) Sacral spinal nerves (S2-S4)
SNS arises from thoracic & lumbar spinal cord levels – forming sympathetic trunk intermediolateral (IML) cell column (prevertebral)
Autonomic sympathetic & parasympathetic pathways
Organization of Efferent Divisions of the ANS
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?
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
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
Synapses in Autonomic Nerves Varicosities NT released to ECF No cleft Effect: large area slow acting long duration Synapses in Autonomic Nerves
Summary of two branches of the ANS
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
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
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
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