Ans pharmacology

KMU (IPM&R)
pharmacology

1. ANS Pharmacology 25 th April, 2013

2. Important Things to Remember about ANS ANS/Visceral/Vegetative System involuntarily regulates smooth muscles and glands heart, respiratory system, GI tract, peristalsis (digestion), bladder, and eyes Has two divisions i.e. PANS & SANS (homeostasis) Both have relay stations (ganglia) b/w CNS & end organ. Use the neurotransmitters Ach & NE

3. Anatomy of ANS Pre & Post- ganglionic Neuron Afferent Neurons Sympathetic & Parasympathetic Divisions Enteric Neurons Innervate motility, exocrine and endocrine, microcirculation of GI

4. Parasympathetic Ganglionic Synapse Action Potential Na + Ca 2+ a a b ACH Acetylcholinesterase Na + Preganglionic neuron Nicotinic Receptor

5. Parasympathetic Organ Synapse Action Potential Ca 2+ Na + ACH Acetylcholinesterase K + G Postganglionic neuron Muscarinic Receptor

6. Sympathetic Ganglionic Synapse Action Potential Na + Ca 2+ a a b ACH Acetylcholinesterase Na + Preganglionic neuron Nicotinic Receptor

7. Sympathetic Organ Synapse Action Potential Ca 2+ Na + NE G Postganglionic neuron Adrenergic Receptor

8. Summary Summary of parasympathetic neurons and synapses Preganglionic neurons Long Synapse with postganglionic neurons at or near organ Release acetylcholine (ACH) to activate nicotinic receptors on postganglionic neurons Postganglionic neurons Short Synapse on the target organ Release acetylcholine (ACH) to activate muscarinic receptors on the target organ Summary of sympathetic neurons and synapses Preganglionic neurons Short Synapse with postganglionic neurons near spinal cord Release acetylcholine (ACH) to activate nicotinic receptors on postganglionic neurons Postganglionic neurons Long Synapse on the target organ Release norepinephrine to activate adrenergic receptors on target organs

9. Summary

10. Exceptions in the sympathetic nervous system: Sweat glands: Postganglionic neurons involved with stress-related excretion release norepinephrine (“sweaty palms”) Postganglionic neurons involved with thermoregulation release acetylcholine

11. Exceptions in the sympathetic nervous system: Kidneys: Postganglionic neurons to the smooth muscle of the renal vascular bed release dopamine Adrenal gland: Preganglionic neurons do not synapse in the paraverterbral sympathetic ganglion Preganglionic neurons synapse directly on the adrenal gland, release acetylcholine, and activate nicotinic receptors on the adrenal gland Adrenal glands release epinephrine into systemic circulation

12. Functions Sympathetic Stimulation (Fight or Flight) ↑HR, BP, blood flow Diffuse distribution (more than one organ innervated) Parasympathetic Stimulation (Rest & Digest) Maintaining homeostasis Discrete distribution/activation Role of CNS Reflex Arcs : Afferent input ~ hypothalamus, medulla oblongata, and spinal cord ~ efferent reflex impulse via ANS Emotions: Innervation by ANS Dual Only sympathetic ( adrenal medulla, kidney, pilomotor muscles, and sweat glands)

13.  Branch  Type  Location  Typical Agonist Drugs  Typical Antagonist Drugs  Sympathetic (adrenergic)   α1  Most vascular arterioles, Sphincters of bladder & GI tract, Iris dilator   Norepinephrine Epinephrine   Phenoxybenzamine Phentolamine Prazosin α2  GI tract, presynaptic sympathetic neurons  Clonidine Epinephrine   Yohimbine   β 1  Heart muscle, Salivary glands, Fat cells  Norepinephrine Isoproteronol Dobutamine Epinephrine  "Beta blockers" Propranolol Metoprolol β 2  Bronchioles of lung, Arterioles of skeletal muscles, brain and lungs, Bladder wall, GIT  Epinephrine Isoproteronol Albuterol   "Beta blockers" Propranolol Butoxamine   Parasympathetic (cholinergic) M  Heart muscle, Sphincters of bladder & GI tract Bronchioles of lung, Sweat glands Iris constrictor  Acetylcholine Muscarine Carbachol  Atropine Scopolamine    N   Neuromuscular junctions, Autonomic ganglia   Acetylcholine Nicotine Carbachol  Curare

14. Dual Innervation of the Iris

15. Without Dual Innervation Some effectors receive only sympathetic adrenal medulla, arrector pili muscles, sweat glands and many blood vessels Sympathetic tone a baseline firing frequency vasomotor tone provides partial constriction increase in firing frequency = vasoconstriction decrease in firing frequency = vasodilation can shift blood flow from one organ to another as needed sympathetic stimulation increases blood to skeletal and cardiac muscles -- reduced blood to skin

16. Classification of drugs affecting the ANS Parasympathetic nervous system Mimic acetylcholine = cholinergic = muscarinic agonists = parasympathomimetic Block acetylcholine = anticholinergic = muscarinic antagonist = parasympatholytic Sympathetic nervous system Mimic norepinephrine = adrenergic = adrenergic agonist = sympathomimetic Block norepinephrine = antiadrenergic = adrenergic antagonist = sympatholytic