ans pharmacology
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ANS Pharmacology
25th April, 2013
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
Anatomy of ANS•Pre & Post-ganglionic Neuron•Afferent Neurons•Sympathetic & Parasympathetic Divisions•Enteric Neurons
• Innervate• motility,
exocrine and endocrine, microcirculation of GI
Parasympathetic Ganglionic Synapse
Action Potential
Na+
Ca 2+
aa
b
ACH
Acetylcholinesterase
Na+
Preganglionic neuron
Nicotinic
Receptor
Parasympathetic Organ Synapse
Action Potential
Ca 2+
Na+
ACH
Acetylcholinesterase
K+
G
Postganglionic neuron
Muscarinic
Receptor
Sympathetic Ganglionic Synapse
Action Potential
Na+
Ca 2+
aa
b
ACH
Acetylcholinesterase
Na+
Preganglionic neuron
Nicotinic
Receptor
Sympathetic Organ Synapse
Action Potential
Ca 2+
Na+
NE
G
Postganglionic neuron
Adrenergic
Receptor
SummarySummary 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
Summary
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
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
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)
Branch Type Location Typical Agonist
Drugs Typical Antagonist
Drugs
Sympathetic
(adrenergic)
α1 Most vascular arterioles, Sphincters of bladder & GI tract, Iris dilator
NorepinephrineEpinephrine
PhenoxybenzaminePhentolaminePrazosin
α2 GI tract, presynaptic sympathetic neurons ClonidineEpinephrine
Yohimbine
β1 Heart muscle, Salivary glands, Fat cells
NorepinephrineIsoproteronolDobutamineEpinephrine
"Beta blockers"PropranololMetoprolol
β 2 Bronchioles of lung, Arterioles of skeletal muscles, brain and lungs, Bladder wall, GIT
EpinephrineIsoproteronolAlbuterol
"Beta blockers"PropranololButoxamine
Parasympathetic
(cholinergic)
M Heart muscle, Sphincters of bladder & GI tractBronchioles of lung, Sweat glands Iris constrictor
AcetylcholineMuscarineCarbachol
AtropineScopolamine
N Neuromuscular junctions, Autonomic ganglia AcetylcholineNicotineCarbachol
Curare
Dual Innervation of the Iris
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
Classification of drugs affecting the ANS
• Parasympathetic nervous systemMimic acetylcholine = cholinergic = muscarinic agonists = parasympathomimetic
Block acetylcholine = anticholinergic = muscarinic antagonist = parasympatholytic
• Sympathetic nervous systemMimic norepinephrine = adrenergic = adrenergic agonist = sympathomimetic
Block norepinephrine = antiadrenergic = adrenergic antagonist = sympatholytic
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