Drugs acting on the Autonomic Nervous System

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amycykho
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282794
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Drugs acting on the Autonomic Nervous System
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2014-09-11 22:26:23
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drugs medicine receptors
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Drugs acting on the Autonomic Nervous System
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  1. What is the general action of a cholinergic agonist?
    A cholinergic agonist increases the effects of acetylcholine on its receptors which can be found at the neuromuscular junction, preganglionic autonomic synapse and postganglionic parasympathetic synapse. Therefore its general actions include increasing skeletal muscle contraction and increasing parasympathetic activity such as bladder and bowel function.
  2. What are some possible adverse effect of cholinergic agonists?
    A cholinergic agonist increases the effects of acetylcholine on its receptors which can be found at the neuromuscular junction, preganglionic autonomic synapse and postganglionic parasympathetic synapse. Adverse effects primarly relate to increase in parasympathetic stimulation: uncontrollable bowel and bladder motility, bronchoconstriction and bradycardia
  3. What are three potential sites of action for cholinergic agonists? Give an example of a real drug that acts at each site and a condition it is used for.
    • 1) direct agonism at the acetylcholine receptor eg. BETHANECOL: urinary retention
    • 2) cholinesterase (breaks down acetylcholine in the synaptic space) inhibition eg. NEOSTIGMINE or PYRIDOSTIGMINE: myasthenia gravis, Alzheimer's
    • 3) reuptake inhibitor eg. HEMICHOLINE: no clinical use and is considered an indirect cholinergic antagonist as the slower the reuptake of choline, the slower the synthesis of acetylcholine
  4. What is the general action of a cholinergic antagonist?
    A cholinergic antagonist decreases the effects of acetylcholine on its receptors found at the NMJ, preganglionic autonomic synapse and postganglionic parasympathetic synapse. Therefore its general actions include decreasing skeletal muscle contraction and decreasing parasympathetic activity such as bowel and bladder function.
  5. What are some possible adverse effects of cholinergic antagonists?
    A cholinergic antagonist decreases the effects of acetylcholine on its receptors found at the NMJ, preganglionic autonomic synapse and postganglionic parasympathetic synapse. This can cause muscle weakness as well as generalised increase in sympathetic nervous system-dominant physiological activity such as tachycardia, hypertension and constipation.
  6. Explain the MOA of THREE muscarinic cholinergic antagonists
    • Muscarinic cholinergic antagonists competitively inhibit the muscarinic cholinergic receptor found at the postganglionic parasympathetic synapse decreasing the EPSP and therefore parasympathetic activity eg.
    • 1) ATROPINE: may be used as an antidote to bad parasympathetic side effects of NEOSTIGMINE
    • 2) SCOPALAMINE: anti-emetic that reduces gut motility by inhibiting parasympathetic activity
    • 3) IPRATROPIUM: anti-asthma that reduces bronchoconstriction in synergy with beta-2 agonists
  7. What is the botulinum toxin?
    The botulinum toxin is produced by the bacteria Clostridium botulinum and is a cholinergic antagonist that acts by preventing acetylcholine vesicles from fusing at the presynaptic membrane causing total blockade of neuromuscular transmission and paralysis. However, it also has therapeutic uses against wrinkles, abnormal eye movements (blepharospasm, strabismus) and hypertonia in UMNs.
  8. Explain the MOA of depolarising nicotinic cholinergic antagonists and give an example
    Depolarising nicotinic cholinergic antagonists competitively bind to nicotinic cholinergic receptors on the postsynaptic membrane causing it to depolarise and repolarise to a desensitised state reducing the EPSP eg. SUCCINYLCHOLINE or DANTROLENE: muscle relaxant pre-op or pre-intubation
  9. Explain the MOA of non-depolarising cholinergic antagonists and give an example
    Non-depolarising nicotinic cholinergic antagonists competitively bind to nicotinic cholinergic receptors on the postsynaptic membrane without depolarising so that acetylcholine cannot activate the receptor eg. TUBOCURARINE: adjuvant drug for surgical anaesthesia

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