ANS Pharmacology: Cholinergic Drugs
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Questions and Answers

Which type of fibers uses acetylcholine as a neurotransmitter?

  • Preganglionic fibers terminating in the adrenal medulla
  • Postganglionic fibers of the sympathetic division
  • Somatic motor neurons
  • All of the above (correct)

    • What is the function of choline acetyltransferase?

  • Transport of choline into the cytoplasm
  • Storage of acetylcholine in vesicles
  • Degradation of acetylcholine
  • Catalysis of the reaction to form acetylcholine (correct)

    • What is the role of voltage-sensitive calcium channels in the release of acetylcholine?

  • To increase the concentration of intracellular calcium (correct)
  • To open the voltage-sensitive sodium channels
  • To synthesize acetylcholine
  • To decrease the concentration of intracellular calcium

    • What is the primary neurotransmitter stored in synaptic vesicles?

    <p>Acetylcholine</p> Signup and view all the answers

    What is the function of hemicholinium?

    <p>To inhibit the transport of choline into the cytoplasm</p> Signup and view all the answers

    What is the sequence of events in neurotransmission at cholinergic neurons?

    <p>Synthesis, storage, release, binding, degradation, recycling</p> Signup and view all the answers

    What is the cotransmitter stored in synaptic vesicles along with acetylcholine?

    <p>Proteoglycan</p> Signup and view all the answers

    What is the function of voltage-sensitive sodium channels?

    <p>To propagate an action potential at the nerve ending</p> Signup and view all the answers

    What is the purpose of recycling choline and acetate?

    <p>To conserve choline and acetate for future use</p> Signup and view all the answers

    Which division of the autonomic nervous system uses acetylcholine as a neurotransmitter?

    <p>Both the parasympathetic and sympathetic divisions</p> Signup and view all the answers

    What is the effect of botulinum toxin on the release of acetylcholine from synaptic vesicles?

    <p>It blocks the release of acetylcholine into the synaptic space</p> Signup and view all the answers

    Which receptors are G protein–coupled receptors?

    <p>Muscarinic receptors</p> Signup and view all the answers

    What is the effect of acetylcholinesterase on acetylcholine in the synaptic cleft?

    <p>It breaks down acetylcholine into choline and acetate</p> Signup and view all the answers

    Which subtype of muscarinic receptors is found on gastric parietal cells?

    <p>M1 receptors</p> Signup and view all the answers

    What is the effect of nicotine on nicotinic receptors at high concentrations?

    <p>It blocks the receptor</p> Signup and view all the answers

    Where are nicotinic receptors found in the nervous system?

    <p>In the CNS, adrenal medulla, autonomic ganglia, and neuromuscular junction</p> Signup and view all the answers

    What is the effect of direct-acting cholinergic agonists?

    <p>They mimic the effects of acetylcholine by binding directly to cholinoceptors</p> Signup and view all the answers

    Which subtype of muscarinic receptors is found on cardiac cells and smooth muscle?

    <p>M2 receptors</p> Signup and view all the answers

    What is the effect of activation of M1 or M3 receptors?

    <p>It leads to the production of inositol-1,4,5-trisphosphate and diacylglycerol</p> Signup and view all the answers

    What is the effect of nicotinic receptors on the effector cell?

    <p>It depolarizes the effector cell</p> Signup and view all the answers

    What is the reason why acetylcholine has no therapeutic importance?

    <p>It has multiple actions and is rapidly inactivated by cholinesterases</p> Signup and view all the answers

    What is the mechanism of action of acetylcholine in decreasing blood pressure?

    <p>It activates M3 receptors on endothelial cells, leading to the production of nitric oxide</p> Signup and view all the answers

    What is the action of bethanechol on the detrusor muscle of the bladder?

    <p>It increases the tone of the detrusor muscle, causing urination</p> Signup and view all the answers

    What is the therapeutic use of bethanechol?

    <p>To stimulate the atonic bladder, particularly in postpartum or postoperative, nonobstructive urinary retention</p> Signup and view all the answers

    What is the effect of pilocarpine on the eye?

    <p>It produces rapid miosis and contraction of the ciliary muscle</p> Signup and view all the answers

    What is the mechanism of action of pilocarpine in glaucoma?

    <p>It opens the trabecular meshwork around the Schlemm canal, causing an immediate drop in intraocular pressure</p> Signup and view all the answers

    What is the adverse effect of pilocarpine?

    <p>It causes profuse sweating and salivation</p> Signup and view all the answers

    What is the action of anticholinesterase agents?

    <p>They inhibit the activity of AChE, leading to an accumulation of ACh in the synaptic space</p> Signup and view all the answers

    What is the effect of atropine on the muscarinic receptors?

    <p>It blocks the muscarinic receptors</p> Signup and view all the answers

    What is the common use of atropine?

    <p>To treat the toxicity of pilocarpine and bethanechol</p> Signup and view all the answers

    What is the primary difference between edrophonium and physostigmine in terms of their duration of action?

    <p>Edrophonium has a shorter duration of action than physostigmine.</p> Signup and view all the answers

    What is the primary use of neostigmine in the management of myasthenia gravis?

    <p>To manage symptoms of myasthenia gravis.</p> Signup and view all the answers

    What is the primary adverse effect of tacrine, donepezil, rivastigmine, and galantamine?

    <p>GI distress.</p> Signup and view all the answers

    What is the mechanism of action of echothiophate?

    <p>Irreversible inhibition of AChE.</p> Signup and view all the answers

    What is the therapeutic use of a topical ophthalmic solution of echothiophate?

    <p>Treatment of open-angle glaucoma.</p> Signup and view all the answers

    What is the primary difference between reversible and irreversible AChE inhibitors?

    <p>Reversible inhibitors bind non-covalently to AChE.</p> Signup and view all the answers

    What is the antidote for edrophonium-induced cholinergic crisis?

    <p>Atropine.</p> Signup and view all the answers

    What is the primary use of pyridostigmine?

    <p>Chronic management of myasthenia gravis.</p> Signup and view all the answers

    What is the primary source of toxicity for irreversible AChE inhibitors?

    <p>All of the above.</p> Signup and view all the answers

    What is the primary difference between edrophonium and neostigmine in terms of their therapeutic uses?

    <p>Edrophonium is used to diagnose myasthenia gravis, while neostigmine is used to stimulate the bladder and GI tract.</p> Signup and view all the answers

    What is the primary mechanism of action of botulinum toxin?

    <p>Inhibition of acetylcholine release from synaptic vesicles</p> Signup and view all the answers

    What is the function of phospholipase C in muscarinic receptor signaling?

    <p>Production of diacylglycerol</p> Signup and view all the answers

    What is the primary difference between muscarinic and nicotinic receptors?

    <p>Muscarinic receptors are G-protein coupled, while nicotinic receptors are ligand-gated ion channels</p> Signup and view all the answers

    What is the effect of butyrylcholinesterase on acetylcholine?

    <p>It is involved in the synthesis of ACh</p> Signup and view all the answers

    What is the primary mechanism of action of M2 receptors?

    <p>Inhibition of adenylyl cyclase</p> Signup and view all the answers

    What is the effect of choline uptake on synaptic transmission?

    <p>It recycles choline back into the neuron</p> Signup and view all the answers

    What is the primary difference between M1 and M3 receptors?

    <p>M1 receptors are found on gastric parietal cells, while M3 receptors are found on cardiac cells</p> Signup and view all the answers

    What is the effect of nicotine on nicotinic receptors?

    <p>It stimulates the receptor at low concentrations and blocks it at high concentrations</p> Signup and view all the answers

    What is the primary mechanism of action of direct-acting cholinergic agonists?

    <p>They bind directly to muscarinic or nicotinic receptors</p> Signup and view all the answers

    What is the effect of acetylcholinesterase on acetylcholine?

    <p>It terminates the action of ACh by breaking it down into choline and acetate</p> Signup and view all the answers

    Which anticholinesterase agent is used for the diagnosis of myasthenia gravis?

    <p>Edrophonium</p> Signup and view all the answers

    What is the primary difference between edrophonium and physostigmine?

    <p>Duration of action</p> Signup and view all the answers

    What is the antidote for edrophonium-induced cholinergic crisis?

    <p>Atropine</p> Signup and view all the answers

    Which anticholinesterase agent is used in the treatment of overdoses of anticholinergic drugs?

    <p>Physostigmine</p> Signup and view all the answers

    What is the primary use of neostigmine?

    <p>All of the above</p> Signup and view all the answers

    What is the primary adverse effect of tacrine, donepezil, rivastigmine, and galantamine?

    <p>GI distress</p> Signup and view all the answers

    What is the mechanism of action of echothiophate?

    <p>Irreversible inhibition of AChE</p> Signup and view all the answers

    What is the therapeutic use of a topical ophthalmic solution of echothiophate?

    <p>Treatment of open-angle glaucoma</p> Signup and view all the answers

    What is the primary source of toxicity for irreversible AChE inhibitors?

    <p>All of the above</p> Signup and view all the answers

    What is the primary use of pyridostigmine?

    <p>Treatment of myasthenia gravis</p> Signup and view all the answers

    What is the primary mechanism of ACh degradation?

    <p>Hydrolysis by acetylcholinesterase</p> Signup and view all the answers

    Which of the following is NOT a component of the mature synaptic vesicle?

    <p>Norepinephrine</p> Signup and view all the answers

    What is the role of sodium in the uptake of choline by the cholinergic neuron?

    <p>Sodium is cotransported with choline into the neuron</p> Signup and view all the answers

    Which of the following receptors is NOT stimulated by norepinephrine or epinephrine?

    <p>Muscarinic receptor</p> Signup and view all the answers

    What is the effect of inhibiting choline uptake on the synthesis of acetylcholine?

    <p>Decreased synthesis of acetylcholine</p> Signup and view all the answers

    What is the primary mechanism by which acetylcholine decreases blood pressure?

    <p>Indirect stimulation of nitric oxide production</p> Signup and view all the answers

    Which of the following steps is NOT part of the neurotransmission process at cholinergic neurons?

    <p>Exocytosis of acetylcholine into the bloodstream</p> Signup and view all the answers

    Which of the following has a strong muscarinic activity and no nicotinic action?

    <p>Bethanechol</p> Signup and view all the answers

    What is the primary function of voltage-sensitive calcium channels in the release of acetylcholine?

    <p>To increase the concentration of intracellular calcium</p> Signup and view all the answers

    What is the primary therapeutic use of pilocarpine?

    <p>Treatment of glaucoma</p> Signup and view all the answers

    What is the primary mechanism of action of hemicholinium?

    <p>Inhibition of choline uptake</p> Signup and view all the answers

    What is the effect of indirect-acting cholinergic agonists on acetylcholine?

    <p>They inhibit the degradation of acetylcholine</p> Signup and view all the answers

    Which of the following is a postganglionic fiber that uses acetylcholine as a neurotransmitter?

    <p>Parasympathetic postganglionic fibers</p> Signup and view all the answers

    What is the primary function of the cholinergic neuron in the autonomic nervous system?

    <p>To modulate the activity of the parasympathetic nervous system</p> Signup and view all the answers

    What is the adverse effect of bethanechol that can be treated with atropine sulfate?

    <p>Overdose</p> Signup and view all the answers

    What is the mechanism of action of pilocarpine in the eye?

    <p>Stimulation of the muscarinic receptors</p> Signup and view all the answers

    What is the duration of action of bethanechol?

    <p>1 hour</p> Signup and view all the answers

    What is the therapeutic use of bethanechol in the gastrointestinal tract?

    <p>Stimulation of intestinal secretions and motility</p> Signup and view all the answers

    What is the effect of acetylcholine on the heart rate?

    <p>Decrease in heart rate</p> Signup and view all the answers

    What is the therapeutic use of atropine in relation to pilocarpine?

    <p>Treatment of pilocarpine toxicity</p> Signup and view all the answers

    Study Notes

    Cholinergic Neurons

    • Cholinergic neurons use acetylcholine (ACh) as a neurotransmitter
    • Found in:
      • Preganglionic fibers terminating in the adrenal medulla
      • Autonomic ganglia (both parasympathetic and sympathetic)
      • Postganglionic fibers of the parasympathetic division
      • Postganglionic sympathetic division of sweat glands
      • Muscles of the somatic system

    Neurotransmission in Cholinergic Neurons

    • 6 sequential steps:
      1. Synthesis
      2. Storage
      3. Release
      4. Binding of ACh to a receptor
      5. Degradation of the neurotransmitter
      6. Recycling of choline and acetate

    Synthesis of Acetylcholine

    • Choline is transported into the cytoplasm of the cholinergic neuron by cotransport with sodium
    • Choline acetyltransferase catalyzes the reaction of choline with acetyl-CoA to form ACh

    Storage of Acetylcholine

    • ACh is stored in presynaptic vesicles by an active transport process
    • Mature vesicles contain ACh, ATP, and proteoglycan

    Release of Acetylcholine

    • When an action potential reaches the nerve ending, voltage-sensitive calcium channels open, causing an increase in intracellular calcium
    • Elevated calcium levels promote the fusion of synaptic vesicles with the cell membrane and the release of their contents into the synaptic space

    Binding to the Receptor

    • ACh released from the synaptic vesicles diffuses across the synaptic space and binds to postsynaptic receptors on the target cell
    • Postsynaptic cholinergic receptors are divided into two classes: muscarinic and nicotinic
    • Binding to a receptor leads to a biologic response mediated by second messenger molecules

    Degradation of Acetylcholine

    • ACh is rapidly terminated by acetylcholinesterase (AChE) that cleaves ACh to choline and acetate in the synaptic cleft
    • Butyrylcholinesterase (pseudocholinesterase) is found in the plasma but does not terminate the effect of ACh in the synapse

    Recycling of Choline

    • Choline may be recaptured by a sodium-coupled transporter that transports the molecule back into the neuron

    Cholinergic Receptors

    • Two families of cholinoceptors: muscarinic and nicotinic receptors

    Muscarinic Receptors

    • G protein–coupled receptors (metabotropic receptors)
    • Bind ACh and muscarine, but show only a weak affinity for nicotine
    • Five subclasses of muscarinic receptors: M1, M2, M3, M4, and M5
    • Mechanisms of acetylcholine signal transduction:
      • M1 and M3 receptors: activation leads to production of second messengers (IP3 and DAG)
      • M2 receptors: activation leads to inhibition of adenylyl cyclase and increase in K+ conductance

    Nicotinic Receptors

    • Ligand-gated ion channels
    • Bind ACh and nicotine, but show only a weak affinity for muscarine
    • Found in:
      • CNS
      • Adrenal medulla
      • Autonomic ganglia
      • Neuromuscular junction (NMJ) in skeletal muscles

    Direct-Acting Cholinergic Agonists

    • Mimic the effects of ACh by binding directly to cholinoceptors (muscarinic or nicotinic)
    • Examples:
      • Acetylcholine
      • Bethanechol
      • Pilocarpine

    Indirect-Acting Cholinergic Agonists (Anticholinesterase Agents)

    • Inhibit AChE, allowing ACh to accumulate in the synaptic space
    • Examples:
      • Edrophonium
      • Physostigmine
      • Neostigmine
      • Pyridostigmine
      • Tacrine, donepezil, rivastigmine, and galantamine
      • Echothiophate (irreversible AChE inhibitor)

    Cholinergic Neurons

    • Cholinergic neurons use acetylcholine (ACh) as a neurotransmitter
    • Found in:
      • Preganglionic fibers terminating in the adrenal medulla
      • Autonomic ganglia (both parasympathetic and sympathetic)
      • Postganglionic fibers of the parasympathetic division
      • Postganglionic sympathetic division of sweat glands
      • Muscles of the somatic system

    Neurotransmission in Cholinergic Neurons

    • 6 sequential steps:
      1. Synthesis
      2. Storage
      3. Release
      4. Binding of ACh to a receptor
      5. Degradation of the neurotransmitter
      6. Recycling of choline and acetate

    Synthesis of Acetylcholine

    • Choline is transported into the cytoplasm of the cholinergic neuron by cotransport with sodium
    • Choline acetyltransferase catalyzes the reaction of choline with acetyl-CoA to form ACh

    Storage of Acetylcholine

    • ACh is stored in presynaptic vesicles by an active transport process
    • Mature vesicles contain ACh, ATP, and proteoglycan

    Release of Acetylcholine

    • When an action potential reaches the nerve ending, voltage-sensitive calcium channels open, causing an increase in intracellular calcium
    • Elevated calcium levels promote the fusion of synaptic vesicles with the cell membrane and the release of their contents into the synaptic space

    Binding to the Receptor

    • ACh released from the synaptic vesicles diffuses across the synaptic space and binds to postsynaptic receptors on the target cell
    • Postsynaptic cholinergic receptors are divided into two classes: muscarinic and nicotinic
    • Binding to a receptor leads to a biologic response mediated by second messenger molecules

    Degradation of Acetylcholine

    • ACh is rapidly terminated by acetylcholinesterase (AChE) that cleaves ACh to choline and acetate in the synaptic cleft
    • Butyrylcholinesterase (pseudocholinesterase) is found in the plasma but does not terminate the effect of ACh in the synapse

    Recycling of Choline

    • Choline may be recaptured by a sodium-coupled transporter that transports the molecule back into the neuron

    Cholinergic Receptors

    • Two families of cholinoceptors: muscarinic and nicotinic receptors

    Muscarinic Receptors

    • G protein–coupled receptors (metabotropic receptors)
    • Bind ACh and muscarine, but show only a weak affinity for nicotine
    • Five subclasses of muscarinic receptors: M1, M2, M3, M4, and M5
    • Mechanisms of acetylcholine signal transduction:
      • M1 and M3 receptors: activation leads to production of second messengers (IP3 and DAG)
      • M2 receptors: activation leads to inhibition of adenylyl cyclase and increase in K+ conductance

    Nicotinic Receptors

    • Ligand-gated ion channels
    • Bind ACh and nicotine, but show only a weak affinity for muscarine
    • Found in:
      • CNS
      • Adrenal medulla
      • Autonomic ganglia
      • Neuromuscular junction (NMJ) in skeletal muscles

    Direct-Acting Cholinergic Agonists

    • Mimic the effects of ACh by binding directly to cholinoceptors (muscarinic or nicotinic)
    • Examples:
      • Acetylcholine
      • Bethanechol
      • Pilocarpine

    Indirect-Acting Cholinergic Agonists (Anticholinesterase Agents)

    • Inhibit AChE, allowing ACh to accumulate in the synaptic space
    • Examples:
      • Edrophonium
      • Physostigmine
      • Neostigmine
      • Pyridostigmine
      • Tacrine, donepezil, rivastigmine, and galantamine
      • Echothiophate (irreversible AChE inhibitor)

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    Description

    Understanding the classification of drugs affecting the Autonomic Nervous System, including cholinergic and adrenergic drugs and their actions on receptors. This includes the role of acetylcholine, norepinephrine, and epinephrine.

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