Cholinergic Agonists and Neurotransmission
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Questions and Answers

Which type of cholinergic receptor is found on smooth muscle, eye, lungs, digestive tract, and exocrine glands?

  • Nm receptors
  • M3 receptors (correct)
  • M1 receptors
  • M2 receptors

    • What is the effect of acetylcholine on cardiac output, heart rate, and blood pressure?

  • Increases cardiac output and heart rate, decreases blood pressure
  • Increases all three
  • Increases blood pressure, decreases cardiac output and heart rate
  • Decreases all three (correct)

    • Which indirect acting cholinergic agonist is used for diagnosis of myasthenia gravis?

  • Physostigmine
  • Edrophonium (correct)
  • Pyridostigmine
  • Neostigmine

    • What is the mnemonic used to remember the side effects of cholinergic agonists?

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

    Which type of cholinergic receptor is found at neuromuscular junctions and is responsible for muscle contraction?

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

    What is the effect of carbachol compared to acetylcholine?

    <p>Has a longer duration of action</p> Signup and view all the answers

    What is the primary location of cholinergic neurons?

    <p>Parasympathetic system</p> Signup and view all the answers

    What is the enzyme responsible for catalyzing the reaction between choline and acetyl CoA?

    <p>Choline acetyltransferase</p> Signup and view all the answers

    What happens to acetylcholine after it is released from the terminal?

    <p>It is broken down by acetylcholinesterase</p> Signup and view all the answers

    What is the function of presynaptic receptors in cholinergic neurotransmission?

    <p>To inhibit the release of acetylcholine</p> Signup and view all the answers

    What is the role of voltage-sensitive calcium channels in cholinergic neurotransmission?

    <p>To allow the fusion of vesicles with the membrane</p> Signup and view all the answers

    What is the purpose of the neurotransmitter acetylcholine in sweat glands and blood vessels?

    <p>To participate in sympathetic innervation</p> Signup and view all the answers

    Study Notes

    Cholinergic Agonists

    • Cholinergic neurons are primarily found in the parasympathetic system, but they also participate in sympathetic innervation of sweat glands and blood vessels in skeletal muscle.

    Cholinergic Neurotransmission

    • Cholinergic neurotransmission involves six major steps:
      • Choline is transported into the neuron by an energy- and sodium-dependent transport system.
      • Choline reacts with acetyl CoA to form acetylcholine, catalyzed by choline acetyltransferase.
      • Acetylcholine is transported into the pre-synaptic vesicle, where it is protected from degradation.
      • The action potential causes voltage-sensitive calcium channels to open, leading to the fusion of the vesicle with the membrane and the release of acetylcholine from the terminal.
      • Acetylcholine binds to post-synaptic receptors, leading to a cholinergic response, and also binds to presynaptic receptors, inhibiting the release of more acetylcholine (negative feedback loop).
      • Acetylcholinesterase terminates acetylcholine function at the synaptic cleft by breaking it down to acetate and choline.

    Cholinergic Receptors

    • There are two types of cholinergic receptors:
      • Muscarinic receptors (high affinity for muscarine):
        • M1 receptors: found on neurons, gastric glands, and other locations
        • M2 receptors: found on cardiac cells
        • M3 receptors: found on smooth muscle, eye, lungs, digestive tract, and exocrine glands
      • Nicotinic receptors (high affinity for nicotine):
        • Nm receptors: found at neuromuscular junctions, responsible for muscle contraction
        • Nn receptors: found in the central nervous system and autonomic ganglia, involved in transmission of cholinergic signals

    Direct Acting Cholinergic Agonists

    • These agents mimic the effects of acetylcholine by binding to muscarinic or nicotinic receptors:
      • Acetylcholine: decreases cardiac output, heart rate, and blood pressure; increases GI activity
      • Carbachol: structurally similar to acetylcholine, has a long duration of action
      • Pilocarpine: used ophthalmically to constrict the pupil and decrease intraocular pressure
      • Bethanechol: selectively stimulates urinary and gastrointestinal tract

    Indirect Acting Cholinergic Agonists

    • These agents bind to acetylcholinesterase, resulting in a buildup of acetylcholine in the synaptic cleft:
      • Edrophonium: reversibly binds to acetylcholinesterase, short duration of action, used for diagnosis of myasthenia gravis
      • Physostigmine: stimulates both nicotinic and muscarinic receptors, intermediate-acting agent
      • Neostigmine: intermediate-acting agent, used for symptoms of myasthenia gravis, stimulating bladder and GI tract, and reversing the effects of anesthesia
      • Pyridostigmine: similar to Neostigmine, used for Alzheimer's disease
      • Donepezil, Rivastigmine, and Galantamine: used to enhance cholinergic effects and improve cognitive function in Alzheimer's disease

    Irreversible Cholinesterase Inhibitors

    • These agents form covalent bonds with acetylcholinesterase, leading to strong cholinergic stimulation:
      • Echothiophate: used to treat open-angle glaucoma, rarely used due to side effects

    Side Effects of Cholinergic Agonists

    • DUMBBELLS mnemonic: diarrhea, urination, miosis, bronchorrhea, emesis, lacrimation, and salivation.

    Cholinergic Agonists

    • Cholinergic neurons are primarily found in the parasympathetic system, but also participate in sympathetic innervation of sweat glands and blood vessels in skeletal muscle.

    Cholinergic Neurotransmission

    • Cholinergic neurotransmission involves six major steps:
      • Choline is transported into the neuron by an energy- and sodium-dependent transport system.
      • Choline reacts with acetyl CoA to form acetylcholine, catalyzed by choline acetyltransferase.
      • Acetylcholine is transported into the pre-synaptic vesicle, where it is protected from degradation.
      • The action potential causes voltage-sensitive calcium channels to open, leading to the fusion of the vesicle with the membrane and the release of acetylcholine from the terminal.
      • Acetylcholine binds to post-synaptic receptors, leading to a cholinergic response, and also binds to presynaptic receptors, inhibiting the release of more acetylcholine (negative feedback loop).
      • Acetylcholinesterase terminates acetylcholine function at the synaptic cleft by breaking it down to acetate and choline.

    Cholinergic Receptors

    • There are two types of cholinergic receptors:
      • Muscarinic receptors (high affinity for muscarine):
        • M1 receptors: found on neurons, gastric glands, and other locations.
        • M2 receptors: found on cardiac cells.
        • M3 receptors: found on smooth muscle, eye, lungs, digestive tract, and exocrine glands.
      • Nicotinic receptors (high affinity for nicotine):
        • Nm receptors: found at neuromuscular junctions, responsible for muscle contraction.
        • Nn receptors: found in the central nervous system and autonomic ganglia, involved in transmission of cholinergic signals.

    Direct Acting Cholinergic Agonists

    • These agents mimic the effects of acetylcholine by binding to muscarinic or nicotinic receptors:
      • Acetylcholine: decreases cardiac output, heart rate, and blood pressure; increases GI activity.
      • Carbachol: structurally similar to acetylcholine, has a long duration of action.
      • Pilocarpine: used ophthalmically to constrict the pupil and decrease intraocular pressure.
      • Bethanechol: selectively stimulates urinary and gastrointestinal tract.

    Indirect Acting Cholinergic Agonists

    • These agents bind to acetylcholinesterase, resulting in a buildup of acetylcholine in the synaptic cleft:
      • Edrophonium: reversibly binds to acetylcholinesterase, short duration of action, used for diagnosis of myasthenia gravis.
      • Physostigmine: stimulates both nicotinic and muscarinic receptors, intermediate-acting agent.
      • Neostigmine: intermediate-acting agent, used for symptoms of myasthenia gravis, stimulating bladder and GI tract, and reversing the effects of anesthesia.
      • Pyridostigmine: similar to Neostigmine, used for Alzheimer's disease.
      • Donepezil, Rivastigmine, and Galantamine: used to enhance cholinergic effects and improve cognitive function in Alzheimer's disease.

    Irreversible Cholinesterase Inhibitors

    • These agents form covalent bonds with acetylcholinesterase, leading to strong cholinergic stimulation:
      • Echothiophate: used to treat open-angle glaucoma, rarely used due to side effects.

    Side Effects of Cholinergic Agonists

    • DUMBBELLS mnemonic: diarrhea, urination, miosis, bronchorrhea, emesis, lacrimation, and salivation.

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    Description

    This quiz covers the role of cholinergic neurons in the parasympathetic system and sympathetic innervation, as well as the six major steps of cholinergic neurotransmission.

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