Muscarinic Receptors Overview
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Muscarinic Receptors Overview

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Questions and Answers

What is the duration of action for Dimenhydrinate?

  • 24 hours
  • 8 hours (correct)
  • 6 hours
  • 12 hours

    • Which first-generation antihistamine has the highest sedative effect?

  • Meclizine
  • Chlorpheniramine
  • Promethazine (correct)
  • Diphenhydramine (correct)

    • Which second-generation antihistamine has the lowest anticholinergic effects?

  • Meclizine
  • Cetirizine (correct)
  • Fexofenadine (correct)
  • Loratadine (correct)

    • What is a primary characteristic of Hydroxyzine among the first-generation antihistamines?

    <p>High antiemetic effect</p> Signup and view all the answers

    What type of drugs specifically block muscarinic receptors?

    <p>Cholinolytic drugs</p> Signup and view all the answers

    Which symptom is associated with atropine poisoning?

    <p>Blurred vision</p> Signup and view all the answers

    How would you classify a drug that acts as a muscarinic receptor agonist?

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

    Which first-generation antihistamine is associated with a medium anticholinergic effect?

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

    What mechanism leads to the increase in intraocular pressure in angle-closure glaucoma?

    <p>Pressure from the posterior chamber pushing the iris against the trabecular meshwork</p> Signup and view all the answers

    What effect do cholinomimetics have on the ciliary muscles in closed-angle glaucoma?

    <p>They constrict the iris sphincter and contract the ciliary muscles</p> Signup and view all the answers

    What surgical method is used to treat closed-angle glaucoma?

    <p>Placement of a hole in the peripheral iris</p> Signup and view all the answers

    How does acetylcholine cause vasodilation in blood vessels?

    <p>By activating M3 receptors leading to nitric oxide formation</p> Signup and view all the answers

    What is the primary effect of stimulating M3 receptors in the respiratory system?

    <p>Bronchial muscle contraction and increased mucous secretion</p> Signup and view all the answers

    Which of the following accurately describes the cardiovascular effects of M2 agonists?

    <p>Decrease heart rate and slow AV node conduction leading to increased PR interval</p> Signup and view all the answers

    What role do longitudinal ciliary muscles play in open-angle glaucoma?

    <p>They facilitate drainage of aqueous humor through trabecular meshwork</p> Signup and view all the answers

    What is a potential consequence of relaxing the circular ciliary muscle around the lens?

    <p>Relaxation of the lens into a more convex shape for near vision</p> Signup and view all the answers

    What effect does stimulation of M2 receptors in the cardiac system have?

    <p>Decreased heart rate and cardiac output</p> Signup and view all the answers

    Which of the following effects is associated with antagonism of M3 receptors in the gastrointestinal tract?

    <p>Decreased gastric secretion</p> Signup and view all the answers

    What is a common effect of muscarinic antagonists on the eye?

    <p>Pupil dilation</p> Signup and view all the answers

    Which of the following accurately describes the activation of M1 receptors in the CNS?

    <p>May lead to tremors</p> Signup and view all the answers

    How do direct-acting cholinergic agonists differ from each other?

    <p>By their chemical structure, receptor affinity, and hydrolysis susceptibility</p> Signup and view all the answers

    What is a primary effect of muscarinic agonists on the exocrine glands?

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

    What impact do muscarinic antagonists generally have on the body’s secretions?

    <p>Decreased bronchial secretions</p> Signup and view all the answers

    What physiological response is facilitated by M3 receptor activation in smooth muscles like those in the bladder?

    <p>Contraction of muscles</p> Signup and view all the answers

    Which type of neuron releases ACh and binds to Nn receptors?

    <p>Preganglionic neurons</p> Signup and view all the answers

    How do parasympathomimetic drugs affect the sympathetic response?

    <p>They decrease the sympathetic response.</p> Signup and view all the answers

    What is the main effect of cholinolytic drugs?

    <p>They block the action of acetylcholine.</p> Signup and view all the answers

    What type of receptors do ACh bind to in sweat glands?

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

    Which of the following correctly pairs the drug type with its action?

    <p>Cholinomimetic drugs; mimic ACh action</p> Signup and view all the answers

    What is the relationship between parasympathetic and sympathetic responses?

    <p>They have opposing actions.</p> Signup and view all the answers

    Which type of neurons release ACh to bind with Nm receptors?

    <p>Somatic motor neurons</p> Signup and view all the answers

    What outcome occurs when the parasympathetic response is inhibited?

    <p>Increased sympathetic activity</p> Signup and view all the answers

    What is the main effect of cholinomimetics on the ciliary muscles in the context of glaucoma treatment?

    <p>They cause contraction of the ciliary muscles.</p> Signup and view all the answers

    In the case of angle-closure glaucoma, what is the primary anatomical issue that prevents drainage of aqueous humor?

    <p>Pressure from the posterior chamber pushing the iris.</p> Signup and view all the answers

    What surgical procedure is commonly used to treat closed-angle glaucoma?

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

    How do cholinomimetics affect intraocular pressure in open-angle glaucoma?

    <p>They decrease intraocular pressure.</p> Signup and view all the answers

    What role does the circular ciliary muscle play during the contraction caused by cholinomimetics?

    <p>It forms a tight sphincter around the lens.</p> Signup and view all the answers

    Which muscle contraction is responsible for facilitating the drainage of aqueous humor in open-angle glaucoma?

    <p>Contraction of the longitudinal ciliary muscle.</p> Signup and view all the answers

    What is the effect of constricting the iris sphincter in closed-angle glaucoma?

    <p>It opens the ocular angle.</p> Signup and view all the answers

    What is the primary function of the trabecular meshwork in the eye?

    <p>To drain aqueous humor.</p> Signup and view all the answers

    Study Notes

    Muscarinic Receptor Subtypes and their Effects

    • Muscarinic receptors (M1-M5) are G protein-coupled receptors, mediating the effects of acetylcholine in the parasympathetic nervous system.
    • M1 receptors are found in the central nervous system (CNS) and contribute to functions such as cognition and movement control.
    • M2 receptors are primarily located in the heart, where their activation slows heart rate and decreases force of contraction.
    • M3 receptors are found in various organs, including the gastrointestinal tract, bladder, bronchi, exocrine glands, and the eye.

    Muscarinic Agonist Effects

    • Cardiac (M2):
      • Decrease heart rate (HR)
      • Decrease force of contraction (FC)
      • General vasodilation via nitric oxide (NO) -mediated mechanism
      • Decrease blood pressure (BP)
    • Smooth muscle (M3) in GIT: Contraction of smooth muscle in the gastrointestinal (GI) tract, leading to increased motility
    • Smooth muscle (M3) (bladder, bronchi): Contraction of smooth muscle in the bladder and bronchi, leading to urination and bronchoconstriction
    • Secretions (M3) (sweating, lacrimation, salivation, bronchial): Stimulation of exocrine glands, which increases secretions
    • Eye (M3) (ciliary muscle, constrictor pupillae): Contraction of the ciliary muscle causes pupil constriction and the lens to thicken, allowing for near vision.

    Muscarinic Antagonist Effects (Anticholinergic)

    • Cardiac (M2)
      • Modest increase in heart rate (tachycardia)
    • Smooth muscle (M3) (bladder, bronchi): Relaxation of smooth muscle in the bladder and bronchi, leading to urinary retention and bronchodilation.
    • Secretions (M3) (sweating, lacrimation, salivation, bronchial): Reduction in secretions from exocrine glands
    • Eye (M3) (ciliary muscle, constrictor pupillae): Pupil dilation (mydriasis), which increases intraocular pressure (IOP)
    • CNS (M1):
      • Activation of M1 receptors may contribute to tremor, hypothermia, and improved cognition.
      • Atropine: may cause sedation and excitatory effects.
      • Hyoscine: may cause sedation and reduce involuntary movement and rigidity.

    Acetylcholine (ACh) Release and Receptor Targets in Specific Neurons

    • Preganglionic neurons: ACh binds to nicotinic (Nn) receptors
    • Somatic motor neurons: ACh binds to nicotinic (Nm) receptors
    • Parasympathetic postganglionic neurons: ACh binds to muscarinic receptors
    • Some sympathetic postganglionic neurons (e.g., sweat glands): ACh binds to muscarinic receptors

    Cholinergic Drugs

    • Cholinergic drugs directly or indirectly influence the cholinergic system (acetylcholine).
    • Parasympathomimetic drugs mimic or enhance the effects of acetylcholine, effectively increasing parasympathetic activity, while decreasing sympathetic activity.
    • Cholinomimetic drugs directly activate cholinergic receptors (agonists).
    • Parasympatholytic drugs block the actions of acetylcholine, effectively decreasing parasympathetic activity and increasing sympathetic activity.
    • Cholinolytic drugs inhibit the actions of acetylcholine (antagonists).

    Pharmacologic Effects of Cholinergic Drugs

    • Direct-acting cholinergic agonists can be classified into three groups:
      • Choline esters
      • Plant alkaloids
      • Other synthetic drugs

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    Drugs Acting on Muscarinic Receptors PDF

    Description

    This quiz explores the various subtypes of muscarinic receptors (M1-M5) and their physiological effects in the body. It highlights their roles in the central nervous system, cardiovascular system, and smooth muscle function. Test your knowledge on the mechanisms underlying these receptors and their impact on health.

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