Autonomic Nervous System: L8

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Questions and Answers

What is the primary pharmacological action of hexamethonium?

Acts as an agonist for acetylcholine

Blocks nicotinic receptors (correct)

Increases gastric acid secretion

Stimulates nicotinic receptors

Which of the following is NOT a side effect associated with hexamethonium?

Dry mouth

Increased heart rate (correct)

Urinary retention

Constipation

In the context of hypertension, how does hexamethonium affect blood pressure?

Reduces blood pressure (correct)

Causes fluctuations in blood pressure

Has no effect on blood pressure

Increases blood pressure significantly

Which of the following compounds belongs to the same series as hexamethonium?

Decamethonium Signup and view all the answers

What role does nicotinic transmission play in the autonomic ganglia?

It facilitates signaling at the ganglia Signup and view all the answers

What is the primary action of M2 muscarinic receptors in the heart?

Inhibit cardiac function Signup and view all the answers

Which of the following is a characteristic of nicotinic receptors?

Ligand-gated ion channels Signup and view all the answers

Atropine is primarily used as what type of agent?

Muscarinic receptor antagonist Signup and view all the answers

What effect does acetylcholine have at high doses according to Dale's experiment?

Bradycardia through muscarinic receptors Signup and view all the answers

Which muscarinic receptor subtype is mainly associated with glandular secretion?

M3 Signup and view all the answers

What is the primary impact of DMPP on the autonomic system?

Stimulates autonomic ganglia Signup and view all the answers

Which neurotransmitter is primarily synthesized and released at cholinergic synapses?

Acetylcholine Signup and view all the answers

Which of the following drugs is most likely to block ganglionic nicotinic receptors?

Hexamethonium Signup and view all the answers

What is the effect of muscarinic antagonists on secretions?

Inhibit secretions Signup and view all the answers

What is one function of M1 muscarinic receptors?

Enhance gastric acid secretion Signup and view all the answers

Study Notes

Transmission at the Post-Ganglionic Sympathetic Synapse

Synthesis, release, uptake, and metabolism of norepinephrine are key processes.
Norepinephrine receptors are classified and their pharmacology is discussed.
Drugs that interfere with sympathetic transmission at the post-ganglionic level are outlined.

Transmission at Cholinergic Synapses in the Autonomic Nervous System

Synthesis and release of acetylcholine (ACh) are detailed.
Ganglionic neurotransmission, focusing on nicotinic receptors, is explained.
Post-ganglionic neurotransmission, focusing on muscarinic receptors, is described.

Dale's Experiment and ACh Effects

ACh elicits diverse effects on blood pressure, as demonstrated experimentally.
The experiment showed a dose-dependent, opposing response to ACh.
This suggests the existence of different receptors for ACh with diverse effects.

Parasympathetic Organ Synapse

Diagram illustrating the process of neurotransmission in parasympathetic synapses.
ACh is released, activating muscarinic receptors on effector organs.
Acetylcholinesterase degrades excess ACh, terminating the signal. Key components of the parasympathetic synapse are highlighted.

Muscarinic Receptor Subtypes

Muscarinic receptors are G-protein coupled.
M1 receptors are primarily neural, affecting gastric acid secretion and gut motility.
M2 receptors are primarily cardiac, mediating cardiac inhibition and neural inhibition.
M3 receptors are primarily glandular, stimulating secretion, smooth muscle contraction, and vasodilation.

Muscarinic Receptor Antagonists

Atropine and pirenzepine are examples of muscarinic receptor antagonists.

Effects of Muscarinic Antagonists

Inhibition of secretions
Effects on heart rate
Effects on the eye
Effects on the gut
Effects on other smooth muscles
Effects on the CNS

Nicotinic Transmission at Autonomic Ganglia

Nicotinic receptors are ligand-gated ion channels permeable to cations.
Diagram showing preganglionic and postganglionic neurons and the role of ACh.
Acetylcholinesterase plays a crucial role in terminating the signal.

Nicotinic Receptors

Nicotinic receptors are ligand-gated ion channels, permeable to cations.
Categorization and differences between N1/NM and N2/NN subtypes are detailed.
N1/NM subtype is located at the neuromuscular junction.
N2/NN subtype is located at autonomic ganglia and other CNS locations, adrenal medulla.

Nicotinic Receptor Agonists

Acetylcholine, nicotine, and dimethylphenylpiperazinium (DMPP) are agonists that elicit responses.
Nicotine stimulates autonomic ganglia.

Nicotinic Ganglionic Receptor Antagonists

Hexamethonium blocks nicotinic receptors at autonomic ganglia.
Hexamethonium causes reduction in blood pressure due to the blockage of nicotine-induced action on the autonomic ganglia.

Hexamethonium's Effects

Blocks nicotinic receptors, resulting in reduced agonist action.
Reduces blood pressure (beneficial in hypertension), but has adverse side effects.
Examples of side effects: dry mouth, reduced gastric acid secretion, constipation, urinary retention, blurred vision, postural hypotension, and sexual dysfunction.

Hexamethonium belongs to a series of polymethylene bismethonium compounds.
Decamethonium is a compound with increased chain length compared to hexamethonium.

Comparative Effects of Polybismethonium Compounds

Paton and Zaimis studied the effects of polybismethonium compounds at autonomic ganglia and neuromuscular junctions.
Relative potency is dependent on factors like the length of carbon chains.
Longer chain length compounds have greater ganglionic blocking potency, but reduced neuromuscular junction block.

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Description

This quiz covers key aspects of neurotransmission in the autonomic nervous system, including the roles of norepinephrine and acetylcholine. It discusses the pharmacology of receptors involved in sympathetic and parasympathetic synapses, as well as experimental insights into acetylcholine's effects on blood pressure. Test your knowledge on these crucial physiological processes.