Physiology

Cholinergic receptors (cholinoreceptors)
a. Nicotinic receptors
■ are located in the autonomic ganglia (NN) of the sympathetic and parasympathetic
nervous systems, at the neuromuscular junction (NM), and in the adrenal medulla (NN).
The receptors at these locations are similar, but not identical.
■ are activated by ACh or nicotine.
■ produce excitation.
■ are blocked by ganglionic blockers (e.g., hexamethonium) in the autonomic ganglia,
but not at the neuromuscular junction.
■ Mechanism of action: ACh binds to α subunits of the nicotinic ACh receptor. The nicotinic ACh receptors are also ion channels for Na+ and K+
.
b. Muscarinic receptors
■ are located in the heart (M2), smooth muscle (M3), and glands (M3).
■ are inhibitory in the heart (e.g., decreased heart rate, decreased conduction velocity
in AV node).
■ are excitatory in smooth muscle and glands (e.g., increased GI motility, increased secretion).
■ are activated by ACh and muscarine.
■ are blocked by atropine.
■ Mechanism of action:
(1) Heart SA node: Gi protein, inhibition of adenylate cyclase, which leads to opening of K+ channels, slowing of the rate of spontaneous Phase 4 depolarization, and decreased heart rate.
(2) Smooth muscle and glands:
Gq protein, stimulation of phospholipase C, and increase in IP3 and intracellular [Ca2+].

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8.22K viewsedited  Nov 21, 2023 at 19:21

Cholinergic receptors (cholinoreceptors)
a. Nicotinic receptors
■ are located in the autonomic ganglia (NN) of the sympathetic and parasympathetic
nervous systems, at the neuromuscular junction (NM), and in the adrenal medulla (NN).
The receptors at these locations are similar, but not identical.
■ are activated by ACh or nicotine.
■ produce excitation.
■ are blocked by ganglionic blockers (e.g., hexamethonium) in the autonomic ganglia,
but not at the neuromuscular junction.
■ Mechanism of action: ACh binds to α subunits of the nicotinic ACh receptor. The nicotinic ACh receptors are also ion channels for Na+ and K+
.
b. Muscarinic receptors
■ are located in the heart (M2), smooth muscle (M3), and glands (M3).
■ are inhibitory in the heart (e.g., decreased heart rate, decreased conduction velocity
in AV node).
■ are excitatory in smooth muscle and glands (e.g., increased GI motility, increased secretion).
■ are activated by ACh and muscarine.
■ are blocked by atropine.
■ Mechanism of action:
(1) Heart SA node: Gi protein, inhibition of adenylate cyclase, which leads to opening of K+ channels, slowing of the rate of spontaneous Phase 4 depolarization, and decreased heart rate.
(2) Smooth muscle and glands:
Gq protein, stimulation of phospholipase C, and increase in IP3 and intracellular [Ca2+].

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