Muscarinic ACh receptors (mAChRs) Location
Muscarinic 1 (M1) |
Ganglia cells |
Muscarinic 2 (M2) |
Cardiac muscle |
Muscarinic 3 (M3) |
Sweat glands |
Muscarinic 4 & 5 (M4 & M5) are NOT very important in this module.
Muscarinic Effects on Organ
Heart |
↓HR |
M2 |
Eye (circular musc.) |
Pinpoint pupil |
M2 & M3 |
Eye (cilliary musc.) |
Contract |
M3 |
Vascular musc. |
Relax |
M3 (NO) |
Lungs (Broncho mus.) |
Contract |
M3 |
GI-tract |
↑ motiility |
M3 |
Genito-urinary musc. |
Contract |
M3 |
Sweat & Salivary Gland |
↑ excretion |
M3 |
Parasympathetic Agonist Effects
Heart |
↓ CO = ↓ contraction & ↓ AV conduction speed = BRADYcardia |
Vascular musc. |
Vasodilation via (NO) production |
Smooth musc. |
↑ intestine & bladder tone (motility) & ↓ sphincter tone |
Eye |
↑ contraction of sphincter (miosis) & ciliary muscle (NEAR vision) |
Glands |
↑ sweating, saliva, gastric acid secretion |
Parasympathetic Agonist = Activation = INactivate sympathetic actions
(Think OPPOSITE of ALL sympathetic activation)
Parasympathetic Antagonist Effects
Heart |
↑CO = ↑AV node firing = ↑ HR = TACHYcardia |
Vascular musc. |
NO EFFECT b/c NO innervation |
Smooth musc. |
Relaxation = ↓GI & Urinary tract contraction |
Eye |
Pupil dilation & Loss of NEAR focus (FAR vision) |
Glands |
↓ sweat, saliva, gastric acid secretion |
Central NS (CNS) |
Belladonna Symptoms |
Belladonna Symptoms: "mad as a hatter, red as a beet, blind as a bat, hot as hell, dry as a bone"
Eye Terminology
Miosis |
Paralysis of ciliary muscle (loss of accommodation, ability to focus) |
Mydriatic |
Contraction of pupil (leads to pinpoint pupil, ie. Ach) |
Cycloplegia |
Relaxation of pupil (dilation); Atropine: belladonna compound) |
Antagonist: Parasympatholytic Agents
Antimuscarinic |
Block ACh in Parasymp. Effector Junctions |
Antinicotinic |
Block ACh in Ganglia (Para- & Sympathic; NN/N1) |
Antinicotinic |
Block ACh in NMJ (skeletal muscle relaxant, NM/N2) |
| |
Antinicotinic |
Block ACh in Ganglia (both Para- & Sympathetic, NN/N1) |
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Agonist: Parasympathomimetic Agents
Directly-Acting: Combine with mACh and/or
nAChs cholinoceptors receptor directly → Direct activation.
Parasympathetic Agents
Agonist |
(1) Acetylcholine, ACh (2) Bethanecol (3) Pilocarpine (4) Methacholine |
Antagonist (-tropine) |
(1) Atropine (2) Scopolamine (3) Homatropine (4) Benzotropine (5) pirenzepine |
Directly-Acting PNS Agonist
mAChs |
Choline Ester |
Acetylcholine; Methacholine |
| |
|
Carbachol; Bethanechol |
| |
Alkaloids |
Muscarine; Pilocarpine |
nAChs |
Ganglionic Stimulants |
Acetylcholine; Nicotine |
| |
|
Vareniclinie (partial) |
Choline Ester: Short-acting; stay in blood stream; NO (X) BBB
Alkaloids: (X) BBB
mAChs Agonists Uses
Acetylcholine |
Ophthalmic (brief miosis) |
Methacholine |
Belladonna poisoning; Urinary retention |
Bethanechol |
Reverse post-op GI depression |
Pilocarpine (alkaloid) |
DOC for Glaucoma |
Acetylcholinesterase Inhibitors (AChEIs)
Reversible |
Edrophonium (Tensilon) |
For myasthenia gravis (extreme muscle weakness) |
Irreversible (comp. Inhibs) |
Neostigmine |
NO (X) BBB; For myasthenia gravis & ileus |
| |
Physostigmine |
(X) BBB; For glaucoma and for treatment of belladonna poisoning |
| |
Pyridostigmine |
Myasthenia gravis |
| |
Ambenonium |
Myasthenia gravis |
Slow Reversible |
Echothiophate |
Glaucoma |
| |
Organophosphate insecticides, nerve gases DFP |
N/A |
Inhibits AChE at both mAChs & nACh via ↑ synaptic concentration & half-life of Ach.
Symptoms from Excess Cholinergic activity
General (SLUDE) |
Salivation, Lacrimation, Urination, Diarrhea, Emesis |
Muscarinic (SLUGBAM) |
Salivation/Sz, Lacrimation, Urination, GI distress (D/V), Bronchoconstriction, Abd. cramps, Miosis |
Nicotinic (MTWThF) |
Mydriasis, Tachycardia, Weakness (musc. paralysis), hyperTHermia, Fasciculation |
| |
Muscarinic (SLUGBAM) |
Salivation/Sz, Lacrimation, Urination, GI distress (D/V), Bronchoconstriction, Abd. cramps, Miosis |
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