At this point, you may be thinking, “how on earth did anyone figure out this stuff?” To answer this question you need to understand that scientists who study physiological processes often employ drugs. Yep, drugs! A drug that has the same effect as acetylcholine will result in all kinds of information about how something works. We use the terms agonist and antagonist when referring to drugs. A drug that has the same effect as the neurotransmitter (acetylcholine) would be considered an agonist. A drug that blocks the effect of the neurotransmitter is called an antagonist.
Look at the table below of different drugs used in the study of muscle physiology and see if you can predict the effect the drug would have on a muscle.
|Class of Drug||Example||Method of Action||Result on muscle?|
|Neuromuscular blocker||tubocurarine (chemical obtained from the bark of a South American plant, used as arrow poison); alpha bungarotoxin (snake poison), pancuronium (lethal injection drug)||Acetylcholine receptor antagonist||Flaccid paralysis|
|Neuromuscular blocker||Succinylcholine (a synthesized chemical, known as the “perfect poison” for murder)||Acetylcholine receptor antagonist (initial depolarization but then blocks the receptor)||Flaccid paralysis|
|Neuromuscular junction||Neostigmine (a synthesized chemical)||Inhibits Acetylcholinesterase activity||Spastic paralysis|
|Contractility||Salbutamol (a synthesized chemical also known as albuterol)||Enhances SERCA pump activity||Reduced contractility|
|Contractility||Caffeine (chemical found in seeds, nuts or leaves, used as an insecticide by the plants)||Enhances Ca2+ release at the sarcoplasmic reticulum||Increased contractility|
|Neuromuscular junction||Botulism||Blocks SNARE proteins||Flaccid Paralysis|
|Neuromuscular junction||Latrotoxin (Black widow spider poison)||SNARE protein agonist||Spastic paralysis|
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