Final Answer:
Atropine and curare are described as direct antagonists because they act on the same receptor but have opposite effects; atropine blocks acetylcholine receptors, while curare blocks nicotinic acetylcholine receptors.
Step-by-step explanation:
Atropine and curare are considered direct antagonists due to their interactions with acetylcholine receptors. Atropine, a muscarinic receptor antagonist, competitively inhibits acetylcholine by binding to muscarinic receptors, preventing the action of acetylcholine at these sites. On the other hand, curare acts as a nicotinic receptor antagonist by binding to nicotinic acetylcholine receptors at the neuromuscular junction, blocking the transmission of signals from motor neurons to muscle fibers.
Although atropine and curare target different subtypes of acetylcholine receptors, their net effect is opposite—where atropine enhances cholinergic activity, curare inhibits it. This characteristic makes them direct antagonists, acting on the same neurotransmitter system but exerting opposing influences.
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Complete Question
Atropine and curare are described as direct antagonists because _________________ .
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