MCAT® ExamBiological and Biochemical Foundations of Living SystemsHard
A patient is prescribed a medication that acts as an antagonist to acetylcholine receptors at the neuromuscular junction. What immediate effect would this drug have on the patient's skeletal muscles?
- AParalysis due to inhibited muscle contraction
- BFaster nerve impulse transmission
- CEnhanced muscle relaxation
- DIncreased muscle contraction
Show answer & explanationAnswer & explanation
Correct answer: A. Paralysis due to inhibited muscle contraction
At the neuromuscular junction, acetylcholine (ACh) binds to its receptors on the muscle fiber, initiating depolarization and subsequently muscle contraction. An antagonist to these receptors would block ACh binding, preventing the muscle from receiving the signal to contract, leading to paralysis.
Why the other options are wrong
- B. The drug acts at the muscle, not directly on nerve impulse transmission speed.
- C. While relaxation might be a secondary effect if contractions are blocked, the primary and most direct effect is the inability to contract, leading to paralysis.
- D. Increased contraction would occur with an agonist, not an antagonist.
Neuromuscular Junction
A specialized synapse between a motor neuron and a skeletal muscle fiber, where the motor neuron transmits a signal (via acetylcholine) to the muscle fiber, causing it to contract.
- Site of communication between nervous and muscular systems.
- Neurotransmitter is acetylcholine (ACh).
- ACh binds to nicotinic acetylcholine receptors on the muscle fiber.
- Binding causes depolarization and initiates muscle action potential, leading to contraction.
Memory trick: NMJ: The Nerve-Muscle Junction, ACh is the key.