GCEBiologyCoordination and Support2023

The diagram below represents events at a neuromuscular junction. Which of the following sequences correctly describes the transmission of an impulse across the synapse?

ANerve impulse arrives → acetylcholine released → depolarisation of postsynaptic membrane → muscle contractionCORRECT
BAcetylcholine released → nerve impulse arrives → repolarisation of presynaptic membrane → muscle contraction
CNerve impulse arrives → adrenaline released → depolarisation of presynaptic membrane → muscle contraction
DNerve impulse arrives → acetylcholine released → repolarisation of postsynaptic membrane → muscle relaxation
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At a neuromuscular junction, a nerve impulse arriving at the presynaptic terminal triggers the release of acetylcholine into the synaptic cleft. Acetylcholine binds to receptors on the postsynaptic (muscle) membrane, causing depolarisation, which then initiates muscle contraction. Adrenaline is a hormone, not the neurotransmitter at neuromuscular junctions, and the correct sequence ends in contraction, not relaxation.
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