A single action potential from a motor neuron triggers a single contraction in the muscle fibers of its motor unit. There is a brief delay between the application of the stimulus and the beginning of contraction. This delay is termed the latent period.
As the stimulus arrives axon terminal of a motor neuron, the resultant muscle action potential is propagated over the sarcolemma as the neurotransmitter is released in the synaptic cleft and binds to its receptors. There is a release of calcium ions from the sarcoplasmic reticulum to trigger excitation. During the latent period, muscles do not contract. The contraction period occurs once the latent period is over.
<span>El Nino is the part of the ENSO cycle in which the surface temperature of the Southern Pacific ocean is warmer than usual. This causes increased rainfall in the Americas, but can reduce precipitation in Indonesia and Southern Asia. Hence the correct answer is A) rain; drought.</span>
