The correct answer is a law
Laws explain what occurs, not why it occurs. This is a law because it states that a limp stalk of celery will become crisp if put into ice water. There is no explanation why or how it occurs, only that it will happen.
Answer:
By action potential nerve contract the muscle
Explanation:
The muscle contract when the nervous system sends action potential to the muscle. So the nervous system delivers signal to muscle, the first signal reaches the neuromuscular junction. The signals are passed by a chemical messenger called neurotransmitter release by motor neurons, the chemicals bring reaction and shorten the muscle fibre. When neurotransmitter are absent or reduce in concentration the process reverse and muscle relax again.
