The muscles in our body are made of huge number of muscle fibres. These muscle fibres are arranged in a number of small groups. Each of these groups comes under the control of a single motor neuron, the axon that sends a terminal branch to every fibre of the group. Now, the muscle fibres in a group contract whenever a nerve impulse goes to their motor neuron.
When a muscle gets stimulated it is followed by a short period during which it takes up the stimulus. Then it contracts and becomes short and thick. It relaxes and stretches after a while.
