Upon muscle contraction, the A-bands do not change their length (1.85 micrometer in mammalian skeletal muscle),[REF] whereas the I-bands and the H-zone shorten.
During stimulation of the muscle cell, the motor neuron releases the neurotransmitter acetylcholine, which travels across the neuromuscular junction (the synapse between the terminal bouton of the neuron and the muscle cell).