This results in a movement within the myofibrils in which the filaments of actin and myosin slide past one another. This action shortens the muscle fiber so that it pulls on its attachments.
A skeletal muscle fiber normally does not contract until a neurotransmitter stimulates it. Acetylcholine is the neutrotransmitter that causes muscle contraction. This neurotransmitter is synthesized in the cytoplasm of the motor neuron and stored in vesicles at the distal end of the motor neuron axons