rding to this Theory, "Contraction Of Muscle Fibre occurs by the slidding of actin over the myosin".▪▪ This Mechanism Included following Steps :-¤¤ An Impulse from the CNS reaches the Neuromuscular junction via motor neurons.Neuromuscular junction is the synapse between a motor neuron and sarcolemma of tje muscle fibres.¤¤ The synaptic vesicles releases a neurotransmitter [ Acetylcholine ]. It generates an Action potential in sarcolemma. It SPREADS through the muscles fibres and cause the releases of calcium ions into the sarcoplasm.¤¤ Calcium Ions binds with a subunits of troponin on actin filament and removes the masking of active sites for myosin.¤¤ Using Energy from ATP HYDROLYSIS, myosin head bind to EXPOSED active sites on the actin to form a CROSS bridge. This pulls actin filaments on both sides towards the centre of A-bands. The Actin filaments partially overlap so that H-zone disappears.¤¤ The Z-line attached to actins is also pulled inward causes a shortening of sarcomere.¤¤ I-bands get shortened, whereas A-bands retain the length. ¤¤ Myosin releases ADP and Inorganic phosphate and goes back to its relaxed state. A new ATP binds and the cross bridge is broken.¤¤ The ATP is against hydolysed by the myosin head and above process is repeated CAUSING further sliding.¤¤ When Calcium ions are pumped back to sarcoplasmic cisternae, actin filaments are again masked. This causes the return of Z-Lines back to their original position. It results in Relaxation.