Describe the sliding filament theory.

The sliding filament theory demonstrates how the muscles in our body contract. As a signal reaches the neuromuscular junction (motor end plate), neurotransmitters such as Acetylcholine will diffuse across the synaptic cleft and bind to Ach receptors on the post synaptic membrane. This causes sodium channels to open, in turn creating an action potential within the post synaptic membrane. This Action potential will travel via the T-tubules between the myofibrils, as it passes along the T-tubules it stimulates calcium release from the sarcoplasmic reticulum. These calcium ions will cause the displacement of tropomyosin (proteins) on the myosin binding site of actin allowing myosin heads to bind to the actin filaments. As they bind they form actin-mysoin cross bridges. The myosin head will rotate, causing an overlap of the myosin and actin filaments. ATP then binds on to the myosin head causing it to become detached and releasing ADP in the process. The myosin head returns to its original position. This process of attachment, rotation and detachment brings the actin filament closer to the M line, causing shortening of the sarcomere and so contraction of the muscle. This continues as long as ATP and Ca 2+ are available.