Tropomysin is a protein that prevents muscle contraction hence acts as a contraction inhibitor. It wraps around the actin blocking the binding sites for myosin on the actin.
Muscle will only contract when they get a rush of calcium ions.
The calcium ions binds to troponin, the troponin changes its shape. The change in shape will remove tropomyosin from the binding sites allowing myosin to bind on the actin leading to muscle contraction.
