OSMT (Ontario Society of Medical Technologists) Practice Exam

The correct answer is that the contracting proteins within a muscle fibre are myosin and actin. These two proteins play a crucial role in the muscle contraction process. Myosin is a thick filament that has motor functions, allowing it to pull on the thin filaments during contraction. Actin, on the other hand, forms the thin filaments that slide past the thick myosin filaments, allowing for muscle contraction to take place. This sliding filament model is fundamental to muscle physiology, where the interactions between myosin and actin are responsible for shortening the muscle fibres, leading to contraction.

Haemoglobin and myoglobin are oxygen-transporting proteins found in red blood cells and muscle tissue, respectively. They are important for oxygen delivery but do not contribute to muscle contraction. Troponins and tropomyosin are regulatory proteins that are involved in the contraction process but do not directly contract themselves; they help control the interaction between actin and myosin by regulating the calcium ions necessary for contraction. Myoglobin, although important for oxygen storage in muscles, also does not directly participate in the muscle's contraction mechanics.