NETA Personal Trainer Practice Exam

What is the initial step in the sliding filament theory of muscle contraction?

1. Actin filaments are pulled

2. An impulse is delivered by the CNS

3. The muscle relaxes

4. Myosin binds to actin

The correct answer is: An impulse is delivered by the CNS

The initial step in the sliding filament theory of muscle contraction involves the delivery of an impulse by the central nervous system (CNS). This impulse, transmitted via motor neurons, triggers the release of acetylcholine at the neuromuscular junction. This chemical messenger stimulates the muscle fibers, leading to the depolarization of the muscle cell membrane and the initiation of the contraction process. Once the muscle fibers are activated, calcium ions are released from the sarcoplasmic reticulum, enabling the binding of myosin heads to actin filaments. The subsequent steps include the pulling of the actin filaments, resulting in muscle contraction. However, without the initial CNS impulse to start this chain of events, the contraction cannot occur. Therefore, understanding this first step is crucial for comprehending how muscle contractions are coordinated and initiated.