What do motor units consist of?

• A. Muscle fibers are always activated
• B. Tissues around muscles
• C. Connective tissues around joints
• D. Cells involved in energy production

Answer: (A)

Motor units are composed of a motor neuron and the muscle fibers it innervates. When a motor neuron transmits a signal, it activates all the muscle fibers within its motor unit simultaneously, leading to muscle contraction. This is fundamental to understanding muscle physiology and how movements are coordinated. The activation of these muscle fibers happens in a manner that allows for smooth and controlled movements, which is essential in various physical activities and sports.

The other response options refer to different aspects of anatomy and physiology that are not directly involved in defining what constitutes a motor unit. For instance, the connective tissues and energy production cells are important for muscle function but do not comprise the motor unit itself. Therefore, the focus on muscle fibers being activated aligns correctly with the definition of a motor unit in the context of physical education and exercise science.