What defines a motor unit?

A motor unit is defined as a neuron and all of the muscle fibers it controls. This concept is central to understanding how muscle contraction is initiated and regulated in the body. The motor neuron transmits electrical signals that lead to muscle contraction, and a single motor neuron can stimulate multiple muscle fibers, allowing for coordinated movement. The relationship between the neuron and the muscle fibers is vital for the efficiency of movement and muscle response.

In this context, the other options do not fully capture the definition of a motor unit. A single muscle fiber alone does not encompass the integral role of the neuron. Multiple neurons working together could influence muscle function but do not describe the singular connection of a motor neuron to its muscle fibers. A whole muscle group represents a collection of motor units but is not itself a motor unit. The precise definition inherent in option B is essential for understanding muscle mechanics and physiology in the field of massage and physical therapy.