Which statement best describes a motor unit?

A motor unit is defined as a single motor neuron along with all the muscle fibers that it innervates. This definition is critical to understanding how muscle contractions are coordinated and how force is generated in muscle tissue. Each motor neuron can innervate multiple muscle fibers, but all of those fibers belong to the same motor unit.

When a motor neuron fires, it triggers all the muscle fibers within its motor unit to contract simultaneously. This ensures that muscle contractions can be smooth and coordinated, as the recruitment of multiple motor units allows for graded responses to varying levels of exertion.

The other options do not accurately describe the structure and function of a motor unit. A single muscle fiber can be innervated by only one motor neuron, while a motor unit can consist of several muscle fibers. Thus, understanding that a motor unit includes the singular motor neuron plus the multiple muscle fibers makes option C the best choice. This reflects the fundamental concept of how neuronal signaling controls muscle function and how motor units contribute to muscle contractions.