What defines a motor neuron?

A motor neuron is specifically defined as an efferent neuron that transmits signals from the central nervous system to muscle cells, facilitating voluntary and involuntary muscle movements. This type of neuron is essential for muscle contraction, as it enables communication between the nervous system and muscle tissue. When a motor neuron fires, it releases neurotransmitters that prompt muscle fibers to contract, resulting in movement.

The other options do not capture the primary function of a motor neuron. Afferent neurons are responsible for relaying sensory information to the central nervous system, which is a different role focused on sensory input rather than muscle activation. The statement suggesting that motor neurons solely connect with the brain overlooks their important connections to spinal cord and muscle tissue. Finally, interneurons play a role in processing information and relaying signals within the central nervous system itself, but they do not have a direct connection to muscle cells for movement like motor neurons do. Therefore, the defining characteristic of a motor neuron is its role in transmitting signals to muscle cells, confirming why the chosen answer is accurate.