National Academy of Sports Medicine (NASM) Certified Personal Trainer (CPT) Practice Exam

Which neurons are responsible for sending messages for muscles to contract?

1. Efferent neurons

2. Afferent neurons

3. Interneurons

4. Motor neurons

The correct answer is: Motor neurons

Motor neurons are the specific type of neurons that send signals from the central nervous system to the muscles, instructing them to contract. This is a vital component of voluntary movement. When the brain determines that action is required, it sends impulses through motor neurons, which directly communicate with muscle fibers. Efferent neurons are a broader category that includes motor neurons, as they transmit impulses away from the central nervous system. However, the term 'motor neurons' specifically identifies those nerve cells that directly affect muscle contraction. Afferent neurons, on the other hand, carry sensory signals from the body to the central nervous system, meaning they are involved in sending feedback rather than commands for contraction. Interneurons serve as connectors within the central nervous system, relaying information between afferent and efferent neurons but do not directly induce muscle contractions themselves. Thus, while all these types of neurons play critical roles in the nervous system's function, motor neurons are the ones specifically tasked with the message to contract muscles.