Which statement best describes how motor execution is carried out?

• A. Sensory integration
• B. Automaticity
• C. Cognition, attention, planning
• D. Motor neuron signals (UMN → LMN → NMJ)

Answer: (D)

Motor execution is the actual pathway that makes muscles contract. It starts with a command from the upper motor neurons in the cortex and brainstem, which descend to synapse on the lower motor neurons in the spinal cord or brainstem. Those lower motor neurons then project to skeletal muscles, and at the neuromuscular junction they release acetylcholine, triggering an action potential in the muscle fibers and causing contraction. This chain—upper motor neurons to lower motor neurons to the neuromuscular junction to the muscle—is how movement is carried out. While cognition, planning, and attention shape what to do and how to guide it, and sensory input helps fine-tune the action, the actual execution rests on this UMN → LMN → NMJ pathway.