Cyclobenzaprine is a centrally acting skeletal muscle relaxant. Its primary mechanism is to reduce muscle activity by acting on which system?

• A. Central nervous system
• B. Skeletal muscle fibers directly
• C. Peripheral nerves at the neuromuscular junction
• D. Inflammatory mediators in joints

Answer: (A)

Cyclobenzaprine is a centrally acting muscle relaxant, so its effect comes from dampening activity in the central nervous system, especially in the brainstem. By reducing the brainstem's regulation of motor neurons, it lowers tonic motor activity and muscle spasm. It does not act directly on skeletal muscle fibers, the neuromuscular junction, or inflammatory mediators in joints. This CNS-mediated reduction of motor tone is why the central nervous system is the correct site of action.