Final answer:
Efferent nerves are responsible for carrying messages from the brain to the muscles, which classify them as motor neurons within the sensory-somatic nervous system.
Step-by-step explanation:
The nerves that carry messages from the brain to the muscles are known as efferent nerves. These efferent nerves are a component of the nervous system, specifically the motor neurons, which are responsible for transmitting instructions from the central nervous system (CNS) to muscles and glands to prompt action.
Unlike afferent nerves, which carry sensory information to the CNS, efferent nerves carry nerve impulses away from the CNS to the target muscles, initiating movement. This is a fundamental aspect of the sensory-somatic nervous system, which manages both sensory information going to the CNS and motor information exiting the CNS to effect physiological responses.