Final answer:
When walking, the brain sends messages to the leg muscles via efferent fibers. These fibers are part of the sensory-somatic nervous system, which controls voluntary movements. Motor neurons within this system transmit signals from the CNS to the muscles, instructing them to contract.
Step-by-step explanation:
When you are walking, the brain sends messages to the skeletal muscles in the legs by way of efferent fibers. The sensory-somatic nervous system transmits information from the central nervous system (CNS) to the muscles, effectively controlling voluntary movements. The motor neurons that facilitate this process are part of the somatic nervous system and send motor information via the spinal cord and potentially from the brainstem for specific muscle groups like those in the face, head, and neck.
The axons of these neurons bundle together to form nerves, which act like cables transmitting electrical signals to the muscles. This action instructs the muscles to contract, thus allowing for movement, such as walking. The term 'efferent' is helpful to remember because efferent fibers are responsible for carrying signals away from the CNS to effectors like muscles (efferent = exit), as opposed to afferent fibers which carry information toward the CNS (afferent = arrive).