Final answer:
Motor neurons transmit signals from the spinal cord and brainstem to skeletal muscle fibers. The axons of motor neurons extend to muscle fibers through neuromuscular junctions, where acetylcholine is released.
Step-by-step explanation:
Motor Neurons and Muscle Fiber Connection:
The motor neurons that instruct skeletal muscle fibers to contract originate in the spinal cord and brainstem.
These neurons have long processes known as axons, which transmit action potentials from the spinal cord to the muscles.
The axons of multiple neurons bundle together to form nerves, allowing for efficient communication between the nervous system and muscles.
Motor neuron axons connect to muscle fibers at neuromuscular junctions, where the neurotransmitter acetylcholine is released, leading to muscle contraction.