To excite skeletal muscle contraction, the action potentials move from the axon of the neuron, then to the sarcolemma, and finally to the T tubules.
Through the axon of the motor neuron (brain cell), electrical signals are transmitted from the brain, through the spinal cord, then to the muscles. The axon branches through the muscle and connects to the muscle fibers. The axons then interact with the folded sarcolemma of the muscle fibers to relay the "information" from the electrical signals. Then, this information is passed on to the T tubules, which are extensions of the sarcolemma, to eventually enable the movement (i.e. contraction) of the muscles.