So notice that the cell membrane contains these receptor proteins, and the axon terminal contains these synaptic vesicles that carry special neurotransmitters. Now, in the case of the motor division of the somatic nervous system, these neurotransmitters are always acetylcholine. So as the action potential travels and eventually ends up on the exxon terminal, it basically causes the release of these synaptic vesicles, and that releases our acetylcholine. The acetylcholine eventually binds onto these receptor proteins that create an action potential. And that action potential ultimately causes the contraction of our biceps muscle. So in this way, it's the brain that generates that electrical signal, but it's the motor neuron of the somatic nervous system that actually causes that movement, that voluntary movement in the first place.