So let's suppose we have the biceps muscle, the triceps muscle and this is the central nervous system, our spine as well as our brain. So we have one motor neuron, the second motor neuron and the third motor neuron. Now every one of these motor units or every one of these motor neurons begins in the central nervous system. And that means each one of these motor neurons, their dendrites and the cell bodies originate begin at the central nervous system. Now the axon of the motor neuron basically extends and the axon terminal of each one of these motor neurons basically ends up at the muscle cells that they control. So motor neuron number one, as well as all the muscle cells that motor neuron number one controls is known as motor unit number one.