And that electrical signal travels to a particular muscle cell and it causes that particular muscle cell to basically contract. So although these two concepts are related, they are not the same thing. So let's begin by discussing the action potential and the muscle contraction of skeletal muscles. And then let's take a look at cardiac muscles. So to contract, or to contract any skeletal muscle, our action potential, our electrical signal, must be generated in the central nervous system of our body. So the brain or the spinal cord.