In the previous several lectures, we discussed what an action potential is and we discussed what a muscle contraction is. So basically, we said that an action potential causes a muscle contraction. We also discussed the graph of an action potential that takes place in skeletal muscles and that take place in cardiac muscles. Now, what we're going to emphasize is in this lecture is the fact that an action potential is not the same thing as a muscle contraction. So oftentimes when students are learning about these two concepts, they forget that these two concepts are different, but they are connected. So an action potential is an electrical signal that is usually generated in the nervous system of our body.