I used this in my A&P I class this semester. I wanted to incorporate all of the components of this concept in a constructive way. This worksheet does include a key. It begins with levels of organization of the muscle, then the organelles of a muscle fiber including diagrams, labeling the components, the sarcomere components and functions, labeling a sarcomere, myofilaments and a myofilament diagram, motor neurons and a diagram, and the NMJ with an image. Finally, students are asked to put al