Binding opens the channel, allowing Na into the cell. It depolarizes and through a series of actions we will discuss soon, causes contraction. A single electric shock will produce a single muscle action, or twitch. If we study the effect of activation on a single muscle cell, we see that the muscle cell either does not respond or it contracts fully. Thus the graded responses seen in large muscles with many cells must result from the summation of many individual contractions.
Many cells make up one muscle, and each cell has smaller subdivisions that are the functional units.
47.7 organization Each cell is called a muscle fiber or myofiber . The Z lines are a protein framework to which the actin filaments attach. The A bands are isolated floating molecules of myosin , located between the Z lines. One sarcomere is the distance between Z lines. Thick filaments made up of long molecules with heads.