Basically, our T tubules allow for the action potential to actually get inside the cell quickly and efficiently. So once again, we see that the sarcoplasmic reticulum contains a high concentration of calcium that is released during muscle contraction. Now, the plasma membrane that surrounds the muscle cell is called the sarcolema. This specialized membrane contains in vaginations known as T tubules or transverse tubules that run perpendicular with respect to our myofriles and which run very deep into the cell. And they allow the action potential to actually travel through the cell quickly and efficiently. Now, how does the action potential actually get to the cell in the first place?