Machinery for conduction of excitation is represented by a sarcotubular system, which is a total of specialized membrane structures to ensure propagation of a depolarization wave from the sarcolemma to myofibrils. It includes a number of components:

• Т-tubule system (light blue color in the diagram #1 #2) is a group of transverse tubules joined to sarcolemma; they are present in any sarcomere enabling fast conduction of action potential to every myofibril;
• sarcoplasmic reticulum (L-system, yellow color in the diagram) is a complex of anastomosing longitudinal tubules #1, #2, #3 around sarcomeres; it looks like a muff (the system is able to store Са⁺⁺ ions and to release them into myofibrils in case of neural stimulation).
• terminal cistern complex of the sarcoplasmic reticulum where the cisterns touch transverse tubules of the T-system (triads in skeletal muscles, diad (D) #1, #2 in the myocardium). The contact is a site for action potential transmission from T-system membranes to L-system membranes.

There are numerous mitochondria #1, #2, #3 between the myofibrils #1, #2.