Unsaved nerve cells called form networks within the body (like a system of wires), in order to communicate with each other in a type of chain reaction.

The correct answer is "neurons".
Neurons are nerve cells which connect to each other using synapses and form neural networks. They exhibit high levels of specialization and are the primary components of the central nervous system.

Myofibrils are contractile fibers which form the striated muscle cells. Sarcomeres are the structural unit of the myofibrils.