Maximum number of Na+ channels per square micrometer is present in

"Saltatory" Conduction in Myelinated Fibers from Node to Node: Even though almost no ions can flow through the thick myelin sheaths of myelinated nerves, they can flow with ease through the nodes of Ranvier.Therefore, action potentials occur only at the nodes. Yet the action potentials are conducted from node to node, this is called saltatory conduction.That is, electrical current flows through the surrounding extracellular fluid outside the myelin sheath, as well as through the axoplasm inside the axon from node to node, exciting successive nodes one after another. Thus, the nerve impulse jumps along the fiber, which is the origin of the term "saltatory."Ref: Guyton; 13th edition; Chapter 5; Membrane Potentials and Action Potentials