The channel is made up of four identical subunits, each having six transmembrane segments, as shown in the figure. The segments are named S1 through S6 from the amino to the carboxy ends of the polipeptide. Segments S5 and S6 and the special P loop structure form the conduction pore. Segments S2, S3 and S4 constitute the voltage sensor, which detects changes in membrane potential and communicates the perturbation to the conduction pore to gate the channel open or closed.