Membrane potential function as a battery, providing power to operate a variety of "molecular devices" embedded in the membrane. Second, in electrically excitable cells such as neurons and muscle cells, it is used for transmitting signals between different parts of a cell. Signals are generated by opening or closing of ion channels at one point in the membrane, producing a local change in the membrane potential. This change in the electric field can be quickly affected by either adjacent or more distant ion channels in the membrane. Those ion channels can then open or close as a result of the potential change,
Signals, Crane and Subway, Charters Towers railway station the signal box, although electrical or hydraulic operation could be used for more distant signals. At night, lights were necessary, and kerosene lamps with movable coloured spectacles displayed different colours, including green (proceed), yellow (prepare to find next signal red), and red (stop). Later, electrical coloured lights were used. Smaller points indicator signals, which confirmed whether or not points had been switched, could be used for shunting within a railway yard, and the most common form was the rotating disk signal. These could also contain a kerosene lamp for night operation. To coordinate signals so that is impossible to give