Figure 1.2 Real and Model Membranes (ion channels are omitted for simplicity). A. In intracellular recording, an electrode is inserted through the membrane and a voltmeter or oscilloscope records the difference in potential between the inside of the cell (+ electrode) and the outside of the cell (− electrode). B. In extracellular recording, both electrodes are outside the cell, so the voltmeter or oscilloscope records the difference in potential between two points (+ and − electrodes) near the external surface of the membrane.