Definition: A portion of a line which starts at a point and goes off in a particular direction to infinity. Try this Adjust the ray below by dragging an orange dot and see how the ray AB behaves. Point A is the ray's endpoint.
Plant cell cross-section, showing the membrane. Animal cell cross-section, showing the membrane. Resting membrane potential is the difference in voltage of the fluids inside a cell and outside a cell, which is usually between -70 to -80 millivolts (mV). View slideshow of images above.
At rest, the membrane potential is -60 millivolts (mV), which means that the inside of the cell is negative in comparison to the outside. This is ultimately due to an unequal distribution of ions, especially sodium and potassium, between the outside and inside of the cell (see Table 1).t rest, neurons (and most other cells, too) exhibit an electrical charge difference across the membrane. This difference, or membrane potential, can be measured with tiny electrodes connected to a voltmeter or an oscilloscope.