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.
The membrane potential of a cell at rest is called the resting membrane potential. resting potential (Vr) is equal to Vin. Its usual range in neurons is -60 mV to -70 mV. potential due to alterations in the flow of electrical current across the cell membrane resulting from the opening and closing of ion channels.