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 resting potential is created by a transport protein called the sodium-potassium pump. This protein moves large numbers of sodium ions (Na +) outside the cell, creating the positive charge. At the same time, the protein moves some potassium (K +) ions into the cellâs cytoplasm.