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 minus sign indicates that the inside of the cell is negative with respect to the surrounding extracellular fluid. It is essential to realize that only a very small number of negative and positive ions need to be separated by the membrane to create the resting membrane potential.embrane Potentials. In cells of all types, there is an electrical potential difference between the inside of the cell and the surrounding extracellular fluid. This is termed the membrane potential of the cell.