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.
Picture of a Action Potential. The first step in the action potential is for the neuronâs membrane potential to reach the threshold. This change in the membrane potential can be caused by a variety of factors including excitatory stimulation by another cell or neuron.hen the membrane potential reaches its peak, the action potential is attained, and the sodium channels become refractory and no more sodium ions enter the cell. Potassium ions continue to leave the cell, and the membrane potential slowly decreases towards the resting potential.