Intro | Depolarization | Hyperpolarization | Action Potential | Threshold of Excitation
Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test
Prior to the onset of an action potential, the charge on the outside of the neuronal membrane is more positive than the charge inside the neuronal membrane. This resting potential is approximately -70 mV. When the axon of a neuron is stimulated by natural or artificial means, this polarized resting state undergoes Depolarization, or a decrease in the differential charge across the neuronal membrane (movement toward zero; less negative, more positive). Small levels of stimulation will exert little effect on the membrane, and it will quickly return to its normal resting state of polarization. Thus, any stimulation that reverses membrane polarity less than 5 to 15 mV is often referred to as sub-threshold stimulation. The greater the movement of polarity away from the resting state (depolarization), the wider the sodium channels found in the cell membrane will open. Sodium channels are called voltage dependent due to this graded response to increased stimulation.