 Dear students, in this topic, we will discuss the propagation of action potentials. The action potential has a property of regenerative propagation. That is very necessary for the signals to be transmitted in the nervous system. An action potential has information of the stimulus in electrical form. This information should be carried to the central nervous system. This sending is actually the basic function of the communication system of animals. The action potential that is produced by the axon hillock of a nerve cell actually occurs on only a few millimeter region of the axon. To propagate it, the events of action potential must regenerate. The events that have started once, if the axon has a long length and it has to pass through the neurons of the axon, then the action potential has a property of regenerating. So, because of this property, action potentials are used as a mode for long-distance transmission. Dear students, now we shall discuss the mechanism of propagation of action potentials. The action potential that is elicited or started at any one point on an excitable membrane has the property to spread this excitation to the adjacent portions of the neuron. This property results in the propagation along the membrane. The site where an action potential is initiated an inflow of sodium ion current starts. This initiates the rising phase of action potential. The sodium current in one region affects about 1 to 3 millimeter area of the adjacent portion. This causes excitation and depolarization in that region too, thereby initiating an action potential in that region also. However, the region in which the action potential was started and in which a few milliseconds ago there was a sodium ion inflow is now at a stage in which repolarization due to potassium ion outflow has started. These depolarization and repolarization events spread through the regions of the membrane along its length. As a result, the local currents of ions cause the action potential to be propagated along the length of the egg zone. Dear students, the propagation of action potentials is unidirectional. When an action potential is generated and the inflow of sodium ions starts and then this sodium current transfers to the next region, then the sodium channels of the previous region are inactivated. Thus, a sodium current works as an activator for the next region and propagates the action potential in the forward direction. Since the sodium channels of the previous region are inactivated, they cannot be activated. That is why an action potential that starts at an egg zone hillock moves only in one direction, that is toward the synaptic terminal. The propagation also occurs without decrement. At each position along the egg zone, the process is identical. That is, the shape and magnitude of the action potential remains constant. It ensures that the propagation of initial excitation occurs without decrement. If the process in the next region is less in the magnitude or shape of the action potential, then this means that the propagation stops after a while. But since the magnitude and shape of the action potential remain the same, until it reaches its final destination, it means that the signal is transferred without decrement.