Hodgkin cycle

In membrane biology, the Hodgkin cycle is a key component of membrane physiology, identified by British physiologist and biophysicist Sir Alan Lloyd Hodgkin, which describes bioelectrical impulses.

The Hodgkin cycle represents a positive feedback loop in which an initial membrane depolarization leads to uncontrolled deflection of the membrane potential to near V_Na. The initial depolarization must reach or surpass threshold in order to activate voltage-gated Na channels. Opening of Na channels allows Na inflow, which, in turn, further depolarizes the membrane. Additional depolarization activates additional Na channels. This cycle leads to a very rapid rise in Na conductance (g_Na), which moves the membrane potential close to V_Na. The cycle is broken when the membrane potential reaches to the sodium equilibrium potential and potassium channels open to re-polarize the membrane potential. This positive feedback loop means that the closer these voltage-gated Na channels are to each other, the lower the threshold of activation.