Final answer:
The statement is false; refractory periods are not present after all potentials but are specific to action potentials in neurons and muscle cells. They prevent the immediate initiation of a second action potential to allow the cell to reset its ionic balance.
Step-by-step explanation:
The statement "A refractory period occurs following all types of potentials" is FALSE. Refractory periods are characteristic to neurons and muscle cells, specifically after an action potential. The structures that are refractory, meaning they cannot fire another action potential immediately, are the membranes of these cells. During the absolute refractory period, a second action potential cannot be initiated, no matter how strong the stimulus is. This is due to the inactivation gate of the voltage-gated Na+ channels, which need time to return to their resting state. After the absolute refractory period, there is a relative refractory period during which a stronger-than-normal stimulus is required to initiate another action potential, because the cell is slightly hyperpolarized due to outflow of K+ ions.
In the context of cardiac contractile cells, refractory periods are particularly important to allow the heart muscle cells to pump blood effectively before they can fire for a second time.