Final answer:
The refractory period puts a limit on the rate at which action potentials can be generated, affecting the normal function of neurons and muscle cells, especially in the cardiac muscle where it's crucial for proper heart contractions.
Step-by-step explanation:
The refractory period limits the frequency at which action potentials can be initiated in neurons and muscle cells. After an action potential, muscle or nerve cells temporarily cannot generate another one. This is due to the voltage-gated Na+ channels being inactivated.
The absolute refractory period refers to the time when no new action potential can be initiated, while the relative refractory period is when a new action potential can only be generated by a stronger-than-normal stimulus. In cardiac muscle, this period ensures that the heart muscle contracts properly and blood is effectively pumped without premature contractions.