Answer:
Hyperpolarization is caused by a delay in the inactivation of Na+ channels.
Depolarization is caused by the opening of Na+ channels making the membrane potential more positive.
Changes in membrane potential making it more positive will trigger a potential action if the membrane potential is big enough to open a big number of ion channels. If the change in membrane potential is not big enough a small number of ion channels will open and the potential action will travel short distances.
Step-by-step explanation:
When the membrane potential increase from -90 mv to -55 mv Na+ channels open their gates and Na+ goes to the inside of the neuron, this process is called membrane depolarization, Na+ will go to the inside of the cell increasing the membrane potencial and opening more Na+ channels. When the potential action reaches +40 mv a potential action occurs. Shortly after this happens the Na+ channels will start to close their gates and the K+ channels will open their gates making K+ ions to rush out of the cell. K+ channels delay the closure of their gates causing an hyperpolarization due to the fact that the membrane potential is more negative than -90mv because of the great number of K+ that rushed out.
Graded potentials are triggered by small changes in membrane potential, they will not give potential actions. Potential actions depolarize all the membrane because they reached the +40mv membrane potential resulting in the activation of a large number of Na+ channels and transmitting the signal globally. Graded potentials will not produce the depolarization of the whole membrane only of a region transmitting a signal locally because the membrane potential was not high enough to open all the Na+ channels but only local Na+ channels.