Comparison - Graded Potentials to Action Potentials
A graded potential in physiology, is described as local changes in membrane potential that occur in varying grades or degrees of magnitude or strength. When compared to graded potential, an action potential is described as brief, rapid, large (100mV) changes in membrane potential during which the potential actually reverses so that the inside of the excitable cell transiently becomes more positive than the outside. As with a graded potential, an action potential involves only a small portion of the total excitable cell. Action potentials occur in several types of animal cells (excitable cells), which include neurons, muscle cells, and endocrine cells, as well as in some plant cells. In neurons, they play a central role in cell-to-cell communication. In other types of cells, their main function is to activate intracellular processes. Action potentials in neurons are also known as “nerve impulses” or “spikes”. A neuron that emits an action potential is often said to “fire”. Depending on the stimulus, graded potentials can be depolarizing or hyperpolarizing. Action potentials always lead to depolarization of the membrane and reversal of the membrane potential. Graded potentials amplitude is proportional to the strength of the stimulus. Amplitude is generally small (a few mV to tens of mV). The duration of graded potentials may be a few milliseconds to seconds. When compared to graded potentials, action potentials amplitude is all-or-none; strength of the stimulus is coded in the frequency of all-or-none action potentials generated (large amplitude). Nearly all cells from animals and plants function as batteries, in the sense that they maintain a voltage difference between the interior and the exterior of the cell, with the interior being the negative pole of the battery. The voltage of a cell is usually measured in millivolts(mV), or thousandths of a volt. A typical voltage for animal cell is -70mV. Because cells are so small, voltages of this magnitude give rise to