What is the difference between membrane potential and action potential

Such potentials are called depolarizations. The polarized state of the membrane is decreased. Larger batteries produce even larger depolarizations. Again, the magnitude of the responses are proportional to the magnitude of the stimuli. However, an unusual event occurs when the magnitude of the depolarization reaches a level of membrane potential called the threshold. A totally new type of signal is initiated; the action potential.

Note that if the size of the battery is increased even more, the amplitude of the action potential is the same as the previous one Figure 1. The process of eliciting an action potential in a nerve cell is analogous to igniting a fuse with a heat source.

A certain minimum temperature threshold is necessary. Temperatures less than the threshold fail to ignite the fuse. Temperatures greater than the threshold ignite the fuse just as well as the threshold temperature and the fuse does not burn any brighter or hotter.

If the suprathreshold current stimulus is long enough, however, a train of action potentials will be elicited.

In general, the action potentials will continue to fire as long as the stimulus continues, with the frequency of firing being proportional to the magnitude of the stimulus Figure 1. Action potentials are not only initiated in an all-or-nothing fashion, but they are also propagated in an all-or-nothing fashion.

An action potential initiated in the cell body of a motor neuron in the spinal cord will propagate in an undecremented fashion all the way to the synaptic terminals of that motor neuron.

Again, the situation is analogous to a burning fuse. Once the fuse is ignited, the flame will spread to its end. The action potential consists of several components Figure 1. The threshold is the value of the membrane potential which, if reached, leads to the all-or-nothing initiation of an action potential. The initial or rising phase of the action potential is called the depolarizing phase or the upstroke. The region of the action potential between the 0 mV level and the peak amplitude is the overshoot.

The return of the membrane potential to the resting potential is called the repolarization phase. There is also a phase of the action potential during which time the membrane potential can be more negative than the resting potential. This phase of the action potential is called the undershoot or the hyperpolarizing afterpotential. In Figure 1. Before examining the ionic mechanisms of action potentials, it is first necessary to understand the ionic mechanisms of the resting potential.

The two phenomena are intimately related. The story of the resting potential goes back to the early 's when Julius Bernstein suggested that the resting potential V m was equal to the potassium equilibrium potential E K.

The key to understanding the resting potential is the fact that ions are distributed unequally on the inside and outside of cells, and that cell membranes are selectively permeable to different ions.

Thus, there will be an electrical force directed inward that will tend to counterbalance the diffusional force directed outward. The potential at which that balance is achieved is called the Nernst Equilibrium Potential. An experiment to test Bernstein's hypothesis that the membrane potential is equal to the Nernst Equilibrium Potential i. Also shown is the line that is predicted by the Nernst Equation. The experimentally measured points are very close to this line.

Note, however, that there are some deviations in the figure at left from what is predicted by the Nernst equation. Such deviations indicate that another ion is also involved in generating the resting potential. There is also an electrical driving force because the inside of the cell is negative and this negativity attracts the positive sodium ions. When a membrane is permeable to two different ions, the Nernst equation can no longer be used to precisely determine the membrane potential.

It is possible, however, to apply the GHK equation. If the GHK equation is applied to the same data in Figure 1. The value of alpha needed to obtain this good fit was 0. Learn how they provide best-in-class solutions for the entire range of patch-clamp experiments. What is an action potential? Stimulus starts the rapid change in voltage or action potential.

In patch-clamp mode, sufficient current must be administered to the cell in order to raise the voltage above the threshold voltage to start membrane depolarization. Depolarization is caused by a rapid rise in membrane potential opening of sodium channels in the cellular membrane, resulting in a large influx of sodium ions.

Membrane Repolarization results from rapid sodium channel inactivation as well as a large efflux of potassium ions resulting from activated potassium channels.

This means that chemicals cause an electrical signal. Chemicals in the body are "electrically-charged" -- when they have an electrical charge, they are called ions. There are also some negatively charged protein molecules. It is also important to remember that nerve cells are surrounded by a membrane that allows some ions to pass through and blocks the passage of other ions.

This type of membrane is called semi-permeable. When a neuron is not sending a signal, it is "at rest. Although the concentrations of the different ions attempt to balance out on both sides of the membrane, they cannot because the cell membrane allows only some ions to pass through channels ion channels.

The negatively charged protein molecules A - inside the neuron cannot cross the membrane. In addition to these selective ion channels, there is a pump that uses energy to move three sodium ions out of the neuron for every two potassium ions it puts in. Finally, when all these forces balance out, and the difference in the voltage between the inside and outside of the neuron is measured, you have the resting potential.

At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron. The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential.

The action potential is an explosion of electrical activity that is created by a depolarizing current. This means that some event a stimulus causes the resting potential to move toward 0 mV.