What is the difference between action potential and graded potential?

The action potential and graded potential are two types of changes in membrane potential that can be given in one excitable cell (neuron, muscle cell, etc). Although both involve a change in voltage, each has different intensity and speed characteristics.

The intensity of the graded potential is weaker and depends on the stimulus received, while the action potential is more intense and is always of the same magnitude, it does not depend on the intensity of the stimulus.

The graduated potential

The graduated potentialalso called step potential or gradual potential, is a change in the membrane potential of variable magnitude that decreases with distance. They are a consequence of sum of the individual activity of ligand-gated ion channelsnot including voltage-gated channels.

A very important characteristic of potential graduates is that they are directly proportional to the magnitude of the stimulus; the greater the number of ion channels involved, the greater the magnitude of the potential.

The triggering stimulus for a graded potential may be the action of a neurotransmitter or a mechanical stimulus that affects the ionic permeability of the membrane; for example, stretching, temperature, etc.

A potential graduate can be depolarizer (EPSP- Excitatory Postsynaptic Potential) either hyperpolarizer (IPSP- Inhibitory Postsynaptic Potential). In the case of depolarizing potentials, they can trigger an action potential if it reaches an intensity above the threshold potential which is usually at a membrane potential of -55 mV. It can occur in postsynaptic dendrites or in skeletal muscle, smooth muscle, or cardiac muscle cells.

action potential

The action potential, unlike the graded potential, It's kind of "all or nothing"in other words, its magnitude is always the same regardless of the intensity of the stimulus. The action potential can travel great distances without losing intensity and involves the opening of the voltage gated ion channels of sodium and potassium.

An action potential can be generated by the opening of sodium channels, which generate an action potential that usually lasts 1 millisecond, or it can be generated by the opening of calcium channelswhich generates an action potential that can last up to 100 milliseconds.

Action potentials can occur in neurons, muscle cells, and endocrine cells. In neurons, they play a fundamental role in intercellular communication and are also known as nerve impulses. In the rest of excitable cells, the action potential is the signal for the initiation of intracellular processes. For example, in muscle cells it triggers muscle contraction, or in the beta cells of the pancreas it triggers the release of insulin.

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