What is Action potential: Definition and 19 Discussions

In physiology, an action potential (AP) occurs when the membrane potential of a specific cell location rapidly rises and falls: this depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, endocrine cells and in some plant cells.
In neurons, action potentials play a central role in cell-to-cell communication by providing for—or with regard to saltatory conduction, assisting—the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon; these signals can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke release of insulin. Action potentials in neurons are also known as "nerve impulses" or "spikes", and the temporal sequence of action potentials generated by a neuron is called its "spike train". A neuron that emits an action potential, or nerve impulse, is often said to "fire".
Action potentials are generated by special types of voltage-gated ion channels embedded in a cell's plasma membrane. These channels are shut when the membrane potential is near the (negative) resting potential of the cell, but they rapidly begin to open if the membrane potential increases to a precisely defined threshold voltage, depolarising the transmembrane potential. When the channels open, they allow an inward flow of sodium ions, which changes the electrochemical gradient, which in turn produces a further rise in the membrane potential towards zero. This then causes more channels to open, producing a greater electric current across the cell membrane and so on. The process proceeds explosively until all of the available ion channels are open, resulting in a large upswing in the membrane potential. The rapid influx of sodium ions causes the polarity of the plasma membrane to reverse, and the ion channels then rapidly inactivate. As the sodium channels close, sodium ions can no longer enter the neuron, and they are then actively transported back out of the plasma membrane. Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state. After an action potential has occurred, there is a transient negative shift, called the afterhyperpolarization.
In animal cells, there are two primary types of action potentials. One type is generated by voltage-gated sodium channels, the other by voltage-gated calcium channels. Sodium-based action potentials usually last for under one millisecond, but calcium-based action potentials may last for 100 milliseconds or longer. In some types of neurons, slow calcium spikes provide the driving force for a long burst of rapidly emitted sodium spikes. In cardiac muscle cells, on the other hand, an initial fast sodium spike provides a "primer" to provoke the rapid onset of a calcium spike, which then produces muscle contraction.

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  1. M

    Soliton model of the action potential

    Has anyone else come across the soliton model of the action potential? https://en.wikipedia.org/wiki/Soliton_model_in_neuroscience It seems extremely non-mainstream, especially given that it presented as an alternative to the Hodgkin-Huxley model, which is undoubtedly the most successful...
  2. F

    Action Potential in human cells

    Hello, I understand that the action potential represents a potential difference variation (depolarization) of the voltage across a cell membrane. This concept is generally presented in the context of nerve cells (neurons) as the change in potential across the axon membrane. What about the...
  3. J

    Cardiac Action Potential Duration Question

    What does the APD (Action potential duration) determine in a cardiac cell and how can it be changed (do I need to effect any of the phases of the AP)? For example, if the vagal nerve releases acetylcholine here are its effects: Inhibits Atrial Muscle Contraction- Negative inotropic effect...
  4. Asmaa Mohammad

    Physiology of the muscles: The T Tubules

    Hi all, My textbook says that the T tubules, which form an extensive network of transverse tubules that surround myofibrils, can carry the wave of action potential from the surface of the muscle fiber to the cell interior. Could you help me understand the sentence in bold because I'm not sure...
  5. I

    Is action potential a signal transduction?

    This might be either an obvious one, or I might be totally off track. I haven't seen, or been able to find neural action potentials being referenced as signal transductions. Aren't they signal transductions? And if not (say if action potential is only referenced to the change in potential)...
  6. I

    Is Action Potential Terminology Applicable Beyond Neural Processes?

    Hello, I noticed that in Wikipedia, action potential is not solely defined as a neural process, but rather as a process that happens between any cells that can release chemical signals and have target cells that can receive the signals. Is this true? Would we say that endocrine system creates...
  7. I

    Can an action potential last for a long time?

    I just learned that "action potential is a short-lasting event" (wiki) If someone is experiencing an emotion of sadness, is that same action potential keeps firing many times back to back or can it actually be a possibility that an action potential lasts for a "very long time". I am guessing...
  8. Conductivity

    Sodium concentration during action potential generation

    ' At the peak of the graph, Is the concentration of Na outside the cell is more than inside? because that must be to overcome the electrical force in the opposite direction but my book says that that inside the cell there are more Na than outside When is the concentration of Na+ greatest inside...
  9. G

    Evolution or action potential.

    Action potential is defined as" the local voltage change across the cell wall as a nerve impulse is transmitted" Now my question is "why it happens? i.e.,why organism evolves?
  10. B

    Action Potential Through Ion Channel, Total Number of Ions Through

    Homework Statement Nerve signals in the body occur when a small voltage, called an action potential, is applied across the membrane of a cell. When this action potential is applied across a region of the cell membrane called an ion channel, current in the form of moving potassium ions will be...
  11. P

    Action Potential with Nerve Cell and Finding Power

    Homework Statement During an action potential, Na + ions move into the cell at a rate of about 3 x 10^-7 mol / m^2 s. How much power must be produced by the "active Na+ pumping" system to produce this flow against a + 30 mv potential difference? Assume that the axon is 40cm long and 30 mu m...
  12. S

    Action potential of a skeletal muscle fibre,where is calcium?

    Now I follow this pic, there is no mention of opening of calcium channels anywhere. So how do skeletal muscles contract, without calcium. Incontrast action potential of a cardiac muscle has plateu phase and calcium channel involvement. Thanks :smile:
  13. N

    How to affect action potential

    If there a way to affect the action potential propagation across neurons, for better or worse? The organism I have in mind is planaria (flat worm) as they are very simple but can be conditioned (like the Pavlovian dog). I don't think that a non-harmful liquid chemical could have much effect, but...
  14. Pythagorean

    Can we use individual spikes as a reliable carrier of information?

    I'm currently reading Spiking Neuron Models by Gerstner and Kistler: But I've also come across this in a review of Spikes: Question(s) Is this really true? Are all action potentials of a given neuron the same? Is that justification for action potential shape not "carrying any...
  15. S

    Action potential and strength of muscle contraction?

    Hello guys, Although the response of a motor unit is all-or-none, the strength of the response of the entire muscle is determined by the number of motor units activated. Nerve impulses passing down a single motor neuron will thus trigger contraction in all the muscle fibers at which the...
  16. somasimple

    Action Potential: Passive Spread Current

    Hi All, The Action Potential propagation involves a passive event called: Passive Spread or Electrotonic conduction. Here is some references: http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mcb.figgrp.6138...
  17. somasimple

    What happens to the Na+ ions during an action potential?

    Hi All, It is a fact that Na+ ions cross the membrane and enter the cell during the rising phase of the action potential. The process happens because Na ions channels are open. Then the ions channels becomes inactivated/closed for a while. What happens to the Na+ ions that entered the cell?
  18. somasimple

    Medical Can action potential propagation be modeled by joining several RC circuits?

    Hi All, I took the following from this page. http://en.wikipedia.org/wiki/Action_potential I'm lost with these comments because I learned that small fibres have low speed and larger ones have a higher one but, in my opinion, since membrane thickness doesn't really vary in unmyelinated...
  19. G

    Medical Voltage Clamping Action Potential: Inward & Outward Currents

    This is about voltage clamping: When Hodgkin and Huxley voltaged clamped a nerve - when hyperpolarised there was a small inward current, why is that? and when they used a depolarising clamp, there is firstly a brief capacitative current - this current is outwards, why?:confused: