How does action potential occur?
1 Answer
An action potential is generated in the following steps: depolarization, repolarization, hyperpolarization and a refactory period.
Explanation:
Assuming you are referring to depolarization (as to how it's caused!):
Receptor cells (cells which detect change) act as transducers (which means, they can convert, for eg. light into energy in an electrical impulse!). These initiate action potentials.
When there no arrival of an impulse/action potential, the neuron is at it's resting potential . They have a high amount of potassium ions in the axon and a high amount of sodium ions outside ( potential difference ). However, the amount of sodium ions outside are much greater than the potassium ions inside - thus results in an electrochemical gradient. This is maintained by sodium-potassium pumps.
(the first part of the axon is at it's resting potential)
- Depolarization: when an electric current stimulates the axon, voltage-gated channels open in the membrane to allow sodium ions to pass through. It diffuses down the electrochemical gradient. This causes the potential different to become less negative inside the axon (as there is an inflow of sodium ions!). Resulting in depolarization. (the second part in the diagram!)
( I'll include explanations of the other steps as well, just incase.. )
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Repolarization: due to depolarization, the axon becomes positive (because of the inflow of postassium ions). Thus, voltage-gated channels for sodium close and potassium ion channels open, so that potassium diffuses out. This is to restore the initial potential difference.
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Hyperpolarization: during repolarization, potassium ions tend to diffuse out toooo much. Causing, hyperpolarization briefly.
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Finally, the refractory period: at this stage, the axon is not responsive. It is recovering from the action potential to restore its resting potential. (aka back to the resting potential where the axon has a high amount of potassium and outside, there's a high amount of sodium!)
Check out this youtube video for more about action potentials!:
