1/7/2024 0 Comments Action potential graphThe voltage-gated sodium channels that were once activated during depolarization also transition to an ‘inactivated’ state. However, during depolarization, the sodium influx is more than the potassium efflux, while the opposite is true for repolarization. The mechanism is a little less simple than that because potassium channels are open even during depolarization. Next begins the falling phase, called ‘repolarization’, where the sodium channels slowly start closing and more voltage-gated potassium channels open. The next phase of the action potential is the peak phase at which point the depolarization stops or reaches the highest point. However, an action potential can only occur when depolarization reaches a threshold value of between -40 and -55 mV. At this depolarization stage, the low membrane potential ceases, and the state of the voltage-gated sodium ions changes from a deactivated (closed) state to an activated (open) state. The opening of the voltage-gated sodium channels causes an influx of sodium ions and increases the voltage. The stimulus could be in the form of a neurotransmitter released by the presynaptic cell that eventually binds to receptors on the postsynaptic cell membrane. The first phase of the action potential is the rising phase called ‘depolarization’, which occurs due to a stimulus and causes the opening of voltage-gated sodium channels. The generation of an action potential depends upon the voltage-gated sodium channels, which exist in three states depending upon the phase of the action potential. Permeability of the membrane translates to the action of the ion channels in allowing certain ions to enter the cell, which would otherwise not be possible in the normal resting stage. Similarly, there are other channels embedded within the cell membrane that are responsible for the generation of an ‘action potential’ General Action Potential PhysiologyĪn action potential is described as a sudden and spontaneous change or reversal in the membrane potential above a threshold value due to increased permeability of the cell membrane. The Na+/K+ ATPase pump, in response, helps to maintain the concentration gradient. The high intracellular concentration of potassium creates a gradient for the efflux of potassium ions through the leaky channels, resulting in the formation of the negative resting membrane potential. This is also supported by the fact that the intracellular fluid contains a high concentration of potassium ions compared to the extracellular environment, which consists of high concentrations of sodium and chloride ions. For example, potassium leak channels cause the escape of potassium ions from inside the cells. The membrane structure also harbours certain ion transporters that support the membrane potential. This is also described as the state of a normal resting membrane potential. Usually, the inside of the cell is more negative than the outside, and the membrane potential is typically at -70 mV (millivolts). The maintenance of a potential across the cell membrane is called ‘membrane potential’. Therefore, there is a difference in ion concentration maintained across the cell membrane, causing it to be polarized. The cell membrane consists of a lipid bilayer structure that usually does not allow electrical ions to pass through freely. How these fluctuations come about is to a large extent dependent upon the cell membrane and the movement of ions across it. These voltage fluctuations allow the propagation of signals and can be thought of as a means of communication between the cells. Certain cells in the body are electrically active and can relay and sustain voltage fluctuations.
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