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The concentration of sodium ions is intimately related to the electrical potential across a membrane. Depolarization often occurs via the influx of sodium ions to the intracellular region. Given that sodium ions have a positive charge, the intracellular region becomes less negatively charged relative to the extracellular region. [1]
Potassium ions continue to move out of the axon so much that the resting potential is exceeded and the new cell potential becomes more negative than the resting potential. The resting potential is ultimately re-established by the closing of all voltage-gated ion channels and the activity of the sodium potassium ion pump. [10]
Once the cell has been depolarized, voltage-gated sodium channels close, causing potassium channels to open; K+ ions then proceed to move against their concentration gradient out of the cell. [ 3 ] However, if the voltage is below the threshold, the neuron does not fire, but the membrane potential still fluctuates due to postsynaptic potentials ...
This is followed by the opening of potassium ion channels that permit the exit of potassium ions from the cell. The inward flow of sodium ions increases the concentration of positively charged cations in the cell and causes depolarization, where the potential of the cell is higher than the cell's resting potential. The sodium channels close at ...
The sodium-potassium ATPase is an active transporter within the membrane that pumps potassium (2 ions) back into the cell and sodium (3 ions) out of the cell, maintaining the concentrations of both ions as well as preserving the voltage polarization.
The ion pump most relevant to the action potential is the sodium–potassium pump, which transports three sodium ions out of the cell and two potassium ions in. [13] [14] As a consequence, the concentration of potassium ions K + inside the neuron is roughly 30-fold larger than the outside concentration, whereas the sodium concentration outside ...
Voltage-gated ion-channels are usually ion-specific, and channels specific to sodium (Na +), potassium (K +), calcium (Ca 2+), and chloride (Cl −) ions have been identified. [1] The opening and closing of the channels are triggered by changing ion concentration, and hence charge gradient, between the sides of the cell membrane.
The open sodium channels allow more sodium ions to flow into the cell and resulting in further depolarisation, which will subsequently open even more sodium channels. At a certain moment this process becomes regenerative (vicious cycle) and results in the rapid ascending phase of action potential. In parallel with the depolarisation and sodium ...