sodium-potassium
Calcium
The hyperpolarization of the membrane potential relative to the resting potential (the undershoot) causes voltage-dependent Potassium conductance (and any Sodium channels not yet inactivated) to turn off, allowing the membrane potential to return to resting level.
Ionic conditions are restored by pumps and channels that regulate the movement of ions across the cell membrane. Electrical conditions are restored by the movement of charged ions, such as sodium and potassium, which generates an electrochemical gradient across the cell membrane.
The potassium (K+) channel gate opens immediately after an action potential has peaked. This allows potassium ions to flow out of the cell, resulting in repolarization of the membrane potential back to its resting state.
fig. 1Formation of an action potentialThe formation of an action potential can be divided into five steps. (1) A stimulus from a sensory cell or another neuron causes the target cell to depolarize toward the threshold potential. (2) If the threshold of excitation is reached, all Na+ channels open and the membrane depolarizes. (3) At the peak action potential, K+ channels open and K+ begins to leave the cell. At the same time, Na+ channels close. (4) The membrane becomes hyperpolarized as K+ ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire. (5) The K+ channels close and the Na+/K+ transporter restores the resting potential.
Calcium
Death.
The hyperpolarization of the membrane potential relative to the resting potential (the undershoot) causes voltage-dependent Potassium conductance (and any Sodium channels not yet inactivated) to turn off, allowing the membrane potential to return to resting level.
The resting potential is restored after the action potential passes through an axon by the sodium-potassium pump, which actively transports sodium ions out of the cell and potassium ions into the cell. This process helps maintain the balance of ions inside and outside the cell, returning the membrane potential to its resting state.
The sodium-potassium pump is responsible for restoring the resting membrane potential by actively transporting sodium ions out of the cell and potassium ions into the cell. The sodium-potassium pump helps maintain intracellular ionic concentrations by moving 3 sodium ions out of the cell for every 2 potassium ions transported into the cell.
Action potentials arise when a neuron's membrane potential reaches a threshold, typically due to depolarization caused by the influx of sodium ions (Na+) through voltage-gated sodium channels. This rapid change in membrane potential leads to a positive feedback loop, where more sodium channels open, causing further depolarization. Once the peak is reached, potassium channels open, allowing potassium ions (K+) to exit the cell, leading to repolarization. The process restores the resting membrane potential, completing the action potential cycle.
Ionic conditions are restored by pumps and channels that regulate the movement of ions across the cell membrane. Electrical conditions are restored by the movement of charged ions, such as sodium and potassium, which generates an electrochemical gradient across the cell membrane.
Resting membrane potential is restored through the activity of the sodium-potassium pump, which actively transports sodium ions out of the cell and potassium ions into the cell. Intracellular ionic concentration is restored through various ion channels and transporters that regulate the movement of ions across the cell membrane based on concentration gradients.
The potassium (K+) channel gate opens immediately after an action potential has peaked. This allows potassium ions to flow out of the cell, resulting in repolarization of the membrane potential back to its resting state.
fig. 1Formation of an action potentialThe formation of an action potential can be divided into five steps. (1) A stimulus from a sensory cell or another neuron causes the target cell to depolarize toward the threshold potential. (2) If the threshold of excitation is reached, all Na+ channels open and the membrane depolarizes. (3) At the peak action potential, K+ channels open and K+ begins to leave the cell. At the same time, Na+ channels close. (4) The membrane becomes hyperpolarized as K+ ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire. (5) The K+ channels close and the Na+/K+ transporter restores the resting potential.
A traveling action potential passes channels that allow ions to flow in both directions across the membrane, which very rapidly restores the potential of the membrane traversed. In the most simple configuration, influx of sodium (Na+) is quickly balanced by efflux of potassium (K+).Beware confusing this with how a cell's initial ion gradients are restored (e.g. sodium potassium pumps in the membrane), or occasional directionally-biased placement of ion-specific channels (e.g. nodes of ranvier), or channel reactivation (molecular voltage gates in channels).
This process is known as the sodium-potassium pump, which uses energy from ATP hydrolysis to pump 3 sodium ions out of the cell and 2 potassium ions into the cell against their concentration gradients. This helps to maintain the resting membrane potential and intracellular ionic concentrations essential for proper cell function.