What is the purpose of the action potential?

Answer 1

An action potential can also be called a nerve impulse which is known to be stimulated by an external stimuli or upon internal excitation.

This action potential travels through a neuron and involves charged ions (the key ones are sodium ions and potassium ions) that cross the membrane barrier of the neuron.

In the longitudinal section of the axon of the neuron (the part that carries the signal which may be covered in Schwann cells to protect the it) the action potential cycle occurs.

There are four main stages: The Resting Membrane Potential, Depolarization, Repolarization, and the Refractory Period.

In the Resting Membrane Potential Stage there is an active force that maintains the resting membrane potential at -70 mV. This active force is the Sodium Potassium Pump where three sodium ions leave the nerve cell and two potassium ions enter. With the Sodium Potassium Pump, it transports these ions actively and so ATP is required. In addition to the Sodium Potassium Pump, there are voltage-sensitive potassium slow leak channels that are involved with passive transport and there are also voltage sensitive sodium gates that are passive sodium channels. They are normally impermeable to sodium however it can't pass through unless there is an electrical current to open it.

In the Depolarization Stage, an external stimuli occurs altering the tertiary structure of sodium gates allowing the nerve cell membrane to become more permeable to sodium than potassium. Therefore, sodium floods in passively making the extracellular fluid (ECF) more negative and the intracellular fluid (ICF). Now the voltage inside the cell is +50 mV compared to the previous stage where it was -70 mV.

Once the cell has reached a voltage of +50 mV, sodium gates close and so the inflow of sodium ions into the cell are discontinued. Because of the altered concentration gradient of ions in the Depolarization Stage, it causes the potassium channels to alter their shape. As a result, there is an inflow of potassium ions outside of the cell and the inside becomes negative again. This stage is known as the Repolarization Stage. This prevents the signal from going backwards. The voltage inside the cell is now at -80 mV.

In the last stage, Refractory Period, the Sodium Potassium Pump actively re-establishes the resting membrane potential. It takes time to reestablish the sodium and potassium concentrations to -70 mV.

Please note that depolarization cannot occur until the resting membrane potential is reached (-70 mV).

As an aside, the action potential follows the All or None Principle. This means that larger signals do not create larger action potentials. A neuron must always reach -70 mV before the signal is passed along a neuron. Therefore, the action potential will occur fully or not at all.

The action potential is an electrical event occurring when a stimulus of sufficient intensity is applied to a neuron or muscle cell, allowing sodium to move into the cell and reverse the polarity.

Normally neurones (neurons, or nerve cells) maintain a resting potential of -70mV across their membrane by the active pumping of 3Na+ ions out of the cell for every 2 K+ ions pumped into the cell by a Na+/K+ pump. When the neurone is stimulated, sodium ion channels open in the membrane and sodium ions flood in to the cell down an electrochemical gradient by diffusion, increasing the potential of the cell to +40mV. This is called depolarisation. At this point the sodium channels close, and potassium ion channels open. Potassium ions flood out of the cell down their electrochemical gradient, decreasing the cell's membrane potential. This is called repolarisation. There is a slight overshoot where too many potassium ions diffuse out of the cell, and there is hyperpolarisation where the cell's membrane potential falls below its normal -70mV, but this is corrected and the resting potential is once again restored. This is the sequence of events that makes up a single action potential. Action potentials are transmitted by saltatory conduction in the neurone, and impulses jump from node to node along the axon of the neurone.

Answer 2

Action potential in Biology is a short event, when the electrical membrane potential of a cell quickly rises and falls, following a consistent trajectory. This can occur in all types of cells.

Answer 3

To reach equillibrium of 40mV in the cell.

Answer 4

The purpose of the action potential is to forward-propagate a nerve signal to other neurons.