An action potential is an electrical impulse that begins at the axon hillock (triggering zone), propagates from the soma and descends into the axon, the synaptic button and the synapse. The action potential is triggered by a depolarization of the neuron from -70mV to -55mV. This depolarization occurs when the neuron receives either repeated stimuli or collective stimuli (local potentials) which open the sodium channels and allow Na+ to flow into the neuron until it reaches a threshold of -55 mV . Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”? Get the original essay When sodium channels open, Na+ flows into the neuron due to its concentration gradient (Na+ is more concentrated in the extracellular fluid, it circulates inside the neuron) and the electrical gradient (the interior of the neuron is more negative so positive sodium ions enter). When the sodium diffuses inside the neuron, it triggers the potassium channels to open and allow the K+ to flow out (since the K+ is more concentrated inside and the inside starts to get more and more more positive.) When the cell reaches -50 mV, the voltage change opens potential-gated sodium channels at the trigger zone. This causes an additional influx of Na+ and further depolarizes the cell, eventually opening neighboring voltage-gated sodium channels along the axon and moving them away from the cell body. Voltage-gated potassium channels also open when changing voltage from -70 mV to -50 mV. The K+ channels here are slower to respond, but they eventually allow enough potassium to flow out of the cell (due to the K+ concentration gradient and electrical gradient) to repolarize the cell. When the action potential reaches 0 mV, the voltage-gated sodium channels begin to close and the potassium channels approach all being open. This causes the voltage to return to the resting membrane value after a slight hyperpolarization (when K+ leaving the cell makes the cell slightly more negative than the resting membrane value.) The resting membrane potential is reached when the voltage is restored to -70 mV due to K+ and Na+ leaving or entering the cell depending on their respective electrical gradients. When the shift of K+ and Na+ finally results in an intracellular voltage of -70 mV, the potential-gated K+ and Na+ channels close. Although the charge is restored to -70 mV, the ions are not restored (Na+ must be more concentrated in the extracellular fluid and K+ in the intracellular fluid.) This is where the Na+/K+ pump comes in. The Na+/K+ pump essentially binds Na+ in the intracellular fluid and exchanges it for K+ in the extracellular fluid. It ultimately restores the ions to their original concentrations at resting potential. The absolute refractory period is a period during which the cell does not allow a stimulus, regardless of its strength, to trigger another action potential. This period depends on the voltage-gated sodium channels and lasts from the onset of the action potential until all voltage-gated sodium channels are closed. The relative refractory period is the period during which a cell can produce another action potential if the stimulus reaches threshold. The relative refractory period encompasses the hyperpolarization phase until all voltage-gated potassium channels close. Since the hyperpolarized membrane is at a voltage slightly lower than the resting membrane potential, the distance between the state..