Define action potential. how is it generated

When a neurone is stimulated sodium ion channels open causing sodium ions to move into the neurone, down the electrochemial gradient as there are more sodium ions outside the cell compared to inside the cell. As sodium ions have a positive charge, when they enter the neurone, they cause the membrane potential to become more positive.

The process of sodium ions entering the neurone, is called depolarisation. This means that pottasium ions move out of the neurone, down the electrochemial gradient. This moving change in membrane potential has three phases. First is depolarization, followed by repolarization and a short period of hyperpolarization. These three events happen over just a few milliseconds. Action potential : A. Schematic and B. The action potential is a clear example of how changes in membrane potential can act as a signal.

The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential.

The action potential is an explosion of electrical activity that is created by a depolarizing current. This means that some event a stimulus causes the resting potential to move toward 0 mV. When the depolarization reaches about mV a neuron will fire an action potential. This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire.

Also, when the threshold level is reached, an action potential of a fixed sized will always fire There are no big or small action potentials in one nerve cell - all action potentials are the same size.

Action potentials are caused when different ions cross the neuron membrane. A stimulus first causes sodium channels to open. Once the neuron has "recharged," it is possible for another action potential to occur and transmit the signal down the length of the axon. Through this continual process of firing then recharging, the neurons are able to carry the message from the brain to tell the muscles what to do—hold the glass, take a sip, or put it down.

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