Action potentials background
Neurons communicate with one another via action potentials. An action potential is a sudden brief change in the distribution of charge on the two sides of a nerve cell membrane (i.e., between the inside of the nerve cell versus the outside of the cell). This is caused by the flow of electrically charged particles (ions, such as Na+, K+, Cl-, Ca++) through special structures in the membrane, called ion channels or ion pumps.
Even at rest neurons have an imbalance in charge on their inside versus the fluid outside (caused by an imbalance in the movement of ions). This imbalance in charge is known as the resting membrane potential (abbreviated RMP or EM). A change in the movement of ions across the membrane caused by some stimuli will change the membrane potential, and a particular suite of changes in the membrane potential, called the Action Potential (AP) is the mechanism used by neurons to transmit information over the length of the cell.
Thus, in brief, an AP is simply a change in the resting membrane potential, which is used to transmit information along the length of a neuron.
The following animation shows the movement of the two main ions that are involved in most neurons in producing the RMP and whose movements are altered by a stimulus to produce an AP.
In these simulations, we will use a mathematical model of a spiking neuron to ask the following:
- What does it take to produce an action potential?
- Is there a limit to how many action potentials a neuron can generate in a certain time interval?
- How do different current intensities affect action potentials?
- How do different current durations affect action potentials?
- How does axon diameter affect action potentials? What about myelination?
Keep in mind that the plots are generated using a model of a spiking neuron (called a leaky integrate and fire model), therefore the action potentials will be oversimplified and may look quite different to how they look when recorded from a neuron!