Action potentials are foundational to the electrical flow of information in the nervous system, and are broken down into discrete steps, which all take place in less time than the blink of an eye:
Resting potential is around -64mv, and is defined by the potential difference between ions on the inside and outside of the membrane. Potassium and sodium are distributed on concentration gradients across the inside and outside of a membrane, with more sodium on the outside, and more potassium on the inside. This equilibrium is maintained via sodium-potassium pumps.
Action potentials are said to be “all or none” because a threshold has to be reached in order to trigger them. What this means practically is that enough voltage-gated sodium channels need to open so that sodium ions can rush into the cell, causing the rising phase, when the membrane depolarizes.
Overshoot occurs when the inside of the neuron is positively charged in relation to the outside, caused by the rush of sodium ions from the rising phase. When measured by an oscilloscope, this is the peak of the action potential waveform.
The falling phase is the part of the waveform in the life of an action potential when the line descends into a negative potential once again. This is caused by potassium leaving the neuron through voltage gated potassium channels, which open after an initial delay.
Voltage-gated potassium channels remain open when there is low sodium permeability, which is responsible for the undershoot, or hyperpolarization phase of an action potential.
Action potentials can be stimulated in a lab setting via sending out an electrical signal via electrode. The higher the frequency, the higher the firing rate of action potentials. When hooking up the resulting waveforms to loudspeakers, actions potentials reportedly sound “like popcorn,” this makes sense from looking at the waveform shape, and knowing how quickly they occur. I wonder what a more elaborate system of neural activity would sound like.