Notes

What is a Neuronal Spike? By now most readers should be aware of how an action potential is generated and propagates through a neuron, but here is a short recap.

• Neuron is at resting potential (-70 mV) which is determined by the balance between extracellular and intracellular K+, Na+ and CL- concentrations.
• Neuron receives inputs at its dendrites which raises the membrane potential. If the membrane potential is below the threshold potential (-55 mV), no AP is generated. If the resulting membrane potential is above the threshold, cell depolarization occurs.
• Voltage gated Na+ channels open causing Na+ influx into the cell which raises the membrane voltage which forces neighboring Na+ channels to also open. This continues up until a peak membrane of 40/50 mV.
• The Na+ channels begin to deactivate and voltage gated K+ channels begin to open causing K+ ion efflux. This rapidly lowers the membrane potential to below the baseline/resting potential levels (-80/-90 mV) which is called hyperpolarization. During this stage, the refractory period, the neuron is unable to fire again while the original ion balance/concentration is reestablished via Na+/K+ ATPases.