The features of the extracellular potential from a single neuron during the firing of an action potential (AP) are studied theoretically. The paper shows how the spike amplitude is dependent on the neuron's morphology, the electrical parameters of the neuronal membrane, the frequency spectrum of the AP, and the position of the recording electrode.
The spike amplitude shows a clear dependence on membrane capacitance and intracellular resistivity, but is effectively independent on the membrane resistance. However, the diameters of the soma-connected dendrites are the most important neuronal parameters for deciding the spike amplitude. Since the membrane capacitance and the inner resistance are assumed to be relatively constant in time and across cells, the following rough rule of thumb is proposed: The extracellular spike amplitude is proportional to the sum of the cross-sectional areas of the soma-connected dendrites.