Neuron Energy Budget: The ATP Cost of a Spike

Firing an action potential is not free: every Na⁺ ion that rushes in and every K⁺ ion that rushes out has to be pumped back across the membrane by the Na⁺/K⁺-ATPase, burning one ATP molecule for every three Na⁺ ions restored. This simulator renders a 3D axon segment carrying a traveling spike, with Na⁺ and K⁺ ion particles flowing across the membrane and ATP sparks marking pump activity, while a simplified version of the classic Attwell & Laughlin energy-budget model computes real ATP-per-spike, ATP-per-second and signaling-power numbers from your chosen firing rate, axon diameter and Na⁺/K⁺ channel overlap. A myelination toggle shows why wrapping an axon in myelin does not just speed up conduction — by shrinking the membrane area that has to be re-polarized down to the nodes of Ranvier, it cuts the metabolic bill per spike dramatically, which is the live comparison in the "energy saved by myelin" readout.