Fig. 4.

Exponentially increasing energy demand for signal propagation in neurons with increasing levels of axonal arborization. A: representative axonal tree (left). Red spots indicate the branch level (1 and 12) point at which the sodium current is plotted (right). B: AP efficiency for 10 continuous paths along a branched axon with a total length of 6.23 cm. C: number of ATP molecules required to restore membrane potential increases exponentially with respect to the length and branch level of the axon both as a result of Ca²⁺ influx (blue) and Na⁺ influx (red). D: number of ATP molecules with respect to the axonal surface area and branch points for different sizes of axonal arborizations follows a power law function. The discontinuity reflects the point where application of synaptic stimulation was required to enhance the signal to successfully invade the distal terminals of the axons with branch level higher than 10. VTA, ventral tegmental area. [Adapted from Pissadaki and Bolam (2013).]