The mechanical properties of nerves, the size of the action potential, and consequences for the brain

TL;DR

This paper reviews the mechanical and thermal changes during nerve action potentials, proposing a thermodynamics approach to understand their properties and implications for neural communication and brain function.

Contribution

It introduces the concept of a mechanical nerve pulse and explores its potential role in neural signaling and brain processes, expanding beyond traditional electrical models.

Findings

Nerve membranes thicken and axons contract during action potentials.

The spatial length of the nerve pulse can reach centimeters.

Mechanical nerve pulses may enable fast mechanical synapses.

Abstract

The action potential is widely considered a purely electrical phenomenon. However, one also finds mechanical and thermal changes that can be observed experimentally. In particular, nerve membranes become thicker and axons contract. The spatial length of the action potential can be quite large, ranging from millimeters to many centimeters. This suggests to employ macroscopic thermodynamics methods to understand its properties. The pulse length is several orders of magnitude larger than the synaptic gap, larger than the distance of the nodes of Ranvier, and even larger than the size of many neurons such as pyramidal cells or brain stem motor neurons. Here, we review the mechanical changes in nerves, theoretical possibilities to explain them, and implications of a mechanical nerve pulse for the neuron and for the brain. In particular, the contraction of nerves gives rise to the possibility of fast mechanical synapses.