  Investigations of nerve activity have focused predominantly on electrical
phenomena. Nerves, however, are thermodynamic systems, and changes in
temperature and in the dimensions of the nerve can also be observed during the
action potential. Measurements of heat changes during the action potential
suggest that the nerve pulse shares many characteristics with an adiabatic
pulse. First experiments in the 1980s suggested small changes in nerve
thickness and length during the action potential. Such findings have led to the
suggestion that the action potential may be related to electromechanical
solitons traveling without dissipation. However, they have been no modern
attempts to study mechanical phenomena in nerves. Here, we present
ultrasensitive AFM recordings of mechanical changes on the order of 2 - 12
{\AA} in the giant axons of the lobster. We show that the nerve thickness
changes in phase with voltage change. When stimulated at opposite ends of the
same axon, colliding action potentials pass through one another and do not
annihilate. These observations are consistent with a mechanical interpretation
of the nervous impulse.
