Solitary electromechanical pulses in lobster neurons

- First AFM recordings of thickness changes in single axons during the action potential of lobster nerves are given.
- The possibility of nerve pulse penetration during collision in the same axon is demonstrated.
- The importance of these _ndings in respect to the validity of the Hodgkin-Huxley model and the soliton theory for nerve pulse propagation is discussed.
- We propose the application of thermodynamic arguments for the interpreta-tion of the nervous impulse.

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, there 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 Å in the giant axons of the lobster. We show that the nerve thickness changes in phase with voltage changes. 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.