Nerve impulse, also called action potential, has mostly been considered as a
pure electrical phenomenon. However, changes in dimensions, e.g. thickness
and length, and in temperature along with action potentials have been observed,
which indicates that the nerve is a thermodynamic system.
The work presented in this thesis focuses on the study of the following features
of nerve impulses, and interpretations from a thermodynamic view are provided.
(1) Two impulses propagating toward each other are found to penetrate through
each other upon collision. The penetration is found in both bundles of axons
and nerves with ganglia. (2) Attempts have been made to measure the temperature
change associated with an action potential as well as an oscillation reaction
(Briggs-Rauscher reaction) that shares the adiabatic feature. It turns out that
some practical issues need to be solved for the temperature measurement of the
nerve impulses, while the measured temperature change during the oscillation
reaction suggests that there are a reversible adiabatic process and a dissipative
process. (3) Local anesthetic e↵ect on nerves is studied. Local anesthetic lidocaine
causes a significant stimulus threshold shift of the action potential, and a
slight decrease in the conduction velocity. (4) The conduction velocity of nerve
impulses as a function of the diameter of the nerve is investigated with stretched
ventral cords from earthworms. The velocity is found to be constant with a decrease
of the diameter, indicating that the conduction velocity is independent of
the diameter of the nerve. All the above results can be explained by a thermodynamic
theory for nerve impulses, i.e. the Soliton theory, which considers the
nerve impulses as electromechanical solitons traveling without dissipation.
Finally, the magnetic field generated by a nerve impulse is measured with a
sensitive atomic magnetometer developed by our collaborators from the Quantum
Optics (QUANTOP) group in our institute. The magnetometer can be operated
at room or body temperatures, and magnetic field from nerve impulses can be
measured several millimeters away. This provides a promising technique for medical
applications.