  The textbook picture of nerve activity is that of a propagating voltage pulse
driven by electrical currents through ion channel proteins, which are gated by
changes in voltage, temperature, pressure or by drugs. All function is directly
attributed to single molecules. We show that this leaves out many important
thermodynamic couplings between different variables. A more recent alternative
picture for the nerve pulse is of thermodynamic nature. It considers the nerve
pulse as a soliton, i.e., a macroscopic excited region with properties that are
influenced by thermodynamic variables including voltage, temperature, pressure
and chemical potentials of membrane components. All thermodynamic variables are
strictly coupled. We discuss the consequences for medical treatment in a view
where one can compensate a maladjustment of one variable by adjusting another
variable. For instance, one can explain why anesthesia can be counteracted by
hydrostatic pressure and decrease in pH, suggest reasons why lithium over-dose
may lead to tremor, and how tremor is related to alcohol intoxication. Lithium
action as well as the effect of ethanol and the anesthetic ketamine in bipolar
patients may fall in similar thermodynamic patterns. Such couplings remain
obscure in a purely molecular picture. Other fields of application are the
response of nerve activity to muscle stretching and the possibility of neural
stimulation by ultrasound.

Biological Physics