Since the classical paper of Hodgkin and Huxley (1952) nerve pulses have been explained as voltage pulses generated by the transient opening of ion channel proteins, and the resulting flux of ions across the nerve membrane. Even though this picture is popular and described in numerous textbooks, there exists quite compelling evidence that it cannot be correct. Several authors have found reversible temperature changes and reversible heat release during the action potential of both myelinated and non-myelinated nerves. This finding indicates that the underlying basis of nerve pulse transmission must be reversible physics while the Hodgkin-Huxley model is exclusively based on irreversible phenomena. Further, various changes in mechanical properties and changes in membrane state have been observed. We introduce here into the thermodynamics of nerves and biological membranes. We show that the physiological conditions imply the possibility of localized density pulse propagation along the nerve membrane that is in agreement with the thermodynamics findings in nerves.