Evidence for phase transition in nerve fibers, cells and synapses

By examining rapid changes in the volume and temperature during excitation of a large number of excitable cells and tissues, we have shown that the excitation process is invariably accompanied by swelling and heat production in the superficial protoplasmic layer. By comparing the behavior of a model system (synthetic anionic gels containing both Ca- and Na- ions) with that of nerve fibers under comparable environmental conditions, we have demonstrated that the onset of an action potential is a reflection of a discontinuous volume transition in the superficial layer of nerve cells and fibers. Evidence for the existence of a first- order phase transition (involving volume and temperature changes) in nerve cells, fibers and synapses is presented.