Biomechanics of stretch-induced beading

To account for the beading of myelinated fibers, and axons of unmyelinated nerve fibers as well of neurites of cultured dorsal root ganglia caused by mild stretching, a model is presented. In this model, membrane tension and hydrostatic pressure are the basic factors responsible for axonal constrict ion, which causes the movement of axonal fluid from the constricted regions into the adjoining axon, there giving rise to the beading expansions. Bead ing ranges from a mild undulation, with the smallest degree of stretch, to more globular expansions and narrow intervening constrictions as stretch is increased: the degree of constriction is physically limited by the compact ion of the cytoskeleton within the axons. The model is a general one, encom passing the possibility that the membrane skeleton, composed mainly of spec trin and actin associated with the inner face of the axolemma, could be inv olved in bringing about the constrictions and beading.