  A new model is proposed to explain coiling of myelins composed of fluid
bilayers. This model allows the constituent bilayer cylinders of a myelin to be
non-coaxial and the bilayer lateral tension to vary from bilayer to bilayer.
The calculations show that a myelin would bend or coil to lower its free energy
when the bilayer lateral tension is sufficiently large. From a mechanical point
of view, the proposed coiling mechanism is analogous to the classical Euler
buckling of a thin elastic rod under axial compression. The analysis of a
simple two-bilayer case suggests that a bilayer lateral tension of about 1
dyne/cm can easily induce coiling of myelins of typical lipid bilayers. This
model signifies the importance of bilayer lateral tension in determining the
morphology of myelinic structures.
