Figure 1.

(a) The sperm structure consists of a spherical head (red), a curved midpiece (yellow to light blue), and a beating tail (dark blue to light blue). A traveling sinusoidal deformation of the tail generates a forward thrust. The curvature plane of the midpiece is tilted by an angle π/3 with respect to the beating plane. (b) Snapshot of a sperm with preferred curvature c₀^(m)L_m = 1 of the midpiece (MCE model), moving along a helical trajectory. The trajectory is indicated by the small gray spheres. See also Movie S1, which is published as Supporting Material on the Biophysical Journal web site. Visualization using VMD (24).