Arthropod mechanoreceptive hairs: modeling the directionality of the joint.

Stimulus transformation in arthropod mechanoreceptive hairs is dominated by the mechanical properties of both the hair shaft and the hair's articulation. Here a mathematical model of the hair's articulation is developed based on simple relationships relevant for every anisotropic articulation. The mechanical behavior regarding deflection under load of a variety of hairs can be described quantitatively by using only two (in the case of double symmetric characteristics) or four parameters (in the case of only one symmetry): (1) joint stiffness S p in the preferred direction of deflection, (2) joint stiffness St in a plane transversal to the preferred direction, and (3, 4) the values of stiffness S for opposite directions of deflection.