Fig. 3. Mathematical modeling of the mechanics of superficial neuromasts. (A) The cupula of the neuromast is modeled as two beams joined end-to-end. The distal beam (light grey) is rigidly fixed to the proximal beam (dark grey), which is anchored to the body with a pinned joint and torsion spring with a stiffness equal to that of the hair bundles. This cupula is excited by a boundary layer of flow acting over the surface of the body, which is modeled as a flat plate. This model predicts the frequency response (B,C) of the sensitivity of cupular deflections to flow. (B) The amplitude of sensitivity (Eqn 7) was used to find the peak amplitude and cut-off frequency of the frequency response (see Materials and methods for details). (C) The phase of cupular sensitivity is defined with respect to the local flow velocity.