Figure 3.

Indirect torque-transducer mechanism according to Binhi (2006). (a) Equilibrium deflection ψ(180° − η) of the magnet for a field orientation θ₀ = 180° − η close to the critical orientation θ₀ = 180° (i.e. η is a few degrees). (b) As θ₀ changes from 180° − η to 180°, the magnet suddenly recoils to the +ψ_± orientation. This way, a small change in external field direction can produce a large change in the magnet's deflection, hence a large change in the magnet's strayfield H_s at the site (green patch) where free-radical reactions are assumed to transduce the strayfield into a nerve signal. Thermal fluctuations can drive the magnet from its pre-critical ψ(180° − η) orientation also into the metastable −ψ_± orientation (dotted arrow). If the energy barriers between the +ψ_± and the −ψ_± state are of the order of the thermal energy, the magnet will repeatedly bounce between the +ψ_± and −ψ_± state.