Total-calcium fast fibres ($w=u+\gamma v,\dot{w}=\mu -u$)

For $\dot{u}=\mu -u-\gamma f/ϵ$ and $\dot{v}=f/ϵ$, total scaled calcium $w$ changes only on the external-input/extrusion time scale. Fast motion therefore follows lines $u+\gamma v=\mathrm{constant}$. The fast normal eigenvalue on $f=0$ is $f_v-\gamma f_u$, so $f_v<0$ alone does not establish attraction. If $v=V(u)$, the slow equation is $\dot{u}=(\mu -u)/(1+\gamma V^{\prime }(u))$. Folds of this reduced description satisfy $V^{\prime }=-1/\gamma$.