A singular periodic orbit (black) concatenated by slow and fast segments of the two singular limit systems, the reduced problem (5.11)–(5.12) and the layer problem (5.16)–(5.17), that leads to MMO in (Eqs. 3.1–3.3) for C > 0. Parameter values are gA = 4.0 nS and gK = 4.0 nS. (A) Critical manifold (surface) with fold curves L− and L+ (red) and fold curve projections P(L±) (blue). Also shown is the strong singular canard (green, SC) of the folded node (FN). (B) Projection onto the (e, V)-plane with the singular funnel highlighted in gray. The FN is at (e, V) = (0.02, −15.26) and has eigenvalue ratio of μ ≈ 0.1. There is also a saddle equilibrium S (black diamond) at (e, V) = (1.4 × 10−4, −15.94).