Relationships between the sizes of MNs in the dl-TMN and IRs, resting membrane potentials, or spike thresholds. Aa, Ba, Small (19 × 17 μm) and large (30 × 21 μm) MNs filled with biocytin (Aa and Ba, respectively). The minor and major axes are indicated with open and filled arrowheads, respectively. Ab, Bb, Membrane potential responses to depolarizing current pulses applied to small and large MNs at the resting membrane potential (Ab and Bb, respectively). C, The inverse relationship between the sizes of MNs and IRs (n = 33). D, The inverse relationship between the sizes of MNs and resting membrane potentials (n = 33). E, The positive relationship between the sizes of MNs and spike thresholds (n = 33). F, The inverse relationship between the IRs and spike thresholds (n = 33).