(A) Martinez-Silva et al. recorded directly from motoneurons innervating fast and slow twitch muscles in anesthetized mice. (B) Motoneurons were identified by simultaneously recording the electrical properties inside the cells (purple) and measuring the muscle force (green) in wild type mice (top graphs) and mouse models of ALS (bottom graphs) as the mice approached the age at which ALS symptoms begin (30–60 days after birth). For slow motoneurons the responses of the muscle to a single action potential (first column) or to repeated action potentials (second column) were similar in the wild type mice and the mouse models of ALS. For fast motoneurons the response to a single action potential (third column) was also similar, but fewer of the fast motoneurons in the mouse model of ALS responded to repeated action potentials (fourth column). Data adapted from Martinez-Silva et al., 2018, Figures 1 and 3 (reused under a CC BY 4.0 license).