Immature SCs are highly dynamic, whereas adult SCs are static. (A–F) Confocal time-lapse microscopy of young (A–C) and adult (D–F) SC-GFP terminal SCs in nerve–muscle explants. (A and D) Sequentially bleached young (A) and adult (D) NMJs with pseudocolored terminal and axonal SCs. (B and E) NMJ labeled for axons (thy1-Membow13) and SCs (white). (C and F) Time-lapse recordings over ∼2 h (areas boxed in A and D). Immature terminal SCs were highly dynamic (C; arrowheads), whereas only minor growth or retraction was observed in the adult (F), especially at contact sites with neighboring cells (arrowheads). (G and H) Quantitative analysis of SC dynamism. (G) Example of individual young and adult terminal SC showing mean area covered (cyan) and maximum territory covered (white outline). (H) Quantification of explored territory within 1 h (young: 31.4 ± 2%, n = 24 individual SCs, eight triangularis sterni explants vs. adult: 10.2 ± 1%, n = 14 individual SCs, six triangularis sterni explants; values are normalized to terminal SC size; *, P < 0.001 using a t test; data are represented as the mean of SCs + SEM). (I and J) Territory exploration plotted over a period of 1 h for young (I) and adult (J) terminal SCs (territory difference per 10 min plotted; bars on the right show the mean ± SD; total territories stay stable for 1 h; change −0.45 µm² for young and −0.28 µm² for adult terminal SCs, shown normalized to SC size in the figure). The timers shown represent hours/minutes. Bars, 5 µm.