Figure 1
Developing sternomastoid NMJs at P0, P3, P7, and P16. (a,c,e,g) Montaged 2D electron micrographs spanning the entire NMJs in individual thin sections of mouse sternomastoid muscle fibers at P0, P3, P7, and P16, respectively. The nerve terminals of the NMJs contain synaptic vesicles and come within ~50 nm of the surface of a muscle fiber (M). The endplate on the muscle fiber is occupied by tSCs (green dotted line), vacancies (black dotted line), and axons (dotted line in color different from green and black). Note that the postsynaptic membranes at P0 and P3 are smooth but show multiple indentations called junctional folds (JFs) at P7 and P16. Multiple axons at the NMJs are also associated with tSCs; vacancies are present, some of which extend to the surfaces of the muscle fibers. (b,d,f,h) Segmentation of the muscle fiber surfaces (red), terminals of axons (here in shades of blue), tSCs (green), and vacancies at the same NMJs. Red line represents the muscle fiber surface. Scale bar, 1 µm.
