Fig. 10.

NMJs in frogs and toads. Examples of NMJs with indenting terminals from the skeletal muscle of the frog (a1, a2) and from the smooth muscle of the intestines of the toad, Bufo marinus (b). a1 This is a simple cross section through the very long endplate on a twitch fiber, showing the shallow/moderate indention of the terminal and close enwrapping of the Schwann cell (Birks et al. 1960; Heuser and Reese 1973; Matthews-Bellinger and Salpeter 1978). a2 This is an enlarged portion of a longitudinal section through the endplate (cutaneous pectoris muscle of the frog, Rana pipiens; Matthews- Bellinger and Salpeter 1978). Note how the Schwann fingers (s) define a synaptic unit with an active zone (red arrow) in between; these units run along the length of the endplate. f, Subjunctional folds. b Note how this terminal is entirely below the rim of the indention that also contains a Schwann cell process (s; Rogers and Burnstock 1966). The postsynaptic membrane is lined with flask-like caveolar structures, and the terminal vesicles include a few small clear ones and some larger granular ones (Color figure online)