HA21 is not a section but a whole-mount preparation of a small piece of skeletal muscle in which the motor neuron was stained black. The motor axon branches across 3-4 myofibers. In this silver stained preparation, the myelin sheaths stain intensely. Nodes of Ranvier can also be seen. By following the wire-like axons to their terminations on the myofibers, it is possible to see several neuromuscular junctions. The nerve terminal is a complex expansion at the end of the axon, and this fits into a shallow pit in the muscle cell membrane called the primary synaptic cleft (HA22). NMJs will be a topic for discussion in the Excitable Membranes presentations also. This short animation describes the cellular signaling events that occur at the NMJ. http://www.youtube.com/watch?v=ZscXOvDgCmQ .