Distribution of the motor end plate (MEP) regions for the mouse forelimb. (A) Lateral view of the mouse forelimb after an aceytlcholinesterase (AChE) histochemical reaction to reveal the location of the MEPs. In this figure, the MEPs appear as black speckles traversing the brown muscle fibers. From this lateral view, the following muscles can be seen: (1) acromiotrapezius, (2) spinodeltoideus, (3) acromiodeltoideus, (4) triceps brachii, (5) extensor carpi radialis, and (6) extensor carpi ulnari. The insert shows a close up view of the MEPs from a portion of the triceps brachii muscle. (B,C) Composite diagrams representing the location of the MEPs from the lateral (B) and medial (C) view of the forelimb. The color-coded forelimb muscles targeted are: acromiotrapezius (turquoise), acromiodeltoideus (green), spinodeltoideus (dark blue), biceps brachii (orange), triceps brachii (yellow), extensor carpi ulnaris (red), extensor carpi radialis (magenta), flexor carpi ulnaris (light blue), and flexor digitorum profundus (purple). The black dotted lines on each muscle are representative locations of the MEP region.