Schemas depicting motor neuron axons (blue) innervating individual muscle fibers. Note the differences in synaptic distribution between fiber types and animals

a Slow fibers (a single fiber shown in blue) are found directly underneath the skin. Synapses (shown in red) are found at the chevron-shaped body segment boundaries. At the individual fiber level, these synapses are at the distal edges. AChR pentamers found in these synapses do not include the λ or ε subunit, and generate currents with slow decay kinetics. b Fast fibers (a single fiber shown in blue) are located in layers deeper than slow fibers. Synapses (red) can be observed as round spots in each fiber. AChRs contain λ or ε subunit (yellow) and generate fast synaptic current kinetics