The Basal Lamina of the Neuromuscular Junction

Each muscle fiber in skeletal muscle is ensheathed by a layer of extracellular matrix material, the basal lamina (BL). BL extends between nerve and muscle at the neuromuscular junction and projects into folds that invaginate the postsynaptic membrane (Fig. la). BL thus comprises a large fraction of the synaptic cleft material of the neuromuscular junction, and it presents this material in a form that is highly structured, morphologically identifiable, and susceptible to experimental analysis. In contrast, extracellular material in the clefts of interneuronal synapses has been particularly difficult to study.