Neuromuscular junctions of the posterior cricoarytenoid muscle in the human adult, human fetus and cat. Histochemical and electron microscopic study.

The motor end plate of the posterior cricoarytenoid muscle (PCA muscle) in the human adult, human fetus and cat was examined by using electron microscopy and histochemical methods. In the present study, we observed the single-type motor end plate and en plaque type neuromuscular junction. At the neuromuscular junction of the fetal PCA muscle, the primary synaptic cleft, the basement membrane and the postsynaptic density could already be observed; however, there was no secondary synaptic cleft. Histochemically, the subneural apparatus was filled with electron-dense products, indicating acetylcholinesterase (AChE) activity. The primary and secondary synaptic clefts in the adult PCA muscle were well developed and intense AChE activity was present. The appearance of the neuromuscular junction and its localization of AChE activity was similar to that in the cat PCA muscle.