Summary
Neuromuscular junctions in the marine polyclad flatworm, Notoplana acticola were studied with the electron microscope. Synapses were found between nerve endings and specialized extensions of the muscle cells. Characteristically these processes contained clear cytoplasm with a basal mitochondrion and numerous microtubules aligned parallel to the long axis of the extension. Sarcoplasmic diverticuli which contained the nucleus had granular cytoplasm with an assortment of membranes and organelles. We have proposed the term sarconeural junction to describe synapses between long sarcoplasmic extensions and nerve cells in flatworms as well as other animals.
Tight junctions between adjacent contractile portions of muscle cells were common. As groups of cells appeared to be connected by tight junctions or shared common nerve terminals we conjectured that these formed discrete functional motor-units.
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Chien, P., Koopowitz, H. The ultrastructure of neuromuscular systems in Notoplana acticola, a free-living polyclad flatworm. Z.Zellforsch 133, 277–288 (1972). https://doi.org/10.1007/BF00307148
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DOI: https://doi.org/10.1007/BF00307148