Scanning electron microscope studies on the Schwann cells in rat motor endplates with special reference to their finger-like projections.

Three-dimensional structures of the Schwann cell in the rat motor endplate were observed by scanning and transmission electron microscopy. A few Schwann cells lodged over the surface of the motor endplates and their nuclear portion swelled roundly. From the Schwann cell body, a few processes extended downwards, divided several times and covered only the upper orifice of the synaptic groove; they did not cover the surface of the protuberances or the ridges of the sarcolemma which separated the synaptic grooves. The lateral sides and ends of the Schwann cell processes were frilled with finger-like projections. They fixed on the surface of the basal lamina of the sarcolemma and sealed the nerve terminals in the synaptic grooves.