Neuromuscular junction in smooth muscle:
Branches of autonomous nerve fibres innervate the smooth muscle in a diffuse manner. The junctions are not connected directly with muscle, but they secrete the neurotransmitters at external space of muscle fibre. Secreted neurotransmitters diffuse through the muscular fibre membrane to transmit the signal.

Structure of Cardiac muscle:
Cardiac muscles having many features as like skeletal muscle. Cardiac muscle cells are separated by a dark area which called as intercalated discs (Figure 16.7). They are striated and interconnected. Gap junctions and desmosomes also present in the cardiac muscle. Interconnected cardiac cells called as syncytium. Heart consists of two syncytium, known as atrial syncytium and ventricular syncytium.

 

Figure 16.7:  Structure of cardiac muscle