D i.e. Gap junction Cardiac muscle have characteristic intercalated discQ (always at z line) &skeletal muscle have cross striation; and smooth muscles don't have both.Skeletal muscle has dark & light bands and peripherally placed nucleusQ;where as cardiac muscle has intercalated disc & centrally placed nucleusQEach cardiac muscle has a single nucleusQ. Cardiac muscle fiber branch & interdigitateQ. Cardiac muscle function as a synctium because of presence of gap junctionQ.