This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
Cardiac muscle is able to function as a syncy-tium because of the structural presence of 
Select and explain. 
A. Branching fibres, B. Intercalated disc, C. Protoplasmic bridges between cells, D. Gap-junctions
D: Gap-junctions
Answer: D: Gap-junctions 
Explanation: 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.