The correct option is (c) 2 and 3 only.
Explanation
Cardiac muscles are a specialized type of striated muscle tissue found exclusively in the heart. They are structurally and functionally distinct from skeletal and smooth muscles, designed to pump blood continuously throughout an organism's life.
Statement-wise Analysis
- Statement 1 is Incorrect. Cardiac muscles are immune to fatigue under normal physiological conditions. They contain numerous mitochondria and have a rich blood supply, allowing for continuous aerobic respiration. Unlike skeletal muscles, they do not require rest periods and function rhythmically without stopping.
- Statement 2 is Correct. Cardiac muscles are involuntary in nature. Their activity is controlled by the autonomic nervous system and the heart's internal pacemaker (Sinoatrial node), meaning they are not under the conscious control of the will.
- Statement 3 is Correct. Structurally, cardiac muscle fibers are cylindrical, branched, and typically uninucleate (having a single central nucleus). The branching pattern creates a network that facilitates the rapid spread of electrical signals. They are connected by specialized junctions called intercalated discs.
Key Takeaway: Cardiac muscles are involuntary, non-fatiguing, and structurally characterized by branching fibers with intercalated discs and a single nucleus.