What is the principal involuntary-muscle tissue of the vertebrate heart made up of striated fibers joined at usually branched ends and functioning in synchronized rhythmic contraction?

• A. Heart Muscle
• B. Cardiac Tissue
• C. Nerve Tissue
• D. Smooth Muscle

Answer: (A)

The tissue in question is cardiac muscle—the heart muscle. It’s an involuntary, striated muscle made of fibers that commonly branch and connect at ends. Those connections form intercalated discs, which include gap junctions that let electrical impulses pass quickly from cell to cell. This setup lets the heart muscle contract in a coordinated, rhythmic way so the heart beats as a single functional unit to pump blood.

That’s different from smooth muscle, which is non-striated and found in hollow organs; and from nerve tissue, which transmits signals rather than contracting. While some texts call it cardiac tissue, the term that best captures the muscular nature of the tissue responsible for heart contractions is heart muscle.