Which one of the following statements about cardiac muscle is FALSE?
A. Cardiac muscle is composed of individual cells with no striations.
B. Cardiac muscle cells can spontaneously and automatically generate action potentials.
C. Cardiac muscle does not fatigue easily.
D. Cardiac muscle requires a constant supply of oxygen and has limited anaerobic capacity.
E. Cardiac muscle cells transmit an action potential from cell to cell via the intercalated disks
The correct answer and explanation is:
The correct answer is A. Cardiac muscle is composed of individual cells with no striations.
Cardiac muscle is actually striated, meaning it has alternating light and dark bands visible under a microscope, similar to skeletal muscle. This striation is due to the organized arrangement of actin and myosin filaments into sarcomeres, the basic units of muscle contraction.
Explanation:
- Option A: This statement is false because cardiac muscle is striated. The striations are a result of the regular arrangement of contractile proteins (actin and myosin), which are organized into sarcomeres within cardiac muscle fibers, just like in skeletal muscle.
- Option B: Cardiac muscle cells can indeed spontaneously generate action potentials. This ability is due to specialized cells in the heart, particularly in the sinoatrial (SA) node, that have pacemaker activity. These cells initiate electrical impulses automatically, allowing the heart to beat rhythmically without external nervous input.
- Option C: Cardiac muscle does not fatigue easily. Unlike skeletal muscle, which can tire after prolonged use, cardiac muscle is designed for continuous, rhythmic contraction over a lifetime. This is supported by its high mitochondrial density, which allows for efficient ATP production and prevents fatigue.
- Option D: Cardiac muscle requires a constant supply of oxygen and has limited anaerobic capacity. This is because the heart’s high demand for ATP for continuous contraction makes it dependent on aerobic metabolism. When oxygen supply is insufficient (such as during a heart attack), the heart muscle may not function properly.
- Option E: Cardiac muscle cells transmit action potentials from cell to cell via the intercalated disks. These specialized structures allow for the rapid transmission of electrical signals between cardiac cells, ensuring that the heart muscle contracts as a coordinated unit.
In summary, the main false statement is that cardiac muscle lacks striations. In fact, it shares this characteristic with skeletal muscle.