Which of the following is unique to cardiac muscle cells?
A.
Only cardiac muscle is capable of autorhythmicity
B.
Only cardiac muscle has gap junctions.
C.
Only cardiac muscle has a high concentration of mitochondria.
D.
Only cardiac muscle contains a sarcoplasmic reticulum.
The Correct Answer and Explanation is :
Correct Answer: A. Only cardiac muscle is capable of autorhythmicity.
Explanation:
Cardiac muscle cells have unique features that distinguish them from skeletal and smooth muscle cells. Among the options provided, autorhythmicity is a property unique to cardiac muscle.
- What is Autorhythmicity?
Autorhythmicity refers to the heart’s ability to generate its own electrical impulses without relying on external stimulation from the nervous system. This property allows the heart to maintain a consistent and rhythmic contraction, which is essential for pumping blood. Specialized cardiac cells, called pacemaker cells (primarily located in the sinoatrial (SA) node), initiate and regulate the heart’s rhythmic contractions. - Why Are Other Options Incorrect?
- B. Only cardiac muscle has gap junctions:
While cardiac muscle cells do have gap junctions, this feature is not unique to them. Gap junctions are also found in smooth muscle cells, where they allow for the coordination of contractions across cells. In cardiac muscle, gap junctions are part of the intercalated discs, which facilitate electrical and mechanical coupling between cells. - C. Only cardiac muscle has a high concentration of mitochondria:
Cardiac muscle cells do have a high mitochondrial density to meet their energy demands, but they are not the only cells with this feature. Skeletal muscle, particularly oxidative (type I) fibers, also contains a high concentration of mitochondria to sustain prolonged activity. - D. Only cardiac muscle contains a sarcoplasmic reticulum:
The sarcoplasmic reticulum, responsible for calcium storage and release during muscle contraction, is present in both skeletal and cardiac muscle cells.
- Significance of Autorhythmicity:
Autorhythmicity ensures that the heart can function independently of conscious control, which is crucial for survival. The nervous system can influence the heart rate, but the heart’s intrinsic ability to beat is unique to its specialized pacemaker and conducting cells.