Which of the following describes one difference between skeletal muscles and cardiac muscles?
A.
Skeletal muscles are autorhythmic, whereas cardiac muscles are not.
B.
Cardiac muscles are voluntary, whereas skeletal muscles are involuntary.
C.
Skeletal muscles are found in the viscera, whereas cardiac muscles are found in the cranium.
D.
Cardiac muscles contain intercalated discs, whereas skeletal muscles do not.
The correct answer and Explanation is :
The correct answer is:
D. Cardiac muscles contain intercalated discs, whereas skeletal muscles do not.
Explanation
Skeletal muscles and cardiac muscles are two types of striated muscles, but they differ in several key aspects related to their structure and function.
1. Intercalated Discs in Cardiac Muscle:
Cardiac muscle tissue is found in the heart and is specialized for continuous and rhythmic contractions necessary for pumping blood throughout the body. One of the defining features of cardiac muscle cells is the presence of intercalated discs. These discs are complex structures that contain gap junctions and desmosomes. Gap junctions allow for the rapid spread of electrical impulses between cardiac cells, ensuring that the heart contracts in a coordinated manner. Desmosomes provide mechanical support by anchoring adjacent cells together, which helps to withstand the mechanical stress of continuous heart contractions.
2. Lack of Intercalated Discs in Skeletal Muscle:
In contrast, skeletal muscle tissue is responsible for voluntary movements of the body, such as walking or lifting objects. Skeletal muscle fibers are long, multinucleated cells that do not have intercalated discs. Instead, skeletal muscle fibers are connected by a network of connective tissues and are activated by the nervous system to contract. The absence of intercalated discs in skeletal muscle reflects the different functional requirements between skeletal and cardiac muscles. Skeletal muscle contraction is controlled by the somatic nervous system and does not require the intercellular communication that intercalated discs provide.
3. Autorhythmicity:
Another difference is that cardiac muscles are autorhythmic, meaning they can generate their own rhythmic contractions due to pacemaker cells in the heart. Skeletal muscles, however, require nervous system stimulation to contract.
4. Voluntary vs. Involuntary Control:
Skeletal muscles are under voluntary control, meaning their contractions are consciously controlled. Cardiac muscles are under involuntary control, functioning automatically to regulate heartbeats.
In summary, the presence of intercalated discs in cardiac muscle cells is a distinctive structural feature that differentiates them from skeletal muscle cells, which lack these structures.