American Society for Clinical Pathology (ASCP) Histotechnologist Practice Test

What type of muscle is characterized as striated but involuntary with centrally located nuclei?

1. Skeletal muscle

2. Cardiac muscle

3. Smooth muscle

4. Transitional muscle

The correct answer is: Cardiac muscle

Cardiac muscle is indeed characterized as striated, which means it has a banded appearance due to the organized arrangement of contractile proteins. This muscle type is unique because, unlike skeletal muscle, which is also striated but under voluntary control, cardiac muscle operates involuntarily. This means it is automatically regulated by the autonomic nervous system and functions without conscious thought. Additionally, cardiac muscle cells, or cardiomyocytes, typically have a single, centrally located nucleus, distinguishing them from the multinucleated fibers of skeletal muscle. The presence of intercalated discs, which are specialized structures at the junctions between cardiac muscle cells, allows for coordinated contractions and efficient pacing of the heart during its rhythmic beating. Understanding these characteristics is crucial for identifying cardiac muscle under a microscope or in histological studies, particularly in differentiating it from other muscle types.