Biology – Control and coordination in mammals | e-Consult

While both skeletal and smooth muscle are characterized by the presence of actin and myosin filaments, their ultra-structural organization differs significantly, reflecting their distinct functional requirements.

Skeletal muscle exhibits a highly organized and ordered ultra-structure. Actin and myosin filaments are arranged in repeating units called sarcomeres, which are clearly visible in electron micrographs. Z-discs are present and play a crucial role in anchoring the thin filaments. The arrangement of filaments within the sarcomere allows for powerful and rapid contractions, essential for voluntary movement. The distinct A-band, I-band, and H-zone are hallmarks of skeletal muscle's striated appearance.

Smooth muscle, in contrast, lacks the organized sarcomeric structure seen in skeletal muscle. Actin and myosin filaments are present, but they are arranged in a less ordered manner, forming dense bodies which are attached to the cell membrane and intermediate filaments. Z-discs are absent. This less ordered arrangement allows for a wider range of contractions, including slow, sustained contractions. Smooth muscle is found in the walls of internal organs such as the digestive tract and blood vessels, where its ability to contract over extended periods is important for functions like peristalsis and vasoconstriction.

Here's a table summarizing the key differences: