Question

fill in the blank question smooth muscle fibers contain protein molecules called scattered throughout the sarcoplasm that help the thin filaments produce a shortening of the cell.

Explanation:

Smooth muscle fibers have myosin and actin proteins in their sarcoplasm which are involved in muscle - cell shortening. Myosin is a motor protein and actin is a thin - filament protein.

Answer:

myosin, actin