What are the cells of smooth muscles made up of?

Smooth muscle cells, also known as myocytes, are spindle shaped with a wide center portion and tapering at both ends. 

The cytoplasm of smooth muscle cells contain large amounts of actin and myosin, two contractile proteins that are involved in muscle contraction. Unlike striated muscles, the thin actin filaments and thick myosin filaments in smooth muscles are not arranged into sarcomeres, which explains their homogenous appearance. 

Each smooth muscle cell has a single, centrally-located nucleus and a calcium-containing sarcoplasmic reticulum that plays a critical role in sustaining muscle contraction.