Muscle tissue which is unstriated, composed primarily of smooth muscle fibers surrounded by a reticulum of collagen and elastic fibers. Smooth muscle differs from striated muscle in the much higher actin/myosin ratio, the absence of conspicuous sarcomeres and the ability to contract to a much smaller fraction of its resting length[GO]. Tissue which consists of smooth muscle . Examples: Arrector muscle of hair, Muscularis mucosae.