ANATOMY

Detailed explanation-1: -The major protein components of smooth muscle thin filaments are actin, tropomyosin and caldesmon, present in molar ratios of 28:4:1 respectively. Other smooth muscle proteins which may be associated with the thin filaments in the cell are filamin, vinculin, alpha-actinin, myosin light chain kinase and calmodulin.

Detailed explanation-2: -Most of the cytoplasm consists of myofibrils, which are cylindrical bundles of two types of filaments: thick filaments of myosin (about 15 nm in diameter) and thin filaments of actin (about 7 nm in diameter).

Detailed explanation-3: -Actin filaments (F-actin) are linear polymers of globular actin (G-actin) subunits and occur as microfilaments in the cytoskeleton and as thin filaments, which are part of the contractile apparatus, in muscle and nonmuscle cells (see contractile bundles).

Detailed explanation-4: -An individual sarcomere contains many parallel actin (thin) and myosin (thick) filaments. The interaction of myosin and actin proteins is at the core of our current understanding of sarcomere shortening.