Muscle structures exhibit striations because of the presence of sarcomere structures. A sarcomere is one of the basic components of striated muscle groups, though they do not occur in smooth muscle groups.
Cardiac and skeletal musculature both exhibit striation in their natural formations. Both muscle structures incorporate sarcomeres as their basic unit. Their striations take different forms but are recognizably similar due to this commonality of component parts.
Sarcomeres are long proteins with a fibrous nature. They interact by sliding past one another in alternating patterns when muscles contract or expand in the natural motions of the body. The proteins are responsible for the unique nature of muscles and for their resilience to overuse and damage, encouraging fast healing with dense nutrient structures and a tough, springy makeup suited to heavy use as in the case of the ever-moving heart.
Myosin and actin form the two types of filament that compose sarcomeres. Myosin forms thick filaments while actin forms thin ones, both of which are needed to allow for proper muscle function. Together they create the striated appearance that makes these muscle groups so immediately distinctive. The heads of myosin filaments bind with and aid in the absorption of adenosine triphosphate, or ATP, which powers muscles with nutrients.