What forms the light and dark bands of striated muscle?
The arrangement of the thick myosin filaments across the myofibrils and the cell causes them to refract light and produce a dark band known as the A Band. In between the A bands is a light area where there are no thick myofilaments, only thin actin filaments. These are called the I Bands.
What is the structure of a striated muscle?
Striated muscle tissue is a muscle tissue that features repeating functional units called sarcomeres. The presence of sarcomeres manifests as a series of bands visible along the muscle fibers, which is responsible for the striated appearance observed in microscopic images of this tissue.
What is the structure and function of striated muscle?
Striated muscles are highly organized tissues (Fig. 1) that convert chemical energy to physical work. The primary function of striated muscles is to generate force and contract in order to support respiration, locomotion, and posture (skeletal muscle) and to pump blood throughout the body (cardiac muscle).
What types of muscles are striated or have dark bands?
Skeletal Muscle and Cardiac Muscle are also called ‘striated muscle’, because they have dark and light bands running across the muscle width when they are looked at under the microscope.
How are myofilaments arranged in the myofibrils?
Myofibrils are composed of overlapping thick and thin myofilaments organized into distinct, repeating units called sarcomeres. Z-discs (also called Z-lines; Z in Figures 5.1, 5.2), comprised largely of α-actinin, form the boundaries of sarcomeres and provide an attachment site for thin filaments.
What is the microscopic structure of striated muscle?
A sarcomere is the basic unit of muscle tissue in both cardiac and skeletal muscle. Sarcomeres appear under the microscope as striations, with alternating dark and light bands.
Are myofibrils muscle fibers?
Myofibrils are long filaments that run parallel to each other to form muscle (myo) fibers. The myofibrils, and resulting myofibers, may be several centimeters in length. The muscle fibers are single multinucleated cells that combine to form the muscle. Myofibrils are made up of repeating subunits called sarcomeres.
What is the striation pattern of a myofibril?
Many sarcomeres are present in a myofibril, resulting in the striation pattern characteristic of skeletal muscle. Each I band has a dense line running vertically through the middle called a Z disc or Z line. The Z discs mark the border of units called sarcomeres, which are the functional units of skeletal muscle.
What causes the striated appearance of skeletal muscle?
The striated appearance of skeletal muscle tissue is a result of repeating bands of the proteins actin and myosin that are present along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes the entire cell to appear striated or banded.
What is a muscle fiber composed of?
A muscle fiber is composed of many fibrils, packaged into orderly units. The striated appearance of skeletal muscle tissue is a result of repeating bands of the proteins actin and myosin that are present along the length of myofibrils.
How many Myofibrils are in a muscle fiber?
Within each muscle fiber are myofibrils—long cylindrical structures that lie parallel to the muscle fiber. Myofibrils run the entire length of the muscle fiber, and because they are only approximately 1.2 µm in diameter, hundreds to thousands can be found inside one muscle fiber.