Striated muscle tissue is a muscle tissue that features repeating functional units called sarcomeres. Under the microscope, sarcomeres are visible along muscle fibers, giving a striated appearance to the tissue. The two types of striated muscle are skeletal muscle and cardiac muscle.
Structure
Striated muscle tissue contains T-tubules which enables the release of calcium ions from the sarcoplasmic reticulum.
Skeletal muscle
Skeletal muscle includes skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue. Skeletal muscle is wrapped in epimysium, allowing structural integrity of the muscle despite contractions. The perimysium organizes the muscle fibers, which are encased in collagen and endomysium, into fascicles. Each muscle fiber contains sarcolemma, sarcoplasm, and sarcoplasmic reticulum. The functional unit of a muscle fiber is called a sarcomere.
Each muscle cell contains myofibrils composed of actin and myosin myofilaments repeated as a sarcomere. Many nuclei are present in each muscle cell placed at regular intervals beneath the sarcolemma.
Based on their contractile and metabolic phenotypes, skeletal muscle can be classified as slow-oxidative (Type I) or fast-oxidative (Type II). These cells are connected to each other by intercalated disks, which contain gap junctions and desmosomes.
Striated versus smooth muscle
Unlike skeletal and cardiac muscle tissue, smooth muscle tissue is not striated since there are no sarcomeres present. Skeletal muscles are attached to some component of the skeleton, and smooth muscle is found in hollow structures such as the walls of intestines or blood vessels. The fibres of striated muscle have a cylindrical shape with blunt ends, whereas those in smooth muscle are spindle-like with tapered ends. Striated muscle tissue has more mitochondria than smooth muscle. Both smooth muscle cells and cardiac muscle cells have a single nucleus, and skeletal muscle cells have many nuclei.
Function
The main function of striated muscle tissue is to create force and contract. These contractions in cardiac muscle will pump blood throughout the body. In skeletal muscle the contractions enable breathing, movement, and posture maintenance.
Skeletal muscle is able to regenerate far better than cardiac muscle due to satellite cells, which are dormant in all healthy skeletal muscle tissue.
Dysfunctions
Skeletal muscle
- Sarcopenia (loss of skeletal muscle mass associated with aging)
- Polymyositis (chronic inflammation)
- Dermatomyositis (chronic inflammation with skin rash)
- Inclusion body myositis (common age-related inflammatory disease)
Cardiac muscle
- Coronary artery disease (narrowed coronary arteries)
- Arrhythmia (irregular heartbeat)
- Cardiomyopathy (disease of the heart muscle)
See also
- Costamere