Skeletal muscle is a type of striated muscle tissue responsible for voluntary body movements. It is composed of long, multinucleated cells called muscle fibers.
The structure of skeletal muscle can be understood at various levels:
1. Whole muscle:
A skeletal muscle is an organ composed of muscle tissue, connective tissue, blood vessels, and nerves.
The entire muscle is wrapped in a dense connective tissue called the epimysium.
2. Fascicles:
Within the whole muscle, the muscle fibers are organized into bundles called fascicles.
Each fascicle is surrounded by a layer of connective tissue called the perimysium.
3. Muscle fibers:
Each fascicle contains multiple muscle fibers (muscle cells), which are long, cylindrical, multinucleated cells.
Muscle fibers are surrounded by a layer of connective tissue called the endomysium, which contains capillaries and nerves that supply the muscle fibers.
4. Myofibrils:
Each muscle fiber contains numerous myofibrils, which are rod-like structures that run parallel to the length of the muscle fiber.
Myofibrils are responsible for muscle contraction and are composed of repeating units called sarcomeres.
5. Sarcomeres:
The sarcomere is the functional unit of a myofibril and is defined by the area between two Z-lines.
It contains thick filaments (myosin) and thin filaments (actin, troponin, tropomyosin), giving skeletal muscle its striated appearance.
6. Sarcoplasmic reticulum (SR) and T-tubules:
The sarcoplasmic reticulum (SR) stores and releases calcium ions, which are crucial for muscle contraction.
T-tubules are extensions of the muscle cell membrane (sarcolemma) that facilitate the rapid
Muscle Tissue
Muscles are soft tissues that can contract to produce movement or maintain posture.
There are three main types of muscle tissue:
1. Skeletal Muscle:
Location: Attached to bones by tendons.
Function: Responsible for voluntary movements.
Structure: Long, cylindrical, multinucleated fibers with a striated (banded) appearance.
2. Smooth Muscle:
Location: Found in the walls of internal organs and blood vessels.
Function: Controls involuntary movements, such as the movement of substances through internal passageways.
Structure: Spindle-shaped, single-nucleated fibers without striations.
3. Cardiac Muscle:
Location: Found exclusively in the heart.
Function: Pumps blood throughout the body.
Structure: Branched, cylindrical fibers with one or two centrally located nuclei, striated, and connected by intercalated discs for coordinated contractions.