Structure des Muscles

Muscle Structure

• Muscles are composed of specialized cells called muscle fibers.
• Muscle fibers are long and cylindrical, containing numerous myofibrils.
• Myofibrils are composed of repeating units called sarcomeres, the fundamental contractile units of muscle.
• Sarcomeres contain overlapping thick (myosin) and thin (actin) filaments.
• The interaction between these filaments is responsible for muscle contraction.
• Muscle tissue is classified into three types: skeletal, smooth, and cardiac.

Skeletal Muscle

• Skeletal muscles are responsible for voluntary movement.
• They are attached to bones by tendons.
• Skeletal muscle fibers are multinucleated, striated, and cylindrical.
• Skeletal muscles are characterized by repeating sarcomeres and a striated appearance under a microscope.
• Skeletal muscle contraction is initiated by nerve impulses that cause the release of acetylcholine.

Smooth Muscle

• Smooth muscle is responsible for involuntary movements.
• It lines the walls of internal organs (stomach, intestines, blood vessels).
• Smooth muscle fibers are non-striated and spindle-shaped.
• Smooth muscle contraction is controlled by the autonomic nervous system and hormones.
• Smooth muscle contractions are slow and sustained compared to skeletal muscle.

Cardiac Muscle

• Cardiac muscle is found only in the heart.
• Cardiac muscle fibers are striated, branched, and interconnected.
• Intercalated discs connect cardiac muscle fibers, facilitating rapid communication between cells.
• Cardiac muscle contraction is involuntary and rhythmic, pumping blood throughout the body.

Muscle Actions

• Muscles produce actions like flexion, extension, abduction, adduction, rotation, and circumduction.
• Different muscle arrangements (parallel, fusiform, pennate, circular) affect force production.
• Muscle strength and range of motion depend on anatomical position.

Muscle Fiber Types

• Muscle fibers are classified by metabolic properties and contractile speed.
• Different fiber types (slow-twitch, fast-twitch) influence function and performance.
• Fast-twitch fibers contract rapidly but fatigue quickly; slow-twitch fibers are less powerful but resistant to fatigue.

Muscle Innervation

• Motor neurons innervate skeletal muscle fibers.
• The neuromuscular junction is the synapse between a motor neuron and a muscle fiber.
• Neurotransmitters (e.g., acetylcholine) are released at the neuromuscular junction to initiate muscle contraction.

Muscle Injuries and Disorders

• Muscle strains, tears, and cramps are common muscle injuries.
• Disorders like muscular dystrophy cause progressive muscle weakness and degeneration.
• Age, lifestyle, and several health conditions affect muscle function.