Muscle Tissue part 1

Muscle Tissue Overview

• Muscle tissue is responsible for body movement, organ function, and temperature regulation.
• Three types of muscle tissue: skeletal, cardiac, and smooth.
• Skeletal muscles represent nearly half of the body's mass.
• Muscle cells possess distinctive properties: contractility, excitability, extensibility, and elasticity.

Skeletal Muscle

• Composed of skeletal muscle tissue, connective tissues, blood vessels, and nerves.
• Muscle fibers are multinucleated and elongated, formed by the fusion of embryonic cells.
• Myofibrils, the contractile units of skeletal muscle, are long, cylindrical structures within the cytoplasm.
• Myofibrils are composed of repeating segments called sarcomeres, which are the functional units of muscle contraction.

Sarcomere Structure

• Z disc: Defines the boundaries of each sarcomere.
• Thin (actin) filaments: Extend from the Z disc toward the center of the sarcomere.
• Thick (myosin) filaments: Located in the center of the sarcomere, overlapping the inner ends of the thin filaments.
• A band: Encompasses the full length of the thick filament, including the inner ends of thin filaments.
• H zone: Central region of the A band where no thin filaments are present.
• M line: Located in the center of the H zone, containing tiny rods that hold thick filaments together.
• I band: Region containing only thin filaments, part of two adjacent sarcomeres.

Specialized Structures in Muscle Fibers

• Sarcoplasmic reticulum (SR): Specialized smooth endoplasmic reticulum responsible for calcium storage and release.
• T tubules: Deep invaginations of the sarcolemma (plasma membrane) that extend into the muscle fiber.
• Triad: A T tubule flanked by two terminal cisterns of the SR, crucial for muscle excitation-contraction coupling.

Muscle Contraction

• Contractility: Shortening of muscle cells due to the sliding of thin and thick filaments.
• Concentric contraction: Muscle shortens to do work.
• Eccentric contraction: Muscle generates force as it lengthens, acting as a brake against gravity.
• Sliding filament mechanism: Explains concentric contraction where the myosin heads pull thin filaments towards the center of the sarcomere.
• Calcium ions released from the SR initiate the sliding filament mechanism.
• ATP provides energy for the sliding process.

Muscle Attachment

• Origin: The less movable attachment of a muscle.
• Insertion: The more movable attachment of a muscle.
• Direct attachment: Connective tissue fibers are short and directly attach to the bone.
• Indirect attachment: Connective tissue forms a tendon or aponeurosis, which connects to the bone.

Explore the fascinating world of muscle tissue, including its types, structures, and functions. This quiz covers skeletal muscle composition, the role of myofibrils, and the intricate design of sarcomeres. Test your knowledge on how these components work together to facilitate movement and maintain body functions.