Muscular System and Muscle Contraction

Introduction

• Muscles are not just visible ones like biceps or triceps.
• Focus on muscle tissue and actin-myosin cycling.

Muscle Tissue Types

1. Cardiac Muscle Tissue

• Found in the heart.
• Branched and striated fibers with one nucleus per fiber.
• Intercalated discs help in organizing contractions.
• Involuntary control.

2. Smooth Muscle Tissue

• Non-striated with spindle-shaped fibers.
• Found in the digestive system, arteries, veins, bladder, and eyes.
• Each fiber has one nucleus.
• Involuntary control.

3. Skeletal Muscle Tissue

• Attached to bone or skin and involved in voluntary control.
• Striated, long cylindrical fibers, multinucleated.

Common Characteristics

• Extensibility: Stretch or extend.
• Elasticity: Retract back to starting length.
• Excitability: Ability to be stimulated and send action potentials.
• Contractility: Ability to contract.

Skeletal Muscle Focus

• Named by location or shape, often have Latin or Greek roots.
• Prime mover muscle: agonist.
• Opposite action muscle: antagonist.

Muscle Contraction

Cellular Level Structure: Sarcomere

• Actin: Protein in thin filaments.
• Myosin: Protein in thick filaments.
• Z lines and M lines in sarcomeres.
• Thick and thin filaments do not shorten but slide past each other.

Sliding-Filament Model

• Myosin heads bind to ATP, hydrolyzing it into ADP and phosphate.
• Cross bridge formation between myosin head and actin.
• Power stroke: Thin filament slides toward the sarcomere center.
• New ATP binds to myosin head for detachment.
• Myosin heads act like tiny oars preventing actin from slipping back.
• Regulation involves tropomyosin and troponin complex blocking myosin binding sites.
• Calcium ions trigger binding by moving tropomyosin off binding sites.

Final Thoughts

• Reflect on the complex events in muscle contraction while carrying out simple tasks like picking up a textbook.

Stay curious! - Amoeba Sisters