Muscles and the Muscular System

Introduction

• Muscles are more than just the visible ones like biceps and triceps.
• Focus on muscle tissue and muscle contraction, specifically actin-myosin cycling.

Types of Muscle Tissue

• Cardiac Muscle Tissue
  • Located in the heart.
  • Branched and striated fibers; each fiber can have one or two nuclei.
  • Intercalated discs help in wave-like contractions.
  • Involuntary control.
• Smooth Muscle Tissue
  • Lacks striations.
  • Spindle-shaped fibers with one nucleus.
  • Found in digestive system, arteries, veins, bladder, and eyes.
  • Involuntary control.
• Skeletal Muscle Tissue
  • Attaches to bone or skin, involved with voluntary control.
  • Striated, long cylindrical fibers, multinucleated.

Characteristics of Muscle Tissue

• Extensibility: Ability to stretch or extend.
• Elasticity: Ability to retract back to original length.
• Excitability: Ability to be stimulated and conduct electrical changes.
• Contractility: Ability to contract.

Skeletal Muscle Focus

• Naming and Arrangement
  • Often named by location or shape.
  • Latin or Greek roots are common, e.g., rectus femoris (thigh) or rectus abdominis (abdomen).
  • Prime movers: Agonist muscles.
  • Antagonists: Facilitate opposite actions.
  • Origin and Insertion: Attachment points on bones.

Muscle Contraction at the Cellular Level

• Muscle fibers contain myofibrils, made of sarcomeres, leading to striated look.
• Sarcomeres
  • Made of actin (thin filaments) and myosin (thick filaments).
  • Sliding-Filament Model: Thin and thick filaments slide past each other without shortening.
  • Z lines and M lines define the sarcomere structure.

Actin-Myosin Interaction

• Myosin heads bind to actin forming a cross-bridge.
• ATP hydrolysis allows myosin heads to bind and perform power strokes.
• New ATP allows myosin heads to detach, preventing rigor mortis.
• Hundreds of actin-myosin interactions occur during muscle contraction.

Regulation of Muscle Contraction

• Tropomyosin and troponin complex regulate myosin binding sites on actin.
• Calcium ions released by neuronal stimulation bind to troponin, causing conformational changes.
• This unblocks the binding sites, allowing contraction.

Conclusion

• Reflect on the complex processes involved in muscle contraction next time you engage in physical activity.