MUSCULAR SYSTEM NOTES

Why the Muscular System?

• Role of the Muscular System
  • Primary function:
  • Produces movement in the body.
  • Other functions:
  • Constriction of organs and vessels.
  • Cardiac contraction.
  • Respiration.
  • Postural maintenance.
  • Body heat production.

Types of Muscle

• Smooth Muscle:

  • Involuntary control.

• Cardiac Muscle:

  • Involuntary control.

• Skeletal Muscle:

  • Voluntary control.
  • Striated.

• Classification:

  • Skeletal Muscle: Voluntary, Striated.
  • Cardiac Muscle: Involuntary.
  • Smooth Muscle: Involuntary and Unstriated.

Muscle Structure

• Muscle Bundles: Fascicles (singular: fascicle).
• Muscle Fiber (Cell):
  • A single muscle cell.
  • Composed of myofibrils.
  • Myofibrils contain myofilaments.
  • Myofilaments: Thin (actin) and thick (myosin) filaments.

Sarcomere Structure

• Sarcomere: Contractile unit of muscle.
  • Extends from Z-line to Z-line.
  • M-line: Myosin attachment.
  • Titin enables stretch and recoil of muscles.

Muscle Fiber Types

• Types of Muscle Fiber:
  • Slow-Twitch (Postural).
  • Fast-Twitch (Rapid movement).
  • Fast-Twitch (Powerful movements).
  • Determined by muscle function and genetic factors.

Sliding Filament Model/Theory

• Mechanism of Muscle Contraction:
  • Interaction of myofilaments causes contraction.
  • Myofilaments slide past each other, causing muscle shortening.

Myosin and Actin

• Myosin: Thick filaments; each head has binding sites for actin and ATP.
• Actin: Thin filaments with myosin binding sites.

Calcium's Role in Muscle Contraction

• Regulatory Proteins:
  • At rest, binding sites on actin are covered by tropomyosin and troponin.
  • Calcium (Ca2+) allows contraction by displacing tropomyosin.

Energy in Muscle Contraction

• ATP Role:
  • Muscle action requires energy from ATP.
  • Processes involving ATP:
  • Power stroke.
  • Release of myosin from actin.
  • Transport of calcium back to the sarcoplasmic reticulum.

Excitation-Contraction Coupling

• Process:
  1. Excitation of a motor nerve.
  2. Propagation of action potential.
  3. Events at the neuromuscular junction.
  4. Calcium release from the sarcoplasmic reticulum.
  5. Sliding of filaments leading to muscular contraction.

Neuromuscular Junction

• Definition:
  • Point of connection between a motor neuron and muscle fibers.
  • Action potentials cause the release of acetylcholine (ACh), leading to muscle contraction.

Conclusion

• Understanding the muscular system is critical for exercise science and physiology.
• The relationship between neural connections and muscle contraction emphasizes the importance of ATP in muscle function.
• Muscle fiber types and structure play significant roles in movement and strength.