Muscular System Notes

Muscle Tissue Types

  • Three Types of Muscle Tissue:

    • Voluntary/Skeletal Muscle:

    • Characteristics: Striated and under conscious control.

    • Control: Somatic nervous system.

    • Location: Found in muscles that are consciously controlled, e.g., biceps, triceps.

    • Involuntary/Smooth Muscle:

    • Characteristics: Visceral (smooth), non-striated, and under unconscious control.

    • Control: Autonomic nervous system (ANS).

    • Location: Found in structures not consciously controlled, e.g., digestive tract.

    • Cardiac Muscle:

    • Characteristics: Striated, involuntary, and forms the heart muscle.

    • Control: Unconscious, initiated by the sinoatrial node (SA node).

Muscle Structure

  • Basic Components of Muscle:
    • Muscle Fibres → Myofibrils → Myofilaments
  • Composition of Muscle:
    • Water: 70%
    • Protein: 23%
    • Minerals and substrates: 7%
  • Tendons:
    • Formed from muscle fascia; attach muscles to bones.
    • Aponeurosis: Flattened tendons, e.g., abdominal muscles.

Muscle Function

  • Functions of Muscles Include:
    • Movement: Muscles contract to create motion.
    • Heat Generation: E.g. shivering for thermoregulation.
    • Maintain Upright Posture: Resisting gravity's force.
    • Protect Skeletal System: Prevents excessive movement.
    • Joint Stabilization: Collaborates with ligaments.
  • Muscle Properties:
    • Contractility, extensibility, elasticity, excitability.
  • Muscle Roles:
    • Agonists: Prime movers.
    • Antagonists: Opposing muscles that relax.
    • Synergists: Assist the prime mover.
    • Fixators: Stabilize parts of the body during movement.

Types of Muscle Contraction

  • Concentric Contraction:
    • Muscle shortens while developing tension to overcome resistance.
  • Eccentric Contraction:
    • Muscle lengthens while maintaining tension to control movement.
  • Isometric Contraction:
    • Muscle develops tension without changing length (e.g., static hold).
  • Isotonic Contraction:
    • Combination of concentric and eccentric contractions, leading to movement.

Delayed Onset Muscle Soreness (DOMS)

  • Occurs 12–72 hours after exercise; common causes include:
    • Starting a new exercise program.
    • Changing sports activities.
    • Increasing exercise duration/intensity.
    • Eccentric training.

Valsalva Effect

  • During resistance training:
    • Breathing Technique: Exhale during lifting; inhale during lowering.
  • This helps regulate blood pressure and heart rate.
  • Valsalva effect may lead to decrease in blood return to heart, affecting cardiac output.

Muscle Fibre Types

  • Skeletal Muscles Composed of Different Fiber Types Based On:
    • Colour
    • Speed of contraction
  • Slow Twitch Fibres (Type I):
    • Red, oxidative, good blood supply, high mitochondria, fatigue resistant.
    • Function: Endurance activities.
  • Fast Twitch Fibres (Type II):
    • Type IIb: White, glycolytic, low mitochondria, fatigue quickly.
    • Type IIa: Pink, oxidative/glycolytic, assist in endurance and strength tasks.

Sliding Filament Theory

  • Mechanism of muscular contraction:
    • Occurs in the sarcomere, which is the unit of contraction.
    • Requires calcium and ATP.
    • Myosin heads attach to actin, forming cross bridges and pull actin towards the center.

Motor Units and Recruitment

  • Motor Units:
    • Consist of a single motor nerve and all muscle fibres it innervates (all or none principle).
    • More motor units are recruited based on required strength.
  • Factors affecting contraction strength:
    • Frequency of nerve impulses to muscle cell.
    • Number of motor units activated.

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