Muscle Tissue

Muscle Tissue

  • Role of Muscles: Provide movement through contraction and relaxation, accounting for 40-50% of adult body weight.

  • Myology: The study of muscle tissue.

Functions of Muscle Contraction

  • Converts chemical energy to mechanical energy to:

    • Generate force

    • Perform work

    • Produce movement

    • Stabilize body position

    • Regulate organ volume/size

    • Generate heat

    • Propel fluids and food through systems

    • Improve circulation in extremities

Types of Muscle Tissue

  1. Skeletal Muscle

    • Attached to bones; striated appearance.

    • Voluntary control (some subconscious control).

    • Examples: Diaphragm, postural muscles.

  2. Cardiac Muscle

    • Found only in the heart; striated and branching.

    • Involuntary control; autorhythmic contractions.

    • Regulated by hormones and neurotransmitters affecting heart rate and contractility.

  3. Smooth Muscle

    • Located in walls of hollow organs (e.g., blood vessels, airways).

    • Non-striated; involuntary control, influenced by hormones.

    • Some have autorhythmic properties (e.g., GI tract).

Properties of Muscle Tissue

  • Electrical Excitability: Responds to stimuli with action potentials.

  • Contractility: Ability to contract when stimulated; generates tension.

  • Extensibility: Ability to stretch without damaging tissue.

Skeletal Muscle Structure

  • Muscle Fibers (Myocytes): Parallel arranged in bundles with connective tissue, blood vessels, and nerves.

Connective Tissue Components

  • Surrounding connective tissues: Subcutaneous tissue (hypodermis), fascia, and three connective tissue layers:

    • Epimysium: Surrounds entire muscle.

    • Perimysium: Surrounds muscle fiber bundles (fascicles).

    • Endomysium: Surrounds individual muscle fibers.

Nervous System Control

  • Skeletal muscles receive abundant nerve supply from somatic motor neurons, allowing for movement control.

Blood Supply

  • Muscles are richly supplied with blood for delivering oxygen and nutrients and removing metabolic waste.

Muscle Fibers (Myocytes)

  • Average length: 10 to 30 cm.

  • Develop from the fusion of myoblasts, containing multiple nuclei.

Muscle Fiber Anatomy

  • Sarcoplasm: Contains glycogen (ATP source) and myoglobin (stores oxygen).

  • Sarcoplasmic Reticulum: Similar to smooth ER; stores calcium ions crucial for contraction.

Contraction Mechanism

  • Sliding Filament Theory: Myosin heads walk along actin filaments, shortening the sarcomere during contraction.

  • Contraction Cycle:

    1. Calcium binds to troponin, exposing myosin-binding sites.

    2. Myosin heads attach and pivot, pulling actin filaments (power stroke).

    3. ATP binds to myosin, causing detachment.

Energy Production in Muscle Fibers

  • ATP Sources:

    • Creatine Phosphate: Quick ATP generation for short bursts of activity.

    • Aerobic Respiration: Slower, efficient ATP production with oxygen.

    • Anaerobic Glycolysis: Rapid ATP production without oxygen, leading to lactic acid accumulation.

Muscle Fatigue and Recovery

  • Fatigue causes include inadequate calcium, depletion of creatine phosphate, and oxygen lack.

  • Efficient recovery through rest and proper nutrition is essential for muscle function.

Types of Muscle Fibers

  • Slow Oxidative Fibers: Dark, fatigue-resistant, suited for endurance.

  • Fast Oxidative-Glycolytic Fibers: Intermediate properties, suited for activities like sprinting.

  • Fast Glycolytic Fibers: White, fast but fatigue quickly, suited for short bursts of activity.

Exercise and Muscle Fibers

  • Muscle fiber composition affects athletic performance. Training can adapt fibers: endurance training shifts FG fibers towards FOG fibers, while strength training increases FG fiber size and strength.