TOPIC 5

Topic Overview

  • The Muscular System (Chapter 6 Micro)

  • Almost all human activity involves muscle contraction.

  1. Functions: Understand the functions of the muscular system and its homeostatic relationships with other body systems.

    • Muscle types: List and differentiate between the three muscle types (location, structure, organ, function).

  2. Muscle Knowledge: Demonstrate knowledge of specific muscles, their locations, actions, and innervations, relating muscle action to lever systems.

  3. Microscopic Structure: Describe the microscopic structure of skeletal muscle.

  4. Action Potential & Muscle Contraction: Understand action potentials, muscle cell coupling, contraction, and the sliding filament theory.

  5. Graded Potentials: Understand graded potentials.

  6. Muscle Disorders: Describe selected muscle disorders.

  7. EMG Usage: Understand the use of an electromyogram (EMG).

Functions of the Muscular System

  • Movement: Enables locomotion and movement of body parts.

  • Posture Maintenance: Helps maintain body posture.

  • Joint Stabilization: Stabilizes joints.

  • Heat Generation: Produces heat to maintain body temperature.

  • Respiration: Assists in breathing.

  • Communication: Facilitates speech through breath control.

  • Heartbeat Regulation: Controls the heartbeat.

  • Swallowing: Involved in the swallowing of food.

  • Digestive Movement: Pushes food through the digestive tract.

  • Childbirth: Involved in the process of parturition.

Integration with Other Body Systems

  • Integumentary: Skin protects muscles & assists thermoregulation.

  • Skeletal: Muscles move bones.

  • Nervous: Stimulates and regulates muscle activity.

  • Endocrine: Hormones regulate muscle development.

  • Cardiovascular: Supplies oxygen/nutrients and removes waste.

  • Lymphatic: Assists in moving lymph fluid.

  • Respiratory: Delivers oxygen and removes carbon dioxide.

  • Digestive: Provides nutrients.

  • Urinary: Controls micturition.

  • Reproductive: Involves muscles in hormonal responses.

Types of Muscle

  • Skeletal Muscle: Voluntary control; attached to bones.

  • Cardiac Muscle: Involuntary control; makes up the heart wall.

  • Smooth Muscle: Involuntary control; found in the walls of hollow organs like the stomach and bladder.

Muscle Properties

  • Excitability: Muscle cells can respond to stimuli.

  • Contractility: Ability of muscle cells to contract and shorten.

  • Extensibility: The capacity to stretch (limited).

  • Elasticity: Ability to return to original length.

  • Terminology: Prefixes "myo" and "mys" refer to "muscle"; "sarco" refers to "flesh."

    • Sarcolemma: Plasma membrane of muscle.

    • Sarcoplasm: Interior of muscle cells.

Connective Tissue Wrappings of Skeletal Muscle

  • Epimysium: Covers the entire muscle (dense irregular connective tissue).

    • Tendon: Connects muscle to bone (e.g., Achilles tendon).

    • Aponeurosis: Indirect attachment (e.g., interosseous membrane).

  • Perimysium: Surrounds muscle fiber fascicles (fibrous connective tissue).

  • Endomysium: Encloses individual muscle fibers (reticular connective tissue).

Muscle Actions and Innervations

  • Muscle Actions: Inversion, eversion, abduction, adduction, circumduction, pronation, supination, flexion, extension, dorsiflexion, plantar flexion, opposition.

  • Innervation: Knowledge of specific muscle innervations should be referenced from a lab manual.

Lever Systems in Muscle Function

  • Basic Principle: Most skeletal muscles use levers to move.

    • Components: Lever (bone), fulcrum (joint), effort (muscle contraction), load (weight/resistance).

    • Mechanical Advantage: When Effort is further from fulcrum than Load.

    • Mechanical Disadvantage: When Effort is closer to fulcrum than Load.

Types of Levers

  • First-Class Levers: Fulcrum between load and effort (e.g., seesaw).

  • Second-Class Levers: Load between fulcrum and effort (e.g., wheelbarrow).

  • Third-Class Levers: Effort applied between load and fulcrum (e.g., tweezers).

Microscopic Anatomy of Skeletal Muscle

  • Sarcolemma: Specialized plasma membrane.

  • Sarcoplasm: Muscular components within the sarcolemma.

  • Sarcomere: Contractile unit of muscle fibers.

  • Myofibrils: Long organelles giving muscle its striations.

  • Striations: Light (I) bands and dark (A) bands due to myofilament arrangement.

    • A Band: Length of thick filaments (myosin).

    • I Band: Contains only thin filaments (actin).

Mechanism of Muscle Contraction

  • Sliding Filament Theory: Muscle contraction occurs when myosin heads attach to actin filaments, pulling them toward the center of the sarcomere.

  • Energy Source: ATP is required for contraction and relaxation phases.

  • Cross-Bridge Cycling: Myosin heads pivot and pull actin filaments, requiring ATP for re-cocking.

Stimulation and Contraction Characteristics

  • All-or-None Principle: Each muscle fiber contracts completely or not at all.

  • Graded Responses: Vary depending on frequency and number of muscle fibers stimulated.

  • Types of Muscle Contractions:

    • Isotonic: Muscle shortens and movement occurs.

    • Isometric: Muscle tension increases without shortening.

Muscle Energy Supply

  • ATP: Immediate energy source, replenished through various metabolic processes during exercise.

  • Muscle Fatigue: Caused by ion imbalances, oxygen deficit, and ATP depletion.

Muscle Tone and Effects of Exercise

  • Muscle Tone: Maintains muscle health and readiness for action.

  • Exercise Effects: Increases size, strength, and endurance of muscles.

    • Aerobic Exercise: Enhances flexibility and resistance to fatigue.

    • Resistance Exercise: Increases muscle mass and strength.

Muscle Disorders

  • Myopathy: General muscle disorders.

  • Myositis: Muscle inflammation.

  • Fibromyalgia: Widespread muscle pain.

  • Carpal Tunnel Syndrome: Inflammation causing nerve compression.

  • Amyotrophic Lateral Sclerosis (ALS): Progressive motor neuron disease leading to muscle atrophy.

  • Muscle Cramps: Sustained involuntary contractions.

  • Muscular Dystrophy: Genetic disorder causing muscle degeneration.

  • Myasthenia Gravis: Autoimmune disease causing muscle weakness.

  • Multiple Sclerosis: Deterioration of myelin in CNS leading to diverse symptoms.

Electromyography (EMG)

  • Purpose: Records electrical activity of muscles, helpful for diagnosing conditions.

  • Clinical Use: Distinguishes between various muscle and nerve conditions.