Muscle Study Notes

Describe the primary functions of muscle

  1. Movement: Facilitates locomotion and movement of body parts.

  2. Blood circulation: Assists in circulation through the contraction of cardiac muscle.

  3. Generation of heat: Muscles generate heat during contraction.

  4. Support: Provides postural support to the body.

  5. Protection: Muscles protect underlying structures.

Explain the visual and functional characteristics of the three categories/types of muscle: Skeletal muscle, Smooth muscle, Cardiac muscle

Skeletal Muscle

  • Characteristics: Striated, tubular, multinucleated fibers.

  • Control: Voluntary; regulated by the central nervous system.

  • Location: Attached to the skeleton via tendons; comprises the bulk of body muscle.

Smooth Muscle

  • Characteristics: Non-striated, spindle-shaped, single nucleated fibers.

  • Control: Involuntary; regulated by the autonomic nervous system.

  • Location: Found in blood vessels, digestive tracts, and other hollow organs.

Cardiac Muscle

  • Characteristics: Striated, branched, single nucleated fibers.

  • Control: Involuntary; found exclusively in the heart.

Explain the arrangement and organization of skeletal muscle, from the muscle fiber level to the muscle attachment level

Connective Tissue Layers & Overall Structure

  • Epimysium: Dense, irregular connective tissue surrounding muscles.

  • Perimysium: Connective tissue surrounding fascicles of muscle fibers.

  • Endomysium: Thin connective tissue surrounding individual muscle fibers.

  • Fascicle: A bundle of muscle fibers.

  • Muscle fiber: The individual muscle cell.

  • Blood vessels: Supply oxygen and nutrients to muscle fibers.

Skeletal Muscle Organization

  • Muscle Contraction: Defined as tightening, shortening, or lengthening of muscles.

  • Muscle Relaxation: A passive process defined as returning to the resting state.

Muscle Attachment

  • Origin: More proximal attachment of a muscle.

  • Insertion: More distal attachment of a muscle.

  • Example: The triceps brachii muscle's common insertion and three heads.

Describe the detailed events of muscle contraction

Muscle Fiber Organization and Arrangement

  • Contractile Proteins: Muscle cells are specialized for contraction.

  • Sarcomere: The smallest contractile unit of muscle, made up of myofibrils and organized into thick and thin filaments.

  • Filament Composition:

    • Thick filament: Primarily myosin.

    • Thin filament: Primarily actin.

Muscle Proteins

  • Composition in Muscle:

    • Water: \sim75\%

    • Protein: \sim18\%

    • Fat: \sim3\%

    • Other: Minerals and carbohydrates.

  • Myofibrillar Proteins (Three subgroups):

    1. Major contractile proteins: Actin and myosin.

    2. Regulatory proteins: Troponin and tropomyosin.

    3. Cytoskeletal proteins: Titin and nebulin.

Mechanism of Muscle Contraction

  1. Action Potential: Triggered from the CNS to the muscle.

  2. Calcium Release: Calcium is released from the sarcoplasmic reticulum.

  3. Troponin Binding: Calcium binds to troponin causing tropomyosin to move.

  4. Myosin Binding: Myosin heads bind to actin forming cross-bridges.

  5. Power Stroke: Myosin pulls actin, shortening the sarcomere.

ATP and Energy Requirements

  • ATP is crucial for muscle contraction and relaxation.

  • Muscle cramping occurs without ATP.

  • Rigor mortis results after death due to a lack of ATP leading to muscle stiffening.

Understand the metabolic differences between oxidative and glycolytic muscle fiber types

Muscle Fiber Types

  • Classification by Metabolism:

    • Oxidative Fibers: Better for endurance due to lipid use.

    • Glycolytic Fibers: Suited for rapid bursts of activity (higher fatigue).

  • Classification by Color:

    • Red/Dark Muscles: Higher myoglobin content; more oxidative.

    • White/Light Muscles: Lower myoglobin; more glycolytic.

  • Classification by Contraction Speed:

    • Type I: Slow, oxidative fibers.

    • Type II: Fast, glycolytic fibers (subtypes include Type IIA, Type IIX, and Type IIB).

Understand key metabolic events that occur during the slaughter of production animals

Conversion of Muscle to Meat

  • Homeostasis Disruption: Slaughter disrupts homeostasis, which affects muscle physiology and biochemistry.

  • Rigor Mortis: Defined as the stiffening of muscles post-mortem due to ATP depletion. Glycolysis post-mortem leads to lactic acid production which decreases pH.