CH. 10

Properties of Muscle Tissue

  • Types of Muscle Tissue:

    • Skeletal

    • Cardiac

    • Smooth

  • Unique Characteristics of Muscle Tissue:

    • Excitability: Responsive to stimuli.

    • Contractility: Ability to contract and shorten when stimulated.

    • Elasticity: Can return to resting length after contraction.

    • Extensibility: Can be stretched beyond resting length.

Characteristics of Skeletal Muscle Tissue

  • Each skeletal muscle is an organ containing:

    • Striated muscle fibers attached to bones.

    • Voluntary control.

Functions of Skeletal Muscle Tissue

  • Body Movement

  • Posture Maintenance

  • Temperature Regulation

  • Storage and Movement of Materials

  • Support

Anatomy of Skeletal Muscle

  • Comprised of bundles of muscle fibers called fascicles.

  • Each muscle fiber contains long myofibrils, which consist of myofilaments.

Connective Tissue Components

  • 3 layers of connective tissue, collectively called mysium:

    • Endomysium: Surrounds each muscle fiber.

    • Perimysium: Encases fascicles.

    • Epimysium: Covers entire muscle.

Connective Tissue Functions

  • Provides protection, blood vessel distribution, and muscle attachment to skeleton.

  • Tendons: Connect muscle to bone; can be cordlike or in sheet form (aponeurosis).

Muscle Attachments and Action Points

  • Each muscle has two attachment points: origin (less movable) and insertion (more movable).

Microscopic Anatomy of Skeletal Muscle

  • Sarcolemma: Plasma membrane of muscle fiber.

  • Sarcoplasm: Cytoplasm of muscle fiber.

  • Sarcoplasmic Reticulum (SR): Smooth ER for calcium storage.

  • Transverse Tubules (T-tubules): Invaginations of the sarcolemma facilitating impulse transmission.

  • Triad: Consists of T-tubule and two adjacent terminal cisternae.

Myofibrils and Myofilaments

  • Myofibrils: Long cylindrical structures enabling muscle contraction.

  • Myofilaments:

    • Thick Filaments: Composed of myosin (cross-bridges with actin).

    • Thin Filaments: Composed of actin, tropomyosin, and troponin.

Molecular Structure of Filaments

  • Thick Filaments: 11 nm in diameter, composed of myosin.

  • Thin Filaments: 5-6 nm in diameter, composed of F-actin (twisted G-actin) along with regulatory proteins.

Organization of Sarcomere

  • Sarcomere: Functional contractile unit between two Z discs.

  • I bands: Lighter bands containing thin filaments.

  • A bands: Dark bands with thick filaments and overlapping thin filaments.

  • Z discs: Attachment site for thin filaments.

Contraction of Skeletal Muscle Fibers

  • Mechanism of contraction explained by Sliding Filament Theory:

    • Thick and thin filaments slide over one another during contraction.

    • Changes during contraction:

    • A band width remains constant.

    • H zone disappears.

    • Z discs move closer together.

    • I bands narrow.

Neuromuscular Junction

  • Region where motor neuron stimulates muscle fiber.

  • Components include:

    • Synaptic Knob: Tip of the axon with vesicles containing acetylcholine (ACh).

    • Motor End Plate: Area of sarcolemma with ACh receptors.

    • Synaptic Cleft: Space between synaptic knob and motor end plate.

    • AChE: Enzyme breaking down ACh in the cleft.

Events in Muscle Contraction

  • Nerve impulse triggers ACh release.

  • ACh binds to receptors, initiating a muscle impulse.

  • Calcium ions released from SR.

  • Calcium binds to troponin, exposing active sites on actin for myosin to bind.

  • Myosin heads cycle through attachment, pivoting, detaching, and returning, facilitating contractions.

Motor Units

  • A single motor neuron and the muscle fibers it controls.

  • Each motor unit contracts as a whole (all-or-none principle).

Muscle Tone and Contraction Types

  • Muscle Tone: Constant tension in a resting muscle due to random motor unit stimulation.

  • Types of Contractions:

    • Isometric: Muscle length remains constant, tension changes.

    • Isotonic: Muscle tension remains constant, length changes (concentric and eccentric contraction).

Types of Skeletal Muscle Fibers

  • Three types of muscle fibers:

    • Slow Oxidative (SO): Endurance.

    • Fast Oxidative (FO): Moderate movement.

    • Fast Glycolytic (FG): Short, intense movement.

Muscle Fiber Organizations

  • Arranged in fascicles with patterns:

    • Circular, Parallel, Convergent, Pennate (uni-, bi-, multi-).

Muscle and Exercise

  • Muscle Hypertrophy: Increase in muscle fiber size with repetitive stimulation.

  • Muscle Atrophy: Reduction in muscle size due to lack of stimulation.

Levers and Joint Biomechanics

  • Levers in the body rotate around a fulcrum.

  • Types of levers: first-class, second-class, and third-class.

Muscle Actions

  • Agonist: Prime mover, e.g., triceps brachii (extension).

  • Antagonist: Opposes agonist action, e.g., biceps brachii (flexion).

  • Synergist: Assists agonist in action.

Naming of Skeletal Muscles

  • Names based on:

    • Action, region, attachments, fiber orientation, shape/size, or number of origins.

Types of Muscle Tissue Comparison

  • Skeletal Muscle: Voluntary control, multi-nucleated, striated, fast contractions.

  • Cardiac Muscle: Involuntary, branched, striated, heart-specific.

  • Smooth Muscle: Involuntary, non-striated, found in internal organs.

Development of Skeletal Muscle

  • Formed from myotomes in the embryo corresponding to body regions.

Muscle Tissue Regeneration

  • Limited regeneration capabilities, primarily via satellite cells, especially in skeletal muscle.