The Muscular System

Muscle Organization and Function

  • Muscle organization influences power, range, and speed of movement.

  • Muscle fibers (cells) are bundled into fascicles.

  • Fascicle arrangement affects muscle function.

Patterns of Fascicle Organization

  • Four types:

    • Parallel (and fusiform)

    • Convergent (triangular)

    • Pennate

    • Circular

Parallel (Fusiform) Muscles

  • Fibers run parallel to muscle's long axis.

  • Most skeletal muscles are parallel.

  • Contract extensively (30% contraction).

Convergent (Triangular) Muscles

  • Broad area converges at attachment site.

  • Fibers can pull in various directions.

Pennate Muscles

  • Angled fibers; types include:

    • Unipennate: fibers on one side of tendon.

    • Bipennate: fibers on both sides of tendon.

    • Multipennate: tendon branches within muscle.

  • Develop more tension than parallel muscles due to increased myofibrils.

Circular Muscles

  • Also called sphincters; circular arrangement of fascicles.

  • Control openings in the body.

Muscle Attachments and Movements

  • Skeletal muscles cause motion through attachments to skeleton.

  • Type of attachment affects muscle performance.

Levers in Muscle Function

  • Bones act as levers; joints as fulcrums.

  • Muscles apply force to overcome resistance.

  • Three lever classes:

    1. First-Class: Fulcrum between effort and resistance.

    2. Second-Class: Resistance between fulcrum and effort.

    3. Third-Class: Effort between fulcrum and resistance, maximizing speed/distance.

Muscle Origins and Insertions

  • Muscles have one fixed (origin) and one movable (insertion) attachment.

  • Origins are typically proximal to insertions.

Muscle Actions

  • Movements include flexion, extension, adduction.

Muscle Terminology

  • Agonist (prime mover): muscle causing movement.

  • Antagonist: opposes agonist.

  • Synergist: assists the agonist.

Muscle Naming Conventions

  • Named based on: location, origin & insertion, fascicle organization, position, characteristics, and action.

  • Examples include:

    • Location: temporalis

    • Origin & Insertion: sternocleidomastoid

    • Size: longus, longissimus, teres