Muscles and Muscle Systems

Fascicle Arrangement

• Skeletal muscle fibers form fascicles. Muscles are classified by fascicle arrangement:

  • Parallel: Fascicles parallel to the long axis. Tension depends on the number of myofibrils (e.g., biceps brachii).

  • Convergent: Fan-shaped, broad attachment converging to a tendon (e.g., pectoralis).

  • Pennate: Fibers pull at an angle to the tendon; contain more myofibrils, develop more tension, but tendons don't move as far.

  • Unipennate: Fascicles on one side of tendon (e.g., extensor digitorum).

  • Bipennate: Fascicles on both sides of a central tendon (e.g., rectus femoris).

  • Multipennate: Tendon branches within muscle (e.g., deltoid).

  • Circular: Sphincters surrounding body openings (e.g., orbicularis oris).

Levers

• Bones act as levers moving on a fulcrum (joint) when muscles apply force.

• Levers can change force direction, distance, speed, and strength.

• Three classes of levers based on the relative position of applied force, fulcrum, and load:

  • First-class: Fulcrum between applied force and load (e.g., neck extension).

  • Second-class: Load between applied force and fulcrum (e.g., plantar flexion).

  • Third-class: Applied force between load and fulcrum (most common; maximizes speed, e.g., using tongs).

Origins and Insertions

• Origin: Fixed attachment point of muscle to bone.

• Insertion: Movable attachment point.

• Actions: Movements produced by muscle contraction (e.g., adduction, elevation).

• Muscle Interactions:

  • Agonist: Prime mover.

  • Antagonist: Opposes agonist.

  • Synergist: Assists agonist.

  • Fixator: Stabilizes a joint to assist an agonist.

  • Muscles work in pairs (agonists and antagonists).

Naming Muscles

• Location (e.g., abdominus).

• Origin and insertion (e.g., genioglossus).

• Fascicle organization (e.g., rectus, oblique).

• Position (e.g., externus, profundus).

• Structural characteristics (e.g., trapezius, biceps).

• Action (e.g., flexor, extensor).

Effects of Exercise

• Muscular system relies on cardiovascular, respiratory, integumentary, and nervous/endocrine systems.

  • Cardiovascular: Delivers $O<em>2$ and nutrients, removes $CO</em>2$.

  • Respiratory: Responds to $O_2$ demand.

  • Integumentary: Disperses heat.

  • Nervous/Endocrine: Directs system responses.