Muscular System Flashcards

Muscular System

Muscle Actions

• Muscles perform several key actions:

  • Produce body heat.

  • Contract to enable movements.

  • Constrict organs and blood vessels.

Muscle Structure

• Skeletal muscles can be broken down into the following components:

  • Sarcomeres: These are the functional units of skeletal muscle. Their shortening leads to muscle contraction.

  • Actin: A component of the sarcomere, known as the thin filament. Myosin attaches to actin during muscle contraction.

    • Actin is anchored to the Z-Line in a sarcomere.

  • Myosin: Another part of the sarcomere, referred to as the thick filament. Myosin has a structure resembling a golf club head and attaches to actin during muscle contraction. The entire length of the thick filaments in one sarcomere is called the A-Band.

  • Tropomyosin: This protein covers the attachment sites on actin where myosin would attach during contraction. Calcium ions facilitate the removal of tropomyosin from actin, allowing myosin to attach and initiate muscle contraction.

Muscle Contraction

• Muscle Contractions are initiated by action potentials sent from the brain.

• Action potentials conclude at the neuromuscular junction, releasing acetylcholine (aCh) into the synapse.

• aCh binds to receptors on the muscle fiber, which allows sodium ions to enter the muscle fiber.

• In turn, the sodium ions interact with the sarcoplasmic reticulum which causes the release of calcium ions.

• Calcium ions enter the sarcomeres (the working unit of muscles).

• Sarcomeres contain thick filaments (myosin) and thin filaments (actin).

• In a relaxed state, myosin and actin do not interact due to tropomyosin blocking the myosin attachment sites on the actin.

• For muscle contraction to occur:

  • Calcium ions bind to tropomyosin, which uncovers the attachment sites on actin for myosin.

  • Myosin binds to actin, pulling the Z-lines closer, thus shortening the sarcomere.

  • The shortening of all sarcomeres in a muscle fiber results in muscle contraction.

Sarcomere Diagram

• Diagram depicting a relaxed muscle and contracted muscle with:

  • Thin (actin) filaments

  • Thick (myosin) filaments

  • Myosin head attaching to actin

  • Working stroke where the myosin head pivots and bends, pulling the thin filament toward the midline of the sarcomere.

  • ATP attaching to the myosin head, causing it to detach from the actin filament; this cycle then repeats.

  • In death, with no ATP production, the cycle stops (rigor mortis).