Muscle Tissue Review Flashcards

Connective Tissue Layers

• Epimysium: Most superficial layer.

• Perimysium: Intermediate layer.

• Endomysium: Deepest layer.

Aponeurosis

• Thin, flattened sheet of regular tissue.

Sarcomere Structure (Slide 19)

• Key structures to identify:

  • M line

  • I band

  • A band

  • Z discs

Muscle Filament and Protein Structure

• Thick Filaments

  • Composed of bundles of many myosin protein molecules.

  • Myosin heads point towards the end of the filament.

• Thin Filaments

  • Twisted strands of actin.

  • Contain myosin binding sites where myosin heads attach.

  • Tropomyosin and troponin are present.

• Other Structural Proteins

  • Sarcomere: Myofilaments arranged in repeating units.

  • Connectin: Stabilizes thick filaments and has a spring-like property.

  • Dystrophin: Anchors some myofibrils to the sarcolemma and proteins.

Skeletal Muscle Functions

• Move the body.

• Maintain posture.

• Protect and support.

• Regulate elimination of materials.

• Produce heat.

Cardiac Muscle Cells

• Short, branching fibers with one or two nuclei.

• Striated and contain sarcomeres.

• Contain many mitochondria.

• Intercalated discs join ends of neighboring fibers.

• Contractions started by heart's autoarrhythmic pacemaker cells.

• Heart rate and contraction force influenced by the autonomic nervous system.

• Contain thick and thin filaments.

Slow Twitch Muscle Fibers (Slow Oxidative Fibers)

• Also known as Type I fibers.

• Contractions are slower and less powerful.

• High endurance due to ATP supply aerobically.

• About half the diameter of other fibers.

• Red in color due to myoglobin.

• Contain a lot of mitochondria.

Muscle Contractions and Motor Units

• Isometric Contraction

  • Increase in tension with an insufficient ability to overcome resistance.

  • Muscle length stays the same.

  • Example: Holding a weight without moving the arm.

• Motor Unit

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

  • Axons of motor neurons from the spinal cord innervate numerous muscle fibers.

  • The number of fibers a neuron innervates varies.

  • Small motor units: Less than five muscle fibers; allow for precise control of force output.

  • Large motor units: Thousands of muscle fibers; allow for production of a large amount of force but not precise control.

  • Fibers in motor units are dispersed throughout the muscle.

• Concentric Contraction

  • Muscle shortens as it contracts.

  • Example: Bicep brachii during elbow flexion when lifting a load.

Force Overcoming Load

• Isometric Contraction: Force is created, but it's not enough to overcome the load.

  • You are trying to push it, but you can't.

  • To achieve movement, more force must be added to overcome the load (VAR).

• Overcoming load results in concentric contraction.

Sarcoplasm, T Tubules, Troponin, and Myosin

• Sarcoplasm: Contains typical organelles, contractile proteins, and other specializations.

• Transverse Tubules (T Tubules): Contain voltage-sensitive calcium channels.

• Troponin: Regulatory protein that triggers cross-bridge cycling when calcium binds to it.

• Myosin: Protein molecule with heads that point toward the ends of filaments; attach to the binding site of G actin.

Isotonic Contraction

• Muscle tension results in movement; the muscle shortens and lengthens as movement occurs.

• Contraction begins at the point of origin, at the beginning of the muscle.

• During isotonic contraction, the muscle becomes shorter as tension increases, and the load can be moved.

• Eccentric Contraction: Form of isotonic contraction where the muscle maintains tension while becoming longer.

  • During isotonic eccentric contraction, the muscle is allowed to become longer while maintaining tension (not going limp).

Skeletal Muscle Fiber Structure (Slide 11)

• Key structures to identify:

  • Sarcolemma

  • Openings to T tubules

  • Myofibrils

  • Nucleus

  • Sarcoplasmic reticulum

Sarcomere

• Repeating unit of myofilaments.

• Overlapping thin and thick filaments.

• Delineated at both ends by Z discs.

• Z discs: Specialized proteins perpendicular to myofilaments; anchors for thin filaments.

• Position of thin and thick filaments gives rise to alternating I bands and A bands.

• I Bands: Light-appearing regions that contain only thin filaments; bisected by Z discs; get smaller when muscles contract and can disappear with maximal contraction.

• A Bands: Dark-appearing regions that contain thick filaments and overlapping thin filaments; contain the H zone and M line; make up the central region of the sarcomere.

Crossbridge Cycling

• Calcium binds to troponin, triggering crossbridge cycling.

• Troponin and tropomyosin move, exposing actin.

• Crossbridge formation: Myosin head attaches to the exposed binding site on actin.

• Power stroke: Myosin head pulls thin filament toward the center of the sarcomere; ADP and phosphate are released.

  • The Z line moves toward the M line, shortening the sarcomere.

• Release of myosin head: ATP binds to the myosin head, causing it to release from actin.

• Resetting the myosin head: ATP is split into ADP and phosphate by myosin ATPase to re-cock the myosin head.

• This process continues as long as calcium and ATP are present.

Sarcomere Length and Tension

• The length of the sarcomere is about 2 micrometers.

• This length provides the maximum tension.

• If muscle is overly contracted, thick filaments are placed next to the Z line.

• If muscle is overstretched, there is not enough overlap between thick and thin filaments.

• If thick and thin filaments do not overlap, there are few crossbridges formed.

Events of Muscle Contraction

1. Motor neuron releases acetylcholine (ACH).

2. ACH binds to receptors on the sarcolemma, initiating an action potential (AP).

3. AP travels through T tubules, causing calcium release from the