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Copy of Lab 13 Mini Lesson Learning Guides

Muscle Physiology Mini-Lesson 1

1. Isometric Twitch Contraction in a Skeletal Muscle Fiber

  • Definition: An isometric twitch contraction occurs when a skeletal muscle fiber generates tension without changing its length.

  • Latent Period: This is the brief delay between the stimulus and the start of tension development, during which excitation-contraction coupling occurs.

  • Experiment:

    • A muscle fiber is electrically stimulated while its ends are fixed so it cannot shorten.

    • A force transducer records the tension generated over time.

  • Graph: The graph shows time on the x-axis and tension on the y-axis, with a rapid rise followed by a plateau and then relaxation.

2. Isotonic Twitch Contraction in a Skeletal Muscle Fiber

  • Definition: An isotonic twitch contraction occurs when the muscle changes length while generating tension.

  • Latent Period: Longer than in isometric contractions because the muscle must develop enough tension to overcome the load before shortening occurs.

  • Experiment:

    • A muscle fiber is stimulated while lifting a load, and the distance shortened is measured.

  • Graph: Time on the x-axis, distance shortened on the y-axis, showing a plateau where the muscle contracts and lifts the load.

3. Isotonic Load-Velocity Relation

  • Concept: The velocity of muscle shortening decreases as load increases.

  • Graph: A downward curve with load on the x-axis and velocity on the y-axis, showing that heavier loads result in slower shortening.

4. Effect of Load on Isotonic Twitch Contraction

  • Latent Period: Increases with heavier loads.

  • Shortening Velocity: Decreases with heavier loads.

  • Duration of Contraction: Shorter for heavier loads.

  • Distance Shortened: Decreases as load increases.

  • Graph: Three curves representing light, intermediate, and heavy loads, showing different shortening distances and velocities.

Muscle Physiology Mini-Lesson 2

1. Summation in Isometric Frequency-Tension Relation

  • Definition: When stimuli are delivered in rapid succession, individual twitches sum to produce greater tension.

  • Experiment:

    • Stimuli of increasing frequency are applied to a muscle fiber while measuring tension.

  • Graph: Shows frequency on the x-axis and tension on the y-axis, with unfused tetanus at moderate frequencies and fused tetanus at high frequencies.

2. Isometric Length-Tension Relation

  • Concept: Tension varies with muscle length due to overlap of actin and myosin filaments.

  • Experiment:

    • A muscle is held at different lengths and stimulated while measuring tension.

  • Graph: Shows optimal length (L0) where active tension is maximized.

3. Titin’s Role in Passive Tension

  • Function: Titin is a protein that contributes to passive tension by resisting overstretching in relaxed muscle.

Muscle Physiology Mini-Lesson 3

1. ATP Generation Pathways

  1. Creatine Phosphate: Rapid but short-lived ATP source.

  2. Glycolysis: Moderate ATP production, anaerobic.

  3. Oxidative Phosphorylation: Slow but sustained ATP production using oxygen.

2. Oxidative Phosphorylation vs. Glycolysis

  • Oxygen Requirement: Only oxidative phosphorylation requires oxygen.

  • Location: Glycolysis occurs in the cytoplasm, oxidative phosphorylation in mitochondria.

  • ATP Yield: Oxidative phosphorylation produces more ATP per glucose.

  • Waste Products: Glycolysis produces lactate, while oxidative phosphorylation produces CO₂ and water.

3. ATP Functions in Muscle Contraction

  • Powers cross-bridge cycling

  • Pumps calcium back into the sarcoplasmic reticulum

  • Maintains ion gradients across membranes

4. Types of Skeletal Muscle Fibers

  • Slow-Oxidative (Type I): Endurance activities.

  • Fast-Oxidative-Glycolytic (Type IIa): Intermediate activities.

  • Fast-Glycolytic (Type IIx): Short bursts of power.

5. Muscle Fatigue

  • High-intensity, short-duration: Ion imbalances, lactate accumulation.

  • Low-intensity, long-duration: Depletion of glycogen, central command fatigue.

Muscle Physiology Mini-Lesson 4

1. Factors Affecting Whole-Muscle Tension

  • Number of motor units recruited

  • Size of motor units

  • Frequency of stimulation

  • Length-tension relationship

2. Motor Unit Size and Function

  • Small motor units: Precise movements, slow-oxidative fibers.

  • Large motor units: High force, fast-glycolytic fibers.

3. Motor Unit Recruitment Order

  • Smallest to largest (Henneman’s Size Principle)

4. Muscle Adaptation

  • Disuse/Denervation: Leads to atrophy.

  • Strength Training: Increases fiber size.

  • Endurance Training: Enhances oxidative capacity.

5. Athlete Fiber Type Differences

  • Sprinters have more fast-glycolytic fibers.

  • Endurance athletes have more slow-oxidative fibers.

6. Myostatin Function

  • Regulates muscle growth; mutations lead to excessive muscle growth.

Muscle Physiology Mini-Lesson 5

1. Smooth Muscle Location and Function

  • Found in blood vessels, digestive tract, airways, etc.

  • Regulates involuntary movements like peristalsis.

2. Structural Differences Between Smooth and Skeletal Muscle

  • Smooth muscle: No sarcomeres, uses dense bodies, single nucleus, involuntary.

  • Skeletal muscle: Organized sarcomeres, multinucleated, voluntary.

3. Inputs Controlling Smooth Muscle Contraction

  • Neural (autonomic nerves)

  • Hormonal

  • Paracrine factors

  • Stretch

  • Pacemaker activity

4. Sources of Cytosolic Ca²⁺

  1. Extracellular Ca²⁺ through membrane channels

  2. Release from sarcoplasmic reticulum via second messenger signaling

Muscle Physiology Mini-Lesson 6

1. Ca²⁺-Mediated Tension Development in Smooth Muscle

  • Ca²⁺ activates myosin light-chain kinase (MLCK), which phosphorylates myosin to initiate contraction.

2. Differences Between Smooth and Skeletal Muscle Contraction

  • Smooth Muscle: Uses thick filament regulation (MLCK pathway).

  • Skeletal Muscle: Uses thin filament regulation (troponin-tropomyosin mechanism).

3. Smooth Muscle Contractile Characteristics

  1. Slow contraction speed

  2. Maintains tension for long periods

  3. Energy-efficient

4. Single-Unit vs. Multiunit Smooth Muscle

  • Single-Unit: Cells contract as a unit via gap junctions (e.g., intestines).

  • Multiunit: Each cell is independently innervated (e.g., eye muscles).