Muscular System Functions & Mechanisms Quiz

Muscular System Functions & Mechanisms

• Movement: Muscles contract to move body parts at joints.
• Posture: Muscles stabilize joints and body segments to maintain posture.
• Joint Stability: Muscles help stabilize joints, preventing unwanted movement.
• Heat Production: Muscle activity generates heat to regulate body temperature.

Muscle Contraction Mechanisms

• Contraction: Muscle fibers shorten in response to nerve signals.
• Elasticity & Extensibility: Muscles can stretch and return to their original shape.

Muscle Connective Tissues

• Epimysium: Outer layer surrounding the entire muscle.
• Perimysium: Connective tissue surrounding fascicles (bundles of muscle fibers).
• Endomysium: Connective tissue surrounding individual muscle fibers (cells).

Sarcomere Structure

• A Band: Contains entire length of the thick myosin filaments.
• I Band: Contains only the thin actin filaments.
• H Zone: Part of the A band with only myosin filaments.
• M Line: Middle of the sarcomere, anchoring myosin filaments.
• Z Disk: Boundary of each sarcomere, anchoring actin filaments.

Muscle Tissue Hierarchy

• Muscle: Surrounded by epimysium.
• Fascicle: Bundle of muscle fibers, surrounded by perimysium.
• Muscle Fiber: Muscle cell, surrounded by endomysium.
• Myofibrils: Within muscle fibers.
• Myofilaments: Actin (thin) and myosin (thick).

Neuromuscular Junction (NMJ)

• Neurotransmitter Release: Acetylcholine (ACh) is released into the synaptic cleft.
• Action Potential Transmission: ACh stimulates an action potential in the muscle fiber, initiating contraction.

Muscle Force Generation

• Muscle Tension: Myosin cross-bridges pulling actin filaments generates tension.
• Stimulus Frequency: Increased stimulus frequency leads to greater force of contraction.

Sliding Filament Theory

• Actin: Thin filament that slides along myosin.
• Myosin: Thick filament with heads forming cross-bridges with actin.
• Troponin/Tropomyosin: Regulatory proteins that control actin binding sites.
• Ca²⁺: Released for contraction; binds to troponin to expose actin binding sites.
• Myosin Cross Bridges: Connect and disconnect with actin in a cycle.
• ATP: Provides energy for detachment and reattachment of myosin heads.
• Sarcoplasmic Reticulum (SR): Stores and releases Ca²⁺.
• Action Potential: Involves depolarization of the muscle fiber.
• Synaptic Vesicles & ACh: ACh from vesicles at the NMJ stimulates contraction.

Types of Muscle Contractions

• Muscle Twitch: A single, brief contraction in response to a single stimulus.
• Wave Summation: Stronger contraction from repeated stimuli before muscle relaxes.
• Tetanus: Sustained contraction from very rapid stimuli.

Muscle Contraction Principles

• All-or-None Principle: Muscle fiber contracts completely or not at all; partial contractions do not occur within a single fiber.

Muscle Energy Sources

• ATP: Primary energy source for muscle contraction.
• Anaerobic Respiration (Glycolysis): Fast but less efficient ATP production without oxygen.
• Lactic Acid: A byproduct of anaerobic respiration causing muscle fatigue.
• Aerobic Respiration: More efficient ATP production using oxygen.

Types of Isometric/Isotonic Contractions

• Isometric: Muscle contracts without changing length (e.g., holding a plank).
• Isotonic: Muscle changes length during contraction (e.g., lifting a weight).

Specific Muscle Actions

• Flexion: Decreases angle between body parts (e.g., bending elbow).
• Extension: Increases angle between body parts (e.g., straightening elbow).
• Adduction: Moves limb toward body midline.
• Abduction: Moves limb away from body midline.
• Rotation: Turns a body part on its axis.
• Pronation: Turns the palm down.
• Supination: Turns the palm up.

Muscle Fatigue

• Causes: ATP depletion, lactic acid buildup, ion imbalances, and other metabolic byproducts.