Lecture Notes: Skeletal Muscle Innervation

Introduction

• Speaker: Andre
• Topic: Skeletal system focusing on muscle innervation

Skeletal Muscle Anatomy

• Striated Muscle Structure
  • Thick filaments: primarily myosin
  • Thin filaments: primarily actin
  • Z Line: Connects actin, marks the sarcomere
  • M Line: Middle of myosin connections
  • Sarcomere: Contractile unit, distance between Z lines

Muscle Contraction

• Sliding Filament Model
  • Thin filaments slide over thick filaments
  • Contraction Effects:
    • Z lines move closer
    • M line remains constant
    • A band constant, I band shrinks
    • H band shrinks

Muscle Fiber Structure

• Sarcolemma: Cell surface membrane
• T Tubule: Invagination of sarcolemma
• Sarcoplasmic Reticulum (SR): Mesh surrounding myofibrils
• Myofibril: Composed of sarcomeres

Physiology of Muscle Contraction

• Key Proteins:
  • Actin, Troponin, Tropomyosin
  • Myosin head binds when troponin/tropomyosin shape changes
• ATP Role:
  • ATP hydrolysis releases myosin head
  • ATP used to disconnect, not initiate contraction

Neuromuscular Junction

• Neuron Interaction
  • Neuron binds to sarcolemma
  • Similar to neuron-neuron connections
• Action Potential and Calcium Release
  • Calcium enters neuron, acetylcholine released
  • Acetylcholine binds to motor end plate receptors
  • Action potential propagates, causing Ca2+ release from SR

Calcium Cycle

• Troponin and Tropomyosin Interaction:
  • Calcium binds to troponin, causing tropomyosin shape change
  • Myosin binds to actin, causing contraction
• Refractory Period:
  • Calcium actively transported back to SR
  • Prepares for next contraction

ATP Supply for Contraction

• Sources:
  • Creatine Phosphate: Immediate ATP supply
  • Stored ATP: Used in low amounts
  • Aerobic Respiration: Long-term ATP supply via mitochondria
  • Lactate Fermentation: Additional ATP supply
• Athletic Implications:
  • Short bursts: rely on creatine phosphate
  • Long endurance: rely on aerobic respiration and lactate fermentation

Conclusion

• Next topic: Anatomy and physiology of the eye

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These notes summarize the main points of the lecture on skeletal muscle innervation, anatomy, and physiology, providing a detailed look into muscle contraction mechanisms and ATP utilization.