Skeletal Muscles Lecture Notes

Introduction

• Focus: Structure of skeletal muscles
• Definition: Muscles attached to bones, voluntary control
• Examples: Biceps, triceps, quadriceps

Types of Muscles

• Skeletal Muscles: Voluntary, attached to bones
• Smooth Muscles: Involuntary, found in intestines, arteries, veins
• Cardiac Muscles: Involuntary, found in the heart

Skeletal Muscle Cells

• Considered as tissues because they're made of cells
• Typical animal cells have:
  • Cell surface membrane
  • Cytoplasm
  • One nucleus
  • Limited length and width (average ~40 micromet)
• Skeletal muscle cells:
  • Can be 2-3 cm long (20,000 to 30,000 micromet)
  • Have multiple nuclei (up to thousands)
  • Referred to as skeletal muscle fibers or syncytium

Structure of Skeletal Muscle Fibers

• Sarcolemma: Cell surface membrane of skeletal muscle
• Sarcoplasm: Cytoplasm of skeletal muscle
• Sarco: Greek for flesh
• Importance of terminology: Know sarcolemma and sarcoplasm for exams

Muscle Attachment

• Tendons: Connect skeletal muscles to bones

Detailed Structure

1. Bundles: Skeletal muscle is made up of bundles visible to the naked eye
2. Muscle Fiber:
   • Technically a cell
   • Contains sarcolemma, sarcoplasm, multiple nuclei, mitochondria (for ATP)
3. Myofibrils:
   • Long, tube-like structures
   • Made of alternating dark and light areas
   • Important for muscle function, discussed in a future video
4. T Tubules (Transverse Tubules):
   • Infoldings of the sarcolemma
   • Connect to the sarcoplasmic reticulum

Sarcoplasmic Reticulum

• Different from endoplasmic reticulum
• Stores calcium ions
• Contains calcium ion channels

Key Points

• Sarcolemma, T Tubules, and Sarcoplasmic Reticulum are interconnected
• Sarcoplasmic Reticulum: Stores calcium ions, has calcium ion channels

Conclusion

• Understanding the structure is crucial for studying muscle contraction
• This forms the basis for further exploration of skeletal muscle function