Muscular System Overview

Introduction to Muscles

• Muscles are integral to the muscular system.
• Commonly recognized muscles include biceps and triceps, but muscle tissue is more complex.
• Focus of this lecture: Muscle tissue types and muscle contraction (actin-myosin cycling).

Types of Muscle Tissue

1. Cardiac Muscle Tissue

   • Location: Heart
   • Structure: Branched, striated fibers with one or two nuclei.
   • Features: Intercalated discs help in organized contraction; involuntary control.

2. Smooth Muscle Tissue

   • Structure: Non-striated, spindle-shaped fibers with one nucleus.
   • Location: Found in digestive system, blood vessels, bladder, eyes.
   • Features: Involuntary control.

3. Skeletal Muscle Tissue

   • Structure: Striated, long cylindrical fibers that are multinucleated.
   • Function: Attaches to bones/skin, involved in voluntary control.

Characteristics of Muscle Tissue

• Extensibility: Ability to stretch.
• Elasticity: Ability to return to original length.
• Excitability: Responsiveness to stimulation, can produce action potentials.
• Contractility: Ability to contract.

Naming and Arrangement of Skeletal Muscles

• Muscles named by location and shape (e.g., rectus femoris, rectus abdominis).
• Terms:
  • Insertion: Attachment to the movable bone.
  • Origin: Attachment to the fixed bone.
  • Agonist: Prime mover muscle.
  • Antagonist: Muscle that performs opposite action.

Muscle Contraction Mechanism

Cellular Structure

• Muscle fibers consist of myofibrils and sarcomeres.
• Sarcomere Components:
  • Actin: Thin filaments.
  • Myosin: Thick filaments.

Sliding-Filament Model

• The sarcomere shortens during contraction without the filaments themselves shortening.
• Cross-Bridge Cycle:
  1. Myosin heads bind to ATP and hydrolyze it.
  2. Myosin heads form cross-bridges with actin.
  3. Power stroke occurs as myosin heads pull actin toward the center of the sarcomere.
  4. A new ATP binds to myosin for detachment.
• Rigor Mortis: Lack of ATP prevents myosin from detaching from actin post-mortem.

Regulation of Muscle Contraction

• Tropomyosin: Blocks myosin binding sites on actin.
• Troponin Complex: Regulates tropomyosin position.
• Calcium Ions (Ca2+): Released by neurons to bind troponin, causing conformational change that uncovers binding sites.

Conclusion

• Understanding the complexity of skeletal muscle contraction enhances appreciation for bodily functions.
• Stay curious about biological processes!

Note: Consider reviewing diagrams for visual understanding of muscle structures and contractions.