Skeletal System Lecture Notes

Overview

• Focus on Skeletal Muscle Tissue (Chapter 10)
• Split Chapter 11 into two lectures
• Topics discussed:
  • Properties and functions of muscle tissue
  • Microscopic anatomy
  • Muscle contraction and innervation
  • Types of muscle fibers
  • Disorders and development of muscles

Types of Muscle Tissue

• Skeletal Muscle: Moves bones, voluntary.
• Cardiac Muscle: Found in heart, involuntary.
• Smooth Muscle: Found in walls of hollow organs, involuntary.

Terminology

• Muscle Fiber: Refers to a muscle cell.
• Prefixes:
  • Myo/mis: Muscle
  • Sarco: Flesh
  • Sarcolemma: Plasma membrane of a muscle cell
  • Sarcoplasm: Cytoplasm of a muscle cell

Properties of Muscle Tissue

1. Excitability: Responds to nerve signals.
2. Contractility: Shortening of muscle cells.
3. Extensibility: Capability to be stretched.
4. Elasticity: Ability to recoil after being stretched.

Functions of Muscle Tissue

• Movement: Moves bones, fluids, substances.
• Passageways: Opens/closes body passageways.
• Posture: Maintains posture and stabilizes joints.
• Heat Generation: Critical for thermoregulation.

Anatomy of Skeletal Muscle

Gross Anatomy

• Muscle Arrangement: Fibers -> Fascicles -> Muscles
• Connective Tissue:
  • Epimysium: Surrounds entire muscle.
  • Perimysium: Surrounds each fascicle.
  • Endomysium: Surrounds each muscle fiber.
• Attachments:
  • Tendon: Connective tissue attachment to bone.
  • Direct/Fleshy Attachment: Short connective fibers.

Microscopic Anatomy

• Muscle Fiber: Single muscle cell, multinucleated.
• Myofibrils: Contractile organelles within muscle fibers.
• Sarcomeres: Basic unit of contraction, repeating segments in myofibrils.
  • Myofilaments: Actin (thin) and Myosin (thick) create striations.
  • Z-disc: Boundary of a sarcomere.
  • M-line: Center of a sarcomere.
• Titin: Protein that helps maintain structure and elasticity of muscle.

Sarcoplasmic Reticulum and T-tubules

• Sarcoplasmic Reticulum: Stores calcium ions.
• T-tubules: Transmit electrical impulses for muscle contraction.

Sliding Filament Mechanism

• Contraction Process:
  • Myosin heads pull actin filaments, causing sarcomere to shorten.
  • Requires ATP and calcium.

Nervous System and Muscle Contraction

• Neuromuscular Junction: Where nerve meets muscle fiber.
• Axon Terminal: Releases neurotransmitter (acetylcholine) to stimulate muscle.

Types of Muscle Contractions

1. Concentric Contraction: Muscle shortens.
2. Eccentric Contraction: Muscle lengthens.

Types of Muscle Fibers

1. Slow Oxidative: Use oxygen, slow contraction, fatigue-resistant.
2. Fast Glycolytic: Use glycogen, fast contraction, tire quickly.
3. Fast Oxidative: Use oxygen, fast contraction, intermediate resistance to fatigue.

Muscle Disorders

• Muscular Dystrophy: Genetic disorder causing muscle degeneration.
• Myofascial Pain Syndrome: Pain from tight muscle bands.
• Fibromyalgia: Chronic pain disorder, often affects women.

Muscle Development and Aging

• Myoblasts: Fuse to form multinucleate muscle fibers.
• Satellite Cells: Assist in muscle repair.
• Muscles can start contracting early in development.
• Aging: Increase in connective tissue, decrease in muscle fibers.

Upcoming Topics

• Next lectures will focus on muscles of the body:
  • Head, neck, and torso
  • Upper and lower limbs