Muscle Structure and Function

Introduction to Skeletal Muscle

• Skeletal muscle is a separate organ comprised of numerous cells called muscle fibers.
• Muscle fibers are organized into fascicles.
• Groups of fascicles form the entire muscle.
• Muscles are supported by connective tissue, blood vessels, and nerves.

Muscle Composition

• Myofibrils: Cylindrical organelles within muscle fibers, composed of actin and myosin proteins.
• Muscle fiber (muscle cell): A long, cylindrical, multinucleated cell made up of myofibrils.
• Fascicles: Bundles of muscle fibers.
• Skeletal Muscle: An entire organ composed of multiple fascicles, blood vessels, and nerves.

Connective Tissue Layers

1. Endomysium:
   • Surrounds each muscle fiber.
   • "Endo" means within; "myo" refers to muscle.
2. Perimysium:
   • Surrounds each fascicle.
   • "Peri" means around.
3. Epimysium:
   • Encases the entire muscle.
   • "Epi" means on top.

• These connective tissue layers extend beyond the muscle to form tendons, which attach muscles to bones.
• The tendons connect to the periosteum, the connective tissue surrounding bones.

Nerve and Blood Supply

• Each skeletal muscle is generally supplied by:
  • One nerve
  • One artery
  • One or two veins
• Somatic Motor Neurons:
  • Stimulate skeletal muscle.
  • Each neuron has one long axon extending from the brain stem or spinal cord, branching to different muscle fibers.
• Blood Supply:
  • Arteries run alongside motor neurons, branching into capillaries.
  • Capillaries provide oxygen and nutrients and remove waste and heat from muscle metabolism.
• Waste products and heat exit the muscle through veins.