NURS 212: Week 15 - Musculoskeletal Function: A Review

• Muscle Structure


  • Two muscle types:
  • Smooth
  • Striated includes:
  • Skeletal and cardiac muscle
• Muscle fibers


  • Contain myofibril filaments arranged in sarcomeres
  • Thick filaments: Myosin
  • Thin filaments: Actin, Troponin, Tropomyosin
• Muscle contraction occurs by

  1. Sliding of actin and myosin past one another

  2. Shortening the sarcomere and thus whole muscle

  3. ATP is required for muscle contraction

  4. Muscle contraction at the neuromotor junction

  5. Excitation-Contraction Coupling

  6. Muscle contraction – The Cross-Bridge Cycle
• Excitation-Contraction Coupling


  1. Action potential (AP) in motor neuron converted to an end-plate potential (EPP) in the muscle fiber across the neuromuscular junction

  2. The EPP is converted to an AP that travels into the transverse tubules that are proximal to the lateral sacs of the sarcoplasmic reticulum (SR), causing the SR to release calcium into the cytoplasm

  3. Calcium interacts with troponin to initiate actin and myosin binding

  4. Calcium-ATPase returns calcium to the SR at the end of contraction
• Tension


  Force generated by the muscle on an object
• Load


  Force generated by an object on a muscle
• Tension and load are opposing forces
• Twitch


  Mechanical response of a muscle fiber to a single action potential
• Summation


  Increase in mechanical response of a muscle fiber to successive action potential
• Tetanus


  Maintained contraction in response to repetitive stimulation
• ATP requirements


  • Energize cross bridges
  • Dissociate actin and myosin
  • Remove calcium
• ATP formation


  • Creatine phosphate
  • Glycolysis
  • Oxidative phosphorylation
• Creatine kinase (CK)


  A type of enzyme found within your muscles that aids in the production of phosphocreatine, a molecule utilized by your muscles for energy
• Injury to the membrane surrounding muscle cells allows CK to leak into the bloodstream
• Injuries to the skeletal muscles often trigger high levels of CK-MM (from skeletal muscle)
• Bone Function


  • Support
  • Protection
  • Movement
  • Storage
  • Blood cell formation
• Skeletal tissues (bone, cartilage, tendons and ligaments) are all classified as connective tissue
• Proteoglycans


  A chemical substance composed of protein and a polysaccharide called glycosaminoglycans. A major component of the extracellular matrix.
• Proteoglycans form large complexes, both to other proteoglycans, to hyaluronan and to fibrous matrix proteins (such as collagen)
• Bone Cells


  • Fibroblasts – collagen production
  • Osteoblasts – bone forming cells
  • Osteoclasts - bone resorption
  • Osteocytes – mature bone cells
  • Chondrocytes - cartilage
• Ground substance


  Gelatinous substance composed of extracellular fluid and proteoglycans, chondrotin sulfate and hyaluronic acid to help control deposition of calcium salts
• Minerals


  • Calcium
  • Phosphate
• ANA – antinuclear antibody test often used as one of the tests to help diagnose SLE
• Types of Bone


  • Cortical (compact)
  • Cancellous (spongy, or trabecular)
• Cortical (compact) bone


  • Forms the cortex
  • Designed to tolerate compression and shearing force
• Cancellous (spongy, or trabecular) bone


  • Spongy or lattice-like appearance
  • In the interior of bones
  • Does not tolerate compression stress
  • Provides structural support to cortical bone and increases a bone's potential to withstand stress
• Cortical bone (compact bone)


  • Organized around haversian system
  • Central canal called the haversian canal which is surrounded by concentric layers called lamellae
  • Contain blood vessels and nerve fibers
  • Strong bone
• Spongy bone (cancellous bone, trabecular bone)


  • No haversian system
  • Lamellae are arranged in plates called trabeculae
  • Spaces between plates filled with red bone marrow (contains blood forming tissue)
• Bone Marrow


  • Red marrow is hematopoietically active (formation of blood cells)
  • Yellow marrow is hematopoietically inactive and consists primarily of fat cells
• In fractures yellow marrow may enter blood stream and cause fat emboli
• Bones are composed of combinations of the two types of bones
• Periosteum


  • All bones covered with connective tissue called periosteum
  • Outer layer is tough and fibrous and inner layer contains blood vessels and nerves which penetrate into the inner bone
• Epiphyseal Plate


  • A flat plate of hyaline cartilage in young growing bone
  • It causes lengthwise growth of a long bone
  • It is replaced by bone at end of puberty
  • Adult bone contains epiphyseal line, a remnant of the epiphyseal plate
• Bone Formation and Remodeling


  1. Linear growth occurs at epiphyseal plates of long bones

  2. Hormones influence bone growth

  3. Children may suffer fx at epiphyseal plate and have impaired growth

  4. Bone continues to accumulate mineral deposits and peak bone mass occurs in third decade of life
• In most people linear bone growth is complete by age 18 women and 22 in men
• ANA – antinuclear antibody test often used as one of the tests to help diagnose SLE
• Bone Formation and Remodeling


  • Bone is capable of altering its shape and density in response to mechanical demands
  • Absence of bone stress because of immobility or altered weight bearing leads to demineralization
  • Remodeling continues throughout life
  • Bone is constantly being absorbed and replaced
  • Wolff's law: Bone is laid down where it is needed and resorbed where it is not needed
• Bone Formation, Growth, Remodeling


  1. Process controlled by hormones (growth hormone and sex hormones)

  2. Bone is a dynamic and active tissue

  3. Responds to calcium levels and stress

  4. Low calcium stimulates PTH

  5. PTH stimulates osteoclasts that break down bone to release calcium into the plasma
• Calcium balance


  1. Serum calcium levels are inversely regulated in relation to serum phosphate levels

  2. A drop in serum calcium stimulates parathyroid hormone (PTH) release leading to an increase in calcium resorption from bone

  3. The kidneys activate vitamin D, which aids in absorption of calcium from the intestine

  4. Calcitonin directly suppresses PTH production, therefore, reduced levels of calcitonin results in increased levels of PTH
• Joints


  • Fibrous joints are composed of fibrous tissue (collagen)
  • Cartilaginous joints are composed of cartilage, and bone ends are united by cartilage
  • Synovial joints are more flexible than other joints and are characterized by articulating bones, which are separated by a fluid-containing joint cavity