BLOCK 3: AHE: MSK DEVELOPMENT
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Questions and Answers

What triggers apoptosis in chondrocytes during endochondral ossification?

  • Formation of the bone collar (correct)
  • Presence of osteoblasts
  • Nutrient supply from blood vessels
  • Increasing size of chondrocytes
  • Where do secondary centers of ossification form?

  • Along the periosteum before birth
  • In the epiphyses after birth (correct)
  • Within the medullary cavity after adulthood
  • In the diaphysis during infancy
  • What remains in the locations of growth after bone development?

  • Bone spicules in the diaphysis
  • Cartilage in the periosteum
  • Medullary cavity with red marrow
  • Growth/epiphyseal plates and articular cartilage (correct)
  • Which cells are responsible for the formation of bone matrix during ossification?

    <p>Osteoblasts</p> Signup and view all the answers

    What characterizes periosteal/appositional growth of bone?

    <p>Growth in bone diameter</p> Signup and view all the answers

    What is the primary origin of muscle fibers?

    <p>Mesodermal cells</p> Signup and view all the answers

    What process begins during Week 5 that is crucial for cartilage formation?

    <p>Chondrogenesis</p> Signup and view all the answers

    Which cells form as a result of muscle fiber differentiation?

    <p>Satellite cells</p> Signup and view all the answers

    How do myotubes form during muscle development?

    <p>By fusing myoblasts</p> Signup and view all the answers

    What do chondroblasts secrete during the process of chondrogenesis?

    <p>Extracellular matrix</p> Signup and view all the answers

    Which connective tissue surrounds muscle fibers?

    <p>Endomysium</p> Signup and view all the answers

    What happens to most muscles by the end of the first year after birth?

    <p>They are mostly formed</p> Signup and view all the answers

    Which zone is NOT typically associated with endochondral bone growth?

    <p>Chondrocyte zone</p> Signup and view all the answers

    What do chondroblasts mature into?

    <p>Chondrocytes</p> Signup and view all the answers

    Which type of bone formation directly develops from mesenchyme?

    <p>Intramembranous bone formation</p> Signup and view all the answers

    What is the initial type of bone created during intramembranous ossification?

    <p>Woven bone</p> Signup and view all the answers

    Which ossification process primarily forms appendicular bones?

    <p>Endochondral ossification</p> Signup and view all the answers

    In which developmental week do mesenchymal cells start forming models of hyaline cartilage?

    <p>Week 5</p> Signup and view all the answers

    What transforms into osteocytes during the ossification process?

    <p>Osteoblasts that become trapped</p> Signup and view all the answers

    Which structure surrounds the diaphysis during endochondral ossification?

    <p>Perichondrium</p> Signup and view all the answers

    How is hydroxyapatite integrated into the bone during ossification?

    <p>It is deposited on the osteoid</p> Signup and view all the answers

    Which type of mesoderm differentiates to form somites?

    <p>Paraxial mesoderm</p> Signup and view all the answers

    What is the primary role of the sclerotome in somite development?

    <p>Maturing into bone and cartilage</p> Signup and view all the answers

    During what week of development does the differentiation of somites begin?

    <p>4th week</p> Signup and view all the answers

    Which component of the somite is responsible for forming the dermatome?

    <p>Dermomyotome</p> Signup and view all the answers

    What structures do the mesodermal cells from the sclerotome condense to form?

    <p>Vertebral body and ribs</p> Signup and view all the answers

    In which direction do somites form during development?

    <p>Cranial to caudal</p> Signup and view all the answers

    What is the primary fate of epithelial cells in the myotome?

    <p>Forming skeletal muscle</p> Signup and view all the answers

    Which of the following is NOT a component of the somite?

    <p>Neurocranium</p> Signup and view all the answers

    What muscles are formed by the epaxial division of myotomes?

    <p>Extensors of the neck and vertebral column</p> Signup and view all the answers

    Which myotomes are responsible for forming the scalene and infrahyoid muscles?

    <p>Cervical myotomes</p> Signup and view all the answers

    What type of muscles do hypaxial myotomes form?

    <p>Anterior/ventral, segmented muscles</p> Signup and view all the answers

    Which of the following best describes the relationship between myotomes and spinal nerves?

    <p>Myotomes take along spinal nerve branches, creating innervation patterns.</p> Signup and view all the answers

    Which muscle is formed by lumbar myotomes?

    <p>Quadratus lumborum</p> Signup and view all the answers

    What type of muscles do the thoracic myotomes contribute to?

    <p>Lateral and ventral flexors of the vertebral column</p> Signup and view all the answers

    Which of the following structures do dorsal rami spinal nerves primarily innervate?

    <p>Epaxial division muscles</p> Signup and view all the answers

    Which statement best describes the segmentation of epaxial muscles?

    <p>Some epaxial muscles retain their segmented nature.</p> Signup and view all the answers

    What happens to cartilage in individuals with certain diseases affecting cartilage maintenance?

    <p>It grows abnormally into bone or excessive amounts.</p> Signup and view all the answers

    What type of growth allows bones to increase in diameter?

    <p>Oppositional growth</p> Signup and view all the answers

    What is maintained by osteoblasts and osteoclasts in the medullary cavity?

    <p>Bone density</p> Signup and view all the answers

    Which part of long bones is responsible for continued growth after birth?

    <p>The epiphysial plate</p> Signup and view all the answers

    What type of growth occurs primarily during lengthening of bones?

    <p>Endochondrial growth</p> Signup and view all the answers

    What role do osteoprogenitor cells play in bone development?

    <p>They differentiate into osteoblasts.</p> Signup and view all the answers

    What is one potential symptom of conditions where cartilage is improperly regulated?

    <p>Stiffness and immobility of affected areas</p> Signup and view all the answers

    Which structure covers the long bones and includes the osteoprogenic layer?

    <p>The periosteum</p> Signup and view all the answers

    What is the primary role of osteoblasts during the process described?

    <p>To replace calcified cartilage with bone</p> Signup and view all the answers

    How does the appearance of the calcified cartilage compare to hyaline cartilage?

    <p>Calcified cartilage appears more purplish</p> Signup and view all the answers

    What structure is observed at the end of the bone in the histological slide?

    <p>Zone of calcified cartilage</p> Signup and view all the answers

    What differentiates the zone of ossification from the zone of calcified cartilage?

    <p>The type of cells present</p> Signup and view all the answers

    Where do the cuboidal bodies of the developing embryo originate from?

    <p>Paraxial mesoderm</p> Signup and view all the answers

    Why is it important to observe histology slides early in the study of musculoskeletal embryology?

    <p>To understand subtle differences in tissue types</p> Signup and view all the answers

    Which cell type would you expect to be present in the zone of ossification?

    <p>Osteoblasts</p> Signup and view all the answers

    What detail is indicated about the lamellae in the histological slide?

    <p>They indicate areas of bone formation</p> Signup and view all the answers

    What is the primary fate of the myotome in somite differentiation?

    <p>Muscle tissue</p> Signup and view all the answers

    Which of the following structures primarily originates from the sclerotome?

    <p>Bone and connective tissue</p> Signup and view all the answers

    What does the term 'dural myotome' imply about somite differentiation?

    <p>It is in a transitional stage before differentiating into the dermatome and myotome.</p> Signup and view all the answers

    How does the configuration of somites influence body patterns today?

    <p>It establishes the pattern for ribs and vertebrae.</p> Signup and view all the answers

    In what manner do the cells originating from the myotome contribute to the body structure?

    <p>They help in muscle formation.</p> Signup and view all the answers

    What is the significance of the notochord during the development of the somites?

    <p>It influences the development of surrounding cell types.</p> Signup and view all the answers

    Which specific type of cells migrate from the sclerotome during somite development?

    <p>Mesodermal cells</p> Signup and view all the answers

    What does the differentiation of somites contribute to in terms of body organization?

    <p>Musculoskeletal patterns</p> Signup and view all the answers

    What initial step occurs during the healing of a bone after a fracture?

    <p>Removal of bone fragments by osteoclasts</p> Signup and view all the answers

    Which type of joint involves highly fibrous connective tissue?

    <p>Fibrous joints</p> Signup and view all the answers

    What is the main purpose of synovial membranes in the joints?

    <p>To facilitate the movement of joints and maintain nutrition</p> Signup and view all the answers

    What is a common result of a Colles' fracture?

    <p>A wrist fracture caused by falling</p> Signup and view all the answers

    During the development of cartilage, what type of cartilage predominates?

    <p>Hyaline cartilage</p> Signup and view all the answers

    What can result from the presence of high link cartilage in bones?

    <p>Nutritional challenges due to avascularity</p> Signup and view all the answers

    After the initial cleanup of bone fragments, what is the next step in bone healing?

    <p>Production of new bone by osteoblasts</p> Signup and view all the answers

    What happens to the solid structure formed in synovial joints during development?

    <p>It undergoes apoptosis to create a cavity</p> Signup and view all the answers

    What type of cells are responsible for the development of muscles in limb buds?

    <p>Myogenic precursor cells</p> Signup and view all the answers

    What is the primary role of the apical ectodermal ridge in limb bud development?

    <p>To induce mesenchymal proliferation and limb lengthening</p> Signup and view all the answers

    In limb bud development, what does the zone of polarizing activity primarily influence?

    <p>The anterior-posterior patterning of the limb</p> Signup and view all the answers

    Which of the following correctly describes the axis of limb bud development that differs from standard anatomical positions?

    <p>Anterior is associated with the thumb and posterior with the pinky.</p> Signup and view all the answers

    What type of transformation do myogenic precursor cells undergo to become muscle cells?

    <p>Epithelial mesenchymal transformation</p> Signup and view all the answers

    Which aspect of limb development influences the medial-lateral differentiation?

    <p>Zone of polarizing activity</p> Signup and view all the answers

    What is the primary function of dermal myotome cells in limb bud development?

    <p>To migrate and contribute to muscle formation</p> Signup and view all the answers

    What anatomical reference describes the direction in which limb buds grow from the midline?

    <p>Proximodistally</p> Signup and view all the answers

    Study Notes

    Bone Development

    • Bone develops in connective tissue (CT) from mesenchyme and cartilage.
    • Bone is constantly replaced by osteoblasts and osteoclasts throughout life.

    Intramembranous ossification

    • Bone develops directly in mesenchyme.
    • Mesenchyme is unorganized CT that forms membranous sheaths.
    • Forms most axial bones.

    Endochondral ossification

    • Bone develops from cartilaginous models.
    • Forms most appendicular bones.

    Endochondral Ossification: Primary Centers

    • During week 5 of development, mesenchymal cells form models of hyaline cartilage surrounded by perichondrium.
    • Bone collar forms around the diaphysis (shaft) from osteoblasts in the perichondrium.
    • Chondrocytes in the diaphysis hypertrophy, cutting off nutrient supply and leading to apoptosis. This creates the marrow cavity.
    • Blood vessels penetrate the periosteum and bone collar, bringing osteoprogenitor cells to form primary centers of ossification.
    • Osteoprogenitor cells become osteoblasts or hematopoietic cells.
    • Osteoblasts deposit bone matrix (osteoid and hydroxyapatite), replacing cartilage.
    • Most diaphyses are ossified at birth.

    Endochondral Ossification: Secondary Centers

    • Form in epiphyses after birth.
    • Develop similarly to primary centers; however, trabecular bone replaces medullary cavity.

    Bone Growth

    • Appositional/Periosteal Growth: Growth in diameter that occurs in compact bone along the diaphyseal shaft.

    Somite Differentiation

    • Somites develop from the paraxial mesoderm, located adjacent to the notochord.
    • Somites form in a cranial to caudal direction.
    • Sclerotome forms bone and cartilage.
    • Myotome forms skeletal muscle.
    • Dermatome forms dermis.

    Differentiation of Somites

    • Somite differentiation begins during the fourth week of development in the mesoderm of the trilaminar embryo.
    • The dermomyotome differentiates into the dermatome (dermis and accessory organs) and myotome (muscle).
    • The sclerotome migrates to form bone and connective tissue.

    Development of the Trunk

    • Mesodermal cells from the sclerotome migrate and condense around the notochord, neural tube, and lateral body wall.
    • Condensed cells form the centrum (vertebral body), vertebral arches (future ribs), and costal processes.

    Development of Trunk Myotomes

    • Myotomes divide and migrate, taking spinal nerve branches with them, establishing a patterned innervation of muscle groups.
    • Myotomes form the epaxial (dorsal to vertebral column) and hypaxial (ventral to vertebral column) muscle divisions.

    Epaxial Muscle Division

    • Form the posterior, segmented muscles of the main body axis.
    • Extensor muscles of the neck and vertebral column.
    • Examples: Neck and vertebral column extensors.

    Hypaxial Muscle Division

    • Form the anterior/ventral, segmented muscles of the main body axis.
    • Flexor muscles of the neck and vertebral column.
    • Examples: Scalene muscles, longus colli and capitis, infrahyoid muscles, geniohyoid (cervical myotomes) and lateral and ventral flexors of the vertebral column (thoracic myotomes).
    • Also includes the quadratus lumborum (lumbar myotomes) and the pelvic diaphragm (sacrococcygeal myotomes).

    Bone Growth & Ossification

    • Epiphyses are the ends of long bones (e.g., humerus, femur) and are initially made of cartilage.
    • Secondary ossification centers form after birth to further develop the ends of long bones.
    • Bone lengthening occurs at the epiphyseal plate, a cartilaginous growth plate.
    • Medullary cavity inside long bones continues to expand through osteoblasts and osteoclasts activity.
    • Abnormal cartilage growth can lead to disorders like stiff person syndrome, where cartilage turns to bone.
    • Bone growth happens in two ways:
      • Interstitial growth (length) occurs at the epiphyseal plate.
      • Appositional growth (width) occurs at the outer compact bone layer.
    • Periosteum is a connective tissue covering long bones that contains osteoprogenitor cells.

    Bone Formation & Development

    • Endochondral ossification is the process by which cartilage is replaced by bone.
      • Cartilage is calcified and hardened.
      • Osteoblasts deposit bone onto the calcified cartilage, replacing it.
    • Axial musculoskeletal system develops from mesodermal cells, specifically the sclerotome, which condense at the midline of the embryo.
    • Limb buds are the precursors to limbs and contain myogenic precursor cells that differentiate into muscle cells.
    • Epithelial mesenchymal transformation is a key process in limb development.

    Limb Bud Development

    • Proximodistal growth (from midline outwards) is driven by the apical ectodermal ridge.
    • Anterior-posterior patterning (thumb to pinky) is influenced by the zone of polarizing activity.
    • Lateral-medial patterning (radial/tibial to fibular/ulnar) is also affected by the zone of polarizing activity.

    Bone Healing

    • Fracture healing involves a series of steps:
      • Osteoclasts remove bone fragments.
      • Bone formation occurs to replace damaged bone.

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