Development of the Musculoskeletal System
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Questions and Answers

What condition describes the complete absence of a limb?

  • Amelia (correct)
  • Ectrodactyly
  • Phocomelia
  • Meromelia

    • Which limb defect is characterized by the partial absence of a limb?

  • Polydactyly
  • Meromelia (correct)
  • Amelia
  • Brachydactyly

    • What is the primary cause of syndactyly?

  • Insufficient apoptotic cell death between digital rays (correct)
  • Excessive proliferation of mesoderm
  • Additional sites of apoptotic cell death
  • Development of abnormal AER

    • Ectrodactyly is often referred to as which of the following?

    <p>Missing digit</p> Signup and view all the answers

    Which condition is characterized by the presence of extra digits?

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

    What is the role of the zone of polarizing activity (ZPA) in limb development?

    <p>To produce a signal that influences digit formation</p> Signup and view all the answers

    In which week do the first digital rays appear in the developing hand and foot?

    <p>Week 6</p> Signup and view all the answers

    Which statement accurately describes limb bone differentiation?

    <p>Limb bones form in a proximal to distal fashion</p> Signup and view all the answers

    How does limb rotation differ between the upper and lower limbs?

    <p>Upper limb rotates laterally and lower limb rotates medially</p> Signup and view all the answers

    What is the primary result of the rotation of the lower limb during development?

    <p>The pattern of innervation twists into a spiral</p> Signup and view all the answers

    Which of the following describes the mechanism of digit formation from digital rays?

    <p>Apoptotic cell death stimulates the growth of separate digits</p> Signup and view all the answers

    What is the primary cause of limb defects noted in clinical correlations?

    <p>Defects in the signaling from the apical ectodermal ridge</p> Signup and view all the answers

    What is the primary signal produced by the zone of polarizing activity (ZPA)?

    <p>Sonic hedgehog (SHH)</p> Signup and view all the answers

    What is the primary origin of the posterior skull and vertebral column?

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

    Which structure differentiates into muscle and contributes to the dermis of the back?

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

    From which cells does the craniofacial skeleton develop?

    <p>Neural crest cells</p> Signup and view all the answers

    What is the segmental pattern of innervation in the adult derived from?

    <p>Each somite's growth of one spinal nerve</p> Signup and view all the answers

    What is formed by the ventro-medial cells of the somite?

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

    Which part of the somite is associated with intrinsic bones and muscles of the back?

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

    Which mesodermal structure gives rise to the sternum and appendicular skeleton?

    <p>Lateral plate mesoderm</p> Signup and view all the answers

    During somite differentiation, what signals the ventro-medial cells to become mesenchymal?

    <p>Notochord and floor plate of the neural tube</p> Signup and view all the answers

    Which of the following is the correct order of development from somites?

    <p>Epithelization, sclerotome, myotome, dermomyotome</p> Signup and view all the answers

    What does the hypomere develop into?

    <p>Muscles and connective tissue of the trunk and limbs</p> Signup and view all the answers

    What is the process by which sclerotome cells organize around the neural tube?

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

    Which part of the sclerotome fuses with the cranial half of the adjacent sclerotome?

    <p>Caudal half</p> Signup and view all the answers

    What happens to the notochord during the formation of vertebrae?

    <p>It becomes the nucleus pulposus</p> Signup and view all the answers

    What is the cause of congenital scoliosis?

    <p>One half of a vertebra does not form</p> Signup and view all the answers

    Which condition results from incomplete resegmentation of sclerotomes?

    <p>Klippel-Feil syndrome</p> Signup and view all the answers

    Which embryonic structure gives rise to all skeletal muscle?

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

    What are the muscles derived from epimere called?

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

    What is the primary event occurring during the limb bud development at week 4?

    <p>Upper limb bud appears</p> Signup and view all the answers

    What signals the overlying ectoderm to grow during limb bud development?

    <p>Fibroblast growth factor (FGF-10)</p> Signup and view all the answers

    Which domain contains only somite-derived cells?

    <p>Primaxial domain</p> Signup and view all the answers

    What condition is characterized by a depressed sternum?

    <p>Pectus excavatum</p> Signup and view all the answers

    Which of the following correctly describes the structure of ribs?

    <p>Ribs are made up of multiple embryonic primordia</p> Signup and view all the answers

    What is the effect of Lmx-1 expression in limb development?

    <p>Establishes dorsal-ventral axis</p> Signup and view all the answers

    Study Notes

    Introduction to Musculoskeletal Development

    • Objectives: Understand cell types from somites, development of axial and appendicular skeletons, and limb development.
    • Timeline: Development occurs around Week 5 (35-38 days into gestation).

    Origin of Skeletal Tissue

    • Paraxial Mesoderm: Forms posterior skull, vertebral column, and ribs.
    • Lateral Plate Mesoderm: Gives rise to sternum and appendicular skeleton.
    • Neural Crest Cells: Contribute to craniofacial skeleton.

    Somite Structure and Function

    • Somites: Segmental structures lateral to the neural tube that differentiate into various tissues.
    • Differentiation:
      • Ventro-medial cells become mesenchymal, forming sclerotome (tendons, ligaments, bones).
      • Dorso-lateral cells form dermomyotome (muscle, dermis).

    Innervation of Somites

    • Each somite correlates with one spinal nerve, leading to segmental innervation patterns for muscles and skin.
    • Divisions:
      • Epimere: Associated with dorsal rami, forming intrinsic back structures.
      • Hypomere: Associated with ventral rami, forming muscles/connective tissues of the trunk and limbs.

    Axial Skeleton Development

    • Vertebrae Resegmentation:
      • Sclerotome cells reorganize around the neural tube before they split and fuse to form vertebrae.
      • Original notochord transforms into nucleus pulposus.
    • Clinical Correlations:
      • Congenital Scoliosis: Results from hemivertebra formation due to partial vertebra development.
      • Klippel-Feil Syndrome: Incomplete resegmentation causes fused vertebrae, leading to a short neck, low hairline, and limited neck motion.

    Formation of Ribs and Sternum

    • Ribs: Develop from sclerotomes that form thoracic vertebrae with three embryonic structures (centrum, neural arch, costal process).
    • Sternum: Unique as it originates from parietal lateral plate mesoderm.

    Appendicular Skeleton Development

    • Limbs derive from parietal lateral plate mesoderm.
    • Skeletal Muscle Development:
      • Somites are the source of all skeletal muscle; epaxial (intrinsic back) and hypaxial (other skeletal muscle) classifications based on somite origin.

    Limb Bud Formation

    • Limb Buds: Upper limbs appear in Week 4, lower limbs in Week 5, consisting of ectodermal caps and mesodermal cores.
    • Apical Ectoderm Ridge (AER): Crucial for limb growth, directing mesoderm proliferation via signaling molecules (FGF-10 and FGF-8).

    Limb Axis and Differentiation

    • Proximal/Distal Axis: AER signals distal limb formation; dorsal/ventral axis differentiation involves homeobox genes like Lmx-1.
    • Cranial/Caudal Axis: Zone of Polarizing Activity (ZPA) directs digit positioning via Sonic hedgehog (SHH) signaling, contributing to varying digit lengths.

    Limb Bone Development

    • Differentiation: Limb bones arise from proximal to distal: humerus/femur (stylopod), radius/ulna/tibia/fibula (zeugopod), and carpals/metacarpals/phalanges/tarsals/metatarsals (autopod).
    • Ossification: Bones form through endochondral ossification, starting from a cartilage template.

    Digital Formation and Limb Rotation

    • Digital Rays: Form by apoptosis in the AER; complete separation of digits typically occurs by Week 8.
    • Rotation:
      • Upper limbs rotate laterally (extensor muscles lateral).
      • Lower limbs rotate medially (extensor muscles anterior).

    Limb Innervation

    • Dermatomes: Skin regions supplied by specific spinal nerves; limb rotation modifies original innervation patterns.
    • Motor Innervation: Reflects segmental development; includes specific mappings for upper limb muscle innervation.

    Clinical Correlations in Limb Development

    • Limb Defects:
      • Amelia: Complete limb absence.
      • Meromelia: Partial limb absence.
      • Phocomelia: Absence of long limb bones.
      • Brachydactyly: Shortened digits from inadequate proliferation.
      • Syndactyly: Fused digits from insufficient apoptosis.
      • Polydactyly: Extra digits resulting from additional apoptotic site development.
      • Ectrodactyly: Missing digits leading to cleft conditions.

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    Development_of_the_Musculoskeletal_System_Corrected.pptx

    Description

    Explore the intricate processes involved in the development of the musculoskeletal system, including somite-derived cells and their correlation to spinal nerves. Learn about the formation of axial and appendicular skeleton components as well as limb development from bud formation to digit maturation.

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