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?

Osteoblasts Signup and view all the answers

What characterizes periosteal/appositional growth of bone?

Growth in bone diameter Signup and view all the answers

What is the primary origin of muscle fibers?

Mesodermal cells Signup and view all the answers

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

Chondrogenesis Signup and view all the answers

Which cells form as a result of muscle fiber differentiation?

Satellite cells Signup and view all the answers

How do myotubes form during muscle development?

By fusing myoblasts Signup and view all the answers

What do chondroblasts secrete during the process of chondrogenesis?

Extracellular matrix Signup and view all the answers

Which connective tissue surrounds muscle fibers?

Endomysium Signup and view all the answers

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

They are mostly formed Signup and view all the answers

Which zone is NOT typically associated with endochondral bone growth?

Chondrocyte zone Signup and view all the answers

What do chondroblasts mature into?

Chondrocytes Signup and view all the answers

Which type of bone formation directly develops from mesenchyme?

Intramembranous bone formation Signup and view all the answers

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

Woven bone Signup and view all the answers

Which ossification process primarily forms appendicular bones?

Endochondral ossification Signup and view all the answers

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

Week 5 Signup and view all the answers

What transforms into osteocytes during the ossification process?

Osteoblasts that become trapped Signup and view all the answers

Which structure surrounds the diaphysis during endochondral ossification?

Perichondrium Signup and view all the answers

How is hydroxyapatite integrated into the bone during ossification?

It is deposited on the osteoid Signup and view all the answers

Which type of mesoderm differentiates to form somites?

Paraxial mesoderm Signup and view all the answers

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

Maturing into bone and cartilage Signup and view all the answers

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

4th week Signup and view all the answers

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

Dermomyotome Signup and view all the answers

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

Vertebral body and ribs Signup and view all the answers

In which direction do somites form during development?

Cranial to caudal Signup and view all the answers

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

Forming skeletal muscle Signup and view all the answers

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

Neurocranium Signup and view all the answers

What muscles are formed by the epaxial division of myotomes?

Extensors of the neck and vertebral column Signup and view all the answers

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

Cervical myotomes Signup and view all the answers

What type of muscles do hypaxial myotomes form?

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

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

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

Which muscle is formed by lumbar myotomes?

Quadratus lumborum Signup and view all the answers

What type of muscles do the thoracic myotomes contribute to?

Lateral and ventral flexors of the vertebral column Signup and view all the answers

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

Epaxial division muscles Signup and view all the answers

Which statement best describes the segmentation of epaxial muscles?

Some epaxial muscles retain their segmented nature. Signup and view all the answers

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

It grows abnormally into bone or excessive amounts. Signup and view all the answers

What type of growth allows bones to increase in diameter?

Oppositional growth Signup and view all the answers

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

Bone density Signup and view all the answers

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

The epiphysial plate Signup and view all the answers

What type of growth occurs primarily during lengthening of bones?

Endochondrial growth Signup and view all the answers

What role do osteoprogenitor cells play in bone development?

They differentiate into osteoblasts. Signup and view all the answers

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

Stiffness and immobility of affected areas Signup and view all the answers

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

The periosteum Signup and view all the answers

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

To replace calcified cartilage with bone Signup and view all the answers

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

Calcified cartilage appears more purplish Signup and view all the answers

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

Zone of calcified cartilage Signup and view all the answers

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

The type of cells present Signup and view all the answers

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

Paraxial mesoderm Signup and view all the answers

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

To understand subtle differences in tissue types Signup and view all the answers

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

Osteoblasts Signup and view all the answers

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

They indicate areas of bone formation Signup and view all the answers

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

Muscle tissue Signup and view all the answers

Which of the following structures primarily originates from the sclerotome?

Bone and connective tissue Signup and view all the answers

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

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

How does the configuration of somites influence body patterns today?

It establishes the pattern for ribs and vertebrae. Signup and view all the answers

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

They help in muscle formation. Signup and view all the answers

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

It influences the development of surrounding cell types. Signup and view all the answers

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

Mesodermal cells Signup and view all the answers

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

Musculoskeletal patterns Signup and view all the answers

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

Removal of bone fragments by osteoclasts Signup and view all the answers

Which type of joint involves highly fibrous connective tissue?

Fibrous joints Signup and view all the answers

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

To facilitate the movement of joints and maintain nutrition Signup and view all the answers

What is a common result of a Colles' fracture?

A wrist fracture caused by falling Signup and view all the answers

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

Hyaline cartilage Signup and view all the answers

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

Nutritional challenges due to avascularity Signup and view all the answers

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

Production of new bone by osteoblasts Signup and view all the answers

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

It undergoes apoptosis to create a cavity Signup and view all the answers

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

Myogenic precursor cells Signup and view all the answers

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

To induce mesenchymal proliferation and limb lengthening Signup and view all the answers

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

The anterior-posterior patterning of the limb Signup and view all the answers

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

Anterior is associated with the thumb and posterior with the pinky. Signup and view all the answers

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

Epithelial mesenchymal transformation Signup and view all the answers

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

Zone of polarizing activity Signup and view all the answers

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

To migrate and contribute to muscle formation Signup and view all the answers

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

Proximodistally 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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Description

Test your knowledge on bone development, including intramembranous and endochondral ossification. Explore the processes through which connective tissue transforms into bone and the roles of osteoblasts and osteoclasts. This quiz covers key concepts relevant to skeletal development.