Lecture 14 - Musculoskeletal Development I

Question 1

Origin of skeletal tissue

Answer 1

Mesenchymal origin

•Mesodermal sclerotomes(of somites): •Vertebral column •Ribs •Sternum •Lateral plate mesoderm: •Limb bones •Girdles •Head mesoderm: •Calvariaand base of skull •Neural crest: •Facial bones

Question 2

Limb skeleton:

Answer 2

Continuous interaction between apical ectodermal ridge and limb bud mesoderm

Question 3

vertebral column

Answer 3

Inductive interaction between sclerotome and notochord or neural tube

Question 4

head

Answer 4

• Interaction between preskeletal neural crest cells and information along migratory paths
• Interactions between areas of the brain and overlying mesenchyme

Question 5

Bone/Cartilage Differentiation Pathways

Answer 5

Common Pathway, Membranous Bone Pathway, Permanent Cartilage Pathway, and Endochondral Bone Pathway

Question 6

Common Pathway

Answer 6

Bone/Cartilage differentiation pathway:
•Mesenchyme is induced to enter the common pathway.
•Production of N-cadherins which promote mesenchymal cell condensation.
•TGF-βstimulates synthesis of fibronectin and N-CAM
•Aggregated state of mesenchymal cells is stabilized.

Question 7

Membranous Bone Pathway

Answer 7

Bone/Cartilage Differentiation Pathway:
•Requires transcription factors Runx-2 and Osx
•Mesenchymal cells differentiate into osteoblasts.

Question 8

Permanent cartilage pathway:

Answer 8

Cartilage Differentiation Pathway:
•Mesenchymal condensation forms chondroblasts
•Sox-9causes chondroblasts to secrete collagen II and cartilage matrix.
•Sox-9is continually expressed in permanent cartilage.

Question 9

Endochondral bone pathway:

Answer 9

Bone Differential Pathway:
•Runx-2, ihh, and BMP-6induce this cartilage to undergo hypertrophy.
•Hypertrophic cartilage cells secrete bone proteins and vascular endothelial growth factor.
•Invading blood vessels erode the hypertrophic cartilage and bring in osteoblasts to replace cartilage with bone

Question 10

Formation of Different Parts of a Vertebra

Answer 10

Centrum, Neural Arches, Costal Processes/ribs

Question 11

Centrum

Answer 11

Derived from ventral and medial parts of paired sclerotomes

Question 12

Neural Arches

Answer 12

•Arise from dorsal regions of sclerotomes

Question 13

Costal Processes/Ribs

Answer 13

• Proximal development depends on expression of myotomic myogenic factors, Myf5 and Myf-6
• Distal development depends on BMP signals from somatopleural mesoderm.

Question 14

Occipital-cervical boundary

Answer 14

Hox 3

Question 15

Cervical-thoracic boundary

Answer 15

Hox 6

Question 16

Attached-floating ribs boundary

Answer 16

Hox 9

Question 17

Single Hoxgene knockouts Knockout of all Hox10 paralogues Knockout of all Hox11 paralogues Mutation of a single Hoxgene

Answer 17

9.2 clin corr

Question 18

Development of the Sternum

Answer 18

• Derived from lateral plate mesoderm.
• Arises as a pair of cartilaginous bands.
• Fused cartilaginous bands secondarily subdivide into craniocaudal elements.

Question 19

Development of Clavicle

Answer 19

• Arises from neural crest
• Follows intramembranous pathway
• One of first bones to become ossified

Question 20

Subdivisions of the Developing Skull

Answer 20

Neurocranium,

Question 21

Subdivisions of the Developing Skull

Answer 21

Neurocranium, Viserocranium, and Occipital Sclerotomes

Question 22

Neurocranium

Answer 22

•Is that part of the skull that surrounds the brain
•Has a cartilaginous portion and a membranous portion
Base is formed from the chondrocranium(cartilaginous):
•Origin of occipital, sphenoid, ethmoid, and parts of temporals
Membranous part:
•Origin of part of occipital, parietals, frontals, part of temporals

Question 23

Chondrocranium

Answer 23

cartilaginous base of the neurocranium

Question 24

Viserocranium

Answer 24

pharyngeal arches

• Surrounds oral cavity and pharynx
• Has a cartilaginous portion and a membranous portion

Question 25

Cartilaginous portion of Viserocranium

Answer 25

Forms:
•Pharyngeal arch I (Meckel’s cartilage, malleus, incus)
•Pharyngeal arch II (Reichert’s cartilage, stapes, styloid)

Question 26

Membranous part of the Viserocranium

Answer 26

Forms:

Part of temporal, zygomatic, maxillary, nasal, lacrimal, palatine, vomer, pterygoid plates, mandible, tympanic ring

Question 27

The mesenchyme that forms the viscerocranium is mostly from the __ __.
There are __ pairs of pharyngeal arches.

Answer 27

neural crest

6

Question 28

Each pharyngeal arch consists of four components:

Answer 28

• Skeletal element
• Muscles
• A branch of a specific cranial nerve
• Artery

Question 29

Formation and Growth of Chondrocranium/Neurocranium

Answer 29

• Basioccipitalportion of chondrocraniumis derived from parachordal cartilages and occipital sclerotomes.
• Other components of the original cartilages fuse to form final chondrocranium.
• Ossification centers form within the cartilage allow continued growth and are separated from each other by synchondroses.
• Elongation of primary ossification centers is due to Shh.
• Membranous components may be incorporated into the endochondral components.

Question 30

Intersection of more than two bones form ___.

Bones of the neurocranium arise as a result of inductive interactions of surrounding ___.

Answer 30

fontanelles

Mesenchyme

Question 31

The occipital bone is formed from __ and __ __.

Answer 31

occipital sclerotomes and parachordal cartilages

Question 32

Anterior Skull Parts

Answer 32

Frontal Bone 
Maxillary Bones
Sygomatic Bones
Nasal Bones
Sphenoid
Ethmoid
Lacrimal
Vomer

Question 33

Lateral Skull

Answer 33

Parietal Bones
Occipital Bones
Temporal Bones

Question 34

Frontal Bone

Answer 34

paired in fetus, fused in adult: metopic suture

Question 35

Maxillary Bones

Answer 35

alveolar process, infraorbital foramina