Musculoskeletal Development

Question 1

What mesenchyme is the vertebral column, ribs, and sternum originated from?

Answer 1

Mesodermal sclerotomes

Question 2

Where do the limb bones and girdles originate from?

Answer 2

Lateral plate mesoderm

Question 3

Where does the skull and base of skull develop from?

Answer 3

Head mesoderm

Question 4

Where do the facial bones develop from?

Answer 4

Neural crest

Question 5

Describe the common pathway for bone/cartilage.

Answer 5

Mesenchyme is induced to enter and the production of N cadherins promote mesenchymal cell condensation. TGF-B stimulates synthesis of fibronectin and N-CAM. Aggregated state of mesenchymal cell is stabilized.

Question 6

Membranous bone pathway?

Answer 6

Requires transcription factors Runx-2 and Osx, mesenchymal cells differentiate into osteoblasts

Question 7

Permanent cartilage pathway?

Answer 7

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

Question 8

Endochondral bone pathway formation?

Answer 8

TF Runx-2, genes ihh and BMP-6 induce cartilage to undergo hypertrophy. Hypertrophic cells secrete bone proteins and vascular endothelial growth factor. Invading blood vessels erode the hypertrophic cartliage and bring osteoblasts to replace cartilage with bone. FGF-18 prevents chondrocyte maturation.

Question 9

Where does the centrum of the vertebra originate?

Answer 9

Derived from ventral and medial parts of paired sclerotomes

Question 10

Differentiate hox gene boundaries for different regions of vertebral column.

Answer 10

Hox-3 is occipital cervical boundary
Hox-6 is cervical thoracic boundary
Hox-9 is attached-floating rib boundary

Question 11

describe development of axis/atlas complex and id primordia.

Answer 11

In a mouse the atlas is developed from a combination of Hoxa1, Hoxa3, Hoxb1 and Hoxd4.

The axis is the same four genes plus Hoxa4 and Hoxb4

Question 12

Where does the neural arches come form?

Answer 12

dorsal regions of sclerotomes

Question 13

What is the relation between formation of neural arches and spina bifida?

Answer 13

The neural arches form a protective roof over the spinal cord when they fuse together. If they do not fuse all the way it reults in spina bifida.

Question 14

Where do the costal cartilages and ribs originate from?

Answer 14

Proximal development depends on expression of myotomic myogenic factors myf-5 and myf-6. Distal development depends on BMP signals from somatopleural mesoderm

Question 15

What is the relationship of Hox gene expression and development of the vertebral column.

Answer 15

Hox genes differentiate regional boundaries of the vertebral column.

Question 16

How does RA affect expression of hox genes and development of the vertebral column?

Answer 16

RA causes a cranial shift in which the last cervical vertebra is transformed into the first thoracic vertebra. If given later it causes a caudal shift in which thoracic vertebra extend into lumbar vertebrae.

Question 17

What are homeotic transformations?

Answer 17

Transformations of hox genes that results in shifts in cranial or caudal levels in overall segmentation and organization of vertebrae.

Question 18

Relate anterior expression boundaries of key hox gene paralogues and major boundaries in axial skeleton.

Answer 18

Posterior extension of axial skeleton is balanced by Cdx and homeobox genes which promote extension. Also the Hox13 paralogue which slows and stops the extension.

Question 19

Single Hox gene knockouts?

Answer 19

Likely to produce a minor defect but not same extent as knockout of all paralogues.

Question 20

Knockout of all Hox 10 paralogues?

Answer 20

Ribs form on all the lumbar and sacral vertebrae. Hox10 represses the influence of more anterior genes

Question 21

Knockout of all Hox 11 paralogues?

Answer 21

Suppresses influence of Hox10 and allows sacrum to form

Question 22

Mutation of single hox gene?

Answer 22

Minor anatomical defect

Question 23

Describe the origin of the sternum.

Answer 23

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

Question 24

Describe origin of clavicle.

Answer 24

Arises from neural crest and follows intramembtanous pathway. One of the first bones to become ossified.

Question 25

What is cleiodcranial dysplasia?

Answer 25

Birth defect that affects bones and teeth. Clavicles poorly developed or absent and shoulders are brought close together

Question 26

What are the subdivisons of the developing skull?

Answer 26

Neurocranium, Viscerocranium, occipital sclerotomes

Question 27

Describe the generalized viscerocranium and bones that develop from viscerocranium.

Answer 27

Surrounds the oral cavity and pharynx. Comes from neural crest. Has cartilaginous portion and membranous. Cartilaginous forms the pharyngeal arch I and II. Membranous forms temporal,,zygomatic, maxillary, nasal, lacrimal, palatine, vomer, pterygoid plates

Question 28

Describe the generalized viscerocranium and bones that develop from viscerocranium.

Answer 28

Surrounds the oral cavity and pharynx. Comes from neural crest. Has cartilaginous portion and membranous. Cartilaginous forms the pharyngeal arch I and II.

Question 29

Describe origin of various endochondral skull bones.

Answer 29

k

Question 30

Describe origin of various endochondral skull bones.

Answer 30

CANT FIND

Question 31

What four components do each pharyngeal arch consist of?

Answer 31

Skeletal element
muscles
branch of specific cranial nerve
artery

Question 32

Elongation of primary ossification centers is due to what?

Answer 32

Shh

Question 33

Elongation of primary ossification centers is due to what?

Answer 33

Shh

Question 34

What bones develop from the membranous viscerocranium?

Answer 34

Membranous forms temporal,,zygomatic, maxillary, nasal, lacrimal, palatine, vomer, pterygoid plates