Skeletomuscular Development

Question 1

Skeletomuscular development

Answer 1

• Coordinated with development of nerves, blood vessels, tendons and ligaments
• In most body regions occurs within somites or limb buds

Question 2

Somites

Answer 2

Form in the neck and trunk
• segments of mesoderm that will form parts of vertebra, ribs, meninges, muscle, and segments of dermis
• Begin development before 3 weeks
• Along with formation of bones and muscles, guide formation of certain nervous system structures

Question 3

Somites have 3 major compartments

Answer 3

• Sclerotomes form part of the vertebra, ribs, and meninges
• Myotomes form a “block” of muscle
• Dermatomes form a segment of skin

Question 4

2 Smaller compartments of the somite

Answer 4

2 smaller compartments form tendons and dorsal blood vessels

• Somites determine the migration paths of peripheral nervous system structures

Question 5

Somites become more “specified” as they mature

Answer 5

• Usually neither cervical or lumbar somites form ribs

* Only thoracic somites can

Question 6

Endochondral Bone Development (most bones)

Answer 6

• built on a hyaline cartilage model (perichondrium)
• ossification results in spongy bone first then an outer layer of compact bone
• primary (first) ossification in the diaphysis (perichondrium turns to periosteum)
• forms periosteal collar (“temporary splint”)
• secondary ossifications in epiphysis
• formation of diagnostic features stimulated by stress on the periosteum

Question 7

Increasing the Diameter of Developing Bone

Answer 7

• through appositional growth on the outer surface
• osteogenic cells differentiate into osteoblasts
• matrix, blood vessels added to outer (periosteal) surface
• osteoclasts remove matrix at the inner (endosteal) surface
• marrow cavity enlarges as bone diameter enlarges

Question 8

Intramembranous Bone Development (dermal ossification)

Answer 8

• roofing bones of the skull, mandible, clavicle
• proceeds without a hyaline cartilage model
• bone tissue deposited “between sheets” of fibrous connective tissue
• spongy bone then outer layers of compact bone = Diploe

Question 9

What mechanisms do skull development involve

Answer 9

Both endochondral and intramembranous mechanisms

Question 10

Limbs form from fields to buds

Answer 10

• Limb fields form from specified lateral plate mesoderm
  
  • Bulge in the center = limb bud-forms from cells migrating from field and somite
• If the limb field is split early it will form > 1 limb

Question 11

Limbs

Answer 11

• There are important differences between the upper and lower limb, but there is a common pattern:
• example of establishing axes and following an organizational path…
• Consider the polarity of your limbs…
• The mirror image pattern

Question 12

Limb polarity (proximal → distal)

Answer 12

• There is an asymmetric arrangement of parts in 4 dimensions (time included)
• 3 parts:
  
  • Stylopod – proximal single sturdy bone
  • Zeugopod – 2 parallel bones
  • Autopod – carpals → fingers OR tarsals → toes
• Both sides ~ match in size! (approximately)