Bone formation

Question 1

What are the two types of ways bones form?

Answer 1

1) endochondral –> formed on a cartilage template

2) intramembranous –> bone that is formed from a condensation of mesenchyme

Question 2

What is primary displacement?

Answer 2

movement of bone due to its own growth

- bone often moves in the opposite direction from which they are depositing matrix

Question 3

What is secondary displacement?

Answer 3

movement of a bone due to the growth of another

Question 4

What is drift?

Answer 4

remodeling that results in movement of a bone towards the deposition surface

Question 5

What is functional matrix?

Answer 5

Tissue that guides a bones growth by exerting a force upon the bone

Question 6

Overall, how can bone growth occur?

Answer 6

• directional bone growth can occur by the deposition of bone on a surface, with concomitant resorption on another
  
  • will occur at the endosteal or periosteal surface

Question 7

What is a growth field?

Answer 7

Where matrix can be laid down or resorbed

Question 8

What are growth sites?

Answer 8

fields of significance to growth of a bone

- mandibular condyle, maxillary tuberosity

Question 9

What are growth centers?

Answer 9

special growth sites, control overall growth of bone

- epiphyseal plates

Question 10

What is the neurocranium?

Answer 10

• bones encasing the brain
• Calvary: skull cap
  
  • intramembranous bone; paraxial mesoderm and neural crest
• Cranial base: Endochondral bone, primarily neural crest

Question 11

What is the viscerocranium?

Answer 11

• Facial bones

- derived from pharyngeal arches, 14 facial bones

Question 12

What makes up the calvaria?

Answer 12

• frontal, parietal, occipital, temporal, sphenoid
  
  • Inner layer (endomeninx): neural crest, gives rise to pia and arachnoid
  • outer layer (ectomenin): neural crest and paraxial mesoderm, dura and calvaria

Question 13

What is a fontanelle?

Answer 13

unossified suture between 2 or more skull bones

- allow for growth of the skull to make room for the brain

Question 14

What are two calvaria defects?

Answer 14

1) Anencephaly: failure of rostral neural tube to close approx. week 4, loss of telencephalon
2) Craniosynostosis: premature fusion of the cranial vault sutures
- variable defects including deformities of calvaria and neurological deficits

Question 15

What makes up the facial bones?

Answer 15

nasal, lacrimal, maxilla, premaxilla, palatine, vomer, mandible, zygomatic

Question 16

What makes up maxilla proper?

Answer 16

intramembranous ossification

Question 17

What makes up the premaxilla?

Answer 17

intramembranous ossification

- forms frontonasal process, primary palate, fuses early with maxilla proper

Question 18

What is derived from secondary cartilage?

Answer 18

• zygomatic process, alveolar plate, hard palate between palatine process –> mostly fetal growth roles

Question 19

How does the Maxilla develop?

Answer 19

• Via primary and secondary displacement from growth of the zygomatic and nasal cartilage
• Ossification center is closely associated with the cartilage of the nasal capsule and zygomatic or malar cartilage
• the alveolar plates form from the maxilla and the junction of the palatal process and house the tooth germs
• ossification form the developing maxilla also spreads to the palatine process to form most of the hard palate

Question 20

How does the mandible form?

Answer 20

• Forms by intramembranous ossification, and forms laterally to meckel’s cartilage (hyaline)
• Secondary/accessory cartilages (condylar, coronoid and symphyseal) form from meckel’s cartilage at approx. 10-14 weeks of development
• Condylar cartilage extends into a cone running along the ramps and ossifies thru endochondral ossification

Question 21

What is Meckel’s cartilage?

Answer 21

• Hyaline
• Primary cartilage
• Largely disappears anteriorly and does not actually become the mandibular proper