Development of Craniofacial Skeleton

Question 1

Bone is ________ formed on a ________ with various attendant ________

Answer 1

1. Hydroxyapatite
2. Collagenous Matrix
3. Non-collagenous proteins

Question 2

Name the two types of bone (from a developmental point of view)

Answer 2

1. Endochondral

2. Intramembranous

Question 3

What is endochondral bone?

Answer 3

Bone that is formed on a cartilage template (the long bones)

Question 4

What is Intramembranous bone?

Answer 4

Bone that is formed from a condensation of mesenchyme (most of the mandible, skull plates)

Question 5

Define Initiation

Answer 5

Start of ossification, whether conversion of cartilage to bone, or condensation and ossification of mesenchyme/neural crest

Question 6

Define Growth

Answer 6

Addition of more bony matrix to a pre-existing bone; thickening, elongation, etc.

Question 7

Define Displacement (primary)

Answer 7

• Movement of a bone due to its own growth

- Can occur in either direction, depending on the ratio of resorption to deposition and other structures

Question 8

Define Displacement (secondary)

Answer 8

• Movement of a bone due to the growth of other bones

- Growth of one bone causes growth in another

Question 9

Define Remodeling

Answer 9

Growth involving simultaneous deposition and resorption on all peri- and endosteal surfaces; changes in size, shape, proportion, relationship with adjacent structres

Question 10

Define Drift

Answer 10

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

Question 11

Define Functional Matrix

Answer 11

A tissue that guides a bones growth by exerting a force upon the bone

Question 12

How can directional bone growth occur? Where can it occur?

Answer 12

1. By the deposition of bone on a surface, with concomitant resorption on another
2. At endosteal or periosteal surfaces (inside or outside of the bone)

Question 13

T/F Bone growth is usually equal in all directions

Answer 13

FALSE, It is usually asymmetric so as to maintain some proportion

Question 14

T/F Deposition and resorption rates at a surface change over time and can even switch

Answer 14

TRUE

Question 15

Define Growth fieds

Answer 15

Where matrix can be laid down or resorbed

Question 16

Define Growth Sites

Answer 16

Fields of significance to growth of a bone (Mandibular condyle, maxillary tuberosity)

Question 17

Define Growth centers

Answer 17

Special growth sites, control overall growth of bone (epiphyseal plates of long bones)

Question 18

What makes up the Neurocranium?

Answer 18

1. Calvaria

2. Cranial Base

Question 19

What is the origin of the Calvaria?

Answer 19

both paraxial mesoderm and neural crest origin

Question 20

What is another name for the Calvaria?

Answer 20

Desmocranium

Question 21

What type of bone makes up the calvaria?

Answer 21

Intramembranous bone

Question 22

What is the cranial base derived from and what is its early form called?

Answer 22

• Derived from special sense organ capsular tissues
• Endochondral bone, primarily neural crest
• Early form called Chondrocranium

Question 23

What is the facial skeleton called?

Answer 23

Viscerocranium

**consists of basically what we call the face: anterior, lower skull

Question 24

What is the viscerocranium derived from?

Answer 24

Pharyngeal arches

Question 25

How many facial bones are there?

Answer 25

14

Question 26

Which part of the skull grows more postnatally, the Viscerocranium or the Desmoranium?

Answer 26

Viscerocranium

Question 27

Name the bones that make up the calvaria

Answer 27

1. Frontal 2. Parietal 3. Parts of Occipital 4. Temporal 5. Sphenoid bones

Question 28

What are the two layers formed by condensed Mesechyme?

Answer 28

1. Endomeninx (inner layer) | 2. Ectomeninx (outer layer)

Question 29

What is the endomeninx?

Answer 29

- Neural crest | - Gives rise to pia mater and arachnoid

Question 30

What is the ectomeninx?

Answer 30

- Neural crest and paraxial mesoderm, | - gives rise to dura mater and the Calvaria/bone

Question 31

What part of the ectomeninx forms the calvaria bones?

Answer 31

The superficial portion

Question 32

What does the inner ectomeninx form?

Answer 32

Dura

Question 33

What does Desmo mean?

Answer 33

Membrane

Question 34

Define sutures

Answer 34

Mesenchymal gaps between bones of the calvaria, holds together the various bones of the skull

Question 35

Define fontanelles

Answer 35

Un-ossified suture between 2 or more skull bones

Question 36

Define Anencephaly

Answer 36

- Calvaria Defect | - Failure of rostral neural tube to close (around week 4), lost of telencephalon)

Question 37

Define Craniosynostosis

Answer 37

- Calvaria Defect - Premature fusion of the cranial vault sutures - Variable defects including deformities of calvaria and neurologic defects

Question 38

What bones make up the Cranial Base (chondrocranium)?

Answer 38

1. Frontal 2. Parietal 3. parts of the occipital 4. Temporal 5. Sphenoid bones

Question 39

How does the chondrocranium form?

Answer 39

Ectomeninx in floor of brain forms cartilage in response to notochord and other epithelial signals, becomes chondrocranium and later undergoes endochondral ossification

Question 40

What is the embryological tissue that forms the nasal cavity?

Answer 40

The nasal capsule

Question 41

T/F All of the nasal capsule ossifies

Answer 41

FALSE, Septal cartilage

Question 42

How does the growth of nasal septal cartilage play a role in facial development?

Answer 42

Plays a role in downward/forward growth of midface

Question 43

What happens to the maxilla as the chondrocranium grows?

Answer 43

Maxilla and the rest of the facial skeleton get pushed down and forward

Question 44

Name the bones of the facial skeleton

Answer 44

1. Nasal 2. Lacrimal 3. Maxilla 4. Premaxilla 5. Palatine 6. Vomer 7. Mandible 8. Zygomatic

Question 45

Define the Maxilla Proper

Answer 45

Intramembranous ossification of mesenchyme, forms from maxillary prominence/process

Question 46

Define the premaxilla

Answer 46

Intramembranous ossification of mesenchyme, forms from frontonasal process, forms primary palate, fuses early with maxilla proper

Question 47

What are the secondary cartilages?

Answer 47

- Zygomatic Process - Alveolar plate - Hard palate between palatine processes **mostly these have fetal growth roles and then break down and go away. We don't have them as adults

Question 48

Describe development and growth of the Maxilla

Answer 48

- The maxilla forms and grows down and forward via both primary and secondary displacement from growth of the zygomatic and nasal septum cartilages - Ossification center is closely associated with the cartilage of the nasal capsule and zygomatic or malar cartilage - Ossification from the developing maxilla also spreads to the palatine process to form most of thee hard palate - Postnatally, thereis quite a lot of growth and expansion here, as the maxillary sinus develops

Question 49

How does 2ndary displacement contribute to maxillary development?

Answer 49

Secondary displacement at sutures pushes maxilla down, forward, and out

Question 50

How do the alveolar plates form?

Answer 50

From the forming maxilla and the junction of the palatal process. **Alveolar plates house the tooth germs

Question 51

How does the mandible form?

Answer 51

- Intramembranous ossification - Bone forms lateral to Meckel's cartilage - Ossification spreads posteriorly to form body and ramus

Question 52

What type of cartilage is meckel's cartilage?

Answer 52

Hyaline

Question 53

T/F the bone of the mandible forms from meckel's cartilage

Answer 53

FALSE, It largely disappears and does not actually become the mandible proper

Question 54

What secondary cartilages form from Meckel's cartilage?

Answer 54

1. Conylar 2. Coronoid 3. Symphyseal

Question 55

Why is the condylar cartilage important?

Answer 55

- It expands into a cone running long the ramus and ossifies through endochondral ossification - Condylar cartilage remains at the articular ends on the head - Important growth center for the ramus, driving intramembranous ossification, and then ossifies itself through endochondral ossification

Question 56

T/F the Mandible is both membarnous and endochondral in nature

Answer 56

TRUE, but the cartilage is not Meckel's, it is secondary

Question 57

What happens to the coronoid cartilage?

Answer 57

It disappears before birth

Question 58

What happens to the symphyseal cartilages (2)?

Answer 58

Disappear in the first year after birth. **They contribute transiently to the growth and development of the surrounding tissues

Question 59

Where does condyle cartilage function?

Answer 59

Both in articulation at TMJ and in growth