Development of Craniofacial Skeleton Flashcards
Bone is ________ formed on a ________ with various attendant ________
- Hydroxyapatite
- Collagenous Matrix
- Non-collagenous proteins
Name the two types of bone (from a developmental point of view)
- Endochondral
2. Intramembranous
What is endochondral bone?
Bone that is formed on a cartilage template (the long bones)
What is Intramembranous bone?
Bone that is formed from a condensation of mesenchyme (most of the mandible, skull plates)
Define Initiation
Start of ossification, whether conversion of cartilage to bone, or condensation and ossification of mesenchyme/neural crest
Define Growth
Addition of more bony matrix to a pre-existing bone; thickening, elongation, etc.
Define Displacement (primary)
- 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
Define Displacement (secondary)
- Movement of a bone due to the growth of other bones
- Growth of one bone causes growth in another
Define Remodeling
Growth involving simultaneous deposition and resorption on all peri- and endosteal surfaces; changes in size, shape, proportion, relationship with adjacent structres
Define Drift
Remodeling that results in movement of a bone towards the deposition surface
Define Functional Matrix
A tissue that guides a bones growth by exerting a force upon the bone
How can directional bone growth occur? Where can it occur?
- By the deposition of bone on a surface, with concomitant resorption on another
- At endosteal or periosteal surfaces (inside or outside of the bone)
T/F Bone growth is usually equal in all directions
FALSE, It is usually asymmetric so as to maintain some proportion
T/F Deposition and resorption rates at a surface change over time and can even switch
TRUE
Define Growth fieds
Where matrix can be laid down or resorbed
Define Growth Sites
Fields of significance to growth of a bone (Mandibular condyle, maxillary tuberosity)
Define Growth centers
Special growth sites, control overall growth of bone (epiphyseal plates of long bones)
What makes up the Neurocranium?
- Calvaria
2. Cranial Base
What is the origin of the Calvaria?
both paraxial mesoderm and neural crest origin
What is another name for the Calvaria?
Desmocranium
What type of bone makes up the calvaria?
Intramembranous bone
What is the cranial base derived from and what is its early form called?
- Derived from special sense organ capsular tissues
- Endochondral bone, primarily neural crest
- Early form called Chondrocranium
What is the facial skeleton called?
Viscerocranium
**consists of basically what we call the face: anterior, lower skull
What is the viscerocranium derived from?
Pharyngeal arches
How many facial bones are there?
14
Which part of the skull grows more postnatally, the Viscerocranium or the Desmoranium?
Viscerocranium
Name the bones that make up the calvaria
- Frontal
- Parietal
- Parts of Occipital
- Temporal
- Sphenoid bones
What are the two layers formed by condensed Mesechyme?
- Endomeninx (inner layer)
2. Ectomeninx (outer layer)
What is the endomeninx?
- Neural crest
- Gives rise to pia mater and arachnoid
What is the ectomeninx?
- Neural crest and paraxial mesoderm,
- gives rise to dura mater and the Calvaria/bone
What part of the ectomeninx forms the calvaria bones?
The superficial portion
What does the inner ectomeninx form?
Dura
What does Desmo mean?
Membrane
Define sutures
Mesenchymal gaps between bones of the calvaria, holds together the various bones of the skull
Define fontanelles
Un-ossified suture between 2 or more skull bones
Define Anencephaly
- Calvaria Defect
- Failure of rostral neural tube to close (around week 4), lost of telencephalon)
Define Craniosynostosis
- Calvaria Defect
- Premature fusion of the cranial vault sutures
- Variable defects including deformities of calvaria and neurologic defects
What bones make up the Cranial Base (chondrocranium)?
- Frontal
- Parietal
- parts of the occipital
- Temporal
- Sphenoid bones
How does the chondrocranium form?
Ectomeninx in floor of brain forms cartilage in response to notochord and other epithelial signals, becomes chondrocranium and later undergoes endochondral ossification
What is the embryological tissue that forms the nasal cavity?
The nasal capsule
T/F All of the nasal capsule ossifies
FALSE, Septal cartilage
How does the growth of nasal septal cartilage play a role in facial development?
Plays a role in downward/forward growth of midface
What happens to the maxilla as the chondrocranium grows?
Maxilla and the rest of the facial skeleton get pushed down and forward
Name the bones of the facial skeleton
- Nasal
- Lacrimal
- Maxilla
- Premaxilla
- Palatine
- Vomer
- Mandible
- Zygomatic
Define the Maxilla Proper
Intramembranous ossification of mesenchyme, forms from maxillary prominence/process
Define the premaxilla
Intramembranous ossification of mesenchyme, forms from frontonasal process, forms primary palate, fuses early with maxilla proper
What are the secondary cartilages?
- 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
Describe development and growth of the Maxilla
- 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
How does 2ndary displacement contribute to maxillary development?
Secondary displacement at sutures pushes maxilla down, forward, and out
How do the alveolar plates form?
From the forming maxilla and the junction of the palatal process.
**Alveolar plates house the tooth germs
How does the mandible form?
- Intramembranous ossification
- Bone forms lateral to Meckel’s cartilage
- Ossification spreads posteriorly to form body and ramus
What type of cartilage is meckel’s cartilage?
Hyaline
T/F the bone of the mandible forms from meckel’s cartilage
FALSE, It largely disappears and does not actually become the mandible proper
What secondary cartilages form from Meckel’s cartilage?
- Conylar
- Coronoid
- Symphyseal
Why is the condylar cartilage important?
- 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
T/F the Mandible is both membarnous and endochondral in nature
TRUE, but the cartilage is not Meckel’s, it is secondary
What happens to the coronoid cartilage?
It disappears before birth
What happens to the symphyseal cartilages (2)?
Disappear in the first year after birth.
**They contribute transiently to the growth and development of the surrounding tissues
Where does condyle cartilage function?
Both in articulation at TMJ and in growth
