Quiz 1 - Colombo - Development Of The Craniofacial Skeleton Flashcards
What is bone?
Hydroxyapatite on a collagenous matrix, with various attendant non-collagenous proteins
Enamel lacks the _______ structure, but has hydroxyapatite
Cartilaginous
T/F - Cementum resembles bone.
TRUE
What are the two bone forming processes?
Endochondral - Formed on a cartilage template (long bones)
Intramembranous - 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
Define primary displacement.
Movement of bone due to its own growth
Define secondary displacement.
Movement of a bone due to the growth of other bones
Define remodeling.
Growth involving simultaneous deposition and resorption on all peri- and endosteal surfaces; changes size, shape, proportion, relationship w/ adjacent structures
Define drift.
Remodeling that results in movement of a bone towards the deposition surface
Define functional matrix.
Tissue that guides a bone’s growth by exerting a force upon the bone
T/F - Directional bone growth can occur by the deposition of bone on a surface, with concomitant (same time) resorption on another.
TRUE
*Bones can also get wider this way
How do bones move?
Thru resorption and deposition
*This is primary displacement - the bone doing this to itself
What is secondary displacement?
Growth of one bone causes growth in another
*I.e. distal phalange grows itself (primary displacement), but most of the movement is due to growth of long bones of the arm (secondary displacement)
T/F - Bone growth is not typically equal in all directions, but asymmetric, and this maintains proportion.
TRUE
What is a growth field?
Where matrix can be laid down or resorbed
What is a growth site?
Fields of significance to growth of a bone
What is a growth center?
Special growth sites, control overall growth of bone
*Epiphyseal plates of long bones
What is the neurocranium?
Encases the brain
2 parts:
Calvaria - skull cap
Cranial base - base of skull
Tell me about the calvaria.
Intramembranous bone, not from a cartilaginous model
From paraxial mesoderm and neural crest in origin
ALSO CALLED THE DESMOCRANIUM
Tell me about the cranial base.
ALSO CALLED CHONDROCRANIUM
This is the base of the skull
Derived from organ capsular tissues
Endochondral bone (cartilage template, primarily neural crest)
Tell me about the viscerocranium.
Formed from pharyngeal arches, this makes up our face bones
Nasal Lacrimal Inferior nasal concha Maxilla Mandible Vomer Zygomatic Palatine
T/F - The viscerocranium grows much more postnatally than the desmocranium.
TRUE
What are the bones of the desmocranium (Calvaria)?
Frontal, parietal, parts of: occipital, temporal, sphenoid
*Intramembranous ossification
The inner layer is called what and what does it do?
Endomeninx - neural crest, gives rise to pia mater and arachnoid
The outer layer is called what and what does it do?
Ectomeninx - neural crest and paraxial mesoderm, gives rise to dura mater and the calvaria
- Superficial ectomeninx - ossifies to form the frontal bone, parietal…
- Inner ectomeninx - Remains unossified forms dura
T/F - Condensed mesenchyme forms a bilateral membrane that encapsulates the developing brain.
TRUE
What are sutures?
Mesenchymal gaps b/t bones of the calvaria
What are fontanelles?
Unossified suture b/t 2 or more skull bones
Allow for growth of skull to make room for brain
*Ossification of sutures marks the end of bone growth
What is anencephaly?
Failure of rostral neural tube to close ~week 4, loss of telencephalon
What is craniosynostosis?
Premature fusion of the cranial vault sutures
Ectomeninx in floor of brain forms cartilage in response to notochord and other signals and becomes what?
CHONDROCRANIUM
*Later undergoes endochondral ossification
What is the nasal capsule?
Embryological tissue that forms the nasal cavity
T/F - Growth of nasal septal cartilage plays a role in downward/forward growth of mid face.
TRUE
What is the maxilla proper?
Intramembranous ossification of mesenchyme, forms from maxillary prominence/process
What is the premaxilla?
Intramembranous ossification of mesenchyme, forms from frontonasal process, forms primary palate, fuses early with maxilla proper
What are secondary cartilages?
Zygomatic process, alveolar plate, hard palate b/t palatine processes
T/F - Maxilla forms and grows down and forward using both primary and secondary displacement from growth of zygomatic and nasal septum cartilages.
TRUE
T/F - Secondary displacement at sutures pushes maxilla down, forward, and out.
TRUE
What houses the tooth germs?
Alveolar plates (form alveolar bone ridges, sockets, etc) form from the maxilla and junction of the palatal process
How does the mandible form?
Intramembranous ossification - Bone forms LATERAL to MECKEL’S cartilage (hyaline)
*Not formed from Meckel’s cartilage, it just supports it. It doesn’t become it, that would be endochondral ossification
What happens to meckel’s cartilage?
Disappears anteriorly
What is the condylar cartilage?
Remains on the articular ends on the head of the condyle
*It expands into a cone running along the ramus and ossifies thru endochondral ossification
How does the mandible form?
Intramembranous ossification supported by meckel’s cartilage, except for condylar head, which is endochondral
T/F - Condyle cartilage is an important growth center for the ramus, driving intramembranous ossification, and then ossifies itself thru endochondral ossication.
TRUE
T/F - The coronoid cartilage disappears before birth, and the symphyseal cartilages disappear int he first year of birth.
TRUE
