Development of the Craniofacial Skeleton Flashcards
what is bone made of?
hydroxyapatite formed on a collagenous matrix, with various attendant non-collagenous proteins
endochondral bone
bone that is formed on a cartilage template
eg: long bones
intramembranous bone
bone that is formed from a condensation of mesenchyme
eg: most of mandible, skull plates
initiation
start of ossification, whether conversion of cartilage to bone, or condensation and ossification of mesenchyme/neural crest
growth
addition of more bony matrix to a pre-existing bone; thickening, elongation
primary displacement
movement of a bone due to its own growth
secondary displacement
movement of done due to growth of other bones
remodeling
growth involving simultaneous deposition and resorption on all peri and endosteal surfaces; changes size, shape, proportion, relationship with adjacent structures
drift
remodeling that results in movement of a bone towards the deposition surface
functional martix
a tissue that guides a bones growth by exerting a force upon the bone
bone growth can occur in either direction, it just depends on what?
the ratio of resorption to deposition and other structures
growth fields
where matrix can be laid down or resorbed
growth sites
fields of significance to growth of a bone
eg: mandibular condyle, maxillary tuberosity
growth centers
special growth sites, control overall growth of bone(epiphyseal plates of long bones)
what is considered the neuroncranium?
the brain pan( basically the bones encasing the brain)
neuroncranium: calvaria
skull cap
*intramembranous bone
*paraxial mesoderm and neural crest origin
also called the desmocranium
neurocranium: cranial base
the base of the skull
- *endochondral bone, primarily neural crest
- early form called chondrocranium
what is the viscerocranium?
the facial skeleton
what is the viscerocranium derived from
pharyngeal arches
what part of the skull grows more postnatally?
viscerocranium more than the desmocranium
what bones make up the calvaria aka the desmocranium?
frontal, parietal, parts of occipital, temporal, sphenoid bones
**remember it is form intramembranously
what is the endomeninx?
the inner layer of the calvaria,
-made of neural crest, and gives rise to pia mater and arachnoid mater
what is the ectomeninx?
outer layer of the calvaria
-made from neural crest and paraxial mesoderm, and gives rise to the dura mater and the calvaria/bone
sutures
mesenchymal gaps between bones of calvaria
fontanelles
un-ossified suture between 2 or more skull bones
what marks the end of bone growth of the calvaria
ossification of sutures
what is anencephaly?
failure of rostral neural tube to close
*results in the loss of telencephalon
what is craniosynostosis
premature fusion of the cranial vault sutures
bones of the cranial base aka chondrocranium
frontal, parietal, parts of occipital, temporal, and sphenoid bones
why does the chondrocranium form via endochondrial ossification and not intramembranous ossification?
ectomeninx in floor of brain forms cartilage in response to notochord and other epithelial signals, becomes chondrocranium, later undergoes endochondral ossification
what is the embryological tissue that forms the nasal cavity?
nasal capsule
what part of the nasal capsule does not ossify?
the nasal septal cartilage, this plays a large role in the downward/ forward growth of midface
what happens as the chondrocranium grows?
it pushes the maxilla and the rest of the facial skeleton down and forward
maxilla proper
intramembranous ossification of mesenchyme, forms from maxillary prominence/process
premaxilla
intramembranous ossification of mesenchyme, forms from frontonasal process, forms primary palate, fuses with maxilla proper
secondary cartilages
zygomatic process, alveolar plate, hard palate between palatine processes-mostly fetal growth roles
the ossification center of the maxilla is associated with what cartilages?
nasal capsule
zygomatic or malar cartilage
the alveolar plates form from what?
the forming maxilla and the junction of the palatal process and houses the tooth germs
the maxilla forms and grows down and forward via?
primary and secondary displacement from the growth of the zygomatic and nasal septum cartilages
how does the mandible form in terms of bone growth
intramembranous ossification
**forms lateral to Meckel’s cartilage (hyaline)
what is the direction of ossification spread of the mandible?
posteriorly to form the body and ramus
anteriorly Meckel’s cartilage largely disappears and does not become the mandible proper
what are the secondary cartilages that form from Meckel’s cartilage?
condylar, coronoid, and symphyseal
why is the condylar cartilage important?
it extends into a cone running along the ramus and ossifies through endochondral ossification.
*condylar cartilage remains at the articular ends on the head
T/F the mandible is both membranous and endochondral in nature?
true
the cartilage of the mandible is not primary (Meckel’s) it is what kind?
secondary (derivatives)
coronoid cartilage
disappears before birth, contribute -transiently to growth and development of the surround tissues
symphyseal cartilages
disappear in the first year of birth
-transiently to growth and development of the surround tissues
Condyle cartilage
important growth center for the ramus
does intramembranous ossification and then ossifies itself through endochondral ossification
* functions both in articulation at TMJ and in growth
