Development Of Orofacial Structures Flashcards
What does the cranium develop from?
Mesenchyme around the developing brain
What is the neurocranium?
A bony case that encloses the brain
Two types: Cartilaginous and membranous
What is the viscerocranium?
Bones comprising the facial skeleton
Also has a cartilaginous and membranous type
What are the two processes involved with development of the cranium?
Intramembranous and endochondral ossification
What is intramembranous ossification?
Mesenchyme produces osseous tissue w/o cartilage formation
Mesenchyme condenses and becomes highly vascular
Differentiate into osteoblasts and deposit osteoid -> bone
Osteoblasts become trapped and form osteocytes
What is endochondral ossification?
Bone formation occurs using a pre-existing cartilaginous intermediate (long bones)
Primary ossification centers appear in the diaphysis
Chondrocytes hypertrophy -> matrix becomes calcified -> cells die
Describe the cartilaginous neurocranium
Several cartilages fuse, forming base of cranium (endochondral ossification) Defined order: occipital bone (base) -> body of sphenoid -> ethmoid bone Temporal bone (petrous and mastoid parts)
Describe the membranous neurocranium
Head mesenchyme at the sides and top of the brain
Will form calvaria (frontal and parietal bones) via intramembranous ossification
Interconnected via sutures
Describe the cartilaginous viscerocranium
NCCs form bones and Ct of craniofacial structures
Describe the membranous viscerocranium
Intramembranous ossification within maxillary prominence: squamous temporal (which will become part of the neurocranium), maxillary and zygomatic bones
Cells of mandibular prominence form the mandible
What are examples of craniosynostosis?
Scaphocephaly, brachiocephaly, plagiocephaly, trigonocephaly
Premature closure of a suture
What is scaphocephaly?
Premature closure of sagittal suture -> cranium becomes long, narrow and wedge shaped (50%)
What is brachycephaly?
Premature closure of the coronal suture -> a high, tower like cranium (30%)
What is plagiocephaly?
Premature closure of the coronal (anterior plagiocephaly) or lambdoid (posterior) suture on one side -> cranium is twisted and asymmetrical
What is trigonocephaly?
Premature closure of the frontal (metopic) suture -> malformation of frontal and orbital bones
What does facial development depend on?
Inductive interactions of forebrain, frontonasal region and developing eye
Describe facial primordia
Five facial primordia appear early in week 4 as prominences around the stomodeum
Separated from cavity of primordial pharynx by a bilaminar membrane known as the oropharyngeal membrane that ruptures at ~26 days
What are the different facial prominences?
Maxillary (2), mandibular (2) and frontonasal (1) prominence
When does facial development occur?
During weeks 4-8
Mesenchyme contains active growth centers
Describe the frontonasal prominence (FNP)
Surrounds ventrolateral part of the forebrain
Frontal portion forms forehead
Nasal portion forms rostral boundary of stomodeum and nose
NCC from forebrain and midbrain
Where do the maxillary and mandibular prominences split from?
PA1
What does the maxillary prominences (MXP) form?
Lateral boundaries of stomodeum
Midbrain and hindbrain NCC