Bones of the skull are derived from what developmental layers?
paraxial mesoderm and neural crest cells
Intraembryonic mesoderm...paraxial mesoderm....somitomeres/somites...._________....base of the skull
Specifically, paraxial mesoderm is used to make the ____ and the neural crest cells are used tomake the ______
paraxial mesoderm = base of skull
neural crest = bones of face and rest of skull
Somitomeres 1 through ____ do not develop further into somites, but separate out into the myotome, sclerotome, and _____.
split into the myotome, sclerotome and neuromere
The notochord induces formation of the ______, which induces bone development
What somites contribute along with the somitomeres to the formation of the head?
occipital somites 1-4 (first one appears around day 20)
What is the neurocranium and what is the Viscerocranium. How are they different/
the neurocranium is the brain case (cranial fault and base of skull
the viscerocranium is the face, containing the visceral senses of taste, sight and smell
What does the neurocranium for around?
What does the viscerocranium form around?
neurocranium = aroudn the rostral end of the neural tube
viscerocranium = around the rostral end fo the developing gut tube
What bones of the neurocranium use endochondral ossification and which use intramembranous ossificaiton?
endochondral = the skull base (ethmoid, sphenoid, occipital base, eptrous temporal, temporal, mastoid)
intramembranous = the flat bones of the cranial vault = patietal, frontal, squamous occipital
What foss is the boundary between the bones of the skull base derived from occipital somites and those derived from neural crest cells?
the hypophyseal fossa
Intramembranous ossification in the flat bones occurs in a ___ pattern?
In the viscerocranium, what bones are formed via endochondral ossificaiton and which are intramembranous ossificaiton?
endochondral; the small bones from the pharyngeal arches (malleus, incus, stapes, hyoid, temporal styloid)
Intramembranous: bones of the face (premaxilla, maxilla, zygomatic, temporal, squamous, mandible)
Where do the neural crest cells migrate to where they form mesenchyme for the development of the viscerocranium?
the pharyngeal arches
What are the two things that the dense connective tissue fontanelles allow for?
1. overlap during passage through the birth canal (molding0
2. growth during development
When does the metopic suture begin to close/when is it obliterated/
CLose in year 2
obliterated by year 8
What are the changes in the face largely due to (4 things)
1. growth of the brain and cranial vault
2. growth of the paranasal sinuses
3. eruption of the teeth
4. growth of the mandible
At what age does the posterior fontanelle close to form the lambda?
What causes craniosynstosis?
premature closure of one or more sutures that produces a misshapen skull
What are the 4 types of craniosynostosis?
oxycephaly, turricephaly or acrocephaly
What happens in brachycephaly?
fusion of the coronal suture, producing a shortened front to back diameter of the skull = flat head
What happens on oxycephaly?
fusion of the coronal and lamboidal sutures, producing a "tower skull"
What happens in plagiocephaly?
fusion of coronal and lamboidal sutures UNILATERALLY producing an asymmetrical skull
What happens in scaphocephaly?
fusion of the sagittal suture producing a long front-back diameter of the skull
What is microcephaly? What are some of the potential causes?
microcephaly is an unusually small head due to a brain that fails to grow
causes include NTD, genetic factors, obstructed blod supply to the brain, prenatal exposure to alcohol or drugs, or maternal rubella or chicken pox
What is cranioschisis and what is the cause?
a skull defect through which the meninges and/or brain herniate =
meningocele = meninges
meningoencephalocele: meninges + brain
meningohydroencephalocele = meninges + brain+ ventricle
(most common in occupital region, but can occur in frontal bone)
Describe Apert Syndrome
It's an autosomal dominant genetic disorder characterized by craniosynostosis and other congenital abnormalities like syndactyll and mental retardation
mutation of the fibrlblast growth factor receptor 1 and 2
Crouzon Syndrome and Pfeiffer Syndrome are similar to apert syndrome, but what makes them each different?
Crouson lacks the syndactyly
Pfeiffer has eyes that bulge out due to lack of space int he cranium and the great toes and thumbs are wide and deviated
What is acrania? What is anencephaly? What is meroanencephaly?
acrania - no skull
anencephaly - no brain
meroanencephaly - some poorly formed brain stem tissue present
What causes anencephaly?
the neural folds fail to elevate and fuse
the cranial neuropore stays open
the brain tissue that's there degenerates in response to the exposure to amniotic fluid