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Basics of Craniofacial development
Cole 6/6/11 lecture 2.5 hrs
113
Anatomy
Undergraduate 4
06/06/2011

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Term
skull
Definition
name for the entire head skeleton
Term
cranium
Definition
the skull without the mandible
Term
calvaria
Definition
the skull minus the facial skelton
Term
brain
Definition
the neurocranium and basicranium enclose the
Term
neurocranium
Definition
covers the brain from above, front, and back on both sides, also supports the brain from beneath a little(in front and back)
Term
basicranium
Definition
part of the skull that mainly supports the brain from beneath
Term
intramembranous ossification
Definition
how does the bone of the neurocranium form?
Term
endochondral ossification
Definition
how does the bone of the basicranium form?
Term
mesoderm (and a small bit of neural crest)
Definition
what embryonic tissue makes up the basicranium?
Term
a mixture of mesoderm and neural crest cells
Definition
what embryonic tissue makes up the neurocranium?
Term
viscerocranium, splanchnocranium
Definition
what are the 2 other names for the facial skeleton
Term
intramembranous ossification
Definition
how do the bones of the face form?
Term
entirely neural crest
Definition
what embryonic tissue makes up the face?
Term
the capsule -> both mesoderm and neural crest cells (there is a potential space between the brain and capsule)
Definition
as the brain is developing, what is the first skull precursor structure that forms around the developing brain? what embryonic tissue forms this structure?
Term
2 layers: endomeninx, and ectomeninx
(there is a potential space between the 2 layers)
Definition
what does the capsule (skull pre-cursor) differentiate into?
Term
endo is closer to the brain, so neural crest cells

ectomeninx becomes the skull which forms from both mesoderm and neural crest cells
Definition
what embryonic tissues make up the endomeninx? the ectomeninx?
Term
each divides into 2 layers
Definition
what is the next step of development after the ecto/endo meninx form?
Term
the internal layer contacts the brain -> pia mater

the outer layer of endomeninx -> arachnoid mater

both neural crest
Definition
what do the 2 layers of the endomeninx form?
Term
the inner layer becomes the dura mater, made mostly of mesoderm (with a little neural crest maybe)

the outer layer is both neural crest and mesoderm and becomes the bones of the membranous neurocranium
Definition
what do the 2 layers of the ectomeninx form?
Term
multiple because it does intramembranous ossification, and there are multiple bones
Definition
how many ossification centers does the neurocranium have?
Term
the tissue starts as the generalized embryonic precursor "loose mesenchyme" -the identical stellate shaped cells separated by a lot of ECM
Definition
what is the starting (embryonic)material for intramembranous ossification?
Term
it becomes condensed mesenchyme as it organizes into layers and elongates into sheets, the extra-cellular spaces are reduced
Definition
what happens in intramembranouse ossification to the loose mesenchyme (what does it do?)
Term
membrane formation -> the extracellular spaces are filled with collagen
Definition
what is the 3rd step in intramembranous ossification?
Term
islands of mesenchymal cells become osteoprogenitor cells which turn into osteoblasts(secrete osteoid which mineralizes) and osteoclasts
Definition
after the extracelluar space begins to fill with collagen, what happens in intramembranous ossification to the cells?
Term
osteoblasts at the periphery expand the bone
Definition
how does the bone grow once the osteoprogenitor cells are trapped in the centers of the bony islands(now called osteocytes) in intramembranouse ossification?
Term
it is spongy, and makes spicules that radiate from the center outward (these rays are visible in fetal skulls that are not fully ossified)
Definition
what is the newly formed bone at the ossification center of intramembranous ossification like?
Term
sutures
Definition
a strip of CT that keeps bones from separate ossification centers from growing together
Term
suture
Definition
a craniofacial articulation in which contiguous margins of bone approximate each other and are united by a thin layer of fibrous tissue
Term
not entirely, they allow molding of the skull, or deformation of the neurcranium to facillitate birth
Definition
are sutures immobile?
Term
1) allow modling of skull for birth
2) allow pre-natal and post-natal bone growth
Definition
name 2 the functions of sutures
Term
calvarial
Definition
______ molding during bith keeps bones from fracturing, but can cause the baby to have a cone head temporarily
Term
sutures
Definition
as neurocranial bones expand these are the site of new bown formation
Term
sutures widths are maintained
Definition
the rate of bone formation at the argins keeps pace with the expanding brain, what does this mean?
Term
to protect the brain
Definition
why must sutures remain narrow?
Term
remodeling:

there must be DEPOSITION on the OUTER surfaces and

RESORPTION of the bones INNER surfaces to flatten the bones and conform to the brians contours

there is more resorption/deposition on the margins of the bone than the centers
Definition
its not enough to add new bone at the margins for the skull to grow, something else must be done to fix the curvature of neurocranial bones, what?
Term
1) loose mesenchyme makes a model
2) becomes dense mesenchyme
3) chrondrocytes form a hyaline cartilage model
4) cartilage model is replaced by bone

*this is used for long bones and the basicranium
Definition
describe the steps in endochrndral ossification
Term
one at the center(diaphysis) then the ossification spreads bidirectionallr to the ends toward the epiphysis
Definition
how many centers of ossificaiton are in endochondral ossification?
Term
synchondroses
Definition
regions of the chondrocranium that do not ossify initially and persist as cartilaginous zones between bones(analogous to growth plates in long bones)
Term
between the sphenoid and the occipital bone(basilar part)

aka the sphenobasilar synchondrosis
Definition
what is the most important/primary site of postnatal growth in the cranial base?
Term
the first is the frontalethmoidsphenoid (FES) at age 6-7

they proceed to close anterioposterior until the final one the sphenobasilar/basoccipital closes age 19-21
Definition
which of the synchondroses in the skull fuse first? last?
Term
anteroposterior
Definition
what is the primary direction of growth for the cranial base with age?
Term
Definition
the primary site of postnatal growth in the cranial base
Term
when the genes are on they inhibit bone growth(to prevent ossification of the synchondrosis)

when turned off(from front to back), the synchodroses fuse and close so there is no more growth
Definition
what do the hedgehog genes (sonic/indian/desert) do to the synchondroses?
Term
it grows in the middle where the hyaline cartilage is and pushes the bone out on both sides
Definition
on what side of the synchondrosis does the growth occur?
Term
1) resting zone (normal hyaline cartilage)
2) proilferative zone (chondrocytes divide and stack up, pushing the bone)
3) hypertrophic zone (chondrocytes swell and the ECM is reduced)
4) zone of degeneration (chondrocytes die & remaining matrix begins to calcify)
5) ossificaiton zone ( osteoprogenitor cells and capillaries move into the spaces left by the dead chondrocytes, then diferentiate into osteoblasts which begin to form bone
Definition
name the zones going out from the hyaline carilage in a syncondrosis!
Term
they thought that the bones are under strict genetic control, and the cells have intrinsic info about what they should look like (not a lot of evidence of this)
Definition
what was the theory on skull development in the 40s-60s?
Term
1950s-70s, it says that:
- skull bones have no intrinsic genetic info
- bne is a passive material that conforms to the shape/size of surrounding structures
- the direct genetic control is in the tissue bone forms around, so bone form is determined epigenetically (by crap around it)
Definition
when did functional matrix theory come about? what is it?
Term
functional matrix theory
Definition
the neurocranium forms around the shape of the brain represents what theory in brain development?
Term
microcephaly, supports functional matrix theory -> no excess space in the endocranial cavity, only large enough to cover the brain.
Definition
this nervous system defect causes the brain to be undersized and thus the skull to be undersized as well. Name the disorder and they theory it supports
Term
microphthalmia
Definition
med term from too small eyeball
Term
anopthalmia
Definition
med term for congenitally absent eyeball
Term
it is also too small, supporting functional matrix theory
Definition
if the eyeball is too small, or not present, what happens to the orbit?
Term
hydrocephaly
Definition
results form an abnormal accumulation of cerebrospinous fluid within or around the brain
Term
it increases in response so that the brain remains covered and protected, but the sutures are wide because it can't quite keep up
Definition
when the volume of endocranial contents increase, what happens to the growth of the neurocranial bone?
Term
ultrasound imaging
Definition
how can hydrocephaly be diagnosed prenatally?
Term
they are also absent -anencephaly
Definition
neural defect causing absence of the brain due to the anterior neuropore not closing. what happens to the skull and meninges? name the disorder
Term
hydrancephaly
Definition
possibly due to a interruption in arterial blood supply to the brain, the cerebrum is nearly absent in this disorder.
Term
it might form normally and give a normal looking baby, the space filling with CSF



this means that the meninges are probably important for determining skull form
Definition
if there is hydrancephaly after the meninges differentiated, what happens to the neurocranium? what does this mean?
Term
bone remodels in response to external physical forces
Definition
describe Wolff's law
Term
Wolff's law
Definition
application of normal forces on bone (such as from muscle) are necessary for the skeleton to maintain proper form. Also the physical presence of other tissue (teeth in their sockets) maintains the socket. Application of abnormal forces causes bone to resorb. What law is this?
Term
orthodontia & helmets to treat neurocranial deformations
Definition
deliberately chanign the shape of bone by applying controlled forces to it is the basis of what?
Term
their mandible (and other bones) do not form properly without muscle pulling them

(a nerve lesion/muscle removal acts similarly)
Definition
what happens in mice if they have a muscular dysgenesis mutation disrupting muscle development?
Term
it fills in, no more tissue blocking it, so the bone remodels
Definition
when teeth are lost what happens to the tooth socket?
Term
the transplantation studies with avian/amphibian embryos, also IHC with mammals
Definition
what evidence supports the idea that there is intrinsic genetic control of bone development?
Term
Bombinator the toad and Triturus the newt
Definition
name the animals important to the hertotopic transplant studies performed in the 40's(1959?) that support the strict genetic control theory
Term
heterotopic transplant studies
Definition
this type of study puts tissue from a donor embryo of one species into the corresponding position of a host. the host embryo is premitted to grow and develop further to see what happens in the transplanted tissue
Term
it was more toad-like than newt-like, but there is clearly BOTH enviromental and genetic factors determining facial bone development contained in the neural crest cells
Definition
what happened to the toad jaw on the newt and what did it show?
Term
1) paraxial mesoderm
2) cephalic neural crest
Definition
name the 2 sources of skull bones (embryonic tissue)
Term
1) somitomeres from prechordal mesoderm (7 pairs)
2) occipital somites (4 pairs)
Definition
the head muscles come frome 2 sources of paraxial mesoderm, name them
Term
muscle and bone, initially only comes from occipital somites and other paraxial condensations (Somitomeres)
Definition
what does paraxial mesoderm become in the head? where is it from initially?
Term
somitomeres (7 pairs) becomes a lot of the head musculature (muscle and dermis only, no bone)
Definition
partially segmented prechordal mesoderm that forms most of the head (like somites but still connected)
Term
bone, skeletal muscle, dermis (like normal somites)
Definition
occipital somites are cranial to the cervical somites, what do they give rise to?
Term
somites, not mesoderm (direct quote from T Cole 26 min after the break in the 1st lecture)
Definition
mesoderm derived bone in the head comes only from where?
Term
either side,

comes from ectoderm of both types (neurectoderm and surface ectoderm)
Definition
where are neural crest cells found in relation to the neural tube? what tissue does it come from?
Term
pluripotent, does a lot of tissue types, but not all
Definition
are neural crest cells omnipotent, pluripotent, or totipotent?
Term
they act like mesoderm and become cartilage and bone (indistinguishable physiologically and histologically)
Definition
what is special about cephalic neural crest cells?
Term
once they have migrated to their destination, they are undifferentiated at the point of origin
Definition
when do neural crest cells differentiate?
Term
It starts in the CNS with the segmentation of the BRAIN, this drives other structures to segment, and establishes the paths of neural crest migration
Definition
where does segementation of the embryo start? why is this important?
Term
forebrain, midbrain, hindbrain
Definition
name the first 3 parts of the brain that segment
Term
1) telencephalon
2) diencephalon
3) mesencephalon
4) metencephalon
5) myelencephalon
Definition
name the parts of the brain when it forms 5 segments
Term
4 protorhombomeres segment into 7 rhombomeres
Definition
the hindbrain first segments into 4 ______ 's then these divide into 7 _______
Term
hindbrain
Definition
what brain segment gives rise to the brainstem?
Term
HOX genes, except the first rhombomere (R1)
Definition
how does the hindbrain know to make rhombomeres?
Term
no, they are expressed in waves of different combinations which correspond to the formation of different rhombomeres, or vertebrae etc (which then go to influence other stuff)
Definition
do hox genes have continuos actions?
Term
1) posterior midbrain + R1 + R2
2) R4
3) R6
4) R7
Definition
where does neural crest streams come from(specifically) to form the first 4 branchial arches?
Term
not in humans, it dissapears
Definition
is there a 5th branchial arch?
Term
R3, R5 they contain the inhibitory Bmp4 gene
Definition
which rhombomeres do not give rise to neural crest cells? what do they do?
Term
BMP4
Definition
a bone morphogenetic protein helps to keep the streams of migrating neural crest cells separate, by inhibiting nueral crest cells from leaving specific rhombomeres; name it
Term
streams
Definition
neural crest cells migrate in ___ not sheets
Term
cranial nerves
Definition
somitomeres of paraxial mesoderm alongside the brain is also segmented, and patterned so that ___ can innervate them
Term
occipital somites
Definition
what gives rise to the mesoderm in the basicranium and neuocranium?
Term
if you transplant tissue from the japanese quail (say neural crest) it will develop into the corresponding neural crest derrived parts, and the quail cells are pigmented, so it is easy to see what comes from where (neural crest vs mesoderm)
Definition
what is special about chicken/japonese quail chimeras (surgically transplanted cells)?
Term
we use transgenic mice with special blue staining transgenes (X-gal staining for beta galactosidase)
Definition
how do we tell what develops from neural crest cells now?
Term
chordal: is primarily mesoderm
pre-chordal: is primarily neural crest

alongside the notochord is occipital somites
Definition
what is the chordal skeleton developed from? the prechordal skeleton?
Term
caudal: paraxial mesoderm, cranial: neural crest
Definition
bone caudal to the end of the notochord is made of ______, cranial to the end of the notochord is made of _____
Term
Treacher-Collins Syndrome
Definition
a syndrome that involves deficient development of the facial skeleton
Term
the affected bones all develop from neural crest cells n the 1st and 2nd branchial arches
Definition
what branchial arches are the deficient neural crest cells from in Treacher-collins?
Term
micrgnathia
Definition
med term for small mandible
Term
treacher-collins
Definition
clinical observations include micrognathia, undersized midface, and very undersized or absent zygomatic bones resulting in lateral orbital clefts, may see inferolaterally slanting eyes, deformed external and middle ears
Term
1) sufficient number of cells in the initial condensation prior to migration
2) pre-migration condensation must occur at the right time
3) rate of cell division(mitosis) in migrating cells have to be correct
4) the correct proportion of cells need to be mitotically active
5) apoptosis has to occur at the proper time and the proper rate
Definition
to get a normal facial structure ,what 5 things have to go right?
Term
mutation in TCOF1, cosed for treacle protein

prevents pre-mature apoptosis of neural crest cells before migration
Definition
what gene mutation cause treacher-colins? what protein does it code for, and what does this protein do?
Term
insufficient number of neural crest cells to begin with (they die too soon with mutated treacle)
Definition
what prevents normal facial structure in treacher-collins?
Term
we compared mice mutants and their mandibles
Definition
how do we know about the TCOF1 gene?
Term
holoprosencephaly
Definition
what problem is suspected to be caused by signaling problems between mesoderm and neurectoderm?
Term
mesoderm
Definition
the notochord is derived from _____ and signals back to the nervous system to tell it to develop
Term
holoprosencephaly
Definition
a condition when the cerebral hemispheres fail to separate, possibly the eyes, and other midline facial structures because the notochord isn't causing proper nervous system development
Term
1) anosmia (normal, no sense of smell)
2) single central incisor
3) cleft lip/palate
4) midline facial clefts
5) cebucephaly
6) proboscis
7) synopthalmia
8) cyclopia
Definition
describe the degrees of expression of the holoprosencephaly sequence from the most minor problems to the most severe.
Term
the prechordal plate
Definition
signals from MESODERM of the _____ to neurectoderm(ex: the forebrain) are essential for proper brain and eye development
Term
the eyes are outgrowths of the CNS, so the splitting of the CNS into 2
Definition
how do you get 2 eyes?
Term
Definition
what is the main gene telling the
Term
a piece of tissue is in the wrong spot and they have no eyes
Definition
what is synopthalmia with a proboscis?
Term
cebocephaly
Definition
close set eyes and a small nose with a single nostril would be called _____
Term
cebocephaly is a basicranium problem
Definition
when the brain does not signal the basocranium properly, what condition results that's part of holoprosencephaly?
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