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11 Cards in this Set

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In general, how are skeletal elements formed?

What is bone patterning and morphology usually influenced by?
condensation of the mesenchyme. this becomes ossified to bone.

influenced by ectoderm of mesodermal structures.
how are the cranial bones divided into groups? do they have different origins? if so what are they?
1)neurocranium - base and roof of the skull. origin from mesenchyme of mesoderm. (not from somitic cells)

2) viscerocranium - facial bones of the face. come from mesechyme of the neural crest cells of the ectoderm. the mesenchyme initially reside in the first and second pharaygneal arches.
what are the two subgroups of neurocranium? how does each of these subgroups become bones?

The visceral cranium has similar group divisions.
1)chondrocranium - they are formed by ossification of cartiligenous regions

2)membranous neurocranium - they form by direct ossification of the mesenchyme. there is no cartilage intermediate.
Describe the formation of the parietal and frontal bones of neurocranium. What is the structure called?

is the neurocranium fully ossified at birth?
they are purely membranous. even at birth they are still ossifying. this is to help the birthing process to be easier.

They are fontanels. prominent ones are located in the front and back.

no.
anecephaly
hydrocephaly
craniosynostosis
-limited amount of neurocranium
-stretching of the neurocranium
-early closure of the fontannels. leads to developmental issues bc not enough room for growth.
What two categories of bones for rest of the skeletal body? where do they arise from?
Axial skeleton - verterbrae, ribs, sternum - arise from schleretome of somites

appendicular skeleton - everything else - arise from lateral plate mesoderm
how is the axial skeleton formed? what gene expression is used and how? What can affect specific times of development and how does it affect it?
It arises from the schleretomal part of somites. Hox genes are responsible. Increasing number of Hox genes from cranial to caudal for vertebral patterning.

Vitamin A or retinoic acid can affect development.
Early exposure causes cranial shift - c7 becomes t1.
late exposure causes caudal shift - l1 becomes t12
klippel feil syndrome

ectopia cordis
reduced number of cervical vertebrae

-heart outside of the body wall due to failure of the sternal bands fusing.
how is each vertebrae formed?
cranial half of one schleretome
caudal half of next schleretome
How do the bones of hte axial and the appendicular form? describe this process.

What happens 5th wk? 6th wk?
What week do the bones fully ossify by?

What is secondary ossification? What is the growth plate?

What bone does not from this method?
endochondral ossification.

1. 5th week, MESENCHYME from lateral plate mesoderm condense along axis of growing limb.

2. 6th wk - CHONDROCYTESin mesenchme differentiate to form -collagen and proteoglycans-ECM ( to make cartilage later)

3. CHONDRIFICATION- make cartilage envelope called PERICHONDRIUM.

4. cells inside peri become OSTEOBLASTS. they form ossification centers. make CALCIUM/PHOSPHATE matrix to put in BONE COLLAR. bones ossify by 12TH WEEK.

5. near birth, DIAPHYSES - long bone shafts.
EPIPHYSES - cartilagenous ends.

6. epipsyses go through secondary ossification at around 20 years.

there is grwoth plate btwn epip and dial which allows dia to keep growing till 20 yrs old.



the clavicle doesn't use this.
how are synovial joints formed?
mesenchyme btwn zones of chondrification differentiate into fiber connective tissue. cartilage is formed next to the bone. between two cartilages, there is CENTRAL zone of connective tissue.

CENTRAL ZONE forms MENISCI, internal ligaments like ANTERIOR CRUCIATE OF KNEE. space develop within central zone to make SYNOVIAL CAVITY that is enclosed by joint cap sue.