Development of the Skeleton Flashcards
What determines the primary center for ossification?
What determines the secondary center for ossification?
Where the blood vessels invade the dying cartilage (diaphysis)
this process repeats later, at both ends of the developing bone, forming the secondary center for ossification (epiphysis)
What is the name of the segmental blocks formed by paraxial mesoderm? At what level does this begin?
somites
8th pair of somitomere (pairs 1-7 don’t develop into somites)
What direction does the somite differentiate? What layers does it form?
medial to lateral
sclerotome (skeleton), syndetome (connective tissue elements), myotome (apendicular and axial muscle), dermomytome (skin)
What is the difference between the cranial and caudal apects of the scletorome?
What happens to these 2 portions?
What are the two major impact this process has on development?
crainal = low density
caudal = high density
the two halves rip apart, and refuse with the segment immediately inferior or superior
spinal nerves line up along this fracture plane, now the spinal nerves come out between the blocks
by rearranging the bone, the muscles work across a joint
What is unique about the development of the first scherotome segment?
The low density cranial portion does not have a caudal portion to fuse with, so it fuses with the skull to produce the inferior portion of the occipital bone
How doe vertebrae progressively form bone?
Where are the sites of ossification?
first form as mesenchyme, then cartilage, finally bone
firght in middle of centrum, and one close to the middle of neural arch
What structures form the precursor for the outer shell (annulus fibrosis) of the intervertebral disc?
What is the precursor for the rest of the intervertebral disc?
leftover portion of the cranial/caudal separation
notochord left in the middle will form the nucleus pulposous (rest of intervertebral disc)
What is the term for dorsally directed curvature?
Is this present in the fetus?
What is the name for ventrally directed cruvature?
Is this present in the fetus?
Kyphosis: thoracic adn sacral segments– yes are present during fetal development
Lordosis: cervical and lumbar– no, they form when infant starts to lift their head and when the infant starts walking
What type of bone formation occurs when neural crest cells differentiate into mesenchyme, then to chrondroblasts?
Endochondral Ossification
What is formed form the brachial pathway of neural crest cells?
formation of the brachial (pharyngeal) arches
these form the viscerocranium (maxilla and mandible)
What type of ossification occurs by somitomeres and otehr paraxial mesoderm?
Endochondral Ossification
differentiate into mesenchyme, which in turn forms chondroblasts that form a cartilage “model” for bone
What is the difference in oragni between the blue and red bone?
What is the name for this area of the skull?
blue: neural crest derived (prechordal chondrocranium)
red: paraxial mesoderm (chordal chondrocranium)
chondrocranium
The bones shown in the image were formed through what type of ossification?
Where is the blue portion derived from? Where is the brown portion derived from?
Which forms faster?
intermenbranous ossification
blue: neural crest derived
brown: non neural crest derived
nerual crest portion forms faster
What 4 structures undergo endochondral ossification?
What 2 structures undergo intermenbranous ossification?
- endochondral ossification
- parietal lateral plate
- somite / scherotome
- somitomere / paraxial mesoderm
- neural crest cells
- intermembranous ossification
- somitomere / paraxial mesoderm
- neural crest cells
What is the term for the space between bone in an embryo?
interzone– precursor for
What is the general term for abnormal timing/closure of cranial sutures?
At what location is this most common?
craniosynestosis
different types of embryonic development meet
What is the name of the condition where the joints seal in with connective tissue?
Arthrogyposis
All bones form as normal, don’t get the joint tissue in between
Identify the types of problems that can occur with development of the vertebrae. Failure of what process is responsible for each type?
What can occur if the zones of ossification located in the neural arch do not fuse with the centrum (no pedicle formation)?
Where is this most common?
Congenital Spondylolisthesis
most common at L4 of L5, great tendency to displace
What disorder occurs when primary centers of ossification fuse with centrum but do not fuse with each other in the midline?
What are the 3 classifications shown in the image?
Spina bifida
