Ebryology

Front 1

mesoderm derived tissue along the axis of the embryo resposible for forming somites (caudally from head region) and somiteres (in head region) on each side of the neural tube. The skeletal system develops from here.

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Paraxial plate mesoderm (somatic layer)

Front 2

mesoderm derived tissue that splits into splanchnopleure (visceral) and somatopleure (somatic) layers surrounding organs and body cavity. the skeletal system develops from here.

Back 2

lateral plate mesoderm (somatic layer)

Front 3

early neuroepithelial embryonic development, the cells of which migrate and differenciate into various cell types. These cells are vulnerable to teratogenic insult. The skeletal system develops from here.

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Neural Crest

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somites and somiteres develop in ...

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segments

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loosely organized segmented collections of paraxial mesoderm in the cranial region. _____ form muscles and bones in the face and skull

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somitomeres

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epithelial balls of cells formed in segmental pairs along the neural tube from paraxial mesoderm. _____differentiate into vertebrae, muscles of the back and body wall and dermis of the skin and parts of the cranium.

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somites

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ventromedial part of each somite that forms the vertebrae

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sclerotome

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dorsolateral development of each somite

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dermomyotome

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any loosely organized tissue composed of fibroblast-like cells and extracellular matrix regardless of the origin of the cells. These cells migrate and differentiate into many cell types (fibroblasts, osteoblasts, chondroblasts..etc). Also known as embryonic connective tissue.

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mesenchyme

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bone forming cells

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osteoblasts

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process of mesenchyme directly differentiating into bone, seen in the flat bones of the cranium

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Intramembranous ossification

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occur a six weeks of gestation. mesenchymal cells usually develop cartilage models before forming bone via endrochondral ossification

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hyaline cartilage models

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mechanism for forming bone by first establishing a carlaginous model followed by ossification. This type of bone formation is characteristic of the bones of the limbs and base of the skull

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endochondral ossification

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part of the skull that forms a protective case around the brain (the other part of the skull is the viscerocranium or face). It consists of two parts, the membranous neurocranium, or flat bones of the skull and the cartilaginous neurocranium or chondrocranium, forming the base of the skull.

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neurocranium

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forms from paraxial mesoderm and neural crest cells. These cells form the cranium via membranous ossification

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membranous neurocranium

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part of the skull that comprises the bones of the face

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viscerocranium

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consist of a layer of spongy bone between two thin layers of compact bone.have marrow, but not a bone marrow cavity. They form protective cases for viscera.

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flat bones

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part of the neurocranium that forms the base of the skull and that arises by first establishing cartilage models for the bones (endochondral ossification)

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chondrocranium

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process of forming bone directly from mesenchyme. This process is characteristic of the flat bones and the cranial vault.

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membranous ossification

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found on the flat bones which result from membranous ossification in skull region. The ______progressively radiate out from ossification centers.

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bone spicules

Front 21

narrow seams of connective tissue, which separate the flat bones of the skull at birth.

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sutures

Front 22

points at which more than two flat bones meet and the resulting sutures are wide.

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Fontanelles

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most prominent fontanelle found on newborn. Found where two parietal bones meet two frontal bones

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anterior fontanelle

Front 24

process of overlapping of flat bones during birth, possible due to the sutures

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molding

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cartilages which are precursors to base of skull found anterior to future sella turcica. Develops from neural crest cells

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prechordal chondrocranium

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cartilages which are precursors to the base of the skull found posterior to the future sella turica. Develops from the paraxial nesoderm.

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chordal chondrocranium

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portion of a dorsal pharyngeal arch which forms a portion of the viscerocranium: maxilla, zygomatic bone and part of the temporal bone.

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maxillary process

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lower jaw bone

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maxilla

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portion of a ventral pharyngeal arch which containes the Meckel cartilage. Dorsal tip also gies rise to the incus, malleus and stapes.

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mandibular process

Front 30

ossifies via membranous ossification and forms the mandible. It disappears except in the sphenomandibular ligament.

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mechel cartilage

Front 31

develop much of the face and skull. Originate from the neuroectoderm.

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neural crest cells

Front 32

cells of the neuroepithelium that form the tips of the neural folds and then migrate to other regions for form many structures, including spinal ganglia, bones and connective tissue of the face, septa for the outflow of tract of the heart, some cranial nerve ganglia, ganglia for the gut tube (enteric ganglia), melanocytes, etc…. These cells are vulnerable to teratogenic insult and provide a rational for why many children with facial clefts also have cardiac defects.

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neural crest cells

Front 33

cranial vault does not close, so brain tissue is exposed to brain fluid, which degenerates it. The result is anencephaly.

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Cranioschisis

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Neural tube defect in which the cranial folds fail to close, leading to tissue degeneration and little or no formation of higher brain centers, cerebral cortex…etc. The abnormality is lethal, 70% of these defects can be prevented by daily maternal use of 400ug of folic acid, beginning 2-3 months prior to conception and continueing throughout pregnancy.

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Anencephaly

Front 35

neural tube defect in which a sac of fluid filled meninges protrudes through an opening in the skull. This is treatable.

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Cranial meningocele

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collection of abnormalities, in which sutures close prematurely.

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Craniosynostosis

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f the saggital suture closes prematurely and the parietal and occipital bone become long and narrow

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Scaphocephaly

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premature closure of coronal suture results in a short, high skull.

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Acrocephaly (Tower skull)

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premature closure of lamboid and coronal sutures, which results in short skull

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Brachycephaly

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derived from paraxial mesodermal germ layer, which forms from the somites and somitomeres

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Skeletal muscle

Front 41

most is derived from the paraxial mesodermal germ layer. ______develops from splanchnic mesoderm and from ectoderm

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smooth muscle

Front 42

derived from splanchnic mesoderm (surrounding the heart tube), as well

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cardiac muscle

Front 43

mesoderm derived tissue along the axis of the embryo responsible for forming somites and somitomeres.

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paraxial mesoderm

Front 44

site of muscle formation, cells from here contribute to myotome formation. Also provides cells for limb and body wall formation

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Ventrolateral edge or lip (VLL) of dermomyotome

Front 45

musculature derived from the dorsolateral portion of each somite that forms muscles of the anterior body wall

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Hypomeric musculature

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second region of muscle formation; cells travel ventral and contribute to the formation of myotome

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Dorsomedial edge or lip (DML) of the dermomyotome

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dorsal musculature derived from the myotome portion of each somite that forms the extensor muscles of the back

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Epimeric musculature

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muscle forming cells. Fuse to make multinucleated muscle tissue

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myoblasts

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derived from sclerotome cells adjacent to myotomes at the ant/post borders of the somites

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tendons

Front 50

regulates the development of sclerotome cells adjacent to myotomes

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scleraxis

Front 51

at the end of the fifth week prospective muscle is either here or in the hypomere; the ____is in the dorsal region; this is formed by the dorsomedial somite cells of myotomes

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epimere

Front 52

this is larger and in the ventral region, formed by migration of the dorsolateral cells. Gives rise to muscles of limbs and body wall

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hypomere

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branch of a spinal nerve that innervates muscles derived from the epimere and skin over the back

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dorsal primary ramus

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ventral branch of a spinal nerve that innervates muscles derived from the hypomere and skin over the anterior body wall and limbs.

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ventral primary ramus

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formed by myoblasts of the epimere

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extensor muscle