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Questions and Answers
Which structure serves as the central axis of the embryo, dividing it between right and left?
During neurulation, what occurs when the neural plate invaginates to form the neural groove?
What is the function of the notochord in embryonic development?
Which structure is obliterated after the notochord is fully developed?
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What is the significance of the prechordal plate in development?
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What is the significance of the closure of neuropores during neurulation?
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During spinal cord development, which zone gives rise to all neurons and macroglia?
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What is the function of ependymal cells in spinal cord development?
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Where do cell bodies in the alar plates of the developing spinal cord form?
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From which structure are the unipolar neurons in the spinal ganglia derived?
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Which of the following structures does NOT arise from the intraembryonic mesoderm?
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What is the primary function of the notochordal process during embryonic development?
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Which of the following pairs correctly matches the embryonic structure with its derivative?
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What is the correct sequence of events leading to the formation of the intraembryonic coelom?
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During the second month of embryonic development, which of the following cavities does NOT develop from the intraembryonic coelom?
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What induces the thickening of the embryonic ectoderm to form the neural plate?
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What does the fusion of neural folds form in the process of neurulation?
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Which part of the embryo condenses to form longitudinal columns of paraxial mesoderm?
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Where do the blood vessels first appear in the embryo?
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From which precursors do fetal and adult erythrocytes develop?
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What is the primary role of the notochordal process during neurulation?
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Which germ layer gives rise to the structures like connective tissue, heart, and blood vessels?
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What role does the somatopleure play during lateral folding in embryonic development?
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Which structure separates the abdominal cavity from the thoracic cavity during cranial folding?
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What is the role of the splanchnopleure in embryonic development?
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Which of the following is NOT a role of the notochord?
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What is the correct sequence of events in the development of the notochord?
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What is the significance of the neurenteric canal in early embryonic development?
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What is the term used to describe the process of the notochordal process developing a lumen?
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Which of the following structures is NOT derived from the somatopleure or splanchnopleure?
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What is the initial event that marks the beginning of gastrulation?
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Which of the following statements about the primitive streak is correct?
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Which germ layer is formed by the invagination of epiblastic cells from the primitive streak?
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What is the term used to describe the epiblast after the primitive streak begins to produce mesenchymal cells?
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Which germ layer is formed by the displacement of the hypoblast by cells from the epiblast?
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What structure is formed by the mesenchymal cells from the primitive streak during the early third week of development?
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What is the primordial axis around which the axial skeleton forms?
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Which of the following structures is involved in the formation of the notochord?
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What is the term used to describe the mesoderm that covers the amnion and umbilical vesicle?
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Which of the following statements about neurulation is correct?
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Study Notes
Neurulation, Folding, and Development of the Nervous System
Week 3: The Notochord
- Establishes the longitudinal axis of the embryo and gives it some rigidity
- Provides signals for the development of axial MSK structures and the CNS
- Contributes to the intervertebral discs
- Develops from mesenchymal cells that migrate cephalad and form a cord called the notochordal process
- The notochordal process develops a lumen known as the notochordal canal
- The notochordal process approaches the prechordal plate, and the floor of the process "fuses" with the endoderm
- The notochordal process is now the notochordal plate
- The notochordal plate cells proliferate and fold inwards, forming the fully-developed notochord with no canal
Gastrulation and Formation of Germ Layers
- The primitive streak appears at the beginning of the third week as a thickening of the epiblast at the caudal end of the embryonic disc
- The primitive streak results from the migration of epiblastic cells to the median plane of the disc
- Invagination of epiblastic cells from the primitive streak gives rise to mesenchymal cells that migrate ventrally, laterally, and cranially between the epiblast and hypoblast
- The epiblast is now known as embryonic ectoderm
- Some cells of the epiblast displace the hypoblast and form embryonic endoderm
- Mesenchymal cells produced by the primitive streak soon organize into a third germ layer, the intraembryonic or embryonic mesoderm
- Cells of the mesoderm migrate to the edges of the embryonic disc, where they join the extraembryonic mesoderm covering the amnion and umbilical vesicle
Neural Development
- The neural plate appears as a thickening of the embryonic ectoderm, induced by the developing notochord
- A longitudinal neural groove develops in the neural plate, which is flanked by neural folds
- Fusion of the neural folds forms the neural tube, the primordium of the CNS
- The neural tube is the primordium of the CNS
- Neuroectodermal cells form a neural crest between the surface ectoderm and neural tube
- The neural crest cells lose affinity to the epithelium and neighbouring cells, detaching and migrating widely throughout the mesenchyme
- Neural crest cells give rise to ganglia of CN V, VII, IX, X, spinal ganglia, autonomic nervous system ganglia, neurolemma sheaths of peripheral nerves, and contribute to the arachnoid and pia mater, adrenal medulla, melanocytes, craniofacial bone and cartilage, and portions of the heart
Intraembryonic Mesoderm
- During the 3rd week, the intraembryonic mesoderm proliferates to form a thick column of mesoderm on either side of the notochord
- The paraxial mesoderm forms beside the axis of the organism (as defined by the notochord)
- The intermediate mesoderm is found just lateral to the paraxial mesoderm
- The lateral mesoderm is lateral to the intermediate mesoderm
- Somites develop adjacent to the neural tube, formed from the paraxial mesoderm
- Somites give rise to most of the axial skeleton and associated musculature, as well as the dermis in those areas
Intraembryonic Coelom
- The primordium of the intraembryonic coelom (embryonic body cavity) appears as isolated spaces in the lateral mesoderm and cardiogenic mesoderm
- These spaces soon coalesce and form a single horseshoe-shaped intraembryonic coelom
- The intraembryonic coelom divides the lateral mesoderm into two layers: a somatic or parietal layer of lateral mesoderm located beneath the ectodermal epithelium and continuous with the extraembryonic mesoderm covering the amnion, and a splanchnic or visceral layer of lateral mesoderm next to the endoderm and continuous with the extraembryonic mesoderm covering the umbilical vesicle
Embryonic Folding
- Embryonic folding is the process by which a relatively "flat" embryonic disk becomes more and more cylindrical in shape
- Folding occurs in two general planes: the median plane (cranial-caudal folding) and the horizontal plane (lateral folding)
- The edges "roll" ventrally towards the umbilical vesicle
- Folding begins at the end of the 3rd week and is easy to see in the 4th week
Cranial Folding
- The brain vesicles first begin to appear
- A few somites are obvious
- The foregut lies between the brain and heart
- The oropharyngeal membrane separates the foregut from the stomodeum
- The septum transversum lies caudal to the heart, develops into the central tendon of the diaphragm, and separates the abdominal cavity from the thoracic cavity
Germ Layer Derivatives
- Ectoderm: skin, bones, CNS, PNS, sensory epithelia of the eyes, ears, and nose, epidermis and its appendages, mammary glands, subcutaneous glands, enamel of teeth, pituitary gland
- Mesoderm: connective tissue, cartilage, bone, striated and smooth muscles, heart, blood, and lymphatic vessels, kidneys, ovaries, testes, genital ducts, serous membranes lining the body cavities, spleen, and cortex of suprarenal glands
- Endoderm: epithelial lining of the digestive and respiratory tracts, parenchyma of the tonsils, thyroid and parathyroid glands, thymus, liver, and pancreas, epithelial lining of the urinary bladder and most of the urethra, epithelial lining of the tympanic cavity, tympanic antrum, and eustachian tube
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Description
Test your knowledge on the development of embryonic tissues. This quiz covers the formation of various tissues such as dorsal root ganglia, autonomic nervous system ganglia, and more during the 3rd week of embryonic development.
