Lecture 12: Neurulation Flashcards
During week 1 of development, the trophoblast differentiates into what 2 structures?
Cytotrophoblast and syncytiotrophoblast
During week 1 of development, once the trophoblast differentiates into the cytotrophoblast and the syncytiotrophoblast, what does it do and what happens to the embryonic disc?
Differentiated trophoblast begins to implant into the uterine endometrium
Embryonic disc becomes bilaminar
During week 2 of development, the amniotic cavity forms and the ___________ expands.
Cells migrate from the ________ to form the primary yolk sac; ________ form within the syncytiotrophoblast; implantation is complete and the syncytiotrophoblast surrounds the _______
Syncytiotrophoblast
Hypoblast; lacunae; embryo
After completion of implantation in week 2 of development, extraembryonic _______ forms and splits to form the __________ cavity.
Trophoblastic ________ anastomose with maternal blood sinusoids.
Cells migrate from _______ to form secondary yolk sac; primary yolk sac is pushed to the side and begins to degenerate, eventually reduced to a remnant at the abembryonic pole of the chorionic cavity
Mesoderm; chorionic
Lacunae
Hypoblast
During week 3 of development, the embryo proper is attached to the ______ by the connecting stalk
Chorion
What is the difference between endoderm and primitive endoderm?
Primitive endoderm = hypoblast
Endoderm comes from the epiblast
Which germ layer is responsible for skeletal muscle, blood cells, lining of vessels, visceral smooth muscular coats, serosal linings, trunk CT, most of the cardiovascular system, and the notochord?
Mesoderm
What germ layer is responsible for the epithelial linings of respiratory and digestive tracts, GI glands and glandular cells of liver and pancreas?
Endoderm
What primary germ layer is responsible for the epidermis of the skin + epidermal derivatives, CNS and PNS, and neural crest cells, eyes, and internal ears?
Ectoderm
Which primary germ layer gives rise to the notochord?
Mesoderm
What effect does the notochord have on overlying ectoderm?
It is the primary inducer of overlying ectoderm to become specified as neuroectoderm, which then becomes neural plate and neural crest (begins in 3rd week)
Without signals from the notochord, the overlying ectoderm becomes epidermis
What 2 structures are derived from the neuroectoderm?
Neural plate
Neural crest
The processes by which the surface ectoderm and neuroectoderm are made physically and functionally distinct = ____________
Neurulation
Primary neurulation consists of what 3 major phases?
Neural plate –> neural folds –> neural tube
What establishes the hinge point between neural plate and neural folds phases of primary neurulation?
Neural groove
This allows physical changes to take place in neural plate; establishment of groove is essential to elevate surrounding areas to become neural folds, those edges then fuse to form neural tube
Secondary neurulation begins as neural tube arises from the __________ and aggregates into a solid cord.
The cord cavitates, creating a hollow tube. This occurs at the level of the ________ vertebrae
Mesenchyme; sacral
What happens to the neural crest as the neural tube closes?
Neural crest cells pinch off and migrate away, either prior to neural tube closure, or as closure occurs (timing varies depending on position on body axis)
What cell type forms from technically all types of neural crest?
Melanocytes
What tissue type arises from cranial neural crest cells only?
Teeth
What are some regions of neural crest cells?
Adrenergic, cholinergic, sensory neurons Schwann cells Melanocytes Odontoblasts Cartilage Bone Head/neck: dermis, skeletal, smooth muscle, adipose tissue Enteric ganglia ANS ganglia Adrenal medulla Teeth
Craniofacial anomalies are common with defects in what cell type?
Neural crest
Cardiac neural crest cells are very important for what developmental process?
Septation of the heart tissue, which originates as a single tube structure
What is the #1 category of congenital malformations?
Congenital heart defects, due to issues with cardiac neural crest migration
[this is followed by craniofacial defects]
Goldenhar syndrome (hemifacial macrosomia), TCS (mandibulofacial dystosis), Hirschsprung disease, piebaldism, micrognathia, and craniosynostosis are all categorized as _________, due to defects in neural crest
Neurocristopathies
The meninges migrate to surround the CNS and develop from what 2 things (dual origin)?
Neural crest cells
Mesenchyme
The meninges initially form as a single layer structure that enwraps the neural tube. In these early stages, the meninges are referred to as _________ _________
Meninx primitiva (primitive meninges)
The primitive meninx differentiates into _________ and _______ at around 34-48 days of development
Ectomeninx
Endomeninx
Between 45-60 days, the ectomeninx becomes more compact and forms spaces for future venous sinuses. The ectomeninx eventually gives rise to what layer of meninges?
Dura mater
Between 45-60 days, the endomeninx becomes more reticulated and subarachnoid spaces/cisterns appear. The endomeninx eventually forms what structures?
Arachnoid mater Pia mater (directly on brain surface)
What is the fate of the spinal ectomeninx as development progresses?
It dissociates from the vertebral bodies and gives rise to the spinal epidural space, which is essential for epidural injections
T/F: neural tube closure occurs simultaneously along its entire length
False; cephalic regions are more advanced than caudal regions, which are still undergoing gastrulation
NT closure is initiated at several locations along the AP axis, at about 5 different sites, and the mechanisms at each all differ
Since neural tube closure is NOT occurring simultaneously along its length, what forms at each end of the tube?
Cranial and caudal neuropores
Defects in adhesion along the neural tube in the process of NT closure at the 5th site may result in what type of pathology?
Spina bifida
How many areas of final site closure are there in the process of NT closure?
5
What pathology results due to failure of neural tube closure at site 1?
Craniorachischisis
What pathology results due to failure of neural tube closure at sites 2 and 3?
Anencephaly
__________ = cranial neural tube defects characterized by a membranous sac enclosing brain tissue; meninges extend out of that area
Depending on the severity, this may be operable but may need to manipulate nervous tissue which risks brain damage
Encephalocele
______________ = cranial neural tube defects indicating lack of a brain, where there is closure abnormality in cranial region resulting in exposed neural tissue in contact with amniotic fluid. Fetus will not be viable.
Anencephaly
What are the 3 types of anencephaly?
Meroencephaly
Holoencephaly
Craniorachischisis
What type of anencephaly results in some formation of brain tissue, but closure defect is severe enough that fetus is not viable?
Meroencephaly
What type of anencephaly results in formation of single brain structure, but again the closure defect is severe enough that the fetus is not viable
Holoencephaly
What type of anencephaly results in both cranial region and neural tube defects extending down the caudal region, involving both brain and spinal cord?
Craniorachischisis
What is the most severe type of anencephaly?
Craniorachischisis
Which of the following is characterized by some extension of skin over the spinal cord, bi-fid vertebrae, but it remains in the appropriate position?
A. Spina bifida occulta
B. Meningocele
C. Meningomyelocele
D. Myeloschisis
B. Meningocele
Which of the following is characterized by complete failure of the neural tube to close in that region, and the developing spinal cord is left exposed?
A. Spina bifida occulta
B. Meningocele
C. Meningomyelocele
D. Myeloschisis
D. Myeloschisis
Which of the following is characterized by spinal cord embedded under the skin, vertebrae are bi-fid, occurs more in sacral region, and may be associated with skin color change or tuft of hair over the affected area?
A. Spina bifida occulta
B. Meningocele
C. Meningomyelocele
D. Myeloschisis
A. Spina bifida occulta
Which of the following is characterized by spinal cord tissue pushed outside the body wall?
A. Spina bifida occulta
B. Meningocele
C. Meningomyelocele
D. Myeloschisis
C. Meningomyelocele
Embryonic folding: head fold occurs as cranial and caudal regions move _________ as the embryo elongates cranially and caudally (4th week/day 22)
Ventrally
Embryonic folding: head fold -
Neural folds project dorsally into the _______ _______
Neural folds grow cranially beyond the ___________ membrane and overhang the primordial heart
This forces translocation of the ________ ________, primordial heart, pericardial coelom, and oropharyngeal membrane to ventral surface
Amniotic cavity
Oropharyngeal
Septum transversum
Embryonic folding: tail fold
Folding of the caudal end of the embryo is due to growth of the distal _____ _____ (SC primordium)
The _______ _______ (tail region) projects over the _________ ________(future anus)
Neural tube
Caudal eminence; cloacal membrane
During tail folding, part of the endoderm will form the _______ (descending colon/rectum), and the terminal hindgut dilates to form the _______ (rudiment of urinary bladder/rectum)
Hindgut
Cloaca
Lateral embryonic folding occurs due to rapid growth of SC and somites, resulting in ventral extension toward midline.
The abdominal wall fuses, incorporating endoderm to form the _______ (SI primordium)
Midgut
During which folding process does the umbilical cord form?
Lateral folding
[ventral fusion during folding reduces contact between the intraembryonic and extraembryonic coelomic cavities; amniotic cavity expands and the amnion forms epithelial covering of umbilical cord]
_____________= anterior body wall malformation involving GI herniation where bowel is contained within membranous sac
Omphalocele
___________ = anterior body wall malformation involving GI herniation where bowel is exposed and protruding through the body wall
Gastroschisis
What anterior body wall malformation is named for the heart developing outside the thoracic cage?
Ectopia cordis
What anterior body wall malformation involving the thoracic wall involves a midline abdominal defect, anterior diaphragmatic hernia, cleft sternum, pericardial defect, and other intercardiac defects?
Pentalogy of Cantrell
