Lecture 12: Neurulation

Question 1

During week 1 of development, the trophoblast differentiates into what 2 structures?

Answer 1

Cytotrophoblast and syncytiotrophoblast

Question 2

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?

Answer 2

Differentiated trophoblast begins to implant into the uterine endometrium

Embryonic disc becomes bilaminar

Question 3

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 _______

Answer 3

Syncytiotrophoblast

Hypoblast; lacunae; embryo

Question 4

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

Answer 4

Mesoderm; chorionic

Lacunae

Hypoblast

Question 5

During week 3 of development, the embryo proper is attached to the ______ by the connecting stalk

Answer 5

Chorion

Question 6

What is the difference between endoderm and primitive endoderm?

Answer 6

Primitive endoderm = hypoblast

Endoderm comes from the epiblast

Question 7

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?

Answer 7

Mesoderm

Question 8

What germ layer is responsible for the epithelial linings of respiratory and digestive tracts, GI glands and glandular cells of liver and pancreas?

Answer 8

Endoderm

Question 9

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?

Answer 9

Ectoderm

Question 10

Which primary germ layer gives rise to the notochord?

Answer 10

Mesoderm

Question 11

What effect does the notochord have on overlying ectoderm?

Answer 11

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

Question 12

What 2 structures are derived from the neuroectoderm?

Answer 12

Neural plate

Neural crest

Question 13

The processes by which the surface ectoderm and neuroectoderm are made physically and functionally distinct = ____________

Answer 13

Neurulation

Question 14

Primary neurulation consists of what 3 major phases?

Answer 14

Neural plate –> neural folds –> neural tube

Question 15

What establishes the hinge point between neural plate and neural folds phases of primary neurulation?

Answer 15

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

Question 16

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

Answer 16

Mesenchyme; sacral

Question 17

What happens to the neural crest as the neural tube closes?

Answer 17

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)

Question 18

What cell type forms from technically all types of neural crest?

Answer 18

Melanocytes

Question 19

What tissue type arises from cranial neural crest cells only?

Answer 19

Teeth

Question 20

What are some regions of neural crest cells?

Answer 20

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

Question 21

Craniofacial anomalies are common with defects in what cell type?

Answer 21

Neural crest

Question 22

Cardiac neural crest cells are very important for what developmental process?

Answer 22

Septation of the heart tissue, which originates as a single tube structure

Question 23

What is the #1 category of congenital malformations?

Answer 23

Congenital heart defects, due to issues with cardiac neural crest migration

[this is followed by craniofacial defects]

Question 24

Goldenhar syndrome (hemifacial macrosomia), TCS (mandibulofacial dystosis), Hirschsprung disease, piebaldism, micrognathia, and craniosynostosis are all categorized as _________, due to defects in neural crest

Answer 24

Neurocristopathies

Question 25

The meninges migrate to surround the CNS and develop from what 2 things (dual origin)?

Answer 25

Neural crest cells | Mesenchyme

Question 26

The meninges initially form as a single layer structure that enwraps the neural tube. In these early stages, the meninges are referred to as _________ _________

Answer 26

Meninx primitiva (primitive meninges)

Question 27

The primitive meninx differentiates into _________ and _______ at around 34-48 days of development

Answer 27

Ectomeninx | Endomeninx

Question 28

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?

Answer 28

Dura mater

Question 29

Between 45-60 days, the endomeninx becomes more reticulated and subarachnoid spaces/cisterns appear. The endomeninx eventually forms what structures?

Answer 29

``` Arachnoid mater Pia mater (directly on brain surface) ```

Question 30

What is the fate of the spinal ectomeninx as development progresses?

Answer 30

It dissociates from the vertebral bodies and gives rise to the spinal epidural space, which is essential for epidural injections

Question 31

T/F: neural tube closure occurs simultaneously along its entire length

Answer 31

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

Question 32

Since neural tube closure is NOT occurring simultaneously along its length, what forms at each end of the tube?

Answer 32

Cranial and caudal neuropores

Question 33

Defects in adhesion along the neural tube in the process of NT closure at the 5th site may result in what type of pathology?

Answer 33

Spina bifida

Question 34

How many areas of final site closure are there in the process of NT closure?

Answer 34

5

Question 35

What pathology results due to failure of neural tube closure at site 1?

Answer 35

Craniorachischisis

Question 36

What pathology results due to failure of neural tube closure at sites 2 and 3?

Answer 36

Anencephaly

Question 37

__________ = 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

Answer 37

Encephalocele

Question 38

______________ = 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.

Answer 38

Anencephaly

Question 39

What are the 3 types of anencephaly?

Answer 39

Meroencephaly Holoencephaly Craniorachischisis

Question 40

What type of anencephaly results in some formation of brain tissue, but closure defect is severe enough that fetus is not viable?

Answer 40

Meroencephaly

Question 41

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

Answer 41

Holoencephaly

Question 42

What type of anencephaly results in both cranial region and neural tube defects extending down the caudal region, involving both brain and spinal cord?

Answer 42

Craniorachischisis

Question 43

What is the most severe type of anencephaly?

Answer 43

Craniorachischisis

Question 44

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

Answer 44

B. Meningocele

Question 45

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

Answer 45

D. Myeloschisis

Question 46

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

Answer 46

A. Spina bifida occulta

Question 47

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

Answer 47

C. Meningomyelocele

Question 48

Embryonic folding: head fold occurs as cranial and caudal regions move _________ as the embryo elongates cranially and caudally (4th week/day 22)

Answer 48

Ventrally

Question 49

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

Answer 49

Amniotic cavity Oropharyngeal Septum transversum

Question 50

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)

Answer 50

Neural tube Caudal eminence; cloacal membrane

Question 51

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)

Answer 51

Hindgut Cloaca

Question 52

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)

Answer 52

Midgut

Question 53

During which folding process does the umbilical cord form?

Answer 53

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]

Question 54

_____________= anterior body wall malformation involving GI herniation where bowel is contained within membranous sac

Answer 54

Omphalocele

Question 55

___________ = anterior body wall malformation involving GI herniation where bowel is exposed and protruding through the body wall

Answer 55

Gastroschisis

Question 56

What anterior body wall malformation is named for the heart developing outside the thoracic cage?

Answer 56

Ectopia cordis

Question 57

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?

Answer 57

Pentalogy of Cantrell