Week 5 Embryology Study Materials: Key Terms and Definitions

What is the most common malformation if the neurenteric canal fails to properly close?

diastematomyelia

T/F: Normally, most of the notochord will eventually degenerate away, but the last bit will give rise to the nucleus pulposus.

T

Notochordal nucleus cells are great at making proteoglycans. What are they key glycosaminoglycans?

chondroitin sulfate and keratan sulfate

Proteoglycans can hold huge amounts of water. What is the percentage of water?

80%

When proteoglycans clump together, they form a molecule called a ________ and once those clump together, they form an _________.

aggrecan; aggregate

At what age does the notochordal cells in the nucleus pulposus start to degenerate/disappear?

~10 y.o

The nucleus pulposus notochord cells are then replaced by ______________, which will then become nucleus pulposus cells.

chondrocyte-fibroblast-like cells

Chondrocyte-fibroblast-like cells have low water content which in turn makes the disc _______ and vulnerable to ___________.

degenerate; annular tears

What is the number one cause of chronic low back pain in humans under 60 years.

annular tears

What is the system that rates annular tears?

Modified Dallas Discogram

The Modified Dallas Discogram is rated on a grade scale 1-5. Which ones are potentially harmful?

3, 4, and 5

Chondrocyte-fibroblast-like cells may become antigenic if they come in contact with blood/immune system. Why do they become antigenic?

they form after the creation of the core immune system

Now if these chondrocyte-fibroblast-like cells get into the outer periphery, they could invoke what?

painful autoimmune inflammation response resulting in terrible low back pain

What if a big chunk of the notochord fails to degenerate away?

a rare cancerous tumor (chordoma) arises

With chordoma, what is the survival rate with removal, chemotherapy, and radiation therapy?

50%

What regions are chordomas typically found?

cranial or sacral region

What percentage of chordoma metastasize?

40%

In the cranial region, chordomas have a tendency to spread into the _________.

nasal pharynx

What is the process of neurulation?

formation of neural tube and early CNS

Neural tube forms the ______ and ______ in the third week and completed by the end of the 4th week?

brain and spinal cord

Neurulation starts with the formation of the _________ and ends with closure of the __________.

neural plate; caudal neuropore

What are the four stages of neurulation?

1. formation of neural plate

2. elongation and shaping of neural plate

3. lateral folding of neural plate

4. rolling up lateral folds

The midline ectodermal cells thicken into a new cell type called _________.

neuroectoderm cells

The conversion of epithelial-type tissue into neural tissue is called _______ which would collectively make up the _________.

neural induction; neuroectoderm

The neural plate develops above the cranial part of the notochord, in the cranial region. It develops between the __________ and __________.

primitive node and oropharyngeal membrane

What are the four structures involved in the conversion of ectodermal cells into neuroectoderm cells?

notochord; primitive node; prechordal plate; AVE

What is the "trick" to make a neuroectoderm cell, from an ectodermal cell?

turn off bone morphogenetic protein-4 (BMP-4)

What are the three inhibitors of BMP-4?

noggin; chordin; cerberus-1 (Cer-1)

The neural plate grows _________ to __________.

cranially to caudally

What is the classical shape of the neural plate in the elongation phase of neurulation?

key-shape

What is the process of creating the spinal cord portion of the neural plate?

convergent extension

During the elongation phase, the wider portion of the neural plate will form the future __________, and the narrow portion will form the future _________.

brain; spinal cord

T/F: In stage 3 of neurulation, lateral folding is the first step towards converting the neural plate into neural tube.

T

How does the folding start in stage 3 of neurulation?

neural plate cells in the midline undergo a structural change (triangular-shaped)

What causes the neuroectoderm cells to become triangular in shape?

the actin binding-protein called shroom causes microfilaments of the cytoskeleton in the apical region to contract causing apical narrowing

The point of the midline at which each side folds upwards is called _________. The newly created walls on either side of the median hinge point makes up the right and left ___________. The midline valley that is created between the neural folds is called the _________.

median hinge point; neural folds; neural groove

At the lateral most region of the folding of the neural plate, a new cell type starts to form. These new cells are called __________ and some authors may even call these cells the __________, that will form many nerves and ganglia of the body.

neural crest cells; 4th germ layer

When does the left and right lateral neural folds come together?

day 21 (end of week 3)

Before the neural crest cells migrated out, they had to go through a transformation called the ______________. The migration of neural crest cells out of the new neural tube before its closure is called _________.

epithelial-to-mesenchymal transformation; delamination

The neural tube does not close all at once. Instead it closes in the _____________ first, then closure progresses __________ towards both ends.

middle region; outward

Therefore, the cranial and caudal ends of the neural tube are left open for. Those open ends are called...

cranial (anterior) and caudal (rostral) neuropore

Cranial neuropore closes about day ________ and the caudal neuropore closes about day _______. At this point (end of week 4), the process of neurulation is complete and the primitive central nervous system is born.

25; 28

What is one of the most common problems with neurulation?

failure of the neural tube to completely fuse is the dorsal midline

One risk factor is the exposure to teratogens during the 3rd week of pregnancy. What are three examples of teratogens?

alcohol, cigarette smoke, X-ray exposure

Prenatal testing may demonstrate abnormal levels of __________. And decreased levels of this protein may indicate chromosomal abnormality such as ____________.

alpha fetoprotein; down syndrome (trisomy 21)

Spina bifida occulta is common if the neural tube fails to close. If a patient presents with a ________ or _________, it would be indicative of spina bifida and diastematomyelia.

sacral dimple or faun tail (faun's beard/hypertrichinosis)

T/F: Spina bifida cystica (aka spina bifida aperta) is a general category but more severe than spina bifida occulta.

T

What are the three types of spina bifida cystica?

meningocele, meningomyelocele, myeloschisis (rachischisis)

In the subclass of spina bifida cystica, when the thecal sac (dural sac) herniates through bony defect is called?

meningocele

In the subclass of spina bifida cystica, when the thecal sac and cauda equina/spinal cord herniates through the neural arch with a 16 year survival rate (85%) is called?

meningomyelocele

This subcategory is the most dangerous and almost always fatal because the neural tube has failed to close which exposes the spinal cord/cauda equina to the outside environment. What subcategory of spina bifida cystica is this?

myeloschisis (rachischisis)

Dysraphism is another word for spina bifida. What is a closed spinal dysraphism?

small defect of vertebral arch and the skin is not disrupted with no herniation of thecal sac or its content

Dysraphism is another word for spina bifida. What is an open spinal dysraphism?

large defect of the vertebral arch and skin is disrupted and neural tissue herniates outward

What is cranioschisis?

failure of the brain portion of the neural tube