MSK 05 - Development of Spinal Cord and Spinal nerves

Question 1

List the steps from zygote formation to implantation

Answer 1

1. Cleavage of the zygote (increase in cell # w/out increse in size)
2. Once cell # hits 16 the zygote is called a morula
3. Cells compact and differentiate into a central cell mass, called the embryoblast, and an outer cell layer, called the trophoblast.
4. The embryoblasts then all migrate to one side creating a clump of cells called the inner cell mass and a cavity called a blastocoel (remember this is all within the trophoblastic layer). This new structure is called a blastocyst.
5. During blastocyst formation, the zona pelucida begins to degrade away
6. After the zona pelucida fully degrades, implantation occurs

Question 2

List the steps from bilaminar disk formation to gastrulation

Answer 2

1. The inner cell mass of the blastocyst begins to develop its own cavity, the amniotic cavity.
2. The cells closest to the blastocoel differentiate, forming the hypoblastic layer. The cell layer just above the hypoblastic layer is now called the epiblastic layer. These two layers form the bilaminar disc.
3. Some of the cells of the epiblastic layer migrate to the midline forming the primitive streak.
4. The cells of the primitive streak then invade into the epi & hypoblast and form a third central layer. The top layer is now callled the ectoderm, middle layer is the mesoderm, and the bottom layer is the endoderm. This process is called gastrulation

Question 3

Describe the process of neurulation

Answer 3

1. In the center of the mesoderm, underneath where the primitive streak was, a population of cells begins to differentiate into a cord structure, called the notochord.
2. The notochord then induces a change in the cells of the ectoderm above it into a thick plate, called the neural plate.
3. The neural plate cells invade into the mesoderm forming a tube, called the neural tube
4. As the neural tube forms, cells of the ectoderm break off and invade the mesoderm. These cells are called neural crest cells

Question 4

What is neuroectoderm?

Answer 4

The cells of the ectoderm that have differentiated to form the neural plate

Question 5

What is a neural fold? What will it do?

Answer 5

As the neural plate cells invade into the mesoderm, two large humps begin to appear on either side of the plate. These humps are referred to as neural folds. As the neural plate invades further into the mesoderm, the neural folds will eventually fuse to form the neural canal.

Question 6

What is the paraxial mesoderm? What does it do?

Answer 6

The area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites, blocks of tissue running along both sides of the neural tube, which form muscle and the tissues of the back, including connective tissue and the dermis.

Question 7

Discuss the appearance of the neural plate before neural fold fusion. How will this change?

Answer 7

Question 8

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Question 9

What are neuropores?

Answer 9

Question 10

When will the neuropores close?

Answer 10

The rorstral neuropore closes around day 25

The caudal neuropore closes around day 27

Question 11

When/where do the neural folds begin to fuse?

Answer 11

Starts on day 22 at the occipital and cervical region

Question 12

Where do neural crest cells come from?

Answer 12

As the neural folds fuse, the neuroectodermal cells along the crest of the folds pinch off and come to lie along the sides of the neural tube.

Question 13

Answer 13

Question 14

What portion of the neural tube will form the spinal cord?

Answer 14

The portion caudal to the 4th pair of somites

Question 15

What are the two primary layers of the neural tube and do these layers give rise to?

Answer 15

1. Outer mesenchyme layer which gives rise to mesenchymal cells which, in turn, give rise to microglial cells
2. Inner neuroepithelial layer which will give rise to many different cells including unipolar neurons and macroglial cells

Question 16

What do neural crest cells give rise to?

Answer 16

A wide array of cell types but the ones we need to know are:

Dorsal root and Sympathetic chain ganglion

Schwann cells

Multipolar neurons

Celiac ganglion

Renal ganglion

Suprarenal medulla (chromaffin cells)

Melanocytes

Question 17

Answer 17

Question 18

Describe the first two zones that develop in the neural tube

Answer 18

The neural tube is lined by a thick layer of neuroepithelium which forms the ventricular zone. A thicker marginal zone forms superficial to that.

Question 19

What is the purpose of the ventricular zone of the neural tube?

Answer 19

Cells in the ventricular zone will multiply and the newly formed cells will migrate to form the intermediate zone (mantle layer) between the ventricular zone and the marginal zone.

Eventually the ventricular zone cells will form the ependymal lining of the central canal of the spinal cord

Question 20

What is the purpose of the marginal zone of the neural tube?

Answer 20

The marginal zone will form the white matter of the spinal cord

Question 21

What is the purpose of the intermediate zone of the neural tube?

Answer 21

Cells in the intermediate zone will differentiate into neuroblasts which will form neurons. It will thicken in 4 regions, forming a pair of alar plates dorsally (dorsal horns) and basal plates ventrally (ventral somatic motor and lateral horns). The dorsal grey columns will also be formed

Question 22

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Question 23

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Question 24

How do the spinal meninges develop?

Answer 24

Question 25

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Question 26

What is a sclerotome?

Answer 26

A sclerotome is the part of each somite in a vertebrate embryo giving rise to bone or other skeletal tissue.

Question 27

What does each vertebra arise from?

Answer 27

Each vertebra develops from the mesenchyme of the pair of sclerotomes which surround the neural tube and notochord at each level.

Question 28

Describe the regions of the sclerotomes that give rise to the vertebrae.

Answer 28

Question 29

Describe how the intervertebral discs develop.

Answer 29

The intervertebral discs develop from the caudal dense parts of the vertebral sclerotomes. These parts form the anulus fibrosus (the tough circular exterior of the intervertebral disc). The nucleus pulposus (the inner core of the vertebral disc) arises from the regions of the notochord between developing vertebral bodies.

Question 30

What is a myotome?

Answer 30

The dorsal part of each somite in a vertebrate embryo, giving rise to the skeletal musculature.

Question 31

Answer 31

Question 32

What is a hemi-vertebra and what causes it?

Answer 32

A hemi-vertebra is a vertebra that has failed to fully develop (usually missing one half of the vertebral body). This occurs if one of the pairs of sclerotomes fail to develop.

Question 33

Describe the development of the bony vertebral column.

Answer 33

1. The remnants of the sclerotome form the mesenchymal primordium of the vertebrae
2. In the fifth week, chondrification centers appear and begin to convert this primordium to cartilage
3. In the seventh week, three ossification centers appear and begin to convert the cartilage to bone. These ossification centers appear in the centrum (body) and the two neural arch centers (future vertebral arches). The neural arches are the first to ossify
4. Shortly after puberty, five secondary ossification centers appear (one on the top and bottom of the vertebral body, one at the tip of each transverse process, one at the tip of the spinous process.
5. These secondary ossification centers unite by age 25

Question 34

What is a chordoma and what causes it?

Answer 34

A chordoma is a rare malignant tumor that occurs most frequently at the base of the skull, it may infilitrate bone. It is caused by remants of the notochord that persist throughout development.

Question 35

What are some common causes of Neural Tube Defects (NTDs)? What is the most commonly seen NTD?

Answer 35

Question 36

What are the types of spina bidida we need to know?

Answer 36

Spina Bifida Oculta

Spina Bifida Cystica with Meningocele

Spina Bifida Cystica with Meningomyelocele

Spina Bifida Cystica with Myeloschisis

Question 37

Describe the cause and symptoms of Spina Bifida Oculta

Answer 37

Question 38

Describe the cause and symptoms fo Spina Bifida Cystica with Meningocele

Answer 38

Question 39

Describe the cause and symptoms of Spina Bifida Cystica with Meningomyelocele.

Answer 39

Question 40

Describe the cause and symptoms of Spina Bifida Cystica with Myeloschisis

Answer 40

Question 41

Label each picture and determine what type of NTD each one represents.

Answer 41

From top to bottom:

Spina Bifida Cystica with Meningomyelocele

Spina Bifida Cystica with Meningocele

Spina Bifida Oculta

Spina Bifida Cystica with Myeloschisis

Question 42

List the types of spina bifida from least to most severe in terms of neurological deficits.

Answer 42

Spina Bifida Oculta

Spina Bifida Cystica with Meningocele

Spina Bifida Cystica with Meningomyelocele/myeloschisis