Development of the CNS

Question 1

Recall the 3 developmental layers of tissue in the embryo

Answer 1

Endoderm, mesoderm, ectoderm

Question 2

When and how does the neuroepithelium first begin to develop?

Answer 2

At 3 weeks the neuroepithelium begins to thicken and fold dorsally

Question 3

What does the neuroepithelium eventually develop into?

Answer 3

All CNS components

Question 4

Recall the 3 types of stem cell in the neuroepithelium and the cell types each of these differentiate into

Answer 4

Neuroblasts –> all neurons with cell bodies in CNS
Glioblasts –> Astrocytes and oligodendrocytes
Ependymal cells –> linings of ventricles and central canal

Question 5

Recall the 3 layers of the neuroepithelium

Answer 5

Germinal layer (ependymal cells)
Mantle layer (Grey matter)
Marginal layer (white matter)

Question 6

Recall the migration of cells in the neuroepithelium during its proliferation

Answer 6

1. Neuroblasts originate in ependymal layer and migrate outwards
2. Glioblasts originate in ependymal cells and migrate to grey and white matter

Question 7

Describe the neural tube at the level of the brainstem

Answer 7

Opens up, with motor nuclei developing medially and sensory nuclei developing more laterally

Question 8

Describe the relative positioning of the developing neuroepithelium and neural crest

Answer 8

Neural crest develops dorsal and laterally to neural tube on both sides

Question 9

Recall the names of the plates at the dorsal and ventral ends of the germinal layer

Answer 9

Dorsal = roof plate
Ventral = floor plate

Question 10

What is the neural crest a basis for?

Answer 10

PNS

Question 11

Recall 4 types of cell that form from the neural crest

Answer 11

Schwann cells, postganglionic autonomic neurons, sensory neurons, non-neuronal derivatives (eg melanocytes

Question 12

How is peripheral neuron development controlled in the neural crest?

Answer 12

Signalling molecules bind to neuroblast surface receptors to control migration and axonal growth by attraction and repulsion - depends on:

1. Concentration gradient of soluble factors
2. Timing

Question 13

Recall the state of brain development at 4 weeks gestation

Answer 13

4 vesicles formed: 
1. Prosencephalon (becomes forebrain) 
2. Mesencephalon (becomes midbrain) 
3. Rhombencephalon (becomes hindbrain) 
4. Future spinal cord
3 flexures begin to fold:
1. Cephalic
2. Pontine
3. Cervical

Question 14

Recall the state of brain development at 5 weeks gestation

Answer 14

1. Prosencephalon differentiates into telencephalon (which becomes cortex) and diancephalon
2. Rhombencephalon differentiates into pons and medulla

Question 15

Recall the state of brain development at 8 weeks gestation

Answer 15

1. Forebrain begins to develop into hemispheres

2. In hindbrain, 4th ventricle and cerebellum begin to develop

Question 16

Describe the orientation of grey and white matter in the brain and spinal cord

Answer 16

Brain: grey matter around outside, white matter underneath
Spine: White matter around outside, grey matter on inside

Question 17

Recall the number of layers in the cortex and the cerebellum

Answer 17

Cortex = 6 layers
Cerebellum = 3 layers

Question 18

Describe the cell migration that leads to the formation of cortical layers

Answer 18

Cells migrate from periventricular zone along radial glial cells to form 6 layers

Question 19

Recall the dorsal and ventral plates in the developing spinal cord and their composition

Answer 19

Dorsal = alar plate (interneurons)
Ventral = basal plate (motor neurons and interneurons)

Question 20

Recall 3 environmental factors that may affect development of the nervous system in utero

Answer 20

1. Mother’s lifestyle
2. Diet
3. Teratogens

Question 21

Recall 2 teratogens that are known to cause defects in nervous system development

Answer 21

1. Alcohol

2. Deficient folic acid –> spina bifida and anencephaly

Question 22

What is spina bifida?

Answer 22

Non-closure of the neural tube inferiorly, with some neural tissue being found outside the body

Question 23

Describe encephalocele

Answer 23

Back of head not sealed off properly - leads to herniation of meninges, incompatible with life