Ch. 5: Development of the Nervous System

Question 1

When does the Preembryonic stage take place?

What do you look like during this time?

Answer 1

• Conception to 2nd week of gestation
• A disk that will become you

Question 2

When does the Embryonic stage take place?

Answer 2

2nd to 8th week of gestation

Question 3

What transformations happen in the Embryonic Phase?

Answer 3

• Organs begin to form from embryonic disk
  
  • Ectoderm: Neural
    
    • Sensory organs, epidermis, nervous system
  • Mesoderm: Bony
    
    • Dermis, muscles, skeleton, excretory system, circulatory system
  • Endoderm: Gut
    
    • Gut, liver, pancreas, respiratory system
• Neural tube forms and closes
• Brain begins to form

Question 4

When is the Fetal Phase?

Answer 4

8th week gestation until birth

Question 5

What happens in the Fetal Phase?

Answer 5

• Brain formation continues
• Myelination begins

Question 6

What are the phases of Nervous System Formation?

Answer 6

• Phase 1: Neural Tube Formation
• Phase 2: Initial Brain Formation

Question 7

What is the Neural Plate?

Answer 7

Neural cells, flat - needs to round out to form

Question 8

What is the Neural Groove?

Answer 8

Forms as outside of disk begins to mound up

Question 9

What is the Neural Tube?

Answer 9

What was flat has now rounded up to form a circle

Question 10

What are Neuropores?

Answer 10

• Rostral and Caudal openings of neural tube (not yet closed)
• Failure to close: can cause Spinabifida or Anencephaly

Question 11

What is the Neural Crest?

Answer 11

• Pockets of cells at edgs where disk mounds up
• Form outside of closed tube & dorsal root ganglion
• Morphology: pseudo-unipolar

Question 12

What is the Mantle Layer?

Answer 12

• Inner Ring
• Nervous System cell bodies

Question 13

What is the Marginal Layer?

Answer 13

• Outer ring
• Axons and glia
• Non-neural support cells when tube closes
• Protective ring around neurons

Question 14

What is a Somite?

What develops from it?

Answer 14

• Somite (mesoderm): small balls, 31 on each side, becomes:
  
  • Sclerotome: vertebrae & skull
  • Myotome: skeletal muscle
  • Dermatome: skin

Question 15

What 2 plates form from the Mantle Layer Divisions?

What do these plates control?

Answer 15

• Motor Plate → motor neurons → ventral horn → becomes Myotome (innervated by 1 segmental spinal nerve)
• Association Plate → interneurons and sensory neurons → dorsal horn → Dermatome

Question 16

What 4 things does the neural crest diversify into?

Answer 16

1. Peripheral sensory neurons
2. Myelin cells (Shwann cells)
3. Autonomic neurons
4. Endocrine organs

Question 17

In initial brain formation, what are the 3 part of the brain?

What do those 3 part develop into?

Answer 17

1. Hindbrain - medulla, pons, cerebellum
2. Midbrain - stays midbrain
3. Forebrain - forms everything else (cerebral cortex, cerebellum, basil ganglia, etc)

Question 18

As the brain develops, where does the mantle layer (or cell bodies) migrate to?

Why?

Answer 18

• Migrate to outside of brain
  
  • more surface area from folding

Question 19

What is differentiation?

When do neurons differentiate in the brain?

Answer 19

• Specialization
  
  • once they arrive at their final location

Question 20

How long does it take Myelination to develop in the brain?

What is the result of undeveloped Myelination?

Answer 20

• Up to 3 years!!
  
  • Result: born uncoordinated

Question 21

Why do some neural deficits take years to develop?

Answer 21

• Will not notice symptoms until use of that part of the brain is needed.
• “Grow into defecits”