Nervous System Development

Question 1

What are the major processes that underlie the formation of the nervous system

Answer 1

1. Induction of the neuroectoderm
2. regional specialization of the neuroectoderm
3. generation of postmitotic, terminally differentiated, diverse neurons and glia
4. Migration of newly formed neurons to their final location
5. growth of axons, directed by environmental cues, to their targets
6. formation of a synapse when a target is reached _
7. Numerical matching of the size of the input to the size of the target
8. Fine tuning of the final number and location of synapses through competition/experience.
9. Myelinzation

Question 2

When does neuroectoderm start?

Answer 2

at about 18 days post conception and completed by day 26

Question 3

which does the mesoderm form?

Answer 3

the notochord

Question 4

which does the ectoderm form?

Answer 4

the neural plate via neuralation

Question 5

When does the commitment for becoming a certain type of neuron occur?

Answer 5

BEFORE any actual neurons have been formed

Question 6

Which structure will become the CNS

Answer 6

the neural tube

Question 7

which structure will become the PNS

Answer 7

the neural crest

Question 8

Where does the neural tube first close

Answer 8

in the cervical region of the spinal cord

Question 9

What specific disease can occur if there are defects in neural tube closure

Answer 9

spina bifida
anencephaly
arnold chiari malformation

Question 10

What are the 3 swellings that form before the neural tube is closed

Answer 10

prosencephalon (forebrain)
mesencephalon (midbrain)
rhombencephalon (hindbrain)

Question 11

What brain divisions are formed as the process of neuroectoderm specialization continues?

Answer 11

• Telencepahalon (cerebral cortex, basal ganglia, cerebral hemispheres)
• Diencephalon (hypothalamus and thalamus)
• Mesencephalon (midbrain, tectum and tegmentum)
• Metencephalon (pons and cerebellum)
• Myencephalon (medulla

Question 12

When does post- mitotic, terminally differentiated neurons generation occur

Answer 12

mostly in the 3rd and 4th months of gestation

Question 13

What factors can negatively impact the process of cell proliferation

Answer 13

maternal use of alcohol
cocaine
other substances

Question 14

What occurs in the spinal cord and brainstem for generation of post-mitotic differentation?

Answer 14

a. Cells span the width of the tube from the ventricle/central canal to the external surface
b. The nuclei of these cells migrate back and forth between the basal surface and the apical surface
c. Mitosis occurs when the nucleus is at the ventricular surface
d. After mitosis, there are 3 options:

Question 15

What occurs after mitosis?

Answer 15

Continue the nuclear migration process and continue dividing

ii. Rest
iii. Migrate elsewhere and differentiate into neurons or glia

Question 16

What occurs in the cerebral cortex for post-mitotic differentiation?

Answer 16

a. During the early stages, the process is similar to that of the spinal cord and brainstem

Question 17

Cells in the cerebral cortex do retain attachment to which surface?

Answer 17

cortical surface

Question 18

how is the type of neuron the cells will become determined?

Answer 18

timing at which it makes its last mitotic division dictates what type of neuron it will become

Question 19

How does migration in the cortex occur?

Answer 19

Radial glial cells guide the migration of neurons to the correct cortical layer. This migrating neuron them attaches to a radial glial fiber and follows it to the cortical surface

Question 20

What is a growth cone?

Answer 20

transient specialization at the end of a growing axon that navigates the axon to its target by elongating the axon

Question 21

What kind of factors does the growth cone respond to?

Answer 21

both positive (tropic) and negative

Question 22

What fibers appear in 3 months

Answer 22

intersegmental fibers

Question 23

what fibers appear in 5 months

Answer 23

corticospinal fibers

Question 24

What occurs during the formation of teh synapse stage?

Answer 24

• Presynaptic membrane specialization
• Synthesis and distribution of receptors on the post-synaptic membrane
• Same target receives presynaptic connections from multiple sources therefore receiving far more than it needs

Question 25

What happens once the axons arrive at the target?

Answer 25

Random initial innervations occurs followed by a fall in the neuronal number
This is due to naturally occurring cell death and synaptic elimination and occurs because of competiton for a limited supply of trophic factors

Question 26

What are trophic factors

Answer 26

made by postsynaptic cells and are able to activate survival genes

Question 27

When does fine tuning begin to slow down?

Answer 27

after early adulthood

Question 28

What is the ongoing competition for synaptic connections dependent on

Answer 28

depends on experiences during critical periods of synaptogenesis

Question 29

when does myelinization begin?

Answer 29

happens after connections are made and begins in the 4th month but mostly after birth for long tracts

Question 30

when is myelinzation completed?

Answer 30

completed by age 3

Question 31

Why are fetal movements important?

Answer 31

•	Development of muscles and joints
•	Role of early reflexes
o	Muscle/skeletal formation
o	Assist in preparation for birth and birthing process
o	Early survival
o	Provide early movement out of womb

Question 32

Where does the brain create new neurons during adulthood?

Answer 32

hippocampus and olfactory bulb/tract