week 9

Question 1

by the time fetus reaches __ weeks, the fetal brain has started productions of all necessary structures/features of brain that exist in adults.

Answer 1

8

Question 2

what are the five EARLY divisions/prenatal phases?

Answer 2

1. induction of neural plate
2. neural proliferation
3. migration + aggregation
4. axon growth + synapse formation
5. neuron death + synapse rearrangement

Question 3

what is gastrulation?

Answer 3

when embryo transforms from a one-dimensional layer (blastula) and reorganizes into a multilayered + multidimensional structure (gastrula).

Question 4

what are the 3 layers of cells after gastrulation? what do they form?

Answer 4

1. ectoderm: cells that become surface structure of body (skin, hair, nails, eye lens, sebaceous glands, tooth enamel + brain foundations).
2. mesoderm: cells that become cardiac muscles, skeletal muscles, smooth muscles/tissue.
3. endoderm: produces cells that become stomach, colon, liver, pancreas, bladder, etc.

Question 5

describe nervous system at day 18 post-conception (2)

Answer 5

• ectoderm thickens, leads to dev of neural plate.
• thickening triggered by chem signals produced by mesoderm.

Question 6

describe nervous system at day 20 post-conception (2)

Answer 6

• neural groove deepened (develops into CNS).
• begin to see neural crest (develops into PNS).

Question 7

what do the lateral, middle, and medial row of the flattened neural groove give rise to?

Answer 7

lateral: sensory neurons

middle: interneurons

medial: primary motor neurons

Question 8

describe nervous system at day 22 post-conception (1)

Answer 8

• crest of neural groove comes together to form neural tube.

Question 9

at what day post-conception are the major divisions of the brain present?

Answer 9

25

Question 10

approx. how many neurons are produced each minute pre-natal?

Answer 10

~250,000

Question 11

what happens when neurons migrate to the wrong areas of the brain?

Answer 11

• disorders like epilepsy, dyslexia, schizophrenia etc. emerge

Question 12

what are the 6 stages of nervous system development?

Answer 12

1. neurogenesis
2. migration
3. differentiation
4. synaptogenesis
5. apoptosis
6. rearrangement

Question 13

describe neurogenesis in terms of the neural tube (2)

Answer 13

• neural tube becomes thick/enlarged.
• innermost layer continues producing neurons while outer parts produce grey and white matter.

Question 14

describe the 2 processes of migration

Answer 14

• somal translocation: extension develops that leads migration; the cell body follows. local process, takes long time (i.e., 1mm/day).
• glial-mediated migration: cell moves along a radial glial network (“railroad tracks” that neurons can jump onto). global process, still slow but more effective for long distances.

Question 15

describe differentiation (3)

Answer 15

• after migration, cells align themselves with others cells and form structures.
• use Cell-Adhesion Molecules (CAMs) which recognize and adhere to molecules.
• pass cytoplasm b/w cells.

Question 16

how can undifferentiated cells be of great promise to treat neurological disorders? provide an example (3)

Answer 16

• could potentially treat neurological disorders by putting undifferentiated cells in affected areas.
• e.g., sub nigra of ppl with parkison’s.

note: easy to get cell into right place; difficult to ensure it becomes right type of cell.

Question 17

describe roger sperry’s experiment (4)

Answer 17

• wanted to determine if we’re like blank slates or preprogrammed (chemoaffinity hypothesis = axons recognize target cells via chem signals).
• cut b/w the retina + optic tectum of tadpoles (analogous to their visual cortex).
• rotated eye 180 degrees and allowed connection to regenerate.
• frog saw world as upside down, indicating that our synaptic connections are preprogrammed/guided.

Question 18

what are trophic factors?

Answer 18

helper molecules that allow a neuron to develop and maintain connections with its neighbors

Question 19

what are the 4 criteria that must be satisfied before concluding that a certain molecule is a trophic factor?

Answer 19

1. cell deficit/death in absence.
2. cell surplus/survival in presence.
3. trophic factor produced at target site.
4. receptors for neurotrophic factors on nerve endings.

Question 20

describe apoptosis (1) and how does this process look like in human embryos (1)?

Answer 20

• normal + necessary cell death.
• e.g., human embryo begins with 175k at 10 weeks post-conception and loses approx. 20% of all neurons by ~30 weeks as a result of not receiving enough trophic factors.

Question 21

what happened to the mouse lacking ‘death’ gene?

Answer 21

brain became so enlarged that it pushed out of skull.

Question 22

describe rearrangement (1), when does this occur for humans (1)?

Answer 22

• synapses rearrange to form optimal connections (mainly dendrite growth).
• post-natal process for humans.

Question 23

describe synaptic density and arrangement across the lifespan (2)

Answer 23

• looks like “sticks” as newborn, more “branches” form with age, adult looks like a “jungle” [slide 43].
• over-proliferation of connections followed by period of refinement where most effective connections are maintained and others die.

Question 24

approximately __ percent more synapses than needed are produced.

Answer 24

50%

Question 25

overproduction of synapses may underlie the greater ___ of the young brain.

Answer 25

plasticity

Question 26

a) which neurons have earliest proliferations and earliest drop-offs?

b) which neurons increase more slowly, reach their peak later and have a longer period of refinement?

Answer 26

a) sensory neurons

b) prefrontal cortex

[slide 45]

Question 27

rearrangement of synapses typifies the ___ of that particular development.

Answer 27

critical period

Question 28

what happens when there is more activity in one eye than the other, i.e., in cases of infantile cataracts (2)? what does this demonstrate about the role of experience (1)?

Answer 28

• connections from deprived eye to visual cortex shrink, while connections from the good eye expand.
• if not treated before critical period, restoring vision in cataract eye will not produce normal sight because brain is not using info from that eye.
• demonstrates that experience affects how brain organizes itself.

Question 29

what does the prefrontal cortex play a role in? (3)

Answer 29

• working memory
• planning and carrying out sequences of actions
• inhibiting inappropriate responses

Question 30

T or F: with age, reorganization levels in the brain decrease.

Answer 30

true

Question 31

what is the denate gyrus part of? what is its significance?

Answer 31

• denate gyrus = part of hippocampus
• evidence of neurogenesis in the dentate gyrus in the adult brain.

Question 32

T or F: despite the hippocampus shrinking with age, it produces enough new cells to mitigate effects of aging?

Answer 32

false