Chapter 7-Development

Question 1

When is the largest brain growth observed? (weight)

Answer 1

From birth to age 5

Question 2

When does brain weight begin to deteriorate?

Answer 2

Around age 30

Question 3

What causes the nervous system to be highly organized?

Answer 3

• During all stages of development the nervous system is highly organized due to genes, environment/experience, and the interaction of the two
• (Think nature vs nurture)

Ex. rats with low maternal licking and grooming will have genes altered in a way that causes high stress hormone levels, high anxiety, and low licking and grooming themselves. A rat with high maternal licking and grooming will have low stress hormone levels, low anxiety, and high self-licking and grooming

Question 4

What does the mesoderm layer of the embryo give rise to?

Answer 4

The skeleton and muscles

Question 5

What does the endoderm layer of the skin give rise to?

Answer 5

The internal organs

Question 6

What does the ectoderm layer turn into?

Answer 6

The nervous system and skin

Question 7

How is the neural plate formed?

Answer 7

• The neural plate is formed by the thickening of the extoderm
• The whole process is called neurulation

Question 8

What is neurulation?

Answer 8

The whole process of the neural plate being formed via thickening of ectoderm

Question 9

How is the neural groove formed and what does it give rise to? What is it?

Answer 9

• The neural groove is a shallow median groove of the neural plate
• Formed by uneven rates of cell division in the neural plate
• The neural plate is the future CNS

formed around day 20

Question 10

What is the neural crest?

Answer 10

• The neural crest cells are progenitors for the entire PNS
• Seen on top edges (tips) of the neural groove

formed around day 20

Question 11

What happens on day 18 of development?

Answer 11

The embryo consists of three layers of cells:endoderm, mesoderm, and ectoderm
-thickening of the ectoderm leads to development of the neural plate (first structure of the brain)

Question 12

What happens on day 20 of development?

Answer 12

• The neural groove begins to develop

Question 13

How is the neural tube formed?

Answer 13

• The neural groove joins together to form the Neural Tube with a fluid-filled central canal
• The neural crest cells are located on top of the canal

Question 14

What does the central canal and neural tube form?

Answer 14

• The central canal (fluid filled canal inside neural tube) will form ventricles and the spinal cord canal- w cerebral spinal fluid
• The cells lining the neural tube will be the progenitors for the entire CNS

Question 15

What happens on day 22 of development?

Answer 15

• The neural tube and fluid-filled central canal are formed by the neural groove joining together
• The rudimentary begininning of the brain is located at the anterior end
• The cranial end forks out to form the brain plate

Question 16

How is the brain plate formed?

Answer 16

• The cranial end of the ectoderm forks out to form the brain plate

Question 17

What happens on day 24?

Answer 17

The major brain divisions are discernible via sepearate sections within the brain plate area forming

Question 18

What does the telencephalon turn into?

Answer 18

• the cerebral cortex, limbic system, and basal ganglia

Question 19

What does the diencephalon turn into?

Answer 19

The thalamus and hypothalamus

Question 20

What does the rhobencephalon (hindbrain) give rise to?

Answer 20

• Cerebellum
• Pons
• Medulla

Question 21

What does the midbrain (mesencephalon) give rise to?

Answer 21

• The substantia nigra and VTA

Question 22

What happens around day 24 as a result of neurogenesis?

Answer 22

The cranial end of the neural tube swells

Question 23

What do neural crest cells become?

Answer 23

the neurons of somatic and autonomic nervous system

Question 24

What happens at day 25?

Answer 24

There is the start of a head

Question 25

What happens at day 40?

Answer 25

Folds in the head (not sulci and gyri)

Question 26

What happens at day 50?

Answer 26

You can tell the brain is distinctly human

Question 27

What happens at 100 days?

Answer 27

The surface of the brain is formed (but with no sulci and gyri)

Question 28

What happens at 10 weeks?

Answer 28

The brain is very similar to a rat's brain

Question 29

What happens at 15 weeks?

Answer 29

The brain is double the size of week 10

Question 30

What happens at 30 weeks?

Answer 30

Fissures and somewhat defined lobes w some grooves

Question 31

List the 6 stages of neural development

Answer 31

* Neurogenesis * Cell migration * Differentiation * Synaptogenesis * Neuronal cell death * Synapse rearrangement

Question 32

When are neurons generated?

Answer 32

* Most are generated before birth, some during childhood, and some during adulthood * The steep increase in brain weight from ages 1-5 is the result of neurogenesis in childhood * Research shows under very spedific conditions this can occur in adults as well

Question 33

What occurs during neurogenesis symmetric division?

Answer 33

* The cells lining the central canal, are known as the ventricular zone * Precursor cells divide symmetrically to expand the ventricular zone via mitosis * neurons and glial cells are dirived from the cells that originate from this ventricular mitosis

Question 34

What happens during neurogenesis- asymmetric division?

Answer 34

* The cell division switches to "asymmetric division" where one daughter cell migrates out, while the other continues to divide * The cell that stays on the outer surface becomes a neuron, while the one that stays on the inner surface (in ventricular zone) will replicate it

Question 35

Cell migration

Answer 35

* Cells move away from the ventricular zone using radial glial cells as guides * The migration is directed by cell adhesion molecules (CAMS) * As the marginal zone fills, the cortical plate is produced * As neurons migrate, they push past previous neurons to populate the outermost part of the cortical plate (layer 6 is built first)

Question 36

How is the brain region a cell ends up in during cell migration dictated?

Answer 36

based on where it was born in the ventricular zone

Question 37

What do radial glial cells do during cell migration?

Answer 37

* These cells connect the ventricular zone with a particular spot in the marginal zone * They act as guides, supporting a migrating neuron that wraps itself around the glial cell and climbs it to wherever it needs to be

Question 38

How do we get the six layers of the cortex?

Answer 38

* During migration, neurons push past previous neurons to populate the outermost part of the cortical plate * the waves of cells form the laminar structure in an inside-out manner

Question 39

Neuron differentiation

Answer 39

* When cells arrive at their destination, they begin to express genes to make the specific proeins they need * They differentiate (take on a specific final morphology- glia, neurons, and particular subtypes of each)

Question 40

What controls what a cell will differentiate into?

Answer 40

Intrinsic factors: Internal genetic/molecular signals Extrinsic factors: molecular/chemical influences around the cell

Question 40

What is sonic hedgehog and what does it do?

Answer 40

* A protein that the notochord (green) releases into ventral developing spinal cord, producing motor neurons (gold) * Transplant notochord to the dorsal side * Sonic hedgehog gene is how the dorsal and ventral roots differentiate, if you transplant the notochord to the dorsal, the motor neurons will be formed in the dorsal spinal cord | notochord is a tube like structure underneath the neural tube

Question 40

Synaptogenesis

Answer 40

* Almost all neurons are generated by birth, but most synapses form post-natal * Neurons must grow axons and dendrites, and make correct synapses/connections * When synapses start to form there's basically "over-connection," everything seems interesting, then pruning happens to become more efficient * Growth cones grow towards another neron and form a synapse, target cells will repel or attract

Question 40

Synaptogenesis- Explain how growth cones work

Answer 40

* Cells/tissue secrete chemicals that attract/repel specific axons/dendrites * Chemoattractive vs chemorepulsive molecules * Two structures that should be connected share a common chemical substrate that lays down the pathway between them

Question 41

Cell death

Answer 41

* Initial neurogenesis overproduces cells, so there is a selective elimination of those not necessary * This depends on if it receives neurotropic factors from target cells that it synapses with * Apoptosis

Question 41

What happens during apoptosis?

Answer 41

* Unneeded cells are instructed to die via a phenomenon of programmed cell death, or apoptosis * Ca2+ influx causes diablo protein to be released, which blocks the inhibitors of apoptosis proteins (IAPs) * This causes widespread biochemical changes, leading to cell death

Question 41

What happens during synapse rearrangement/remodeling?

Answer 41

* The initial synaptogenesis overproduces synapses so they are selectively eliminated (AKA pruned) * Selective formation of new synapses (this continues for life) * Regulated by neuronal activity (action potentials), "neurons that fire together, wire together" * selective formation of new formation is what allows learning to occur * neurons thtat coordinated info and respond in a similar time will be connected together

Question 42

How is gray and white matter affected with age?

Answer 42

* White matter increases as you age (myelin sheath)... signal transduction becomes better as a person ages

Question 43

How is PFC and Striatum connection affected w age?

Answer 43

* PFC (decision making) and striatum (reward processing) barely connects in children, but is very strong in adults especially around 25 years old * the Striatium to PFC is strong for children (but not PFC to striatum) which leads to strong reward processing with not great decision making skills