Lecture 7 -- Neurodevelopment

Question 1

What are the six stages of neural development?

Answer 1

Neurogenesis
Cell migration
Cell differentiation, Synaptogenesis
Neuronal cell death
Synapse rearrangement

Question 2

What occurs during neurogenesis?

Answer 2

The mitotic division of non-neuronal progenitor cells to produce neurons occurs in the ventricular zone of the neural tube.

Question 3

What happens during cell migration?

Answer 3

Neurons or their precursors move to establish distinct nerve cell populations (e.g., layers of the cortex).

Question 4

What are 2 methods of migration?

Answer 4

SOMAL TRANSLOCATION: an extension develops that leads migration; the cell body follows

GLIAL-MEDIATED: the cell moves along a radial glial network.

Question 5

What is cell differentiation and 3 important processes or involved molecules?

Answer 5

The process by which cells become specialized as neurons or glial cells, guided by gene expression and local cell-cell interactions. Cells align themselves with
others cells and form structures

1. Aggregation - The collection and formation of neighbouring cells
2. Cell-Adhesion Molecules (CAMs) - aid migration and aggregation be recognizing and adhering to molecules
3. Gap junctions pass cytoplasm between cells. May play a role in aggregation and other processes

Question 6

What is synaptogenesis?

Answer 6

The formation of synaptic connections between neurons as axons and dendrites grow.

Question 7

What is neuronal cell death (apoptosis), and why is it important?

Answer 7

The selective, programmed death of neurons; crucial for refining neural circuits and preventing overgrowth.

Question 8

What happens during synapse rearrangement?

Answer 8

Synaptic connections are refined—some are lost and others are strengthened—throughout life.

Question 9

What does Roger Sperry’s Chemoaffinity Hypothesis propose?

Answer 9

Axons differentially recognize chemical signals produced by target matching cells.

In this way, neurons connect only to specific cells or groups of cells.

Trophic factors are synthesized by target tissues and made available to developing neurons in order to guide their potential axonal pathway

Question 10

What two phases of brain development involve loss of structures?

Answer 10

Neuronal cell death, Synapse rearrangement

Question 11

What guides a developing neuron to take on the right structure and function?

Answer 11

Cell-cell interactions that influence gene expression and chemical signaling from neighboring cells.

Question 12

What are stem cells, and why are they important in brain development?

Answer 12

Undifferentiated cells that can become neurons or glial cells; they may integrate into damaged regions of the brain and replace lost functions.

Question 13

Why is adult neurogenesis significant?

Answer 13

It contributes to learning and memory, particularly in the hippocampus; influenced by factors like exercise and enriched environments.

Question 14

Where in the adult brain does neurogenesis primarily occur?

Answer 14

In the dentate gyrus of the hippocampus.

Question 15

What are neurotrophic factors?

Answer 15

Chemicals released by target structures that promote neuron survival by supporting those that make successful synaptic connections.

Question 16

What happens to neurons that don’t receive enough neurotrophic factors?

Answer 16

They undergo apoptosis and die.

Question 17

What is apoptosis?

Answer 17

Programmed cell death, an essential process for shaping the nervous system and eliminating excess neurons.

Pruning cells that are not in the right location. 40% of neurons are killed.

Question 18

What does interfering with apoptosis do? What about removing it?

Answer 18

Interfering leads to the developmental disorders (EX: Fragile X syndrome) If we remove apoptosis (experiment that makes mice lack the “death” gene) we can see an enlarged brain.

Question 19

When does the nervous system begin to form during development?

Answer 19

Shortly after fertilization, from the ectoderm layer, forming the neural groove and then the neural tube.

Question 20

What are the three initial subdivisions of the brain in the neural tube?

Answer 20

Forebrain (cortex, thalamus, hypothalamus), midbrain, and hindbrain (cerebellum, pons, medulla).

Question 21

What is synapse rearrangement (synaptic remodeling)?

Answer 21

A developmental process in which some synapses formed early are lost and many new ones are formed, typically after the period of neuronal cell death.

Question 22

When does synapse rearrangement occur during development?

Answer 22

After the period of naturally occurring neuronal cell death.

Question 23

What drives which synapses are retained and which are eliminated?

Answer 23

Neural activity and competition for neurotrophic factors; active synapses are stabilized, while inactive ones are pruned.

Question 23

what may underlie the greater plasticity of the young brain?

Answer 23

Overproduction of synapses during synaptic rearrangement

Question 24

How does cortical gray matter change during adolescence?

Answer 24

It thins due to pruning of dendrites and axon terminals, with changes proceeding from back (caudal) to front (rostral); the prefrontal cortex matures last. It thins for adult-level cognitive and emotional functioning.

Question 25

What is the functional benefit of synapse pruning?

Answer 25

It refines neural circuits, improving efficiency and cognitive function. Excess synapses can impair intellectual development.

Question 26

What condition demonstrates the negative effects of insufficient synapse pruning?

Answer 26

Fragile X syndrome; individuals have too many immature dendritic spines, which may contribute to intellectual disability.

Question 27

What does fragile X syndrome reveal about synaptic development?

Answer 27

That failure to eliminate excess synapses can impair normal brain function and cognitive development.

Question 28

How does early visual experience affect brain development?

Answer 28

It’s crucial for proper development of the visual system; deprivation can lead to permanent deficits such as amblyopia.

Question 29

What is amblyopia?

Answer 29

A condition where vision in one eye is reduced due to lack of use or misalignment, despite the eye being physically normal.

Question 30

What is binocular deprivation and its effect on development?

Answer 30

Blocking vision in both eyes early in life causes loss of dendritic spines and synapses in the visual cortex, leading to blindness even if eyes later function normally.

Question 31

What is monocular deprivation and how does it affect the brain?

Answer 31

Blocking vision in one eye during the sensitive period alters the structure and function of the visual cortex, favoring input from the non-deprived eye.

Question 32

What is a critical (sensitive) period in visual development?

Answer 32

A limited time in early life when visual input is required for proper development of vision; deprivation during this period causes permanent deficits.

Question 33

What is an ocular dominance histogram?

Answer 33

A graph showing how many neurons in the visual cortex respond preferentially to input from one eye versus the other.

Question 34

How does monocular deprivation alter an ocular dominance histogram?

Answer 34

It shifts the distribution so most neurons respond only to the non-deprived eye.

Question 35

What are Hebbian synapses?

Answer 35

Synapses that grow stronger when they effectively activate the postsynaptic cell; "cells that fire together, wire together."

Question 36

How do Hebbian synapses affect visual system development?

Answer 36

Effective synapses from active eyes are maintained and strengthened, while inactive ones from a deprived eye are lost.

Question 37

What neurotrophic factor is implicated in synapse rearrangement in the visual cortex?

Answer 37

Brain-derived neurotrophic factor (BDNF).

Question 38

Why did Michael May continue to have poor vision even after regaining sight?

Answer 38

He was deprived of patterned visual input during a sensitive developmental period, preventing proper synaptic development in the visual cortex.

Question 39

What lasting effect can early cataracts have on infants, even after removal?

Answer 39

Impaired face recognition and visual processing due to disrupted visual experience during early development.

Question 40

In prenatal brain development, how many cell types are there?

Answer 40

200 differentiated cell types that start to form appropriate functional connections

Question 41

What is Gastrulation?

Answer 41

the process by which a gastrula forms from a blastula: "during gastrulation, cells move into the interior of the embryo"

Question 42

What are the 3 layers of cells?

Answer 42

Consists of 3 layers of cells: Ectoderm -- tissue that becomes different kinds of things that are on the surface of our body (EX: enamel, skin) Mesoderm -- forms muscular structures of the body. Ectoderm -- Layer that forms

Question 43

When can we differentiate the 4 lobes?

Answer 43

within the first 8 weeks developmentally we can differentiate the 4 lobes, but after 10 months of conception the brain is fully formed

Answer 44

Observations of the effects of neurotrophic growth factors as a chemotrophic molecule have defined four criteria that must be satisfied before concluding that a certain molecule is a trophic factor:

Answer 45

Changes in cognitive function with aging linked to reduction in hippocampal volume correlated with memory decline.