Brain Development

Which embryonic cell layer gives rise to the nervous system?

The ectoderm, the outermost of the three early cell layers.

What are the three early embryonic cell layers?

Endoderm, mesoderm, and ectoderm.

What is the neural groove?

A groove formed as cells along the ectoderm's midline thicken.

How does the neural tube form?

The neural groove folds and its sides fuse.

What does the neural tube develop into?

The central nervous system.

What do neural crest cells become?

They migrate and contribute to the peripheral nervous system.

What are the three primary brain vesicles?

Forebrain, midbrain, and hindbrain.

Which regions are listed as forebrain structures?

Cortex, thalamus, and hypothalamus.

Which structures are listed as hindbrain structures?

Cerebellum, pons, and medulla.

What do the hollow interior of the neural tube and its spinal extension become?

The brain's fluid-filled ventricles and the spinal cord's central canal.

What is the difference between an embryo and a fetus in the slides?

Embryo: the first 10 weeks after fertilization; fetus: from week 10 on.

What is neurogenesis?

Mitosis producing neurons from non-neuronal precursors.

Do mature neurons themselves divide according to the slides?

No. Neural stem-cell proliferation produces new neurons; neurons themselves do not divide.

What is cell migration during development?

New neurons move from the ventricular zone to their final positions, guided by signals and cellular scaffolds.

What role do radial glia play?

They provide pathways along which developing neurons migrate.

What is cell differentiation?

Cells express particular genes and become distinctive types of neurons or glia.

What is synaptogenesis?

The formation of synaptic connections as axons and dendrites grow.

Why is programmed cell death a normal part of brain development?

It eliminates excess or poorly connected neurons and helps refine neural circuits.

What is apoptosis?

Programmed cell death.

What are neurotrophic factors?

Target-derived chemicals that support neurons.

How does neurotrophic-factor competition affect neuron survival?

Neurons receiving enough neurotrophic factor survive; those receiving too little die.

What is synapse rearrangement, or synaptic remodeling?

The loss and gain of synapses that fine-tunes circuits.

Does synapse rearrangement stop in adulthood?

No. It continues throughout the lifespan and supports learning and adaptation.

What is adult neurogenesis?

The birth of new neurons in adulthood, highlighted in the slides as occurring most prominently in the dentate gyrus of the hippocampus.

What factors are listed as boosting adult neurogenesis?

Exercise, environmental enrichment, and training.

What happens to synapse numbers in human cortex from late childhood to mid-adolescence?

There is a net loss of synapses as unused connections are pruned.

Why can losing synapses improve brain function?

Weak and unused connections are removed, circuits become more efficient, signal-to-noise improves, and behavior is controlled more precisely.

What does “use it or lose it” mean for synapses?

Used synapses are strengthened, while unused ones are eliminated.

Which brain region develops last according to the slides?

The prefrontal cortex.

What does caudal-to-rostral cortical thinning mean?

Developmental thinning proceeds from back to front.

How can later prefrontal development relate to adolescence?

It is one reason for adolescent impulsivity and the slow maturation of decision-making.

What is Fragile X associated with in the slides?

An excess of small, immature dendritic spines and a failure of normal postnatal synapse elimination.

What are critical or sensitive periods?

Windows when experience shapes brain structure; early visual experience is required for normal vision development.

Application: A developing neuron is produced but ends up in the wrong brain region. Which developmental process was disrupted?

Cell migration.

Application: A neural precursor becomes a specific type of neuron after expressing particular genes. Which process is this?

Cell differentiation.

Application: Many neurons are initially produced, but some die because they receive too little target-derived support. What explains this?

Apoptosis and competition for neurotrophic factors.

Application: A child loses unused synapses while frequently used connections are strengthened. What process is occurring?

Synapse rearrangement or synaptic pruning.

Application: A visual system develops abnormally because appropriate visual input was missing during an early window. What concept explains this?

A critical or sensitive period.

Application: A teenager's decision-making is still maturing because the prefrontal cortex develops late. What developmental pattern does this illustrate?

Cortical development proceeds from back to front, with the prefrontal cortex developing last.