SHS 567 Module 1: Conception to Birth

What is the overall sequence from fertilization to neural plate formation?

Zygote → Morula → Blastocyst → Gastrulation → Neural Plate

What is a zygote?

A fertilized cell that begins dividing

What is a morula?

A solid ball of approx. 16-32 cells formed after early cell divisions.

What is a blastocyst?

A stage in which cells compact and a cavity forms.

What happens during gastrulation?

Cells undergo major rearrangement, and the neural plate begins to form.

What are the 3 stages of neural tube formation?

Neural plate → neural groove → neural tube

Around what days does the neural tube close?

Approx. days 22-26

In what direction does the neural tube closure occur?

It begins around the middle and proceeds outward toward both ends.

What does the neural tube become?

The central nervous system (CNS)

What does the CNS include?

Brain and spinal cord

What does the neural crest become?

Primarily structured of the peripheral nervous system (PNS)

What do somites become?

Spinal vertebrae

What are the two neuropores?

The anterior neuropore and posterior neuropore

What happens if the anterior neuropore fails to close?

Anencephaly

What happens if the posterior neuropore fails to close?

Spina Bifida

What is anencephaly?

A neural tube defect resulting from failure of the anterior neuropore to close, preventing normal development of the forebrain.

What is Spina Bifida?

A neural tube defect resulting from failure of the posterior neuropore to close, leaving the spinal cord and vertebrae exposed.

What is DNA?

The molecule that carries genetic instructions.

What is a gene?

A segment of DNA that codes for a particular function or trait.

What is a chromosome?

A packaged structure of DNA; humans normally have 46.

What is a trait?

An observable characteristic or outcome.

What is an inheritance?

The passing of genetic material from parent to child.

What is the difference between a gene and a chromosome?

A gene is a segment of DNA, while a chromosome is a packaged DNA structure containing many genes.

What two major factors influence traits and development?

Genes and environment

Why is it important to consider both genes and environment?

Traits and developmental outcomes are rarely determined by genetics alone; environmental experiences also influence development.

What happens to the anterior neural tube during early brain development?

It swells into three primary brain vesicles.

What are the 3 primary brain vesicles?

Forebrain, midbrain, hindbrain

When are the three primary brain vesicles present?

Around week 4

How many secondary brain vesicles develop from the three primary vesicles?

5

When do the five secondary brain vesicles develop?

Around week 6

What does the forebrain develop into?

Telencephalon + diencephalon

What does the midbrain develop into?

Mesencephalon

What does the hindbrain develop into?

Metencephalon + myelencephalon

What does the telencephalon become?

Cerebral hemispheres, cerebral cortex, and basal ganglia

What does the diencephalon become?

Thalamus and hypothalamus

What does the mesencephalon become?

Tectum, tegmentum, and cerebral aqueduct

What does the metencephalon become?

Pons and cerebellum

What does the myelencephalon become?

Medulla

What are the five major processes involved in brain development?

Proliferation → Migration → Differentiation → Aggregation → Synaptogenesis

What is proliferation?

The process of producing new cells through cell division

Where does neuronal proliferation occur?

In the ventricular zone.

About how many cells can be produced per minute during peak proliferation?

Approximately 250,000 cells/minute.

What does post-mitotic mean?

A cell has permanently exited the cell cycle and no longer divides.

What is migration?

The movement of newly produced neurons to their appropriate locations.

What are radial glial cells?

Cells that act as guide wires for migrating neurons.

What is radial migration?

Neurons move from the ventricular zone toward the surface along radial glial fibers.

How does radial migration build the cortex?

It creates an inside-out pattern, with later-born neurons moving past earlier-born neurons to form more superficial layers.

What is differentiation?

The process by which neurons become specialized in structure and function.

What is aggregation?

Neurons find one another and organize into functional groups or layers.

What is synaptogenesis?

The process of forming synapses between neurons.

What do axonal growth cones do?

They seek out target cells using chemical gradients.

What is synaptic pruning?

What is synaptic pruning?

Is pruning a malfunction?

No. It is a deliberate and adaptive part of normal brain development.

Approximately what percentage of neurons born do not survive?

Approximately 40–75%.

Why do some neurons survive while others do not?

Neurons compete for limited neurotrophic factors from target cells. Well-connected neurons receive support and survive, while poorly connected neurons may undergo programmed cell death.

What is programmed cell death called?

Apoptosis.

What is myelination?

The development of myelin around axons, which supports efficient neural communication.

When does myelination begin?

Prenatally

Does myelination stop at birth?

No. It continues for years and can continue into adulthood.

Which areas of the brain finish myelinating last?

Association areas, which can continue developing until approximately age 30.

What is a teratogen?

Anything that can disrupt normal prenatal development.

What are three categories of teratogens?

Physical, chemical, and microorganisms

Give an example of a physical teratogen.

radiation exposure

Give examples of chemical teratogens.

Alcohol, certain medications, toxins

Give an example of a microorganism teratogen.

Certain infections during pregnancy