Neuodevelopment and Associated Disorders

1st stage of embryogenesis where neurulation occurs

1st stage of embryogenesis where neurulation occurs

Dorsal Induction

Part of embryogenesis where the cells that become the central nervous system fold over to form a neural tube

Neurulation

When does neurulation occur?

3-7 weeks of gestation

A disorder where the neural tube does not close or produce a brain. (the infant is stillborn and has organs but no brain)

Anencephaly

Disorder where the posterior neural tube doesn’t close which causes problems with the brain stem

Myelomeningocele / Spina Bifida

Where the folding over of the neural tube is completed

Secondary neurulation

When does secondary neurulation occur?

4-7 weeks of gestation

2nd stage of embryogenesis where the brain forms, left and right hemisphere split, and cerebral cortex separates from rest of lower brain structures

Ventral Induction

When does ventral induction occur?

5-6 weeks of gestation

Disorder where the brain fails to divide properly into the right and left hemispheres. This can cause a single brain sphere and facial abnormalities (ex. a single eye)

Holoprosencephaly

3rd stage of embryogenesis where brain development happens through cell division, and the new cells that are produced move past older cells to form brain structures

Neural Proliferation

When does neural proliferation occur?

2-4 months of gestation

Where too few brain cells form during neural proliferation

Microcephally

Where too many brain cells form during neural proliferation

Macrocephally

4th stage of embryogenesis where brain development happens in which older cells move past newer cells due to glial cells acting as ladders for older cells. Gyri form at this time.

Migration Period

When does the migration period occur?

3-5 months of gestation (overlaps with neural proliferation stage)

Disorder where ladders of the glial cells do not go to certain parts of the brain and cause gyri to not be created in those areas

Schizencephaly

Disorder where the brain does not form sulci and gyri

Lissencephaly

Disorder that causes abnormally wide gyri and subsequently not enough gyri

Pachygyria

Disorder that causes abnormally small gyri and subsequently too many gyri

Polymicrogyria

Disorder that causes neurons to not migrate completely, which lead to islands or pockets of neurons in a specific area

Heterotopia

5th stage of embryogenesis where the brain needs help from the environment to form properly (connections of axons and dendrites). Cell death and selective elimination occur

Organization

When does organization occur?

6 months to several years post natal

Disorder that can be caused by poor brain organization

Mental Retardation

Chromosomal disorder that causes an abnormal number of axons and dendrites, as well as poor connections between them

Down’s Syndrome

6th and final stage of embryogenesis where myelin begins to wrap around axons to promote efficient electrical communications

Myelination

When does myelination occur?

Birth to about 35 years of age

Anencephaly and myelomeningocele / spina bifida occur during which stage of embryogenesis?

Dorsal Induction

Holoprosencephaly occurs during which stage of embryogenesis?

Ventral Induction

Microcephally and Macrocephally occur during which stage of embryogenesis?

Neural Proliferation

Schizencephaly, lissencephaly, pachygyria, polymicrogyria, and heterotopias occur during which stage of embryogenesis?

Migration Period

Mental retardation and Down’s Syndrome occur during which stage of embryogenesis?

Organization Period