Each step must occur properly for normal development
Formation of the neural tube
Cell proliferation
Cell migration & differentiation
Growing of neural connections
Apoptosis or selective cell death or "pruning"
Myelination of axons and continued formation of synapses

Neural Crest Cells Become:
Sensory ganglia & incoming sensory nerves
Autonomic ganglia & nerves to organs
Parts of endocrine system related to NS (e.g. adrenal medulla)
Parts of eye and ear; some smooth muscles
Peripheral glial cells; pigmented cells

Neural Tube Defects (NTD)
Closure of the neural tube normal induces the normal development of spinal column, skull & overlying skin. If closure does not occur normally, nervous system may remain exposed ("open NTD"). In other cases the neural tube may not be exposed to the surface ("closed NTD"), but the spinal vertebrae and skin surrounding the spine may not be completely normal.

Improper Closing of the Anterior Neuropore (~ 25 days )
Anencephaly forebrain & its coverings fail to develop.
Baby has a flattened, open skull.
With only hindbrain & midbrain structures intact, survival is brief      (hours-days).

Anterior NeuroporeFails to Close Properly
Sometimes the forebrain develops but the skull does not fuse completely.
As a result part of the brain (often the occipital region) may bulge out of the opening.
This is encephalocele.

Improper migration of cells can cause abnormal development of brain areas, especially cortex

Much More Common: Improper Closing of PosteriorNeuropore(~27 days)
Spina bifida ("open spine")
May be so minor you don't know you have it ("spina bifida occulta"), or
may be so severe it causes death or disability
Has been linked to diet (insufficient folic acid), geography, and drugs, temperature, and illness during pregnancy, age of mom, and does tend to run in families.

3 Types of SpinaBifida

Prenatal Diagnosis
Open NTDs are associated with elevated levels of alpha-fetoprotein in mother's blood and amnionic fluid (~16-18 weeks)
Some NTDs are visible on ultrasound Some experimental surgeries to repair spinal abnormalities in utero

Healthy Sonogram

Signs of Anencephaly

Signs of SpinaBifida

Cerebral Palsy (500,000 in US) aka Static Encephalopathy
Not a single disease or disorder but a category of nonprogressive motor impairments that result from faulty brain development or early brain damage.
Specific motor symptoms vary, as does severity and presence of other disabilities.
Once thought to be primarily the result of difficult labors/birth injuries but majority of cases due to genetic, developmental, intrauterine factors.
(see study guide and CP website)

Autism
Developmental disorder with the following key features:
Impaired social interactions
Impaired verbal & nonverbal communication
Impaired cognition (unable to imagine, impaired imitation)
Restricted repertoire of activities and interests; often show repetitive and stereotyped behavior patterns

Once thought to be due to poor parenting
Growing evidence that autism results from an interaction between abnormal genes and environmental factors very early in development (in most cases).
Improper development of the neural tube at the pons/medulla junction (area of 7th & 8thcranial nerves & cerebellum) at 20-24 days as well as other congenital malformations of cerebellum, hippocampus, corpus callosum. Improper migration and apoptosis
Environmental factors: rubella, alcohol, valproate, thalidomide, PKU, & others

Fetal Alcohol Syndrome
Most common variety of drug-related faulty development, causing underdevelopment, distinctive physical features as well as nervous system impairments. Also affects cell division, migration and apoptosis.
FAS Facial Features