What is neuralation?
The early process of differentiation from embryonic tissue to the development of the nervous system.
Specifically, it involves the development, folding, and closing process of the nerual tube from the neural plate.
What is the chronological sequence of events involved in neuralation?
first the neural plate appears from the ectoderm.
Then a neural grove forms as the plate begins to fold. (18 days)
Then it closes first at the midpoint, then at the anterior to form the neural tube (3-4 weeks)
Cells proliferate in the neural tube, leading to the development of vesicles.
What are the possible neural tube defects?
Failure of anterior to close--> anencephaly
Failure of posterior to close--> spina bifida
What are the primary vesicles? What structure causes their developement? When do they start to develop?
Forebrain, Midbrain, Hindbrain, Spinal Cord
Neural Tube (cell proliferation after closing)
4 weeks
What are the Secondary vesicles? What structure causes their development? At what time do they start to develop?
Secondary vesicles are the Primary ones with more specification:
Forebrain (Cerebral Hemispheres, Hypothalamus, and Thalamus), Midbrain, Hindbrain (Pons medulla and cerebellum), Spinal Cord
Neural tube cause their development
5 weeks
How large is the brain at birth? How large is an adult sized? By what age does the brain reach adult size?
At birth: 300-350g
Adult size: 1250-1500g
Reaches adult size by age 4
What occurs during the fetal period? At what time does this occur?
Cells begin to migrate.
8-10 weeks
What is the result of cell migration (during which development phase is this happening)? When does this result occur (week or months)?
the development of the cortical layers during the fetal period
6 months
At what time is the brain considered developed?
9 months
What happens at the 5th month of fetal development to the brain?
Convolutions and sulci begin to develop over the smooth surface of the brain due to the increased cell density
What parts of the cell is increased cell density attributable to?
glial cells, myelination, axons, dendrites,
What is a teratogen? What are some examples? What can teratogens lead to? When are organ systems most affect by teratogens?
A teratogen is a threat to development. they are agents that can cause congential abnormalities and/or development inteferrance
Examples: infections, drugs, alcohol, radiation, environmental pollutants
Whatever organ system is rapidly developing during the introduction of the teratogens is the most affected.
What are some threats to development during the pre-embryonic phase? The embryonic phase? the fetus phase?
Pre-embryonic- teratogens effect ALL cells and result in DEATH
Embryonic- bc of organ and tissue differentiation of this period, there is extreme sensitivity to teratogens. Exposure can lead to severe functional/morphological defecits.
Fetus- organ/tissue differentiation has passed, so less sensitivity. Exposure results in smaller number and size of cells.
What are the six microscopic neural processes happening during gestation?
1. Cell proliferation
2. Cell differentiation
3. Cell migration
4. Synaptogenesis
5. Selective Cell Death/ Pruning
6. Myelination
What is Cell proliferation?
The development of new cells (aka neurons). Most are developed by 4-6 weeks gestation. More are produced than will be needed.
What is Cell differentiation?
The designation of different types of cells/neurons to serve different functions
What is cell migration?
The movement of cells/neurons to their proper location in the CNS.
Glial cell guide the process.
Formed in an inside-out fashion (deeper layers created first)
Errors corrected by later pruning/cell death
abnormalties can lead to things like dyslexia, epilepsy and MR
What is Synaptogenesis?
The phase where cells build their connections via extensions of the axons (terminal buttons/synapses) to dendrites
Begins at 7 weeks gestation, countinues after birth
cells that don't create connections die
more created than needed.
What is selective cell death/ pruning?
a microscopic gestational cell process that initiates at 7 months gestation (an continues thru life).
Cells without connections, erroneous cell migration cells, and extra synapses are eliminated.
Another decline at 4 years (reached peak size)
prenatal cell death is genetic. Post natal is based largely on experience.
What is myelination?
Begins at 4-5 gesation and focuses on the primitive areas first (brain & spinal cord, aka the primary vesicles)