What is gastrulation?
When the bilaminar disc becomes the trilaminar disc Go from hypoblast and epiblast to endoderm, mesoderm and ectoderm
How is the neural tube formed?
Induction of the neural plate
Elevation of its lateral edges
The depressed mid region is the neural groove
Neural folds crash ally approach each other in the midline and fuse, producing the neural tube
What does the notochord serve as the basis of?
The midline, axial skeleton and neural tube
Where does fusion of the neural folds begin?
In the cervical region, then proceeds in both a cranial and caudal direction
What is neurulation?
The notochord-driven induction of ectoderm leading to formation of the neural plate and neural tube
When does neurulation begin?
When do the anterior and posterior neuropores close?
Anterior - day 25
Posterior - day 28
What are the different neural tube defects and how do they occur?
Spina bifida - failure of the neural tube to close caudally
Anencephaly - failure of the neural tube to close cranially
Where does spina bifida most commonly occur?
The lumbosacral region (but can occur anywhere along the length of the spinal cord)
What normally happens as a result of spina bifida?
Hydrocephalus nearly always
Not associated with mental retardation
What can happen if hydrocephalus is not treated in spina bifida?
Can cause cognitive delay
What are the different types of spina bifida?
Spina bifida aculta - no visible cyst, stays within the body column. Can be asymptomatic
Meningocoele - The arachnoid and meninges herniate out of the spinal cord
Myelomeningocoele - Both the neural tissue and meninges herniate out
What happens in anencephaly?
Failure of neural tube closure cranially
Absence of cranial structures including the brain
Not compatible with life
What is rachischisis?
Failure of neural fold elevation leading to a splayed neural tube
How are neural tube defects diagnosed?
Raised maternal serum alpha-fetoprotein
How to prevent neural tube defects?
Take folic acid for 3 months pre-conception and then for the first trimester
What is the cauda equina?
When the vertebral column grows faster than the spinal cord, the spinal roots need to elongate to exit at their intervertebral foramen, and so form the cauda equina beneath the spinal cord
Names for the forebrain, midbrain and hindbrain?
Forebrain = prosencephalon
Midbrain = mesencephalon
Hindbrain = rhombencephalon
How do the forebrain, midbrain and hindbrain develop?
During neural fold formation, three primary brain regions develop.
After neural tube closure in the fourth week, the dilations become the three primary brain vesicles
When do the secondary brain vesicles develop?
At 5 weeks of development
What are the folds in the cranial neural tube?
Cervical flexure: spinal cord-hindbrain junction
Cephalic flexure: midbrain region
Why do flexures develop in the neural tube?
Because there is not enough available space if the tube just grows linearly.
Role of the ventricular system?
Cushion the brain and spinal cord within their bony cases
How is congenital hydrocephalus treated?
Use a shunt
What can cause hydrocephalus in a newborn?
Any blockage in the ventricular system
E.g. tumour, infection
What do the roof and floor plates of the neural tube do later on?
Regulate dorsal and ventral patterning
Alar plate - sensory
Basal plate - motor
Where are neural crest cells found intitially and what do they do?
In the lateral border of the neuroectoderm tube
Become displaced and enter the mesoderm. Undergo epithelial mesenchymal transition
In the nervous system, name some things that are derived from neural crest cells
Cranial nerve ganglia
Dorsal root ganglia
Leptomeninges (arachnoid and pia)
What is derived from neural crest cells outside of the nervous system?
Connective tissue and bones of face and skull
Dermis of face and neck
C-cells of thyroid gland
Conotruncal septum of the heart
What can cause defects in neural crest cell migration?
Environmental insult, especially alcohol
What is the syndrome seen when there is a defect in neural crest cell migration affecting multiple structures?
- Cardiac defects
- Abnormal faces
- Thymus aplasia
- Cleft palate
- 22 chromosome
What is the name of the syndrome when there is a defect in neural crest cell migration affecting one structure?
Hirschsprung's disease (aganglionic megacolon)
What are the layers of the neural tube?
The neuroepithelial layer made of neuroepithelial cells
The intermediate layer (mantle layer) made of neuroblasts
The marginal layer which has processes