Development of the Nervous System Flashcards
In which week does the neural tube begin to develop?
Week 4, after the 3 germ layers (ectoderm, mesoderm, endoderm) are formed by gastrulation in week 3.
Describe the 5 steps involved in the formation of the neural tube.
- Gastrulation produces the notochord
- The notochord releases signalling molecules which are diffusion limited. They induce differentiation of overlying ectoderm into neuroectoderm.
- The signalling molecules also promote thickening of the neuroectoderm into the neural plate.
- Elevation of the lateral edges, and depression of the middle region of the neural plate (neural groove) begins to form a tube down the length of the embryo.
- Neural folds meet at midline and fuse forming neural tube.
Where do neural crest cells emerge from?
NCCs form at the lateral border of the neuroectoderm tube.
They leave the tube and enter the mesoderm where they undergo epithelial–>mesenchymal transition.
They then spread throughout the body.
What are the openings at the end of the neural tube called? Which one closes first?
Anterior / Cranial neuropore (closes first)
Posterior / Caudal neuropore
By what day is the NT completely closed in development?
Day 28-32
What conditions arise if the neuropores fail to close properly?
Ant. neuropore = Anencephaly
Post. neuropore = Spina bifida
What condition arises if the neural plate fails to elevate / fold?
Raschichisis = incompatible with life
What are the different types of spina bifida? Which one is worse?
Meningocoele = CSF filled cyst, with spinal cord contained in vertebrae Myelomeningocoele = WORSE as spinal cord not contained within vertebrae and vulnerable to compression.
What region of the spinal cord is spina bifida most commonly seen?
Lumbosacral region (region where the vertebral column ends)
What findings in utero might reveal the presence of a neural tube defect?
Raised maternal serum alpha fetoprotein - not contained within the foetus, leaks out and crosses placenta.
Ultrasound
Why does the cauda equina form?
After the 3rd month, the vertebral column grows faster than the length of the spinal cord. The spinal roots elongate (from around L2) to be able to exit at their intervertebral foramen.
What are the 3 brain regions that form during neural fold formation called?
Forebrain (Prosencephalon)
Midbrain (Mesencephalon)
Hindbrain (Rhombencephalon)
What 5 secondary brain vesicles form in the 5th week of development?
Forebrain (Telencephalon, Diencephalon)
Midbrain (Mesencephalon)
Hindbrain (Metencephalon, Myelencephalon)
What structures make up the forebrain and from what are they derived?
Telencephalon = cerebral hemispheres Diencephalon = Hypothalamus, thalamus, pineal.
What structures make up the hindbrain and from what are they derived?
Metencephalon = cerebellum, pons Myelencephalon = medulla
Where are the cephalic and cerivcal flexures found?
Cephalic = in midbrain region Cervical = between spinal cord and hindbrain.
What regions of the brain does the ventricular system develop in?
Lateral ventricle = telecephalon (1a)
Third ventricle = diencephalon (1b)
Cerebral aqueduct = mesencephalon (2)
Fourth ventricle = meten (3a) /myelencephalon (3b)
What is hydrocephalus? When does it commonly arise?
Hydrocephalus is a condition in which an accumulation of CSF occurs within the brain, causing raised ICP.
Occurs with spina bifida, or if any blockage of the ventricle system (tumour/ infection).
Where are choroid plexus cells found?
Neuroepithelial layer of the neural tube - makes CSF.
What do the intermediate (mantle) and marginal layers of the neural tube contain?
Int = neuroblasts Marg = processes
How do the roof and floor plates regulate dorsal and ventral patterning?
Dorsal plate = alar plate (sensory)
Ventral plate = basal plate (motor)
Neural crest cell migration is very vulnerable to environmental insult. Name a condition that arises when a defect arises in a single component, and multiple components of NCC migration.
One structure = Hirschsprungs disease (fail to form enteric ganglia)
Multiple structures = DiGeorge syndrome (defects with thyroid, thymus, heart, and face)
