nervous system development Flashcards
Primary neurulation: What are the main events of the two phases?
Phase 1: Neural Plate formation
Phase 2: neural tube formation
Where are the mesenchyme cells located that is the location of the start of secondary neurulation? Explain the three phases
Mesenchyme located in the tailbud, or caudal eminence.
Phase 1- Mesenchyme in tail bud forms neural chord
Phase 2- Lumen forms within neural cord (eventually becomes continuous w/central canal of spinal cord
Phase 3- Tailbud regresses early in fetal period
What results from errors in primary neurulation? Characteristics? Examples/explanations?
Neural tube defects (Dysraphic errors).
Faulty neural tube closure. Closure defects usually occur at the ends, where the neuropores were located.
Meroanencephaly- Calvaria missing, as well as forebrain/midbrain. Diagnosed by ultrasound and elevated apha fetoprotein levels.
Encephalomeningocoele- skull defect, brain and meninges herniate
Cranial meningocoele- only meninges herniate, sac filled w/CSF
Cranium bifidum- opening b/w skull bones
Explain the 4 types of spina bifida
- Myeloschisis- neural plate open dorsally. No swelling. . Most severe type. Legs paralyzed.
- Meningomyelocoele- Herniation of spinal cord and meninges. Cystic swelling, may be covered by skin or membrane.
- Meningocoele- Herniated meningial sac.
- spina bifida occulta- Vertebral defect, doesn’t close. Usually asymptomatic.
Spina bifida cystica includes which two types?
Meningomyelocoele and meningocoele
What is diastematomyelia?
bone spur in spinal canal. May be associated w/hair tuft or dimple
(Mero)anencephaly and spina bifida relative alpha fetoprotein levels?
anencephaly very high, then spina bifida.
What supplement during pregnancy can reduce NT defects incidence by 50%?
folic acid supplements
What 3 cell types are derived from the neuroepithelium of the neural tube? What order are they formed in?
- neuroblasts- pre-neurons.
- glial cells- will form astorcytes and oligodendrocytes (collectively called macroglia).
- ependymal cells- become epithelial cells in the ventricles
What are radial glia?
Special population of glial cells, guide the migration of neuroblasts and glioblasts. They are only temporary glial cells.
What 3 layers form in the wall of the neural tube?
Ventricular- Closest to lumen of NT. Becomes ependymal cells.
Intermediate- Area to which neuroblasts migrate. Will become gray matter.
Marginal- Most superficial layer. Becomes white matter.
The intermediate layer of the neural tube differentiates into what parts? What forms in each, and what causes the formation?
- Dorsal half becomes alar plate. Dorsalizing signals cause formation of sensory neurons here.
- Ventral half becomes basal plate. Ventralizing signals cause the formation of motor neurons here.
What is the sulcus limitans?
A groove that runs the length of the spinal cord, forming a boundary between sensory and motor parts.
What is the ventral signal from the notocord? Dorsal signal?
Ventral signal is shh, and dorsal signal is BMP.
Which of the 3 flexures in the neural tube cause ventral bending?
- Cervical flexure- at junction of brain and spinal cord.
2. Mesencephalic flexure- Forms in area that will become brain.
Which of the 3 flexures in the neural tube cause dorsal bending?
Rhombencephalic flexure- eventually causes brain to fold back on itself
What are the three brain regions are visible at the open neural fold stage, and where are they compared to the mesencephalic flexure? What do they further divide in to?
- prosencephalon- before flexure. Divides into diencephalon and telencephalon.
- mesencephalon- at flexure.
- rhombencephalon- after flexure. Divides into metencephalon and myelencephalon
What mediates the subdivision of the hindbrain into temporary segments called ________?
Expression of hox genes. called rhombomeres.
What is holoprosencephaly? Possible cause?
Failure of regionalization of prosencephalon. CNS and facial malformations. Alcohol use may be a factor.
Forebain vs. brainstem?
Forebrain includes divisions of prosencephalon, which are the diencephalon and telencephalon. Brainstem is the mesencephalon, and the divisions of the rhombencephalon which are the metencephalon and myelencephalon
What forms in the roof of most ventricles, and what does it do
choroid plexus, which secretes CSF.
Communicating v. non-communicating hydrocephalus?
Communicating (non obstructive)- CSF can get into sub arachnoid space, but cannot be resorbed.
Non-communicating (obstructive)- CSF cannot get into subarachnoid space.
What is the primary precursor of the peripheral nervous system?
Neural crest.
What are ectodermal placodes?
Thickening of ectodermal surface. Contribute to primary sensory neurons in the peripheral nervous system.
