10: Neurulation And PNS Development Flashcards
Two important regions of ectoderm
Neuroectoderm, surface ectoderm
Secondary neurulation
Formation of neural tube from the tail bud
Where does secondary neurulation occur
Caudal to somite 31
Where does primary neurulation end?
Closure of caudal neuropore at somite 31
Secondary neurulation 5 steps
- Tail bud condenses -> medullary cord
- Medullary cord cavitates -> forms a lumen
- Lumen of medullary cord merges with neural tube
- NCCs arise from roof of neural tube
- Formation of caudal somites around lateral tail bud
Where does neural tube closure begin?
Several locations around the AP axis, begins at cranial regions first and moves caudally
Neural tube defect
Failure at a closure site in the neural tube - caused by genetic, nutritional, and/or environmental factors
Anencephaly/meroencephaly
Brain tissue open to amnionic fluid
Encephalocele
Opening in neural tube, but is covered by skin (can have brain tissue in the opening)
Craniorachischisis
Large portion of brain and spinal cord exposed
Spina bifida occulta
Skin has closed appropriately over the neural tube defect but will typically have a tuft of hair over it
Meningocele vs meningomyelocele
Meningocele: Protruding sac extending from sacral region due to absense of vertebral arch (no spinal cord involvement)
Meningomyelocele: spinal cord protrudes into meningocele sac
Myeloschisis
Failure of neural tube to fuse -> open spinal cord exposed -> lower extremities deformed and nonfunctional
What types of cells are NCCs
Neuroectodermal cells
Epithelial-mesenchymal transition
NCCs lose cams -> gain ability to migrate/become mesenchymal
When do NCCs migrate?
Before neural tube closes completely + once its all the way closed
Nine important derivatives of NCCs
- Melanocytes
- Odontoblasts
- Schwann cells
- Spinal and autonomic ganglia
- Enteric NS
- Adrenal medulla
- Aorta
- Pharyngeal arches -> face and head
- Meninges
Two cell types that help form the meninges
NCCs, mesenchyme
Five examples of neurocristopathies
- Hirschsprung’s disease
- Piebaldism
- TCS
- Goldenhar syndrome
- Micrognathia
Piebaldism
Melanocytes defect with characteristic pattern of non-pigmented skin
What are both PNS and CNS derived from?
Neural tube
Three components involved in PNS formation
NCCs, neuroectoderm, Ectodermal placodes
When do dorsal and alar plates of the neural tube form?
End of 4th week
Sulcus limitans
Line dividing neural tube into dorsal and ventral regions
What does the sulcus limitans give rise to?
Range of cell types in the brain and spinal cord
SHH gradient impact on neurons
Increased SHH -> motor neurons
Decreased SHH -> interneurons
What does SHH activate? What does this cause formation of
Activates NKX2.2 + NKX6.1 -> ventral neuron formation
BMP/TGF-B function
Counteract SHH -> dorsal neuron formation
What two molecules are activated by BMP4?
PAX3 and PAX7
What releases BMP4?
Roof plate
What happens to the dorsal-most cells of the basal plate?
Become intermediolateral columns -> lateral horns
Which type of neuron forms first typically, motor or sensory?
Motor first
What area do axons exiting ventral horns pass through to form ventral roots?
Cranial sclerotome
What axons join the ventral root?
Lateral horn axons
when does the ANS start to develop?
Week 5
What type of cells forms the preganglionic ANS cells/fibers? What cell type forms the ganglionic neuron and postganglionic fibers?
Preganglionic: neuroectoderm
Postganglionic: NCCs
What do NCCs form in the sympathetic ANS?
trunk and collateral ganglia
What do NCCs form in the parasymp ANS?
Head/neck ganglia and terminal ganglia in the trunk
