Nervous System Embryology Flashcards
Nervous System Embryology ~ from
ectoderm (neural + epidermis)
Neuroblasts + Glioblasts ~ from
Ventricular Zone Neuroepithelial Cells and Migrate Out
Neuroblasts: form all
neurons in the CNS
Glioblast: form
radial glial cells, astrocytes, oligodendrocytes, ependymocytes (choroid), tanycytes
Radial Glial Cells: form before
neuroblasts –> neurons; other glial cells form after
Occurs because radial glial cells serve as “guide wires” for neuron migration
Microglia: from
monocyte linage in blood and migrate to CNS in 3rd Week (before vessels)
Neural Tube Development ~ Ectodermal Tube ~3rd Week:
notochord initiates long. thickening of ectoderm —> neural plate
Neural Tube Development Folding:
neural plate folds in (posterior surface) —> neural folds form w/ neural crest cells on top
Neural Tube Development Fuse:
folds approach each other —> fuse —> neural tube forms
Rostral Neural Tube: develops into
brain
Caudal Neural Tube: develops into
spinal cord
Alar Plate:
develops into sensory nuclei/nerves, including dorsal horn (spinal cord), DRG and brainstem nuclei
Basal Plate:
develops into motor nuclei/nerves, including ventral horn (spinal cord) and brainstem nuclei
Sulcus Limitans:
useful landmark in developing spinal cord, but remains landmark in adult brainstem
Brain Development ~ occurs
4th Week (Rostral Neural Tube - makes sense 1 week later)
Brain Development ~ 4th Week:
differential enlargements (vesicles) and bends (flexure) of tube
1° Vesicles:
prosencephalon (forebrain)
mesencephalon (midbrain)
rhombencephalon
(hindbrain; fuses with spinal neural tube)
~5th Week: formation of
5x 2° vesicles (2° enlargements of 1° vesicles)
Prosencephalon: forms
telencephalon & diencephalon
Telencephalon: forms
cerebral hemispheres + deep structures
Diencephalon: forms
thalamus, hypothalamus, subthalamus
Mesencephalon:
remains undivided as “midbrain”
Rhombencephalon: forms
metencephalon & myelencephalon
Metencephalon: forms
pons & cerebellum
Myelencephalon:
medulla
Spinal Cord Development 3 Month Fetus:
end of cord (conus) ends at end of spinal column
Spinal Cord Development 6 Month Fetus:
conus ends at S1
Spinal Cord Development 3. 9 Month Fetus:
conus ends at L3
Spinal Cord Development Adult:
conus ends at L2 (dural sheath ends at S2)
Anterior Pore Closure Failure —>
Anencephaly / Encephalocele
Posterior Pore Closure Failure —>
Spina Bifida / Meningocele / Myelomeningocele
Folic Acid: deficiency —>
failure of neural tube closure
ɑ-Fetal Protein: closure fail —>
↑ ɑ-fetal protein in amniotic fluid
xPosterior Pore Closure - Defects occur @ any
level
Spina Bifida Occulta: failure of
Presentation: tuft of hair over area / sinus tract
mesodermal cells to form vertebra around spinal cord - No bony dorsal vertebra, no neuro symptoms, no meningeal involvement
Presentation: tuft of hair over area / sinus tract
Spina Bifida Aparta:
+meningeal/spinal cord involvement, +neuro symptoms, ↑severe
Spina Bifida Aparta: With Meningocele:
meninges outpouch
Spina Bifida Aparta: With Myelomingocele:
meninges + spinal cord/filum terminale outpouch
Arnold-Chiari Malformations Definition:
displacement of cerebellar tonsils below foramen magnum
Chiari Type I Malformation:
just displaced cerebellar tonsils
Chiari Type II Malformation:
displaced tonsils + cervical/occipital encephalocele
Orientation of Brain: Rostral —> Caudal
Rostral —> Caudal
Forebrain –> Mid –> Hind –> Spinal Cord –>
Nerve Root –> Peripheral Nerve —> NMJ
Coronal Cut:
dorsal –> ventral; same plane as if you imagined a crown slicing down into brain
Horizontal Cut:
|| to the ground, aka axial cut
Sagittal Cut:
anterior –> posterior; follows calvaria sagittal suture
Gray Matter CNS:
any accumulation of neuronal cell bodies (allow ↑SA/# with grooves (sulci) / ridges (gyri))
Includes: Cortical Layer, Deep Structures, & Brain Stem:
Cortical Layer:
covering forebrain / cerebellum
Deep Structures:
forebrain, basal ganglion, limbic system
Brain Stem:
intrinsic pathways, cranial nerve nuclei
Nuclei: collection of nerve cell bodies in CNS (same as ganglion in PNS)
White Matter:
sum of all fiber tracts (tract = bundle of axons; same as nerve in PNS)
Contrast Brain Gray & White matter w/Spinal Cord:
note core is gray matter (nuclei) with surrounding white matter
