Neuroembryology Flashcards
Ectoderm, mesoderm, and endoderm important for Neuro
Ecto - CNS
Meso - notochord
Before the notochord and once establish
Before, ectoderm produces factors that promote epidermis formation but inhibit neuroectoderm formation
Once established, notochord produces factors allowing midline ectoderm cells to become neuroectoderm by blocking other factors
Neural plate formation
Neuroectoderm cells multiply forming a plate in response to cheimcal signals from underlying notochord
Neural groove and fold formation
Neural plate folds inward flanked by 2 neural folds
Neuropore formation
Neural folds fuse in area of 4-6th somites and close the groove…fusion occurs both ways and forms cranial (close 26) and caudal (close 28th) neuropore
Lamina terminalis
Site of closure of rostral neuropore
Neural tube
As the neural tube closes, it separates the ectodermal surface to give rise to CNS, ventricular system, and central canal
Anencephaly
Failure of rostral neuropore to close…absenc eof brain hemispheres and only a rudimentayr brainstem
Spina bifida
Failure of caudal neuropore to close…vetebral arches reamin unfused at L5 or S1 level
Occulta (mild)
Cystica (meningocele)
Cells adjacent to the tube lumen do what?
Migrate away from luminal surface to accumulate in regions of the mantle layer (future gray matter)
Alar and basal plate
Dorsal manlte layer - alar plate - cell bodies of dorsal horn sensory neurons
Ventral mantle layer - basal plate - cell bodies of ventral horn sensory neurons
Marginal layer
Myelinated axonal process of mature neurons will become white matter
Roof and floor plates
Roof plate (dorsally) and floor plate (ventrally) connect the right and left alar and basal plates
Plates respond to chemical signals from ectoderm and notochord
Roof plate will fuse with pia mater to form the choroid plexus
Dorsal pole of spinal cord
Ectoderm cells produces factors which induce the roof plate cells to produce BMP4 and 7 to induce formation of sensory neurons
Ventral pole of spijnal chord
Notochord releases SHH which induces floor plate ot release Shh to induce motor neuron formaiton
Primary brain vesicles
prosencephaoln (fore)
Mesencephalon (mid)
Rhombencephaoln (hind)
Secondary vesicles
Telen Dien Mesen Meten Lyelen
Prosencephalon
Forebrain
Divides to telencephalon (striatum, cerebral cortex…lateral ventricles) and diencepaholon (hypothalamus and thalamus…3rd ventricle)
Mesencephaolon
Midbrain
Becomes red nucleus and substantia negra…cerebral aqueduct
Rhobencephalon
Hindbrain
Becomes metencephalon (pontine nuclei and cerebelumm…4th ventricle) and myelencephalon (medulla, inferior olive…4th ventricle central canal)
Segmentation
As vesicles ontinue to form, notochord produces signaling molecules
Hindbrain forms 7 rhombomeres…serve as molecular framework for cranial nerve development
Hox genes
Homeotic selector genes control the regional ID of vertebrate CNS and give each segment uniwue ID
Restricts cranial nerve growth to specific rhombomeres
Prevents axons from other cranial nerves from growing into adjacent rhombomeres
Flexures
Cephalic - midbrain/diencepaholon…persists in adult as brainstem/forebrain bend
Cervical - hindbrain/spinal cord
Pontine - caused by proliferation of alar plate of the future pons pushing pontine region anteriorly
Pontine flexure results in
Rostral medulla moving laterally and alar plate cells becoming lateral and migrating anterior to basal plate cells
Also enlarges the central cavitiy which will become 4th ventricle
Choroid plexus develops from
Roof plate and overlying pia mater
Cerebellum and pontine nuclei from
Cerebellum - from alar plate neuroblasts into the roof plate
Pontine - from the alar plate cells that have migrated to anteriro pons
Cerebral aqueduct
Superior colluculus, inferior colliculus, red nucleus, and substantia negra formation
As midbrain walls thicken, narrowing of centra lcanal produces cerebral aqueduct
Alar plate cells migrating medially towards roof plate
Entire diencephalon derived from
Alar plate
Cnetral caivty of diencephalon formed from the
3rd ventricle
Telencephalon from both the
Alar plate (mostly cortical cells) and the basal plate *basal ganglia)
Majority of telencephaln is
White matter and neurons have migrated to area adjacent to the surface
Lissencephaly
Smooth brain
improper neuronal migration
Could be from viral, insufficienct blood uspply, or gene mutations
Hydrocephaly types
non-communicationg - caused by changes in CSF flow
Communicating by Overproduction or poor absorption
Cranial meningocele and meningoencephalocele
A) meningnes and CSF in cyst
B) brain tissue but meninges in cyst through a bone defect
Cerebral palsy
Infection, Insufficent O2
Spastic - hypertonia and spasticity
Ataxic - motor skills uncoordination and balance can be affected
