Oct2 M3-Normal CNS Development Flashcards
how human brain differs from rat
lot of cellular proliferation and development leads to
- folds (gyri)
- flexion forward of the brain
steps to reach nervous system in embryo
- gametes
- zygote. then cell division
- blastula. then gastrulation
- gastrula
- gastrula splits in endoderm (gut), mesoderm (muscle and skeleton) and ectoderm (skin and NS) (in this order from bottom to top)
how neural tube forms
- dorsal mesoderm creates the midline notochord
- notochord induces the ectoderm to form a neural plate
- neural plate (and associated NCCs) invaginates AND fuses to form the neural tube (with assoc NCCs nearby) and notochord outside of it
how neural tube closes
closing starts medially and two closing streams go rostrally and caudally, when not closed yet, you still have neuropores (opening remaining) = a rostral and a caudal one
things on dorsal surface of neural tube
somites, derived from endoderm
- segmentally arranged
- line dorsal embryo on both sides
orientation of neural tube
- rostral (top)
- caudal (bottom)
- ventral (front)
- dorsal (back)
1st step after neural tube formed
3 brain vesicles (forebrain, midbrain, hindbrain) form, then 5. (are bulgings of the cells forming the neural tube, are cells themselves)
what happens to middle of neural tube (it’s a hollow tube)
is filled with fluid, will give the ventricular system
- two lateral ventricles
- one third ventricle
- cerebral aqueduct connecting 3rd and 4th ventricles
- one 4th ventricle
what first vesicle gives
cerebrum (cortex and subcortical structures)
what 2nd vesicle (diencephalon) gives
- retina (of the eye), is part of the brain. (whereas lens and other parts of eye are not)
- thalamus
- hypothalamus
what 3rd vesicle (mesencephalon) gives
midbrain
what 4th vesicle gives
pons and cerebellum
what 5th vesicle gives
medulla
how ventricular system changes in development
- initially simple linear shape
2. becomes complex curved shape because lateral ventricles follow the dev of cerebral hemispheres
components of ventricular system in order of CSF flow
- two lateral ventricles
- two interventricular foramenae of Monroe connecting LVs to 3rd ventricle
- one third ventricle
- one cerebral aqueduct connecting 3rd and 4th ventricles
- one 4th ventricle
- one midline foramen of Magendie (1 M for midline) and two lateral foramenae of Luschka (2 Ls for lateral)
- sub-arachnoid space surrounding the brain
CSF is prod where
in ventricles, by choroid plexuses
central canal def
- in embryo, space in middle of spine where CSF flows
- in adult, virtual space where nothing happens
C shape principle in brain (important for limbic system understanding)
lot of C shape regions and structures (including ventricles) because
- neural tube closure
- rostral cellular proliferation and migration to form vesicles
- continued prolif leading to flexion and curvature (leads to mature C shape)
rostral and caudal in adult brain
because of brain folding and curvature (bc of prolif),
- in the brain (high up in NS), rostral = anterior and caudal = posterior
- lower, after subcortical nuclei (brainstem and spinal cord), rostral = top and caudal = bottom. so they retain their structure
* the brain is perpendicular*
special structures contributing to cranial nerves and brainstem
- branchial (pharyngeal) arches
- placodes
branchial arches do what
- come from mesoderm
- form parts of 4 CNs: V, VIII, IX, X
- homeobox genes control rostrocaudal pattern (homeobox 1 expressed more rostrally for ex)
placodes do what
- are an ectoderm thickening
- with help of the NCCs, form the peripheral nerve ganglia
diff origins of one cranial nerve and diff origins of the divisions of one cranial nerve
- pharyngeal arches (to form the cranial nerve, trigeminal nerve (V) for ex)
- placodes (to form the ganglia, trigeminal ganglia for ex)
- etc
- all under genetic control*
somites form what
- sclerotome (skeleton)
- myotome (skeletal muscles)
- dermatomes (skin)
- each spinal level and spinal root coming off gives a dermatome (skin region inn by it), myotome (group of muscles inn by it)
what does a cranial nerve having branchial motor and somatic motor functions mean
it’s just ways to refer to its origin. (branchial arches and somites)
spinal cord dev
- embryo = end of cord in coccyx
- adult = cord grew rostrally so ends now at L1, L2 vertebral bodies
- some nerves leave spinal cord at its bottom (L1,2) and travel down to exit at lower vertebral levels = forms the CAUDA EQUINA
- filum terminale (extension of pia mater which used to be exterior to spinal cord at lvl of spinal cord and is now in middle of canal wit cauda equina)
coatings surrouding spinal cord and brain
in to out
- pia mater (tightest)
- arachnoid (middle)
- dura mater
origin of the ANS
NCCs (they also form the neural crest)
diff levels things NCCs form and which ones are ANS (migrate further and further to form each of these)
- dorsal root ganglion
- melanocytes
- branchial arch structures (CN V, VII, IX, X)
- para-vertebral sympathetic ganglia
- adrenal medulla
- pre-vertebral sympathetic ganglia
- parasympathetic plexus
how development continues at the cellular level after birth
- programmed cell death (apoptosis) to remove the excess neurons (keep only ones who reach the right target)
- synaptic formation and synaptic pruning (so synapses also in excess initially)
- myelination (only complete at age 2)
ongoing development of brain after childhood
parts of cortex can shrink and grow depending on if the thing they control is used a lot or not used at all
important visual features of brain dev
- rostral-caudal dev + neural tube closure at midline and rostrally and caudally
- rostral and caudal neuropores
- brain vesicles give regions
- C-shape
- segmentation with myotomes and dermatomes
2 types of defects in brain dev
- defect of closure of neural tube
- problems of neuronal prolif and migration
anencephaly def
- anterior neuropore (rostral) doesn’t close
- cerebral hemispheres don’t form
what is meant by older parts of the brain
brain stem and cerebellum
new = basal ganglia + cortex, forming hemispheres
encephalocele def
- mild defect of closure of anterior neuropore
- hemispheres form but part of cranial contents herniate through a skull defect
things an encephalocele can contain
- meninges (pia, arachnoid, dura) only
- meninges + CSF
- meninges + CSF + brain
myelocele def
incomplete closure of posterior (caudal) neuropoe with herniation of contents of thecal sac (cord and or roots and meninges). same things can herniate as in encephalocele
spina bifida def
- least severe type of myelocele
- spinal column problem (vertebral)
- can be occulta (no outward sign except the hairy patch)
- can be aperta (skin open)
causes of neural tube defects
- genetics
- toxic (like anti-epilepsy drug valproic acid)
- folic acid helps REDUCE the risk
neural proliferation and migration steps general concept
- series of stem cells around ventricles give rise to cells forming neurons of the cerebral cortex
- these migrate out and form one of the six layers of cortex
types of neuronal prolif and migration defects
- bad migration (sit in white matter or still in ventricle)
- go to wrong layer of cortex
typical consequences of neuronal prolif and migration defects (two types)
- more common, more simple and less severe = predisposition to epilepsy
- more severe problem = abnormalities of cognition and other fcts too
