Embryology of the Nervous System Flashcards
notochord
iniates entire process of neurulation
signals formation of neural plate (thickened cells)
-dorsal surface of embryo
lateral edges start to fold
neural tube
formed from fusion of neural tube
cranial neuropore closure
day 25
caudal neuropore closure
day 27
neural tube
forms all of CNS
-brain and spinal cord
neural crest cells
form just above neural tube
- from neuroectoderm
- migrate into underlying mesoderm
become all of the PNS
fate of cranial neural crest
bones, cartilage, fascia, ligaments and tendons of face, neck
sensory ganglia and autonomic ganglia
fate of spinal neural crest
dorsal root ganglion
autonomic ganglion
heart - fibrous skeleton
shared fate of cranial and spinal neural crest
meninges
schwann cells
melanocytes
spinal cord formation
neural tube caudal to 4th pair of somites forms spinal cord
cells of neural tube
neuroectoderm
- migrate out away from lumen
- establish regions of spinal cord
zones of neuroectoderm migration
ventricular zone
mantle zone
marginal zone
ventricular zone
embryo - thick, pseudostratified epithelium called neuroepithelium
adult - simple layer of ependymal cells
derivatives of ventricular zone
give rise to all neurons and most glia of spinal cord
mantle zone
zone superficial to the neuroepithelium
composed of neuronal cell bodies
alar and basal plates
forms gray matter
sulcus limitans
separates basal and alar plates of mantle zone
basal plate
form motor, ventral horn
alar plate
form sensory, dorsal horn
marginal zone
outermost layer
composed of nerve processes (axons/dendrites)
form white matter
derivatives of neuroepithelium
neuroblasts
gliablasts
neuroblasts
form ventral horn motor neurons
and dorsal horn sensory neurons
gliablasts
form astrocytes and oligodendrocytes
spinal nerve
form from ventral root and dorsal root
dorsal root ganglion
derived from neural crest
microglial cells
derived from mesenchymal cells
migrate in later
cranial portion of neural tube
forms three vesicles
prosencephalon
forebrain
mesencephalon
midbrain
rhombencephalon
hindbrain
3 primary vesicles
prosencephalon
mesencephalon
rhombencephalon
secondary vesicles
telencephalon diencephalon mesencephalon metencephalon myelencephalon
derivatives of prosencephalon
telencephalon and diencephalon
derivatives of rhombencephalon
metencephalon and myelencephalon
lumen of telencephalon
lateral ventricles
lumen of mesencephalon
cerebral aqueduct
lumen of diencephalon
third ventricle
lumen of rhombencephalon
fourth ventricle
flexures in brain
result of differential growth
cervical - SC to myelencephalon
cephalic - rapid cerebrum growth
-takes place at midbrain
pontine -
derivatives of telencephalon
cerebral hemispheres
derivatives of diencephalon
thalamus, hypothalamus, pituitary, optic vesicles, pineal
derivatives of mesencephalon
midbrain
derivatives of metencephalon
pons
cerebellum
derivatives of myelencephalon
medulla
lumen of metencephalon and myelencephalon
fourth ventricle
tela choroidea
pia mater + ependymal layer of cells
proliferates and evaginates into ventricles
in roof of third and fourth ventricles
in medial walls of lateral ventricles
brainstem vs. spinal cord
similar development
- alar and basal plates
- alar, dorsal, sensory
- ventral, vasal, motor
however, gray matter is in distinct nuclei - not columns
-also, sensory nuclei displaced laterally
development of myelencephalon
forms medulla
get three layers, like in SC
pontine flexure
lateral flexures
pushes alar plates of myelencephalon laterally
order of nuclei in myelencephalon
lateral to medial
alar - somatic afferent > SVA > GVA
basal - GVE > SVE > somatic efferent
SA > SVA > GVA > GVE > SVE > SE
- motor - medial
- *sensory - lateral
CNs of myelencephalon
CN VIII, IX, X, XII
8,9,10, 12
development of metencephalon
forms pons and cerebellum
pons development
portion of metencephalon
- three layers like in SC
- basal - motor
- alar - sensory
some alar plate cells migrate into white mater
-become nuclei
cranial nerves with pons
V, VI, VII, VIII
5,6,7,8
cerebellum development
portion of metencephalon
- formation of rhombic lip
- fuse over roof plate
- form cerebellar plate
- waves of neuroblasts migrate through marginal layer
- form outer cerebellar cortex
- gray matter - external
- white matter - internal
cerebellar plate
fusion of rhombic lips
-forms entire cerebellum
deep nuclei of cerebellum
derived from original marginal layer
mesencephalon development
forms midbrain
from 3 layers, like SC
basal - motor
alar - sensory
CNs of midbrain
mesencephalon
III, IV
3, 4
roof of diencephalon
forms epithalamus
- contains choroid plexus
- gives rise to pineal gland
alar plates of diencephalon
alar plate forms two swellings
superior and inferior
superior swelling of alar plate in diencephalon
forms thalamus
-bulges into third ventricle
70% of people have interthalamic adhesion form
inferior swelling of alar plate in diepcephalon
hypothalamus
neurohypophysis formation
downgrowth of diencephalon neuroectoderm
posterior pituitary
adenohypophysis formation
upgrowth of oral ectoderm
anterior pituitary
optic nerve formation
from diencephalon
-evagination of brain
also, most of retina
lamina terminalis
where the cranial neuropore closes
-in diencephalon
radial glial cell
act like ladders for neurons in the telencephalon development
to form outer gray cortex
new neurons in telencephalon
6 waves of cells migrate
-youngest cells most external
development of telencephalon
two lateral diverticula will form cerebral hemispheres
- neuroblasts migrate
- gray - superficial
- white - deep
also forms corpus striatum
neuroblast waves in telencephalon?
waves migrate through marginal zone
-along radial glial cells**
continued growth of cortex during final part of fetal life
gyri - outward convolutions
sulci - fissures
corpus striatum formation?
swelling within floor of cerebral hemispheres
CN of telencephalon
olfactor
CN I
CN of diencephalon
CN II
CN of mesenephalon
CN III, IV
spinal accessory nerve formation
from cervical spinal cord
spina bifida occulta
more common
no neural involvement
only defect in vertebral arch
spina bifida cystic
more severe
do have neural involvement
meningocele - only meninge
meningomyelocele - meninge and spinal nerve/spinal cord involvement
spina bifida
neural tube does not fuse posteriorly
-also, vertebral arch does not fuse
anencephaly
aka meroencephaly
caused by cranial neuropore not closing
-forebrain - does not form
-no di or telencephalon formation
craniorachischisis
closure defect extends in spinal cord
microcephaly
small cranium
formed from brain underdevelopment
encephalocele
failed neural tube fusion and defect in skull
-foramen magnum or lamdoid suture
- allows portion of CNS to protrude
- results in cyst-like structure at base of skull
meningocephalocele
meninges and part of brain bulge through defect
meningohydroenephalocele
meninges, brain, and part of ventricular system bulge through defect
congenital hydrocephalus
increased CSF within ventricles
- imbalance in production and absorption
- most often obstruction cause
dilation of ventricles proximal to obstruction
skulls expand (sutures not fused)
thin calvaria bone is result
Tx for congenital hydrocephalus
shunt procedure
cannula into ventricle system
common obstuction site for hydrocephalus
IV foramina of monro**
cerebral aqueduct of silvius**
lateral apertures of luschka
median aperture of magendie
arnold chiari syndrome
herniation of cerebellar hemispheres through foramen magnum
- underdevelopment of posterior cranial fossa
- skull defect
often associated with spina bifida cystica
type I - congenital
presentation - fingerline projection of cerebellum through the foramen magnum
holoprosencephaly
rare
failure of forebrain neural tube to form cerebral hemispheres
lateral ventricles fuse
