Development of the Nervous System Flashcards
When does gastrulation occur?
week 3
What are the parts of the primitive streak?
primitive node
primitive groove
primitive pit
What is the notochordal process?
mesoderm below the ectoderm that induces the neural plate
When does neurulation begin?
what signal is necessary for this to occur?
Begins at day 22-23
Shh from notochord induces neurulation
How does the neural tube close?
Starts in middle –> zippers both rostral and caudal directions
When does the rostral neuropore close?
The caudal neuropore?
rostral = day 25
caudal = day 28
What is primary neurulation?
What is secondary neurulation?
closure of rostral and caudal pores –> brain and spinal cord to lumbar region
secondary: caudal eminence –> coccygeal and sacral regions of spinal cord
What cns cell types can neuroectoderm form?
apolar neuroblast –> neuron
glioblast –> astrocytes and oligodendrocytes
ependyma –> epithelium of choroid plexus
What is the only cell type of the CNS not from neuroectoderm?
microglia:
from mesoderm –> blood monocytes –> microglia
What forms the brain?
neural tube cranial to fourth somites
What are the 3 primary brain vesicles?
prosencephalon - forebrain
mesencephalon - midbrain
rhombencephalon - hindbrain
What occurs in brain development in the 5th week?
forebrain and hindbrain divide:
prosencephalon –> telencephalon and diencephalon
rhomencephalon –> metencephalon and myelencephalon
What does the telencephalon form in the adult brain?
cerebral hemispheres
subcorticla white matter
olfactory bulb and tract
basal ganglia
amygdala
hippocampus
What does the diencephalon form in the adult brain?
thalamus and hypothalamus
epithalamus
eye and optic nerve
What does the mesencephalon form in the adult brain?
midbrain =
cerebral peduncles
superior and inferior colliculi
2 cranial nerves
What does the metencephalon form in the adult brain?
cerebellum
pons
What does the myelencephalon form in the adult brain?
medulla
(olive and pyramid)
Where is the cephalic flexure?
btw mes and met = btw midbrain and pons
Where is the cervical flexure?
divides brainstem from spinal cord
Where is the pontine flexure?
divides hindbrain into caudal myelencephalon and rostral metencephalon
Which brain flexure persists?
cephalic flexure
When do the basal ganglion and cortical structure develop?
btw weeks 6 to 32
What is holoprosencephaly (HPE)?
results from incomplete separation of cerebral hemispheres
most associated w/ facial abnormalities and reduced closure of FNP
hypotelorism = close placed eyes
What can cause HPE?
genetic and environmental factors
maternal diabetes and teratogens (alcohol) increase risk
How does the pituitary gland form?
first arch surface ectoderm –> hypophysial diverticulum/rathke’s pouch –> anterior lobe
neuroectoderm of diencephalic floor –> posterior lobe
What forms the central canal?
neural canal
What is the sulcus limitans?
divides alar and basal plates
What do the alar and basal plates form respectively?
alar –> sensory neurons that stay in CNS
basal –> motor neurons that go to skeletal muscle
What are the 3 layers of the neural tube from the center –> out and what do they form?
ventricular zone –> stem cells
intermediate zone –> gray matter = cell bodies
marginal zone –> white matter
where can you see the alar and basal plate pattern extend?
into brainstem –> 4th ventricle moves structures laterally –> breaks apart so basal is in center/ w two alar plates on the sides
see motor neurons centrally (basal) and sensory neurons peripherally ( alar) which shows the pattern
What structures form from the alar plate in the myelencephalon?
all sensory: (VCSSI)
vestibular nuclei
coclear nuclei
spinal trigeminal tract and nucleus
solitary nucleus
inferior olive
What structures form in the myelencephalon from the basal plate?
all motor (HDA)
hypoglossal nucleus
dorsal motor vagal nucleus
nucleus ambiguus (9 and 10)
What structures form from the basal plate in the metencephalon?
abducens nucleus (6)
facial motor nucleus (7)
trigeminal motor nucleus (5)
superior salivatory nucleus (7)
Which structures form from the alar plate in the metencephalon?
cochlear nuclei
cerebellum
vestibular nuclei (8)
solitary nucleus (7, 9, 10)
pontine nuclei
What structures form from the basal plate in the mesencephalon?
edinger-westphal nucleus (3)
oculomotor nucleus (3)
red nucleus
What structures form from the alar plates in the mesencephalon?
substantia nigra (maybe)
superior colliculus
What do the ventricles form from?
telencephalon –> lateral
diencephalon –> 3rd
mesencephalon –> cerebral aqueduct
btw met and myel –> 4th
What is spastic cerebral palsy?
damage adjacent to ventricles
see toe walking and scissor gait
What is dyskinetic cerebral palsy?
athetoid: damage to basal ganglion; see slow writing mvts of extremities and/or trunk
dyskinetic: damage to basal ganglion and VL thalamus
What is ataxic cerebral palsy?
damage to the cerebellum
see incoordination, weakness and shaking durion voluntary mvt
*fall toward side of lesion
“drunken sailor gait”
What are the main types of cerebral palsy?
spastic
athetoid
dyskinetic
ataxic
can have a mix of any of these
What are the basal ganglia?
nuclei located in the base of the telencephalon - control motor
What is syringomyelia?
fluid in middle of spinal cord
common in C2-C8
associated with chiari I malformation
What is hemiplegia cerebral palsy?
both limbs on one side of body affected
What is diplegia cerebral palsy?
lower limbs more affected than upper limbs
What is Arnold-Chiari type I?
herniation of cerebellar tonsils through foramen magnum
usually no Sx, but can have:
CN 6 issues - lateral eye mvnts
CN 8 issues - decreased hearing
associated w/ syringomyelia
What is Arnold-Chiari type II?
herniation of medulla and cerebellum through foramen magnum
see hydrocephalus and lower cranial nerve problems
present in infancy or early childhood
*assoc w/ spina bifida = meningomyelocele
When can the diagnosis of Chiari II be made?
in utero by fetal MRI
What is the dandy walker malformation?
large posterior fossa cyst continueous w/ 4th ventricle
hypoplasia of cerebellum, partial or absent vermis
atresia of foramina of luschka and magendie
What is hydranencephaly?
absences of cerebral hemispheres or represented by membranous sac
unk cause, but maybe due to obstruction of blood flow to areas supplied by ICAs
brainstem intact - can breath, but little other fxn
excessive head growth after birth
When do gyri and sulci develop?
5 mos - cortex is smooth
folded by birth
to increase SA of brain but decrease volume for delivery
How many lamina are in the cerebrum?
6
What do lamina 4, 5, and 6 of the cerebrum do?
4: receives inputs from thalamus (large in sensory areas)
5: projects mostly to subcortical structures (large in motor areas)
6: projects to thalamus
How does the cerebrum cytodifferentiate?
inside - out:
first neurons produced in ventricular zone –> preplate forms –> axons from these neurons grow inward and form the intermediate zone
then neurons to be born migrate into the middle of the preplate and divide into 3 parts:
marginal zone, cortical plate (lamina 4 and 5), and subplate
What order do the cerebral lamina form?
5, 6
4, 3, 2
What is lissencephaly/ agyria?
smooth brain
incompletion or failure of neuronal migration during weeks 12-24
microcephaly, ventriculomegaly
wide sylvian fissures and minimal operculum of insula
complete/partial agenesis of corpus callosum
What two things can cause microcephaly?
abnormal or lack of brain development
injury or insult ot a previously normal brain
What do neurons forming in the cerebrum follow during migration?
radial glial cells
What forms the white matter of the cortex?
axons from neurons in the cortical plate and suplate that join the marginal zone
What are cerebral commissures?
nerve fibers that interconnect the cerebral hemispheres
What order do the cerebral commissures form?
Anterior commissure and hippocampal form first
then corpus callosum
lamina terminalis stretched –> septum pellucidum
What does the anterior commisure connect?
olfactory bulb w/ hemispheres
What does the hippocampal commissure connect?
hippocampal formations
What genetic loci have been associated w/ holoprosencephaly?
over 12 loci: SHH, six3, TGIF, ect
inhibition of cholesterol synthesis
How does the cytodifferentiation of the cerebellum occur?
inside out:
ventricular matrix grows out –> forms cerebellar nuclei and purkinje fibers (molecular and purkinje layers)
Then external germination center migrates up and around nuclei –> grows back in –> forms granular layer
Where is the end of the spinal cord in newborns and adults?
newborn: L2 or L3
adult: L1 or L2
What cells give rise to spinal ganglion cells and sensory neurons in the periphery?
Neural Crest
What germ cells form the PNS?
Neural crest –> dorsal root ganglia, sensory ganglia of CNs, schwann cells, post-synaptic autonomic cells
ectodermal placode
What is an encephalocele?
cycst bulging out of face or head
can be with or without brain tissue
What is anencephaly?
failure of skull to close around brain
brain exposed to environment –> high risk of infection and death
