Nervous system is entirely ectoderm
Mesoderm  CT (general and special), muscle,
blood, structural/ physiological support to the body
Endoderm  epithelium of GI tract, respiratory
system, major GI glands
Ectoderm  nervous system, epidermis, neural crest
- notochord and prechordal plate induce the nervous system formation and development
- notochord
o formed during the gastrulation process (cell migration process where epiblastic cells proliferated
and migrated down between epiblast and hypoblast)
o inducing/controlling structure  produces substances that block other chemicals from working
upon that tissue and allowing that tissue to remain in its more primitive state
o gives off sonic hedgehog (SHH) which diffuses to overlying ectoderm to block activity of bone
morphogenic proteins (BMP) causing the ectoderm to remain in its more primitive state,
neuroepithelium
o BMP normally cause dorsalization in the region  regular epidermis is the more differentiated
tissue derived from ectoderm
- neural plate- area of ectoderm overlying the notochord and prechordal plate, formed from neural
epithelium
- neural crest- transition tissue that forms at the margin of the neural plate
- neural plate folds to form the neural groove
- neural groove- ultimately seals across dorsally,
sinks down away from the overlying epidermis,
and becomes surrounded by mesodermal tissue
o zippers closed starting from the cervical region
o zippers both cranially (into the developing brain
region) and caudally (into the developing spinal
cord region)
- neural tube- the now closed space made by the
neural groove, initially open cranially and caudally
o the cranial and caudal neuropores will
eventually close forming a completely closed
tube with a central lumen
o the substance of the neural tube is neural
epithelium
o the neural tube is surrounded by mesodermal
structures
- neural crest- tissue that was at the margin, breaks
free during closure of the neural groove/tube
o some neural crest stays in position close to the
neural tube and becomes the sensory ganglia
(spinal and cranial nerve ganglia)
o other neural crest tissue migrates throughout
the body
- the notochord helps induce/control the neural plate development into the brainstem and spinal cord
portions of the neural tube
- the prechordal plate is another controlling structure  helps control the development of the
forebrain (diencephalon and telencephalon)
- mesoderm in the form of somites and pharyngeal arches surrounds the neural tube
- this tissue that surrounds the spinal cord and brainstem also influences the internal development of
the structures within the neural tube
o Ex: in the spinal cord region: if you remove the limb bud of a developing animal, the spinal cord
doesn’t have as much peripheral tissue to innervate  cells that will ultimately become the anterior
cell column (motor neurons and interneurons) and dorsal cell column tissue will not develop 
tissue isn’t maintained in that area because there is no peripheral tissue to interact with those cells
o peripheral tissues help structures within the spinal cord maintain their tissues
o neural tube and neuroepthelium has inherent intrinsic potential, but that potential is determined by
surrounding tissues that interact with the nervous system
- see the neural plate and neural fold looking down onto the embryo
- somites are developing on either side and will ultimately be in the
cervical region
- the neural groove will zipper cranially and caudally
-
the neural tube is temporarily open
zippering leaves cranial and caudal neuropores
the anterior cranial pore closes around early-20 days
the caudal pore closes around 26-28 days
if the pores remain open or the neural tube does not
close, the lumen remains open to the outside and
chemicals developing within the neural tube can diffuse
more easily into amniotic fluid (ex: alpha fetal protein)
- high levels of alpha fetal protein in the amniotic fluid or in
mother’s blood signals neural tube defect (but you can
have elevated levels of alpha fetal protein and have a
normal neural tube)
- neural crest tissue is formed because of the signal molecules in
the territory and diffusion gradients developing at the periphery
of the neuroepthelium as it grades over into the more
differentiated epidermal tissue  develops all the way around
the neural plate
- as the neural groove forms and closes, the neural crest tissue
breaks free from the overlying ectoderm (which becomes
epidermis) and the neural tube epithelium separates form that
- depending upon its destination will stay in the area (and forms
the sensory ganglion) or will migrate away (will form more
specialized tissue)
- ependymal cells- cells of
neural epithelial origin that
don’t differentiate into
neuronal or glial cells lines
(not as highly differentiated),
form the layer that lines
ventricular system (in
brainstem and cerebral
hemispheres) and the central
canal of the spinal cord
(original lumen of neural tube)
- the cells within the neuroepithelium in the neural tube start out as
pluripotential
- one of the cell lineages derived from the neuroepithelium of the neural
tube is the neuron (with cell bodies in CNS, ex: motor neurons,
interneurons)
- other neuroepithelial cells become glial progenitor cells
o oligodendrocytes- myelinate axons in the CNS
o astrocytes- buffer and support for neurons
 Type 1 = fibrous astrocytes, stringy, help hold things together
physically (no CT in the nervous system)
 Type 2 = protoplasmic astrocytes, form a matrix within the nervous
system around the cell bodies, serve as extracellular space/matrix,
buffer chemicals around the neurons, act like ground substance
(capability of storing some oxygen and nutrients, holds things
together, buffer between the vascular system and the neurons)
o radial glial cells- temporary developmental glial cells, help orient
neurons in migrations as they move throughout the nervous system,
especially in the cerebral cortex developmentally, may become more
specialized cells within the nervous system and its outgrowths (ex:
retina)
o microglial cells- phagocytic macrophages within the CNS, mesoderm
origin (not neuroepithelial origin!), migrates into the neural tube
when the BV invade
o
-
-
- neural crest cells are their own tissue  originally
from ectodermal origin
- once they break free during the closure of the neural
tube they take on a life of their own
- many remain next to the neural tube  become
sensory neurons within the spinal and cranial nerve
general ganglia (pseudounipolar neurons within those
ganglia- DRG and ganglia of CN 5,7,9,10)
- others differentiate into Schwann and satellite cells
which support the peripheral portions of neurons
o satellite cells are within the ganglia
o Schwann cells are found around the processes,
myelinate peripheral processes of neurons (outside
the CNS)
some neural crest cells become the postganglionic autonomic neurons (postsympathetic and
parasympathetic)
some become the chromaffin cells within the adrenal medulla  some of them functioning as
postganglionic sympathetic neurons
some becomethe myenteric plexus and submucosal plexus within the gut
some become melanocytes (pigment cells that migrate out to into the dermal-epidermal junction of
the skin  become the pigmented cells  made into keratinocytes)
within the head and neck area, neural crest cells give rise to all the cell types on the right side of the
picture above and also give rise to mesodermal-like cells/mesenchymal cells which make the CT within
the head and neck
neural crest cells migrate into the great arteries and help form the walls of the pulmonary trunk,
aorta, and carotid vessels
neural crest gives rise to cartilages and general CT within the pharyngeal arches and other facial
regions during development
- generally the neuroepithlium in the
epithelial plate is pseudostratified in
early development, with all cells
making contact with the luminal
surface (central canal)
- some cells extend all the way out to
the pial surface
- mitosis occurs in the cells near the
lumen
- non-mitotic cells are away from the
lumen
- the cell nucleus is away from the lumen
during interphase
- as the cell goes into prophase and mitosis, the
nucleus tends to be next to the lumen
- cells divide next to the lumen  some will
retain their connection to the lumen, others
will break free and migrate away
- cells continue to undergo mitosis
- the nucleus moves away from the lumen
(toward the outside) during interphase
- mitosis occurs within in an area close to the
lumen  nuclei then migrate or cells migrate
by themselves away from the lumen
- ventricular zone- next to the lumen where the
proliferating mitotic cells are located
- the lumen in the more cranial portions becomes the
ventricles and the central canal
- ventricular cells- cells around the original lumen
- as neurons and glial cells migrate away from the
proliferative zone, they go to 2 additional zones:
o mantle zone/region- intermediate in position, mostly
cell bodies, becomes gray matter in the spinal cord
o marginal zone/region- next to the pia (in the
periphery of the spinal cord), becomes white matter
(ascending and descending fibers tracts myelinated by
oligodendrocytes
- the neuroepithelial cells that did not migrate away from
the luminal aspect remain as ependymal cells lining the
central canal
- see closed neural tube with cells proliferating and some
cells migrating away
- see a thick ventricular zone at this time, a developing
mantle region that will become cell bodies, and
aggregation of nerve cells processes (marginal region)
outside of that
- outside, see a spinal DRG forming (labeled SG in the
picture)
- dorsal root ganglion are from neural crest (different origin
from the cells within the neural tube itself)
- top: see the different zones and cells migrating away, see neural
crest cells that have central process going into the developing
neural tube to interact with neurons within that tube
- bottom: farther along in development  see dense population of
cell bodies and nuclei giving rise to gray matter
- older spinal cord has ascending and descending myelinated
processes forming the marginal zone
- ganglion/neural crest cells at the periphery
- gray matter in the spinal cord is not homogenous:
o anterior cell column- motor neurons (efferent) whose axons go
to the periphery, interneurons
o dorsal cell column- interneurons that are receiving info from the
primary sensory neurons (central processes of ganglion neurons
coming in)
- neurons are told where they are in the neural tube and how they
should develop by signal molecules released by the surrounding
tissues
- the concentration of signal molecules determines the appropriate
neural populations related to their functions
- bone morphogenic proteins are released from the overlying epidermis  diffuse ventrally
o BMP causes PAX genes to be organized and expressed dorsally
- the notochord lies ventral to the developing neural tube  releases SHH  SHH diffuses dorsally
through the tissues  influences the ventral aspect of the neural tube
o SHH from the notochord induces SHH formation by cells in the area of neural tube known as the
floor plate (ventral/anterior-most portion of neural tube)
o in areas of high [SHH] both from notochord and neural tube origin, the PAX genes aren’t allowed to
work  motor neurons and interneurons develop
o in areas of low [SHH], high BMP concentrations and increased PAX gene expression allow neurons to
know they’re in the dorsal aspect of the neural tube  they become interneurons that receive info
from the primary sensory neural-crest derived neurons
- various chemicals migrate down from the dorsal aspect of the neural tube
- basal plate- functional area of the anterior mantle
that forms under SHH influence (alpha/beta/gamma
motor neurons and interneurons), highly cellular area
- alar plate- functional area of the dorsal mantle
- intermedial lateral cell column- intermediate area
between the basal and alar plates (between anterior
and dorsal cell columns), contains preganglionic
sympathetic neurons that developed from being in a
mixture of PAX and SHH, also have general visceral
afferent neurons here
- within the basal plate, the motor neurons aggregate and segregate themselves into nuclear groupings
that relate to the populations of skeletal muscle which they will innervate
o in the upper cervical and thoracic levels, there’s a medial collection of nuclei of motor neuron cell
bodies that innervate axial musculature
o get enlargements of spinal cord where limbs are associated  enlargements of the anterior cell
column into the lateral portion, have nuclear cell groupings related to the functional groupings of
muscles within the limbs
o basal plate has lots of neurons sending processes out to the periphery and other neurons that don’t
send processes peripherally (serve as interneurons)
- the neurons in the alar plate receive the central processes of the peripheral sensory neurons bringing
info into the spinal cord/neural tube
o have lamina (1-6) in the dorsal cell column within the alar plate
o various strata form, receive info, send processes into the marginal zone as the ascending tract fibers
 take info to higher levels
- the neural tube differentiates
under influence of different signal
molecules
- basal plate mantle zoneanterior/ventrally, contains
somatic/visceral efferent neurons
and interneurons
- alar plate mantle region- forms
interneurons receiving info from
primary sensory neurons of neural
crest origin, sends info to the basal
plate for reflex activity or sends
info up to long axons in the
marginal zone to higher levels for
higher integration
- the neural tube, spinal cord, and spinal column are the
same length in early development, but the spinal column
begins to grow more rapidly than the neural tube grows
- by the time there’s differential growth, the neural crest
cells have already sent central processes into the neural
tube and motor axons have already gone out to the
periphery  points of exit for spinal nerves have already
been determined between the developing vertebra and
the neuron processes are anchored
- in some congenital problems (spina bifida), the spinal cord
may be tethered more strongly to the vertebral column 
doesn’t allow differential growth to occur as readily 
spinal cord can’t slide up, but it’s still attached to the
brainstem  brainstem/medulla and cerebellum gets
pulled inferiorly through foramen magnum and into spinal
cord (Arnold Chiari malformation)
- the cerebral area is still a portion of the neural tube
- the cerebrum has a large expression of radial glial cells
- radial glial cells- specialized type of glial cells that extend
from the luminal/ventricular surface out to the periphery,
serve as a guide for migrating neurons
- proliferation takes place next to the luminal surface, but
especially within the cerebrum, the neurons migrate away
from the ventricular zone non-randomly  migrate along
the radial glial cells
- cerebral cortex development: cells migrate away from the
luminal surface following radial glial cells toward the pia
o first migration occurs  second migration cells migrate
through the first migration  goes to the outside 
happens about 6 times (newest cells are always on the
outside)
o layers are organized according to columns: neurons
migrating up the radial glial cells have a common origin
and termination related to themselves  organize
themselves into the various cortical columns
o cortical columns have different functions depending on if
they’re in primary sensory, primary motor, or associative
cortical areas
- the cranial portion of the neural tube within
the developing head and neck region initially
has swellings and constrictions (whereas the
spinal region lumen is uniform)
- 3 initial swellings:
o forebrain (prosencephalon)
o midbrain (mesencephalon)
o hindbrain (rhombencephalon)
- the wall thickness may be different in these
areas as well
- the constriction and swellings are dependent upon signal molecules from various tissues surrounding
the neural tube which influence various genes
- prosencephalon balloons out at the cranial end:
o telencephalon- part that ballooned out, telecnephalic vesicles become the cerebral hemispheres
o diencephalon- part that did no balloon out, becomes the thalamus and hypothalamus
- rhombencephalon segregates into 2 regions:
o metencephalon- becomes the pons and cerebellum
o myelencephalon – becomes the medulla (myelon = spinal cord, encephalon = head)
- the lumen also changes as the configuration of the neural tube changes
o lateral ventricles are from the lumen of the telencephalon
o third ventricle is from the lumen of the diencephalon
o cerebral aqueduct is from the lumen of the mesencephalon
o fourth ventricle is from lumen of the metencephalon and myelencephalon (rhombencephalon)
o central canal continues from the 4th ventricle into the spinal cord
- all of the lumens are initially lined by ventricular zone (where early proliferation of neurons occurs) 
ventricular zone cells that don’t differentiate become the ependymal cells
- the cranial portion of the neural tube is within the
developing head and upper neck region  bends by 2
flexures (cervical and mesencephalic flexures)
- there is a general cranial-caudal growth gradient:
o the structures in the more cranial regions are larger and
are farther along in development than structures that
are more caudal  the more cranial portion is
surrounded by more advanced tissue
- the early embryo has a large head  branchial region is
slightly smaller  the body tapers down (small pelvic and
lower limb region)
- the embryo is C-shaped  bend the skeletal and
muscular structures as well as the nervous system
- flexures develop to allow for curvature: one in the cervical
region (between spinal cord and medulla) and one in the
midbrain area
- the ventricular system is not uniform, thickness and
configuration of the neural tube wall is not uniform: big
4th ventricle, thin 3rd ventricle, small cerebral aqueduct
- bottom left: brown colored area = basal plate, yellow
colored = alar plate
- infundibulum- at the cranial end of the connection of these
two plates  notochord stops at this point (only extends up
into the sphenoid bone)
o no notochord = no SHH, no SHH = no basal plate
o basal plate derivatives end in the mesencephalon (floor of
the hypothalamus) due to diminished SHH concentrations
o the floor of the hypothalamus is the breakpoint of the alar
plate and pure basal plate derivatives (have both plates
since there’s diminished SHH concentration)
o the infundibulum becomes the median eminence/
neurohypophysis
- pure basal plate derivatives are found in mesencephalon and
farther down  gives rise to efferent neurons (somatic and
primary visceral/autonomic)
- can see the cervical flexure in the medulla area
- can see the cephalic flexure in the midbrain region
- also see a counterflexure in the rhombencephalon 
straightens out the brainstem
- rhombencephalic flexure- between the metencephalon and
myelencephalon, bends opposite the cervical and cephalic
flexures
- top: see the flexures
- bottom: diencephalon has begun to enlarge  optic
vesicles come out of here  give rise to eyes
- more caudally in the myencephalon/medulla area: have the
cervical flexure
- can see the counter bend between the metencephalon and
myelencephalon  differentiates the rhombencephalon
into a more cranial metencephalon and caudal
myelencephalon
- the rhombencephalic flexure causes the brainstem area
to buckle  the neural tube stretches over the
myelencephalon
- the neural tube over the medulla (caudal
rhombencephalon) gets stretched thin  only have
ependymal ventricular cells and overlying pia there
- more cranially in the metenecephalon area (cranial
rhombencephalon), there is cell proliferation which
dorsally gives rise to the cerebellum
- the cerebellum proliferates and grows back over the
thinned out roof of the 4th ventricle
- within the developing cerebellar area, tissues proliferate and subdivide into a floccularnodular lobe
o get anterior and posterior lobes with the primary and posterior-lateral fissures developing early
- as the cerebellum increases in size, it swings together and the parts merge
- nervous systems in animals: functionally and developmentally 3 different regions:
o as soon as the cerebellum develops, the largest part is the floccularnodular region
(vestibulocerebellum), animals that work in 3D space have a well developed vestibulocerebellum 
controls vestibular nuclei (equilibrium)
o the next area that develops is the anterior lobe and the vermis region (spinal cerebellum) 
integration/coordination of activity of axial and paraxial musculature
o the last part to develop is the lateral portion of posterior lobes/lateral hemispheres (cerebral
cerebellum)  participates with the cerebrum in the planning of movement
- movement:
o basal ganglia- functionally help to determine which motor groups are active in an upcoming
movement = pattern of movement
o cerebral cerebellum- told which movement is anticipated and adds information based on past
experience, estimates how long a given motor column should be active and how strong it should be
 timing/sequence of movement before the movement begins
o spinal cerebellum- corrections to carry out smooth movement
o vestibulocerebellum- balance
- all cells within the cerebellum develop from the ventricular zone
- some cells migrate to the surface, others (Purkinje cells) don’t
migrate quite as far
- in the external granular cell layer, many cells migrate back
deeper to be at the level of Purkinje nuclear cell bodies and even
deeper to become the granular cells
- info comes in  goes to granular cells  granular cells have
axons out to superficial cerebellum (surface white matter in the
cortex)  branch  activate many Purkinje cells
- processes in the periphery that interact with Purkinje cell
dendrites can be thought of as spun off as the granular cell
bodies migrated from the superficial aspect of the cerebellum
into a deeper layer of cortex  they were left behind
- the deep nuclei are related to the site of cellular proliferation
from the ventricular zone a little later  cell bodies don’t
migrate, deep nuclei send axons out of the cerebellum to other
areas of the nervous system
- cerebellum
o NOT FULLY DEVELOPED AT BIRTH  important in coordinating activity so it must make adjustments
o plastic structure: synapses constantly change
o body segments change proportions with age (growth), changes in weight once growth has stopped,
changes in clothing and shoes  requires accommodations to allow for smooth movements
o still have proliferations in the ventricular zone (gives rise to deep nuclei) and within the cortex (gives
rise to more cortical cells)
- have the same influences initially from overlying ectoderm and
underlying notochord (SHH)
- BMP influence PAX genes
- make basal plate and alar plate derivatives
- the notochord only goes up to the midbrain and its influences
don’t extend much beyond there
- the diencephalon and telencephalon are not under notochord
control  they are under prechordal plate control
- in between the proliferation that gives rise to the basal plate and
the proliferation that gives rise to the alar plate internally is a
depression of the central canal called the sulcus limitans
- sulcus limitans- lateral evagination of the central canal that is a
landmark for the area between the basal and alar plate
- basal plate- somatic and visceral efferent neurons
- alar plate- neurons receiving info from other areas of the spinal
cord or other inteneurons, don’t directly receive input from
peripheral neurons
- there is organization within the basal and alar plate (nuclei and
lamina)
- have the stretched roof plate
- the floor plate is used as a pivot point
- the small central canal has opened up into a 4th ventricle
(brainstem)
- still have floor plate (median sulcus)
- have a little linear depression more laterally (sulcus limitans)
- have a reflection into the roof most laterally
- basal plate stays centrally placed (between the midline of the
median sulcus and neural tube)
- alar plate gets carried laterally- nuclear groups are lateral to sulcus
limitans (cranial nuclear groups can migrate into other areas)
- cells from alar plate origin can migrate ventrally into the rest of the
neural tube
- in the PONS, most medial is somatic efferent
- the closest motor to sulcus limitans (area between alar and basal
plate where intermedial lateral and intermedial medial cell columns
are) are general visceral efferent, also have afferent nuclei there
- the gray matter in the spinal cord is continuous, whereas gray
matter in the brainstem is broken up into CN nuclei
- somatic efferent neurons are closest to the midline (CN 3, 4, 6, 12)
- general visceral efferent neurons (CN 3, 10) are further away from
the midline
- special visceral efferent (CN 5, 7) and nucleus ambiguous (CN 9, 10,
11)  moved away from the ventricular surface  more
ventrolateral
- the nuclei are essentially in columns that relate to the original
segregation of basal and alar plates
- there should not be a basal plate derivative in the dorsal lateral
aspect of the brainstem  they are all in the ventral aspect
- in the MEDULLA, the alar plate is once again giving rise to sensory
nuclei and the basal plate is giving rise to the motor nuclei
- somatic motor nuclei next to midline
- special visceral efferent: brancial arch innervating motor nuclei 
axons leaving more lateral, the motor nuclei are more ventrolateral
within the brainstem
- general and special visceral afferents  lumped together in the
solitary nucleus/fasciculus
- somatic afferent nuclei most lateral in the brainstem are vestibular
and cochlear nuclei
-
the diencephalon and telencephalon are originally separate, but fuse
thalamus- diencephalic origin
basal ganglia- telencephalic origin
can’t see a clear distinction here
- can see the internal capsule coming through
- deep telencephalic nuclei are medial (caudate nucleus)
or lateral (putamen and globus pallidus) to the internal
capsule
- the thalamus, hypothalamus, and epithalamus are all from
the diencephalon
- telencephalon- develops into corpus striatum
- corpus striatum- nuclear grouping in ventral aspect of the
telencephalic vesicles
- as the telencephalic vesicles enlarge they overflow the
diencephalon and cover over it both laterally and anteriorposteriorly, they grow out from the area of the
interventricular foramen of Monro but then expand out
laterally/posteriorly/anteriorly and will ultimately fuse with
the diencephalon
- the corpus striatum developing
in the telencephalon ultimately
fuses with the thalamus
- the fusion zone is lost
- now there are neurons going from the thalamus to the cortex
- thalamus = gatekeeper to the cortex
- everything entering the cortex from lower levels must pass through the
thalamus (except for some olfaction)
- fibers leaving the cerebral cortex back to thalamus to the brainstem and
spinal cord just pass through the corpus striatum  through the fusion
zone  into diencephalon/metenecphalon/rhombencephalon
- corpus striatum has been secondarily split into nuclear groups (caudate
nucleus, putamen, globus pallidus) as internal capsule fibers grew right
through
- the anterior commissure and corpus collosum connect
equivalent areas left and right
- optic chiasm- decussation of fibers (nasal retinal fibers)
- all develop initially in a region known as the lamina
terminalis
- lamina terminalis- cranial-most portion of the diencephalon
- lamina terminalis- where the anterior cranial neuropore
was (cranial-most portion of the neural tube)
- growing through that, using that as an outgrowth of
diencephalon  optic nerve fibers  ganglion cells/axons
migrate from retina to thalamus some crossing in lamina
terminalis to form the optic chiasm
- other neurons from the anterior-medial temporal lobe
cortex crossing over  form the anterior commissure
- the beginning of the corpus callosum develops in the
lamina terminals
- as more and more fibers are added to the corpus callosum
(more and more of the neocerebrum/neocortex develops),
the corpus callosum gets larger and migrates back  it
divides some parts of the most primitive portion of the
telencephalon away from others
o forms the fornix and a stretched area known as septum
pellucidum ventral to the corpus callosum while
hippocampus and its continuations lie immediately
dorsal to the corpus callosum
- the ventricular system develops within the neural tube and
expands out forming the ventricles and cerebral aqueduct
- areas stretched out within the
ventricles where only pia and
ependymal cells are found
- tila choroidia (??)- only pia and ependyma
- the pia is vascularized
- in tila choroidia, vessels proliferate to give rise to the choroid
plexus which extends into the ventricular system
- choroid plexus extends into the lateral fissure of the lateral
ventricles, hangs from the roof of the 3rd ventricle, and hangs
from the posterior roof of the 4th ventricle
- the choroid plexus produces some CS
- CSF can be reabsorbed in arachnoid granulations and anywhere
cranial/spinal nerves exit
- if the spinal cord can’t migrate superiorly enough, it keeps tethering
the brainstem (meningocoel or meningomyelocoel)  pulls medulla
and cerebellum into foramen magnum  CSF can’t get down around
spinal cord where some would be removed  CSF builds up 
external hydrocephalus  get ventricular shunts  remove CSF from
ventricular system and shunt it elsewhere in the body
- ependymal cells lining the ventricular system are
not impervious to CSF migration
- regular ventricular cells allow CSF fluid contents
and water to migrate back and forth
- the ependymal cells related to the choroid plexus,
however, are a blocking/determining element 
determine what can move from interstitial fluid
created by the capillary plexus into CSF
- choroidal epithelial cells are one element of the
blood-CSF barrier
- blood-brain barrier: endothelial cells of capillaries
(endothelial cells know they’re in the neural tissue
because of healthy astrocytes)
WE WILL NOT BE TESTED ON OBJECTIVES 13 and 14,
BUT THEY “HAVE RAMIFICATIONS”