• The nervous system develops when the
notochord induces its overlying ectoderm
to become neuroectoderm and
• This now develop into the neural plate.
• The neural plate folds along its central axis
to form a neural groove
• lined on each side by a neural fold
• The two neural folds fuse together and pinch off
to become the neural tube.
• Fusion of the neural folds begins in the middle
of the embryo and moves cranially and
• The cranial open end of the tube is the
anterior (rostral) neuropore, and
• the caudal open end of the tube is the
posterior (caudal) neuropore.
• The anterior neuropore closes on or before day
• the caudal neuropore closes before the end of
the fourth week.
• Some cells from the neural folds give rise to
pleuripotent neural crest cells,
• they migrate widely in the embryo to give rise to
many nervous structures:
• · Spinal ganglia (dorsal root ganglia)
• · Ganglia of the autonomic nervous system
• · Ganglia of some cranial nerves
• · Sheaths of peripheral nerves
• · Meninges of brain and spinal cord
• · Pigment cells
• · Suprarenal medulla
• · Skeletal and muscular components in the
Summary: Embryonic Development
• Nervous system develops from ectoderm
– by 3rd week, neural plate becomes a
groove with neural folds along each
– by 4th week, neural folds join to
form neural tube
– lumen of the neural tube develops
into central canal of
spinal cord & ventricles of the brain
– cells along the margin of the neural
groove is called the neural crest
• develop into sensory and sympathetic neurons & schwann cells
– NB: By 4th week, neural tube exhibits 3 anterior dilations
• By wk 4, the neural tube forms three
primary brain vesicles.
• The primary brain vesicles give rise to five
secondary brain vesicles,
• which give rise to the various adult
Telencephalon Cerebral hemispheres, consisting of the
cortex and medullary center, basal
ganglia, lamina terminalis,
hippocampus, the corpus striatum, and
the olfactory system
Diencephalon Thalamus, epithalamus, hypothalamus,
subthalamus, neurohypophysis, pineal
gland, retina, optic nerve, mamillary
Metencephalon Pons and cerebellum
Ventricular System (Cerebrospinal
• Fluid filled cavities found within the
developing brain system originate from
lumen of the developing neural tube
• 5 cavities- lateral vent-1 pair
• Lined by choroid plexus made of ependymal
Ventricular communication in the
vent foramen of Monro
• 3rd to 4th
vent cerebral aqueduct of
to lateral aperture foramen of luschka
to median aperture foramen of
Development of Spinal Cord
• The neural tube consists of three cellular
layers from inner to outer:
• the ventricular zone (ependymal layer),
• the intermediate zone (mantle layer), and
• the marginal zone (marginal layer).
• The ventricular zone gives rise to
neuroblasts (future nerve cells) and
• glioblasts (future supporting cells), which
migrate into the intermediate zone to form
two collections of cells (the alar plate and
the basal plate)
• separated by a groove called the sulcus
Alar and basal plate cells
• Cells in the alar plate become afferent (sensory)
• form the dorsal (posterior) horn of the spinal cord.
• Cells in the basal plate become efferent (motor)
• form the ventral (anterior) horn of the spinal cord.
• The two ventral horns bulge ventrally to create a
ventral median fissure.
• While, the dorsal horns merge to create the dorsal
• The lumen of the neural tube becomes the central
canal of the spinal cord.
• The spinal cord extends throughout the entire
length of the vertebral canal at week 8 of
• At birth, the conus medullaris extends to the
• In the adult, the conus medullaris extends to
the L1 vertebra.
• NB: Spinal lumbar punctures procedure must
be performed caudally to the conus medullaris
to avoid damaging the spinal cord.
Development of Meninges
• The dura mater arises from paraxial
mesoderm that surrounds the neural tube.
• While, both the pia mater and arachnoid
mater arise from neural crest cells.
Hypophysis (Pituitary Gland)
• The anterior pituitary gland (adeno-
hypophysis) arises from an evagination of
the oropharyngeal membrane known as
• The posterior pituitary gland (neuro-
hypophysis) arises from an evagination of
neuroectoderm from the diencephalon.
Clinical Correlations of spinal
• Spina Bifida
• · Spina bifida occulta is a defect of the vertebral
column only, and is a common problem affecting as
many as 10% of live births.( NB: normal afeto-
• · Spina bifida with meningocele (spina bifida
cystica) is a defect of the vertebral column with
protrusion of the meninges through the defect.
• · Spina bifida with myelomeningocele is a
defect of the vertebral column protrusion of the
meninges and herniation of the spinal cord through
• · Spina bifida with myeloschisis results
from the failure of the caudal neuropore to
close at the end of the fourth week of
development. -- Newborn infants are paralyzed
distal to the lesion.
• These defects usually occur in the cervical
and/or lumbar regions and may cause
neurologic deficits in the lower limbs and
• Neural tube defects can be detected by the
presence of alpha-fetoprotein (AFP) in the
fetal circulation after the fourth week of
Anormalies of the brain
• Anencephaly is the failure of the anterior neuropore to
close, resulting in a failure of the brain to develop.
• Microcephaly (small head) results from
microencephaly (small brain), or the failure of the
brain to grow normally.
• This can be the result of exposure to large doses of
radiation up to the sixteenth week of development, or
from certain infectious agents (cytomegalovirus,
herpes simplex virus, and toxoplasma gondii-
Applied anatomy of CNS
• Hydrocephalus is an accumulation of CSF in the
ventricles of the brain, caused most commonly by
stenosis of the cerebral aqueduct. In the absence of
surgical treatment in extreme cases the head may
swell to three times its normal size.
• Arnold-Chiari Malformation
• Arnold-Chiari malformation is herniation parts of the
cerebellum (medulla oblongata and cerebellar vermis)
through the foramen magnum of the skull.
• Fetal Alcohol Syndrome
• Ingestion of alcohol during pregnancy is the most
common cause of infant mental retardation. It also
causes microcephaly and congenital heart disease.
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