Embryology of nervous system

1. ABHILASHA CHAUDHARY
EMBRYOLOGY OF NERVOUS
SYSTEM

2. INTRODUCTION
 Human embryology is the study of this
development during the first eight weeks after
fertilisation
 Embryogenesis continues with the next stage
of gastrulation when the three germ layers of the
embryo form in a process called histogenesis ,
and the processes of neurulation
and organogenesis follow.

3.  The three germ layers are the ectoderm, mesoderm
and endoderm and are formed as three overlapping
flat discs.
 The upper layer of ectoderm will give rise to the
outermost layer of skin, central and
peripheral nervous systems, eyes , inner ear, and
many connective tissues.
 The middle layer of mesoderm will give rise to the
heart and the beginning of the circulatory system as
well as the bones, muscles and kidneys.
 The inner layer of endoderm will serve as the starting
point for
thedevelopmentofthe lungs, intestine, thyroid, pancre
as and bladder.

4.  Neural development is one of the earliest
systems to begin and the last to be completed
after birth.
 The whole of the nervous system is derived from
ectoderm excepts its blood vessel and some
neurological elements

5. Neural ectoderm
Neural tube
Central nervous
system
Neural crest cells
Most of peripheral
nervous system
Ectodermal placodes
Cranial sensory
ganglia
Hypophysis
Inner ear

6. FORMATION OF NEURAL
TUBE
 Neurulation is the formation of the neural tube from
the ectoderm of the embryo. It follows gastrulation in
all vertebrates.
 After gastrulation the notochord—a flexible, rod-
shaped body that runs along the back of the
embryo—has been formed from the mesoderm.
 The ectoderm overlying the newly formed notochord
thickens in the midline forming the neural plate at
about 16th day of embryonic life As somatic
mesoderm develops on either side of notochord, the
margins of neural plate are elevated as neural folds,
as a result the centre of plate sinks, creating the
neural groove.

7.  On 20th day the neural
folds fusion begins and
gradually it moves
together towards
midline and finally fuse
together towards the
midline and finally fuse
to form a cylindrical
neural tube that loses
its connection with the
surface ectoderm.
 The process of neural
tube formation termed
neurulation.
 The fusion of the neural
folds begins in the
middle and it
simultaneously
proceeds in the cephalic
and caudal directions.

8.  The fusion at the cranial and caudal ends of
neural tube are somewhat delayed, forming small
openings called anterior and posterior
neuropores.
 The anterior neuropore closes in the middle of the
4th week and posterior neuropore closes at the
end of 4th week.
 Enlarged cranial and caudal part gives rise to
brain and spinal cord,respectively.

10. FORMATION OF NEURAL CREST
CELLS.
As the neural folds come together and fuse the cells
at the tips of neural folds break away from the
neuroectoderm to form neural crest cells.
 The neural crest cells at first remain in the midline
between the dorsal surface of the neural tube and
the surface ectoderm, and then forms two cell
clusters dorsolaterally, one on either side of the
neural tube.

12.  The neural crest cells
differentiate to form
the cells of
 dorsal droot ganglia
 sensory ganglia of
cranial nerves
 autonomic ganglia
 adrenal medulla
 chromaffin tissue
 melanocytes and
Schwann cells

14. CORD
 The spinal cord and with it the central nervous
system, begins its development in the 3rd week of
the embryonic period.
 The spinal cord develops from the caudal
elongted part of the neural tube. The neural tube
increases in thickness due to repeated mitosis of
its epithelial lining. By the middle of the 5 the
week of embryonic development, the transverse
section of the recently closed neural tube reveals
3 layers.
 Matrix (ependymal ) zone
 Mantle zone
 Marginal zone

16.  Matrix zone: it is thick and lines the enclosed
cavity (neurocele). Its numerous cells undergoes
mitosis and and produces neuroblasts and
spongioblasts; the former develops into neurons
and later into neuroglial cells.
 Mantle zone : The neuroblast migrate to adjacent
mantle zone which turns to future grey matter.
 Marginal zone : It contains nerve fibers emerging
from neuroblasts in the mantle layer, future white
matter. As a result of myelination of nerve fibers,
this layer takes on a white appearance and
therefore is called the white matter

17. BASAL, ALAR, ROOF, AND FLOOR
PLATES
 As a result of continuous addition of neuroblasts to
the mantle layer, each side of the neural tube shows a
ventral and a dorsal thickening.
 The ventral thickenings, the basal plates, which
contain ventral motor horn cells, form the motor areas
of the spinal cord
 The dorsal thickenings, the alar plates, form the
sensory areas . A longitudinal groove, the sulcus
limitans, marks the boundary between the two.
 The dorsal and ventral midline portions of the neural
tube, known as the roof and floor plates, respectively,
do not contain neuroblasts; they serve primarily as
pathways for nerve fibers crossing from one side to
the other.

19.  The cells of dorsal region or alar lamina are
functionally afferent/ sensory while those of basal
lamina are efferent/ motor.
 The axons of cells of basal lamina leaving the
cord as ventral roots join with the peripheral
processes of dorsal rootganglia, to form spinal
nerves.

21. DEVELOPMENT OF THE
BRAIN
 The brain develops from
the enlarged cranial part
of the neural tube. At
about the end of 4th
week, the enlarged
cephalic part shows 3
distinct dilations called
primary brain vesicles .
 Craniocaudally, these
are :
 Prosencephalon
(forebrain)
 Mesencephalon
(midbrain)
 Rhombencephalon

22.  The prosencephalon gives a rostral
telencephalon and caudal diencephalon.
 The telencephalon develops lateral diverticuala
by evagination which enlarge, overgrow and
cover the caudal diencephalon to form the
cerebral hemispheres.
 The diencephalon thus becomes hidden in the
lower parts of the cerebral hemispheres and
forms thalamus, hypothalamus, epithalamus.

23.  The mesencephalon gives rise to midbrain. Its
cavity gets narrowed to form cerebral aqueduct.
 The rhombencephalon also consists of two parts:
(a) the metencephalon, which later forms the
pons and cerebellum, and (b) the
myelencephalon. gives rise to medulla oblongata.

26.  DEVELOPMENT OF VENTRICULAR SYSTEM
 The cavity of the rhombencephalon is the fourth
ventricle, that of the diencephalon is the third
ventricle, and those of the cerebral hemispheres
are the lateral ventricles.
 The lumen of the mesencephalon connects the
third and fourth ventricles. This lumen becomes
very narrow and is then known as the aqueduct of
Sylvius. The lateral ventricles communicate with
the third ventricle through the interventricular
foramina of Monro.

29. SUMMARY
 Introduction
 Development of neural tube
 Development of neural crest cells
 Development of spinal cord
 Development of brain
 Development of ventricular system

30. Conclusion
 Human embryology is the study of this
development during the first eight weeks after
fertilization. The whole of the nervous system is
derived from ectoderm excepts its blood vessel
and some neurological elements
 The neural ectoderm later differentiates into 3
strucutres: neural tube which gives rise to the
central nervous system, the neural crest cells
form nearly all the peripheral nervous system

31.  RESEARCH EVEDIENCE
 Topic : Mechanics of neurulation: From classical to current perspectives
on the physical mechanics that shape, fold, and form the neural tube.
 Authors : Vijayraghavan DS , Davidson LA
 Journal name : Birth Defects Res A Clin Mol Teratol
 ABSTRACT
 Neural tube defects arise from mechanical failures in the process
of neurulation. At the most fundamental level, formation of
the neuraltube relies on coordinated, complex tissue movements that
mechanically transform the flat neural epithelium into a lumenized
epithelial tube. Genetic and molecular perturbation have identified a
multitude of subcellular components that correlate with cell behaviors
and tissue movements during neural tube formation. In this review, we
focus on methods and conceptual frameworks that have been applied to
the study of amphibian neurulation that can be used to determine how
molecular and physical mechanisms are integrated and responsible

32. REFERENCES
 BOOKS
 Mancall Elliott, Brock David. Gray’s clinical neuroanatomy, 12th
ed. Newdelhi: Elsevier; p.113-114.
 Singh Inderbir, Seshayyan. Inderbir singh’s textbook of anatomy.
6th ed. Newdelhi: Jaypee; p .122-28
 Lewin Roger. Human evolution. 4th ed. New delhi: Blackweel
science; p.200-16
 Singh Vishram. Textbook of clinical neuroanatomy . 2nd ed.
Newdelhi : Elsevier;p.1-5
 JOURNAL:
 1.Vijayraghavan DS , Davidson LA. Mechanics of neurulation:
From classical to current perspectives on the physical mechanics
that shape, fold, and form the neural tube. Birth Defects Res A
Clin Mol TeratoL;2016

33. THANK YOU