1. EMBRYOLOGY OF
NERVOUS SYSTEM
Dr NAVEEN THOTA
SVIMS

2. Introduction
 Formation of neurons and neuroglial cells
 Neural tube and its sub divisions
 Spinal cord
 Medulla oblongata
 Pons
 Midbrain
 Cerebral hemisphere
 Corpus striatum
 Cerebral cortex
 Autonomic nervous system

3. Formation of neurons and
neuroglial cells
 Neural tube first lined by single layer
of cells
 Proliferate to form several layers
◦ Matrix layer
◦ Mantle layer
◦ Marginal layer

4. Contd..
 Stages in the formation of a nerve cell
are:
◦ Apolar neuroblast
◦ Bipolar neuroblast
◦ Unipolar neuroblast
◦ Multipolar neuroblast
◦ Axon and dendrites

5.  Neuroglial cells are also formed from
germinal cells of the ependymal layer
 Glioblasts migrate in to mantle and
marginal layer as medulloblasts
 They differentiate either into
astroblasts or oligodendroblasts
 Microglial cells are mesodermal in
origin

7. Myelination of fibers
 Nerve fibers which remain with in the
brain and spinal cord receives support
from and are ensheathed by neuroglial
cells
 Peripheral nerves special sheath
called the neurolemma derived from
schwann cells
 Myelin of the CNS derived from
oligodendrocytes

9. Neural tube and its
subdivisions
 Whole of the nervous system is
derived from ectoderm except blood
vessels and neuroglial elements
 Ectoderm situated on the dorsal
aspect of embryonic disc forms the
neural plate
 Neural groove
 Neural tube
 Enlarges cranial part and caudal
tubular part

12. Contd..
 The cavity of the brain shows three
dilatations
 Prosencephalon, mesencephalon,
rhombencephalon
 Prosencephalon
◦ Diencephalon
◦ Telencephalon
 Rhombencephalon
◦ Metencephalon
◦ Myelencephalon

14. Contd..
 The relative position is altered by
number of flexures
◦ Cervical flexure
◦ Mesencephalic flexure
◦ Pontine flexure
◦ Telencephalic flexure

16. Neural crest
 Cells between the neural plate and the
rest of the ectoderm form primordia of
the neural crest
◦ DRG
◦ Sensory ganglia of 5, 7, 9, 10
◦ Neurons and satellite cells of sympathetic
ganglia
◦ Parasymathetic ganglia
◦ Schwann cells

17. Contd..
◦ Specific cells adrenal medulla
◦ Chromaffin tissue
◦ melanoblasts

20. Spinal cord
 Devolops from caudal cylindrical part of
neural tube
 Cavity of the tube bounded by thick
lateral wall, thin roof and floor
 Tube subdivides in to three layers matrix
layer, mantle layer and marginal layer
 Ventral layer of the mantle layer grows
faster than dorsal layer
 Line seperating the compressed ventral
part from the dorsal part is called sulcus
limtans

22. Contd..
 Dorsal or alar lamina
 Ventral or basal lamina
 Posteriomedeian fissure
 Anteriomedian fissure
 Nerve cells that devolop in mantle
zone of the basal lamina becomes the
neuron of anterior grey column and
from the alar lamina the neuron of the
posterior grey column

24. Contd..
 Dorsal nerve root ganglia are formed
by axons of the cells that develop from
neural crest
 Axons from the post grey column
enter the marginal layer to form the
ascending tract
 Descending tracts are formed by the
axons projecting from the brain
 Grey columns divide the white matter
in to anterior, posterior and lateral
columns

26. POSITIONAL CHANGES OF

THE CORD
In the third month of development the spinal cord extends
the entire length of the embryo, and spinal nerves pass
through the intervertebral foramina at their level of origin.
 With increasing age, the vertebral column and dura
lengthen more rapidly than the neural tube, and the terminal
end of the spinal cord gradually shifts to a higher level.
 At birth, this end is at the level of the third lumbar
vertebra.
 As a result of this disproportionate growth, spinal nerves run
obliquely from their segment of origin in the spinal cord to
the corresponding level of the vertebral column.
 The dura remains attached to the vertebral column at the
coccygeal level.
 In the adult, the spinal cord terminates at the level of L2 to
L3,
 The dural sac and subarachnoid space extend to S2.
 Below L2 to L3, a threadlike extension of the pia mater
forms the filum terminale, which is attached to the
periosteum of the first coccygeal vertebra and which marks
the tract of regression of the spinal cord.
 Nerve fibers below the terminal end of the cord collectively
constitute the cauda equina.

27. Medulla oblongata
 Myelencephalon
 Early devolopment simillar to spinal
cord sulcus limitans divides in to alar
and basal lamina
 Roof plate becomes greatly widened
resuting which alar plate comes
dorsolateral to basal plate
 Alar plate forms olivary nuclei and
cranial nerve nuclei

28. Contd..

29. Pons
 Ventral part of metencephalon
 Contribution alar lamina of the
myelencephalon and gives rise to
pontine nuclei axons arising from them
forms MCP
 Lateral part of alar lamina becomes
rhombic lips to form the cerebellum
 Nuclei arising from basal and alar
plate lie in dorsal or tegmental part of
pons

30. Contd..
 Ventral part of pons constitutes:
◦ Middle cerebellar peduncle
◦ Corticospinal, corticobulbar and
corticopontine fibers

32. Mid brain
 Nuclei of the basal lamina
◦ Occulomotor nuclei
◦ Trochlear nuclei
◦ Edinger Westphal nuclei
 Alar lamina gives rise to
◦ Colliculi
◦ Red nucleus
◦ Substantia nigra

33. Contd..
 Marginal layer ventral part of
mesencephalon invaded by down
growing fibers of CST, corticobulbar
and cortico pontine pathway and
forms crus cerebri

35. Cerebellum
 Devolops from dorsolateral part of alar
lamina of the metencephalon
 Rhombic lips on either side grows and
fuses medially to form cerebellum
 Consists of usual matrix, mantle and
marginal layer
 Cells of the mantle layer migrating in to
marginal layer forms cortex and those
don’t forms dentate, emboliform, fastigial
and globose nuclei

36. Contd..
 Superior cerebellar peduncle
 Middle cerebellar peduncle
 Inferior cerebellar peduncle

38. Cerebral hemispheres
 Median diencephalon and lateral
telencephalon
 Telancephalon
◦ Cerebral cortex and corpus striatum
 Diencephalon
◦ Epithalamus, thalamus and hypothalamus
 Telencephalic vesicles are small
initially rapidly grows upwards,
forwards and backwards completely
covers the diencephalon

39. Contd..
 Cavity of diencephalon form third
ventricle and of telencephalic vesicles
form lateral ventricles
 Each lateral is at first a small spherical
space
◦ Forward and backward growth elongates
anterioposteriorly
◦ Grows downwards and forwards to form the
temporal lobe and horn
◦ Backward growth to form occipital pole and
posterior horn

43. Thalamus and hypothalamus
 Devolops from diencephalon
 Lateral wall of diencephalon becomes
thickened
 Divided by epithalamic and
hypothalamic sulci
 Epithalamus represented by
habenular and pineal body

45. Corpus striatum
 Derivative of telencephalon
 Telencephalic vesicle can be
subdivided in to basal part which is
thick and superior part is thin
 Some cells migrate in to marginal
layer and forms cortex and remaining
cells form copus striatum
 Corpus striatum subdivided into
medial and lateral divisions

46. Contd..
 Fibers descending from cerebral
cortex passes through medial and
lateral parts constitutes internal
capsule
 Medial or deeper part form caudate
nucleus and superficial or lateral part
forms lentiform nucleus

50. Cerebral cortex
 Formed by migration of cells from the
mantle layer in to overlying marginal
layer
 Region of insula relatively slow in
growth and gradually overgrown by
adjacent area forms the opercula
 Cortex divided in to
◦ Hippocampal
◦ Pyriform
◦ neocortex

51. Contd..
 Pyriform cortex that recives olfactory
sensation constitutes uncus,
parahippocampal gyrus and anterior
perforated substance
 Telencephalon has a medial wall
opposing each other gives rise to
hippocampal cortex
 Pyriform cortex arises from marginal
layer superficial to corpus striatum
 With formation of inferior horn
hippocampus follows the curve and
assumes aring shaped configuration

52. Contd..
 Superior part of the hippocampus
becomes ridimentary and forms
indesium gresium
 White matter of the cerebral cortex is
formed by projection, association,
commisural and ascending fibers

56. Cerebral commisures
 Part of the neural tube that closes the
cranial end of prosencephalon is
lamina terminalis
 Anterior commisure
 Hippocampal commisure
 Corpus collosum
 Optic chiasma, habenular commisure,
posterior commisure.

58. Autonomic nervous system
 Sympathetic nervous system
 Parasympathetic nervous system

59. Sympathetic nervous system
 Preganglionic neurons devolop from
mantle layer of thoracolumbar region
of the spinal cord
 Located in lateral horn of the cord
 After short course in the spinal
nervethey leave them and grows
towards the postganglionic neurons

60. Contd..
 Postganglionic neurons are of two
types
◦ Sympathetic trunk
◦ Visceral ganglia

62. Parasympathetic nervous
system
 Cranial parasympathetic out flow
◦ Derived GVE nuclear column of the brain
stem
 Edinger westphal nucleus
 Salivatory nucleus
 Lacrimatory nucleus
 Dorsal nucleus of vagus
 Sacral parasympathetic out flow
◦ Preganglionic cells are formed in the
mantle layer of the spinal cord near the
sulcus limitans S2-S4

63. Contd..
 Postganglionic neurons lies near the
viscera

65. Thank u