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
6.
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
8.
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
10.
11.
12. Contd..
The cavity of the brain shows three
dilatations
Prosencephalon, mesencephalon,
rhombencephalon
Prosencephalon
◦ Diencephalon
◦ Telencephalon
Rhombencephalon
◦ Metencephalon
◦ Myelencephalon
13.
14. Contd..
The relative position is altered by
number of flexures
◦ Cervical flexure
◦ Mesencephalic flexure
◦ Pontine flexure
◦ Telencephalic flexure
15.
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
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
21.
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
23.
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
25.
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
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
31.
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
34.
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
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
40.
41.
42.
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
44.
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
47.
48.
49.
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
53.
54.
55.
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.
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
61.
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