Neuroanatomy

1. Development of nervous system
Dr. Mohammed Mahmoud Mosaed

2. The Neural Ectoderm
• At the beginning of the 3rd week of
development, the ectodermal germ layer has
the shape of a disc that is broader in the
cephalic than in the caudal region.
• Appearance of the notochord induces the
overlying ectoderm to thicken and form the
neural plate.
• Cells of the plate make up the neuroectoderm

3. Neurulation
• Neurulation is the process whereby the neural
plate forms the neural tube.
• By the end of the third week, the lateral edges of
the neural plate become elevated to form neural
folds, and the depressed midregion forms the
neural groove.
• Gradually, the neural folds approach each other in
the midline, where they fuse.
• Fusion begins in the cervical region (fifth somite)
and proceeds cranially and caudally. As a result,
the neural tube is formed.

5. Neuropores
• Until fusion is complete, the
cephalic and caudal ends of the
neural tube communicate with
the amniotic cavity by way of the
anterior (cranial) and posterior
(caudal) neuropores,
respectively.
• Closure of the cranial neuropore
occurs at approximately day 25
(18- to 20-somite stage),
whereas the posterior
neuropore closes at day 28 (25-
somite stage).

6. • Neurulation is then complete, and the central
nervous system is represented by a closed tubular
structure with a narrow caudal portion, the spinal
cord, and a much broader cephalic portion
characterized by a number of dilations, the brain
vesicles

7. Neural Crest Cells
• As the neural folds elevate and fuse, cells at the lateral
border or crest of the neuroectoderm begin to
dissociate from their neighbors and form the neural
crest,
• Derivatives of neural crest
• Cranial nerve ganglia
• Spinal (dorsal root) ganglia
• Sympathetic chain and preaortic ganglia
• Parasympathetic ganglia of the gastrointestinal tract
• Meninges
• Schwann cells
• Glial cells

8. Neural tube
• The wall of a recently closed neural
tube consists of neuroepithelial
cells, they divide rapidly, producing
more and more neuroepithelial cells
which constitute the neuroepithelial
layer.
• Once the neural tube closes,
neuroepithelial cells begin to give
rise to another cell type, the
primitive nerve cells or neuroblasts
which form the mantle layer.
• The outermost layer of the neural
tube is the Marginal layer which
contains nerve fibers emerging from
neuroblasts in the mantle layer

9. 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 form the motor areas
in the neural tube;
The dorsal thickenings, The Alar
plates, form the sensory areas.
The dorsal and ventral midline
portions of the neural tube, known as
the roof and floor plates,
respectively, do not contain
neuroblasts

10. Origin of the nerve cell and glial cells

11. Development of spinal cord
• The spinal cord arises from the lower part of the neural tube
• At third month of intrauterine life the spinal cord fills the vertebral
canal
• At the 5th month of intrauterine life the lower level of the cord at
the level of L5 or S1 vertebra
• At birth the lower level of spinal cord at the level of 3rd lumber
vertebra

12. Development of spinal cord
• The Basal plate forms the motor horn of spinal cord;
• The Alar plate forms the sensory horn.
• In addition to the ventral motor horn and the dorsal sensory horn, a
group of neurons accumulates between the two areas and forms a
small intermediate horn. This horn, containing neurons of the
sympathetic portion of the autonomic nervous system (ANS), is
present only at thoracic (T1–T12) and upper lumbar levels (L2 or L3)
of the spinal cord.

13. • Motor axons growing out from neurons in the basal plate
• Sensory components arise centrally and peripherally from
growing fibers of nerve cells in the dorsal root ganglion.
• Nerve fibers of the ventral motor and dorsal sensory roots join to
form the trunk of the spinal nerve.
DEVELOPMENT OF SPINAL NERVE

14. In the spinal cord, the myelin sheath is formed
by oligodendroglia cells; outside the spinal
cord, the sheath is formed by Schwann cells.
Myelination of spinal nerve

15. NEURAL TUBE DEFECTS
• Most defects of the spinal cord result from abnormal
closure of the neural folds in the third and fourth weeks
of development.
• The resulting abnormalities, neural tube defects (NTDs),
may involve the meninges, vertebrae, muscles, and skin

16. DEVELOPMENT OF BRAIN
The cephalic end of the neural tube
shows three dilations, the primary
brain vesicles:
(1) Prosencephalon, or
Forebrain;
(2) Mesencephalon, or Midbrain;
(3) Rhombencephalon, or
Hindbrain.
Simultaneously, it forms two
flexures:
(a) Cervical flexure at the
junction of the hindbrain and
the spinal cord
(b) Cephalic flexure in the
midbrain region.

18. RHOMBENCEPHALON
The rhombencephalon also consists of two parts: metencephalon and
myelencephalon. The boundary between these two portions is marked
by the pontine flexure
(1) Metencephalon, which later forms the pons and cerebellum and
(2) Myelencephalon. Gives rise to the medulla oblongata.
.
Development of the hind brain

19. • MYELENCEPHALON differs from the spinal cord in that
its lateral walls are everted.
• Alar and basal plates separated by the sulcus limitans .
• The roof plat of the myelencephalon consists of a single
layer of ependymal cells covered by vascular mesenchyme,
the pia mater

20. Development of the hind brain
• METENCEPHALON differentiate into:
• Pons: (The pathway for nerve fibers between the spinal
cord and the cerebral and the cerebellar cortices)
• Cerebellum: (coordination center for posture and
movement)

21. The basal plate contains motor nuclei which divided into 3 groups:
(a) General Somatic Efferent group (medial in position)
(b) Special Visceral Efferent group (intermediate)
(c) General Visceral Efferent group (lateral in position)
The alar plate contains 4 groups of sensory relay nuclei
(a) Special Somatic Afferent group (lateral in position), receives
impulses from the ear by way of the vestibulocochlear nerve.
(b) General Somatic Afferent receives impulses from the head and
face
(c) Special Visceral Afferent group receives impulses from taste buds
of the tongue and from the palate, oropharynx, and epiglottis.
(d) General Visceral Afferent, group (medial in position) receives
interoceptive information from the gastrointestinal tract and
heart

22. Development of cerebellum
• The dorsolateral parts of the alar plates bend medially and
form the rhombic lips
• the rhombic lips immediately below the mesencephalon
approach each other in the midline.
• As a result of a further deepening of the pontine flexure,
the rhombic lips compress cephalocaudally and form the
cerebellar plate.
• In a 12-week embryo, this plate shows a small midline
portion, the vermis, and two lateral portions, the
hemispheres. A transverse fissure soon separates the
nodule from the vermis and the lateral flocculus from the
hemispheres.

24. Development of the midbrain
• A deep furrow, the rhombencephalic isthmus, separates the
mesencephalon from the rhombencephalon.
• The mesencephalon, or midbrain has basal efferent and alar afferent
plates.
• The mesencephalon’s alar plates form the anterior and posterior
colliculi as relay stations for visual and auditory reflex centers,
respectively. Also form nucleus ruber and substantia nigra.

25. Development of forebrain
• The prosencephalon consists of two parts:
• Telencephalon; the primitive cerebral hemispheres;
• Diencephalon, characterized by outgrowth of the optic
vesicles. It Forms the optic cup and stalk, pituitary,
thalamus and hypothalamus.

27. Development of prosencephalon
• In the 7th week: The prosencephalon subdivides into the
diencephalon posteriorly and the telencephalon anteriorly.
• The diencephalon consists of a thin roof plate and a thick
alar plate in which the thalamus and hypothalamus
develop.
• At 10th week: The telencephalon consists of two lateral
outpocketings, the cerebral hemispheres, and a median
portion, the lamina terminalis
• In 4 month embryo: The lamina terminalis is used by the
commissures as a connection pathway for fiber bundles
between the right and left hemispheres.

28. 7-WEEK EMBRYO
In the 7th week: The prosencephalon subdivides into the
diencephalon posteriorly and the telencephalon anteriorly.
The diencephalon consists of a thin roof plate and a thick
alar plate in which the thalamus and hypothalamus develop.

29. 10-WEEK EMBRYO
At 10th week: The
telencephalon consists
of two lateral
outpocketings, the
cerebral hemispheres,
and a median portion,
the lamina terminalis

30. 4-MONTH EMBRYO
In 4 month embryo:
The lamina terminalis
is used by the
commissures as a
connection pathway for
fiber bundles between
the right and left
hemispheres

31. Development of cerebral cortex
• in 7th to 9th month embryo: The cerebral hemispheres,
originally two small outpocketings, expand and cover the
lateral aspect of the diencephalon, mesencephalon, and
metencephalon.
• Eventually, nuclear regions of the telencephalon come in
close contact with those of the diencephalon

32. DEVELOPMENT OF VENTRICULAR SYSTEM
• The lumen of the spinal cord, the central canal, is continuous with that of the brain
vesicles. 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. Each lateral ventricle
communicates with the third ventricle through the interventricular foramina of Monro .

33. CONGENITAL ANOMALIES
HYDROCEPHALUS ANENCEPHALY