CNS Histology and introduction

1. Central Nervous System
Dr. Arpit Gohel
Assistant professor
(MD. Path)

2. HISTOLOGY OF NERVOUS
SYSTEM

3. NERVOUS SYSTEM
• The most complex system in the human
body
• Formed by network more than 100
million neuron
• Each neuron has a thousand
interconnection  a very complex
system for communication
• Nerve tissue is distribute throughout the
body, anatomically divide into : CNS &
PNS
• Structurally consist : nerve cells &
glial cells

4. CELLS OF NERVOUS SYSTEM

5. STRUCTURE OF NEURON
• Principle cells of Nervous
Tissue
• The specialized cells that
constitute the functional units
of the nervous system are
called neurons.
• Consist of 3 parts :
• CELL BODY (perikaryon/soma)
• A single AXON
• Multiple DENDRITES

6. Neuron

7. • neurons are supported by special kind of
connective tissue cells that are called
neuroglia.
• Nervous tissue, composed of neurons and
neuroglia, is richly supplied with blood.
• It has been taught that lymph vessels are not
present, but the view has recently been
challenged.

8. CELL BODY (PERIKARYON)
• A neuron consists of a cell body that gives off
a variable number of processes.
• The cell body is also called the soma or
perikaryon.
• Like a typical cell it consists of a mass of
cytoplasm surrounded by a cell membrane.

9. Cytoplasm of neuron
• Contains a large central nucleus (usually with a
prominent nucleolus), numerous mitochondria,
lysosomes, and a Golgi complex.
• In the past it was stated that centrioles are not
present in neurons, but studies with the electron
microscope have shown that centrioles are
present.
• In addition to these features, the cytoplasm of a
neuron has some distinctive characteristics not
seen in other cells.

10. ULTRASTRUCTURE OF NEURON
• Cytoplasm:
• Abundant of R.E.R
Polyribosomes
• Basic dyes (a+b) 
Nissl Bodies
• lots of S.E.R.
• Golgi bodies
(perikaryon)
• protein secreting cell

11. EM view of neuron (schematic)

12. Nissl Substance
• The cytoplasm shows the presence of a granular
material that stains intensely with basic dyes; this
material is the Nissl substance (also called Nissl
bodies or granules)
• EM  rough surfaced endoplasmic reticulum
indication of the high level of protein synthesis
in neurons.
• The proteins are needed for maintenance and
repair, and for production of neurotransmitters
and enzymes.

13. Nissl substance: Extends to the dendrites but
not into the axon.

14. Neurofibrils
• Another distinctive feature of neurons is the
presence of a network of fibrils permeating
the cytoplasm.
• These neurofibrils are seen, with the EM, to
consist of micro filaments and microtubules.
(The centrioles present in neurons may be
concerned with the production and
maintenance of microtubules).

15. Neurites
• The processes arising from the cell body of a
neuron are called neurites.
• These are of two kinds.
– Most neurons give off a number of short
branching processes called dendrites
– and one longer process called an axon.

16. Dendrites
• They terminate near the cell body.
• Irregular in thickness, and Nissl granules
extend into them.
• They bear numerous small spines that are of
variable shape.
• In a dendrite, the nerve impulse travels
toward the cell body

17. Axon
• The axon may extend for a considerable
distance away from the cell body.
• The longest axons may be as much as a meter
long.
• Each axon has a uniform diameter, and is
devoid of Nissl substance.

18. • The cytoplasm within the axon is called
axoplasm and its cell membrane is called
axolemma.
• The axoplasm contains all the cell organelles
of neurons cell body except ribosomes.
• Hence, proteins synthesized in the cell body
are continuously transported toward the axon
terminals by a process called axoplasmic
transport.

19. • In an axon the impulse travels away from the
cell body.
• Axons constitute what are commonly called
nerve fibers.
• The bundles of nerve fibers found in CNS are
called as nerve tracts, while the bundles of
nerve fibers found in PNS are called peripheral
nerves.

21. Difference between Axon & Dendrite

22. Types of neuron

23. NEURONS CLASSIFICATION:
• On the basis of number of processes
– Unipolar neurons
– Bipolar neurons
– Multipolar neurons
• On the basis of function
– Sensory neuron
– Motor neuron
• On the basis of length of axons
– Golgi type I
– Golgi type II

24. NEURONS CLASSIFICATION:
• On the basis of number of processes
– Unipolar neurons: These neurons have single
process (which is highly convoluted). After a very
short course, this process divides into two.
– One of the divisions represents the axon; the
other is functionally a dendrite, but its structure
is indistin guishable from that of an axon.
– E.g. Neurons in dorsal root ganglion.

25. NEURONS CLASSIFICATION:
• On the basis of number of processes
– Bipolar neurons: These neurons have only one
axon and one dendrite.
– E.g. Neurons in vestibular and spiral ganglia.

26. NEURONS CLASSIFICATION:
• On the basis of number of processes
– Multipolar neurons: It is most common type of
neurons; the neuron gives off several processes
these neurons have one axon and many
dendrites.
– E.g. Motor neurons

27. NEURONS CLASSIFICATION:
• On the basis of function
– Sensory neuron: They carry impulses from
receptor organ to the central nervous system
(CNS).
– Motor neuron: They transmit impulses from the
CNS to the muscles and glands

28. NEURONS CLASSIFICATION:
• On the basis of length of axons
– Golgi type I: These neurons have long axons,
and connect remote regions.
• E.g. pyramidal cells of motor cortex in cerebrum
– Golgi type II: These neurons have short axons
which end near the cell body.
• E.g. Cerebral and cerebellar cortex.

29. FUNCTION OF NEURON
• Neurons are regarded not merely as simple
conductors, but as cells that are specialized for
the reception, integration, interpretation, and
transmission of information.

30. NEUROGLIAL CELLS
 Metabolic and mechanical
support for neuron
 10 times abundant than
neurons
 Neuroglial cells undergo
mitosis
 Classification :
 Oligodendrocytes
 Astrocytes
 Ependymal Cells
 Microglia
 Schwan cells  PNS

31. Types of neuroglia in CNS & PNS

32. Cells in CNS

33. NEUROGLIAL CELLS
• Astrocytes
 Pedicles binds to capillaries
and to the pia mater form
glial limitans
• Controlling the ionic &
chemical environment of
neurons
• Energy metabolism Form
cellular scar tissue
• Form the blood-brain
barrier
• Helps in repair by
Gliosis.

34. NEUROGLIAL CELLS
• Oligodendrocytes
 interfascicular
 Produce myelin
sheath (electrical
insulation) in CNS
– A single cell wrap
several axons (40 to
50)
– Form nodes of Ranvier
• satellite

35. NEUROGLIAL CELLS
• Schwann cells
 Analogue to
Oligodendrocyte
– Produce myelin
sheath in the PNS

36. NEUROGLIAL CELLS
• Microglia
– Scattered throughout the
CNS
– Clearing debris
– Act as APC
– Protect the CNS from
viruses and
microorganism

37. NEUROGLIAL CELLS
 Ependymal Cells
• Low columnar ciliated
epithelial cells  line the
ventricles of the brain &
central canal spinal cord
• Formation of choroid plexus
 produce CSF
• Facilitates the movement of
CSF

38. The various types of neuroglial cells

39. Neurons of cerebellum and their
organisation

40. Cerebellum (H&E stain, X10)

41. Section o cerebellum in (a) low magnification and (b) high magnification—inset shows
a further magnified view o cerebellum (H&E pencil drawing).

42. Cerebellum

43. Neurons of cerebrum and their
organisation

44. Section of cerebral cortex in low
magnification (H&E pencil drawing)

45. Cerebrum (H&E stain, X5)

46. Cerebrum

47. MENINGES
• Meninges are three layers o connective tissue
surrounding the CNS.
• From superficial to deep, they are the dura
mater, arachnoid mater and pia mater.
• Arachnoid mater and pia mater are
collectively called leptomeninges.

48. Arachnoid granulations

49. The skull and the layers of
the meninges covering the brain

50. CSF
• clear, colorless fluid formed in the ventricles of
the brain mainly by choroid plexus (meshwork of
tiny small blood vessels in lateral third and fourth
ventricles).
• It is mainly an ultrafiltrate of plasma.
• CSF is contained within the cerebral ventricles,
the spinal canal and the subarachnoid space
(space between arachnoid externally and pia
mater internally) surrounding the brain and spinal
cord.
• CSF is reabsorbed into the blood through the
arachnoid villi of dural venous sinuses.

51. Normal Composition of CSF

52. Specimen Collection
• CSF is obtained by the following techniques:
• i. Lumbar puncture
• ii. Cisternal puncture
• iii. Ventricular cannulas or shunts
• iv. Lateral cervical puncture

53. Indication of CSF examination
• Normally, up to 2 ml of CSF is withdrawn.
• Most often, CSF tap is done by lumbar
puncture for which indications can be divided
into following 4 categories:
• a. Meningeal infection
• b. Subarachnoid haemorrhage
• c. CNS malignant tumours
• d. Demyelinating diseases.

54. CSF findings in various types of
meningitis

55. CEREBRAL HERNIATION
• The cranial cavity is separated into compartments by
infoldings of the dura.
• The two cerebral hemispheres are separated by the
falx, and the anterior and posterior fossae by the
tentorium.
• Herniation refers to displacement of brain tissue into a
compartment that it normally does not occupy.
• These are of three main types:
– Transtentorial,
– Transfalcine (subfalcine) and
– Tonsillar (foraminal).

56. Major herniation syndromes of the
brain: subfalcine, transtentorial, and
tonsillar.
The most common herniations
are Transtentorial herniation.

57. Transtentorial Herniation
• The most common herniations are from the supratentorial
to the infratentorial compartments through the tentorial
opening, hence transtentorial.
• These may be divided into temporal (Uncal) or central
herniations.
– • Uncal transtentorial herniation refers to impaction of the
anterior medial temporal gyrus (the uncus) into the tentorial
opening just anterior to and adjacent to the midbrain. The
displaced brain tissue compresses the third nerve and results in
mydriasis and ophthalmoplegia (pupil point down and out) of
the ipsilateral pupil.
– • Central transtentorial herniation denotes a symmetric
downward movement of the thalamic medial structures through
the tentorial opening with compression of the upper midbrain.
Miotic pupils and drowsiness are the heralding signs.

58. Transfalcine Herniations
• These are caused by herniation of the medial
aspect of the cerebral hemisphere (cingulate
gyrus) under the falx, which may compress the
anterior cerebral artery.

59. Tonsillar Herniation
• Masses in the cerebellum may cause tonsillar
herniation, in which the cerebellar tonsils are
herniated into the foramen magnum.
• This may compress the medulla and respiratory
centers, causing death.
• Tonsillar herniation may also occur if a lumbar
puncture is performed in a patient with increased
intracranial pressure.
• Therefore, before performing a lumbar puncture,
the patient should be checked for the presence of
papilledema.

60. CEREBRAL HEMORRHAGE
• It can be
– Epidural,
– Subarachnoid,
– Subdural and
– Intraparenchymal.

61. Epidural hemorrhage:
• It results from hemorrhages into - space
between the dura and the bone of the skull.
• These hemorrhages result from severe trauma
that typically causes a skull fracture.
• The hemorrhage results from rupture of one
of the meningeal arteries, as these arteries
supply the dura and run between the dura
and the skull.

62. Epidural hemorrhage:
• Since the bleeding is of arterial origin (high
pressure), it is rapid and the symptoms are
rapid in onset, although the patient may be
normal for several hours (lucid interval).
• Bleeding causes increased intracranial
pressure and can lead to tentorial herniation
and death.

63. Epidural hemorrhage:
• The artery involved in epidural hemorrhage is
usually the middle meningeal artery, which is
a branch of the maxillary artery, as the skull
fracture is usually in the temporal area.

64. Subarachnoid hemorrhage:
• It is much less common than hypertensive
intracerebral hemorrhage.
• It most often results from the rupture of a
berry aneurysm.
• These aneurysms are Saccular aneurysms that
result from congenital defects in the media of
arteries.
• They are typically located at the bifurcations
of arteries.

65. Subarachnoid hemorrhage:
• They are not the result of atherosclerosis.
• Instead, berry aneurysms are called congenital,
although the aneurysm itself is not present at birth.
• The chance of rupture of berry aneurysms increases
with age (rupture is rare in childhood).
• Rupture causes marked bleeding into the subarachnoid
space and produces severe headaches, typically
described as the “worst headache ever”.
• Additional symptoms include vomiting, pain and
stiffness of the neck (due to meningeal irritation
caused by the blood), and papilledema. Death may
follow rapidly.

66. Subarachnoid hemorrhage:
• Excluding trauma, Berry aneurysm is the
commonest cause of subarachnoid
hemorrhage.

67. Subdural hemorrhage:
• The space beneath the inner surface of the
dura mater and the outer arachnoid layer of
the leptomeninges is also a potential space.
• Most commonly occurs due to rupture of
bridging veins.

68. CEREBRAL ISCHEMIA
• Decreased brain perfusion may be generalized
(global) or localized.
• Global ischemia results from generalized
decreased blood flow, such as with shock,
cardiac arrest, or hypoxic episodes (e.g. near
drowning or carbon monoxide poisoning).

69. CEREBRAL ISCHEMIA
• The gross changes produced by global hypoxia
include watershed (border zone) infarcts,
which typically occur at the border of areas
supplied by the anterior and middle cerebral
arteries, and laminar necrosis, which is related
to the short, penetrating vessels originating
from pial arteries.

70. CEREBRAL ISCHEMIA
• The microscopic changes produced by global
hypoxia are grouped into three categories.
– The earliest histologic changes, occurring in the
first 24 h, include the formation of red neurons
(acute neuronal injury), characterized by
eosinophilia of the cytoplasm of the neurons.
– Followed in time by pyknosis and karyorrhexis.
– Subacute changes occur at 24 h to 2 weeks. These
include tissue necrosis, vascular proliferation, and
reactive gliosis.

71. CEREBRAL ISCHEMIA
• The Purkinje cells of the cerebellum and the
pyramidal neurons of Sommer’s sector in the
hippocampus are particularly sensitive to
ischemic damage.

72. DEVELOPMENTAL ABNORMALITIES OF
THE BRAIN
• Developmental abnormalities of the brain
include the Arnold-Chiari malformation, the
Dandy-Walker malformation, and the
Phakomatoses, which include tuberous
sclerosis, neurofibromatosis, von Hippel-
Lindau disease, and Sturge-Weber syndrome.

73. • Dandy-Walker malformation has severe
hypoplasia or absence of the cerebellar
vermis.
• There is cystic distention of the roof of the
fourth ventricle, hydrocephalus, and possibly
agenesis of the corpus callosum.

74. • Arnold-Chiari malformation consists of
herniation of the cerebellum and fourth
ventricle into the foramen magnum, flattening
of the base of the skull, and spina bifida with
meningomyelocele.
• Newborns with this disorder are at risk of
developing hydrocephalus within the first few
days of delivery secondary to stenosis of the
cerebral aqueduct.

75. • Tuberous sclerosis may show characteristic
firm, white nodules (tubers) in the cortex and
subependymal nodules of gliosis protruding
into the ventricles (“candle drippings”) Facial
angiofibromas (adenoma sebaceum) may also
occur.

76. • von Hippel-Lindau disease shows multiple
benign and malignant neoplasms including
hemangioblastomas of the retina, cerebellum,
and medulla oblongata; angiomas of the
kidney and liver; and renal cell carcinomas.

77. • Sturge-Weber syndrome is a non-familial
congenital disorder, display angiomas of the
brain, leptomeninges, and ipsilateral face,
which are called port-wine stains (nevus
flammeus).

78. THANK YOU