This power point presentation was made for a second year lecture class of neuroanatomy. It was based on answers of different questions regarding neuroanatomy. The class was taken by Dr. Zobayer Mahmud Khan, Lecturer, Department of Anatomy, Sir Salimullah Medical College, Dhaka.

2. Introduction to the
Nervous System
Dr. Zobayer Mahmud Khan
MS Anatomy
Lecturer, Sir Salimullah Medical College

3. Objective
To understand the basic organization of the
main structures that form the nervous system

4. Classify nervous system
Metencephalon
Myelencephalon
CNS PNS
Telencephalon
Diencephalon
Nervous system
Spinal cordBrain Nerve Ganglion
12 pair cranial
nerves
31 pair spinal
nerves
Prosencephalon
(Forebrain)
Mesencephalon
(Midbrain)
Rhombencephalon
(Hindbrain)
Anatomical
classification
Sensory
Autonomic

5. Classify nervous system
Nervous system
Somatic Autonomic
Sensory Motor Sympathetic Parasympathetic
Functional
classification

6. Gray matter
consists of nerve cells embedded in neuroglia;
it has a gray color.
White matter
consists of nerve fibers embedded in neuroglia;
it has a white color due to the presence of lipid
material in the myelin sheaths.
Organization of the interior of central nervous
system

7. Neuron
Neuroglia (Supporting cell)
Cellular organization of the nervous
system

8. The neurons are the structural and functional
units of the nervous system.
They are specialized for reception, integration
and onward transmission of information.
What is neuron ?

9. Classify neuron with examples
Unipolar
e.g.,
Neurons of
the posterior
root ganglia
Bipolar
e.g.,
Bipolar cells of the
retina, cells of the
sensory cochlear &
vestibular ganglia
Multipolar
e.g.,
Most of the
neurons like motor
neurons control
skeletal muscles
Neuron
According to
the polarity

10. Classify neuron with examples

11. Classify neuron with examples
Neuron
Golgi type- I
e.g.,
Pyramidal cells of the cerebral cortex
Purkinje cells of the cerebellar cortex
Motor neurons of the spinal cord
Golgi type- II
e.g.,
Stellate cells forming
synaptic contacts
with other
neighboring neurons
According to the
length of axons

12. Classify neuron with examples

13. Cell body (Soma, Perikaryon, nerve cell body)
Neurites (Processes)
Typical long process (Axon)
Short process (Dendrite)
Structure of the neuron

14. Structure of the neuron

15. Structure of the neuron
Cell Body
Neucleus
Cytoplasm
Nissl bodies or granules
Mitochondria
Neurofibrils
Lipofuchsin granules
Microtubules

16. Short note on “Nissl bodies”
Composition
Nissl substance is composed of large aggregation of rough
endoplasmic reticulum.
Function
High concentration of rough endoplasmic reticulum is
thought to be necessary for the production of enzymes
involved in neurotransmitters synthesis.
Location
Nissl substance present in the cytoplasm of the neuron, may
extends into the dendrites but are absent in the axon hillock.

17. Short note on “Dendrites”
Short note on “Axons”

18. What is neuroglia?
The neurons of the central nervous system are
supported by several varieties of nonexcitable
cells, which together are called neuroglia.

19. What is neuroglia?

20. Classification of neuroglia
Astrocytes
Fibrous
Protoplasmic
Oligodendrocytes
Microglia
Ependyma
Ependymocytes
Choroid epithelial cells
Tanycytes

21. Classification of neuroglia

22. Astrocytes fill up most of the extracellular spaces
among the neurons providing supporting
framework and their processes contact the
surfaces of neurons and capillaries of the CNS.
They are involved in the exchange of metabolites
between the neurons and capillaries. The
astrocytes are thought to be primary glycogen
storehouse in the brain.
They are involved in forming Blood-brain barrier
Function of neuroglia

23. Write in short about “Blood brain
barrier”

24. Oligodendrocytes form myelin sheath
around axons in the CNS, having same
function as Schwann cells in peripheral
nervous system.
Function of neuroglia

25. Function of neuroglia
Ependymal cells line the ventricles of the brain
and central canal of the spinal cord.
Assist in production, circulation and monitoring
of cerebrospinal fluid.

26. Microglia enlarges and become phagocytic in
areas of inflammation and cell destruction.
They remove cell debris, wastes and pathogens
that invade the CNS by phagocytosis.
All the neuroglia (glial cells) are derived from
ectoderm except microglia, which are derived
from mesoderm.
Function of neuroglia

27. Following death of the neurons the
astrocytes proliferate and fill the spaces
previously occupied by the neurons. This
process is called replacement gliosis.
What is replacement gliosis?

28. Where two neurons come into close
proximity and functional interneuronal
communication occurs, the site of such
communication is referred to as a synapse.
What is “Synapse”?

29. Classify “Synapse”?
Depending on the site of the synapse,
they are often referred to as
axodendritic
axosomatic
axoaxonic

30. Classify “Synapse”?

31. Ultrastructure of “Synapse”

32. Properties of “Synapse”
Nerve impulse passes only in one direction
Passage of nerve impulse is slightly delayed
at the synapse.
The synapse is susceptible to fatigue.
Feed-forward inhibition
Feed-back inhibition

33. An individual receives impressions from the
outside world and from within the body by
special sensory nerve endings named
receptors.
What is receptor?

34. According to the relations of receptor cells and
primary sensory neurons
Neuro-epithelial receptors
(e.g., olfactory neurons of the nasal mucosa)
Epithelial receptors
(e.g., gustatory & sensory hair cells of auditory
and vestibular system)
Neuronal receptors
(e.g., all cutaneous receptors & proprioceptors)
Classify receptors with example

35. Classify receptors with example

36. According to the modalities of sensation
Mechanoceptors
(e.g., touch, pressure etc.)
Chemoreceptors
(e.g., Olfactory, gustatory, carotid body
receptor)
Photoreceptors
(e.g., Rods & cones of retina)
Thermoreceptors
Osmoreceptors
Nociceptors
Classify receptors with example

37. According to the location of stimuli
in the environment
Exteroceptors
Proprioceptors
Interoceptors
Free nerve endings
Encapsulated endings
Classify receptors with example

38. Nerve fiber is the name given
to an axon of a nerve cell.
What is nerve fiber?

39. According to the speed of conduction and size
Classify nerve fibers
A Fibers
Alpha
Beta
Gamma
Delta
B Fibers
C Fibers

40. Bundles of nerve fibers found in the
central nervous system are often
referred to as nerve tracts.
What is nerve tracts?

41. Bundles of nerve tracts found in the
central nervous system are often
referred to as lemniscus.
What is lemniscus?

42. Bundles of nerve fibers found in the
peripheral nervous system are
called peripheral nerves.
What is peripheral nerves?

43. Structure of a peripheral nerve

44. Myelinated
and
Nonmyelinated
Nerves present in CNS & PNS

45. The myelination is the process by which
nerve fibres acquire myelin sheaths which
enhance the conduction of nerve impulses.
It is done by the Schwann cells in peripheral
nervous system and oligodendrocytes in the
central nervous system.
The myelin sheath is a segmented,
discontinuous layer interrupted at regular
intervals by the nodes of Ranvier
What is myelination?

46. Mention the importance of myelination
Provides support to the nerve fibers
Aids in conduction of the nerve impulses
Insulates an axon from the extracellular
environment
Responsible for the color of the white
matter of the brain and spinal cord

47. Process of myelination of peripheral
nervous system
The Schwann cell rotates on the
axon so that the plasma membrane
becomes wrapped around
the axon in a spiral
Axon first indents the side
of a Schwann cell
The external plasma membrane of
the Schwann cell forms a mesaxon

48. Process of myelination of peripheral
nervous system
To begin with, the wrappings are
loose, but gradually the cytoplasm
between the layers of the cell
membrane disappears, leaving
cytoplasm near the surface and
in the region of the nucleus.

49. At the node of Ranvier
Proximal segment of an axon
close to the cell body
Near the termination of axon
before it divides into telodendria
Where myelination is absent in a myelinated
nerve?

50. Process of myelination in CNS
Oligodendrocytes are responsible for the
formation of the myelin sheaths
A single oligodendrocyte may be connected to
the myelin sheaths of as many as 60 nerve fibers
The process of myelination in the central
nervous system cannot take place by rotation of
the oligodendrocyte on the axon
Myelination in the central nervous system occurs
by the growth in length of the process of the
oligodendrocyte, the process wrapping itself
around the axon

51. The chromatolysis reflects a series of
structural changes in the cell body of a neuron
in response to the damage of its axon by
mechanical injury or by toxic agents.
What do you know about chromatolysis?
Changes
Nissl body degenerate and disappear
The cell body is swollen
Neucleus is eccentric in position
Neurofilaments are broken into small fragments

52. The immediate reaction to cut of a nerve
fiber is called degeneration of a neuron.
What is degeneration of a neuron?

53. Distal to the site of injury
(Antegrade degeneration or Wallerian degeneration)
Axoplasm breaks into membrane bound bodies &
degeneration extends from the site of injury
to the termination of axon
Myelin sheath degenerates into droplets
of unsaturated fatty acid
Schwann cells proliferate by mitosis and
form longitudinal columns of cells
What are the stages of degeneration?

54. What are the stages of degeneration?

55. Proximal to the site of injury
A similar process of degeneration (retrograde
degeneration) extends up to the next node of Ranvier
Within 48 hours of injury, the cell bodies of affected
neurons, show chromatolysis due to axon reaction
What are the stages of degeneration?

56. At the site of injury
Schwann cells proliferate and the gap
between proximal and distal stumps
are bridged by the Schwann cells
What are the stages of degeneration?

57. When the cell body recovers from the axon reaction,
the axon of the proximal stump sprouts and divides
into multiple branches with swollen tips called
growth cones to explore the distal stump
In the distal stump, Schwann cells send processes
in the direction of the growth cones
What are the stages of regeneration?

58. Guided by the strands of Schwann cells the
successful fibers reach the distal portion of the
nerve, and the remaining fibers are absorbed.
Schwann cells help as contact guidance for the axons
Myelin sheath begins to develop in about 15 days
and myelination is complete within a year
What are the stages of regeneration?

59. What are the stages of regeneration?

60. Hazards of regeneration (4th
edition, p.
22)

61. Classify nervous system
Organization of the interior of central nervous system
Cellular organization of the nervous system
What is neuron ?
Classify neuron with examples
Structure of the neuron
Short note on “Nissl bodies”
Short note on “Dendrites”
Short note on “Axons”
What is neuroglia?
Classification of neuroglia
Function of neuroglia

62. What is replacement gliosis?
What is “Synapse”?
Classify “Synapse”?
Ultrastructure of “Synapse”
What is receptor?
Classify receptors with example
What is nerve fiber?
Classify nerve fibers
What is nerve tracts?
What is lemniscus?
What is peripheral nerves?
Structure of a peripheral nerve
Nerves present in CNS & PNS

63. What is myelination?
Mention the importance of myelination
Process of myelination of peripheral nervous
system
Where myelination is absent in a myelinated nerve?
Process of myelination in CNS
What do you know about chromatolysis?
What is degeneration of a neuron?
What are the stages of degeneration?
What are the stages of regeneration?
Hazards of regeneration (4th
edition, p. 22)

64. Thank
You