Histology of the nervous system

Nervous System is a uniquely designed organ system of our body. This presentation is highlighting over the cellular configuration of this system. Neurons & Neuroglia are the two main players of the system. Neuron is the structural & functional unit of the system, while, Neuroglia are the supporting elements. At the end of this presentation, the young learner would be able to recognize different cell types of the Nervous system & their exclusive function.

1. HISTOLOGY OF THE
NERVOUS SYSTEM
(AN OVERVIEW)
Dr. SAHAR HAFEEZ
[email protected]

2. Learning Objectives
The students should be able to;
Enlist the names & functions of different types of Neurons
Enlist the names & functions of different types of Neuroglia
Demonstrate an understanding towards the structural differences
of neurons and neuroglia
Define the terms Ganglia& Nucleiand Gray & White Matters.
Demonstrate an understanding towards the arrangement of different
layers of a typical nerve.

3. ANATOMICAL ORGANIZATION of the
NERVOUS SYSTEM
Nervous
System
CNS PNS ANS
BRAIN
SPINAL
CORD
CRANIAL
NERVES
SPINAL
NERVES
SYMPATHETIC
PARA-
SYMPATHETIC

4. Cell types present in the Nervous System
Nervous tissue is made up of 2 types of cells;
Neurons (structural & functional unit)
Neuroglia(Supporting cells)

5. Parts of a Neuron
Cell body:
Trophic unit
Dendrites:
Receptive unit
Axon:
Conductive unit

6. Perikaryon/Cell Body /Soma
“part of a neuron that encloses the nucleus and other organelles
necessary to maintain and repair the neuron”.
Cell Body Organelles
Nucleus
Golgi apparatus
RER
Ribosomes (=Nisslsubstance)

7. Perikaryon/Soma/Nerve cell body
Most neurons have their cell bodies located in different parts of
CNS
Clusters of cell bodies in the CNS are known as Nuclei
Clusters of cell bodies in PNS are known as Ganglia

8. Axon Characteristics
Carries information to another neuron or muscle
cell.
Often relatively long.
Single (one per neuron).
Ends in short branched processes called
telodendria.
May have collateral branches.
Covered by neurolemmamade up of Schwann
cells.
Note: axon is the only part of a neuron
that is ever myelinated.
Myelin
Sheath
Telodendria

9. Dendrites (Characteristics)
Carry information to the cell body.
Usually multiple.
Relatively short.
Often branched.
Have receptors for
neurotransmitters.
Conduct local potentials.

10. Relationship B/W Axon & Dendrites

11. Classification of Neurons
Neurons are classified according to;
Structure
Unipolar/Pseudo unipolar neurons
Bipolar neurons
Multipolar neurons
Function
Sensory neurons
Motor neurons
Association neurons

12. Structural Classification of Neurons
Pseudo unipolar Neurons:
Present in the dorsal root
ganglia of spinal cord
Bipolar Neurons: Present in
the Olfactory epithelium of
nose as well as in the Retina
of eye
Multipolar Neurons: Present
everywhere else.

13. Functional Classification of Neurons
Sensory (afferent) Neurons:
Transmit impulses from the
sensory peripheral receptors to
CNS
Motor (efferent) Neurons:
Carry impulses away from
CNS to peripheral organs
Association/Inter-Neurons:
Present only in the CNS and
transmit impulses across the
neurons of CNS

14. Neuroglia = nerve glue
Distinguished by their much smaller size as compare to
neurons.
Outnumber neurons in CNS by 9:1 ratio.
Are mainly of six types:
4 of them are found in CNS
Astrocytes
Microglia
Oligodendrocytes
Ependymal cells
2 of them are found in PNS
Satellite cells
Schwann cells

15. Neuroglia of CNS
Astrocytes= star-shaped
Derived from neuroblast cells.
Most abundant type of glial cells
Function to physically support neurons.
Brace the neurons & anchor them to
the near by capillaries (create BBB)

16. Neuroglia of CNS
Oligodendrocytes:
Derived from neuroblast cells.
Function to myelinate axons within CNS.
Microglia:
Derived from embryonic mesenchyme.
May transform into phagocytes within CNS
Ependymal Cells:
Derived from neuroblast cells.
Line ventricles of brain & central canal of Spinal cord.
(The protective role of Microglia is very important as
cells of the immune system are denied across the
CNS)

17. Neuroglia in the PNS
Schwann Cells:
Derived from neural crest
cells.
Myelinateaxons in the PNS.
Satellite Cells:
Surround nerve cell body
May aid in controlling
neuronal chemical
environment

19. Myelination of Axons
•Myelin protects & electrically
insulates the fibers
•In CNS, Axons are myelinated by
‘oligodendrocytes
•In PNS, Axons are myelinated by
‘Schwann cells’.
•Schwann cells myelinate the
fibers like a jelly roll.
•One Axon in PNS is myelinated
by many Schwann cells.
•The gap b/w individual Schwann
cells is k/a ‘Node of Ranvier’

21. Epineurium:Outermost
connective tissue sheet
covering all the bundles of
fibers in a nerve.
Perineurium:Middle
connective tissue sheet
covering individual bundle of
fibers.
Endoneurium:Innermost
sheet covering the individual
Axon of each fiber in a
bundle.
Coverings of a Typical Peripheral Nerve

22. Ganglia
Button-shaped enlargements with in
the PNS produced by a collection of
neuron cell bodies.
Functionally speaking, Ganglia are the
relaying station outside CNS.
Unipolar cell bodies are found in
spinal/Dorsal root ganglia
Multipolar cell bodies are found in
autonomic ganglia

23. White & Grey Matter of CNS
White Matter: Areas of CNS mostly
made up of Myelinated axons (as the
myelin is white colored)
Grey Matter: Areas of the CNS mostly
made up of somas of neurons.
Arrangement of white & grey matter;
In the Spinal cord:
White matter outside & Grey matter
inside
In the Brain: Grey matter outside &
white matter inside. Some isolated
clusters of grey matter embedded within
the inner white matter (Nuclei)

24. THANK YOU
&
BEST OF LUCK