The document summarizes the structure and types of neurons and glial cells in the nervous system. It discusses that neurons are excitable cells that conduct nerve impulses, while glial cells provide support and insulation. The major types of glial cells are astrocytes, microglia, ependymal cells, oligodendrocytes, and Schwann cells. Neurons consist of a cell body, dendrites, and an axon. The axon conducts impulses away from the cell body and terminates in synaptic knobs. Neurons are classified structurally as multipolar, bipolar, or unipolar based on their processes, and functionally as afferent, efferent

1. Structure of neurons
Aswathi K S
1st MSc BCM
Roll No: 04
Central University of

2. CELLS OF THE NERVOUS
SYSTEM
Two types of cells make up the
nervous system:
1. Neurons
• Exitable cells that conduct impulses
• ‘wiring’ of nervous system’s
information circuits

3. 1
1. Glia
• aka neuroglia
• discovered accidentally by Camillo
Golgi, upon dropping a piece of brain
tissue in a bath of silver nitrate
•Appeared as wast network of various
kinds of darkly stained cells surrounding
neuron
•Glia means ‘glue’
•Unlike neurons, retain capacity for cell
division throughout adulthood

4. •Funtion as supporting roles of
nervous system
Types of neural glia
1. Astrocytes
2. Microglia
3. Ependymal cells
4. Oligodendrocytes
5. Schwann cells
First 4 types are found in the CNS and 5th
type is found in the PNS

5. 1. Astrocytes
• Star shaped glia (greek: astron-star)
• Found only in CNS
• Largest and most numerous type of
glia
• Tiny delicate points extend through
brain tissue attaching neurons and
tiny blood capillaries
• ‘Feed’ neurons by taking up glucose
from blood, converting to lactic acid
and giving to neurons

6. • The BBB is a double barrier made up of
astrocyte feet and endothelial cells of
blood capillary walls
• Small molecules (oxygen, carbon
dioxide, water) diffuse rapidly to reach
brain neurons and other glia, larger
molecules penetrate slowly or not at all

7. 2. Microglia
• Small, usually stationary cells found
in CNS
• Also known as Brain’s immune cells
• In inflamed or degenerating brain
tissue, microglia enlarge, move
about, and carry on phagocytosis
• they engulf and destroy micro
organism and tissue debris
• Although named as glia, are
functionally and developmentally
unrelated to nervous system cells

9. 3. Ependymal cells
• Resemble epithelial cells
• Thin sheets that line fluid filled
cavities in brain and spinal cord.
• Some take part in producing fluid
that fills these spaces
• others have cilia that helps keep fluid
circulating within cavities.

10. 4. Oligodendrocytes
• Smaller than astrocytes and have
fewer processes
• Oligo-few, dendro-branch, cyte-cell :
meaning cells with fewer branches
• Some lie clustered around nerve cell
body, some arranged in rows between
nerve fibre in brain and spinal cord
•Help hold nerve fibre together
• Important function : produce fatty
myelin sheath around nerve fibre of
CNS

11. Oligodendroc
yte
Axon
Nucleus
Myelination in the
Central Nervous
System

12. 5. Schwann cells
• Found only in PNS
• Also called as ‘Neurolemmocytes’
•Sometimes called satellite cells
•Functional equivalents of
oligodendrocytes
• Support nerve fibre and form myelin
sheath around them
• Many schwann cells wrap around
single neuron
• Myelin sheath is formed by layers of

13. • Microscopic gaps in the sheath,
between adjecent Schwann cell-
Node of Ranvier or myelin sheath
gaps
•The myelin sheath and gaps in
nerve fibre are important for transfer
of nerve impulses
• Schwann cell’s nucleus and
cytoplasm are squeezed to perimeter
to form neurilemma.
• neurilemma important for
regeneration of injured nerve fibres.

14. Node of
Ranvier

15. • Nerve cells with many Schwann
cells attached and having thick
myelin sheath -White fibre or
Myelinated fibre
• Several nerve fibres held by single
Schwann cell and does not wrap
around to form thick myelin sheath –
Grey fibre or Unmyelinated fibre

16. 2. Neurons
• The human brain estimated to
contain about 100 million , or 10% of
total neurons of nervous system
• Neuron consist of:
i. Cell body
ii. Axon
iii. Dendrites
iv. Axon ends

17. i. Cell body
• Largest part of a nerve cell
• Contain nucleus, cytoplasm and
various organells
like mitochondria and golgi apparatus
• also called as perikaryon ; meaning
surrounding the nucleus
•Plasma membrane encloses the whole
neuron
• RER and attached ribosomes provide
proteins for neuron

18. • Neurotransmitters
are proteins packaged
in vesicles that aid
neurotransmission
• other proteins used
for repair of neuron
• Mitochondria
replicate themselves in
the cell body: some
transported to end of
axon to provide energy
for signal transduction
• Nissl granules are

19. ii. Dendrites
• Branch extensively from
cell body like tiny tree
• Greek word : tree
• Distal end of sensory
neurons called receptors :
receive stimuli that initiate
nerve signals
• some dendrites in brain
have knoblike dendritic
spines: serve as
connection point of other

21. iii. Axon.
• Extend from tapered portion of cell
body called axon hillock
• Conduct impulse away from cell
body.
• Axon has side branches called Axon
collaterals
• Distal ends of axon form branches
called telodentria and each terminate
in a synaptic knob

22. • Some axons have vericosities or
swellings, and act as point of contact
with other cells or smooth muscle fibres
• Axons vary in size from a meter long to
just millimeters long
• Axon diameter also vary: larger the
diameter, greater the conduction
• Myelination of axon also affects
conductance
• Only axons have myelin and not
dendrites

24. • Neurofibrills arebundles of
intermediate filaments called
neurofilaments extending through
cytoplasm of the neuron
• Microtubules and microfilaments also
present

25. • Along with providing structural
support, act as railway for rapid
transport of small organelles
• Small motor molecules attach to
vesicles and mitochondria , carry them
to end of axon
• Used vesicles and transmitters
returned by same process to the cell
body : Axonal transport

26. • There are 4 functional regions of neuron
based on their role in receiving and
conducting impulsea. Input zone: receive
and initiating impulse
in response
b. Summation zone:
adding together all
impulse received
c. Conduction zone:
conduct impulse to end
of axon
d. Output zone: release

27. Classification of Neuron
Structural classification
1. Multipolar
2. Bipolar
3. Unipolar
Functional Classification
1. Afferent neurons
2. Efferent neurons
3. Interneurons

28. Structural Classificationl
Classified according to number of
extensions from cell body
1. Multipolar neurons: one axon but
several dentrites, most of the
neurons in brain and spinal cord are
multipolar

29. 2. Bipolar neurons: one axon and one
heavily branched dentrite, least
nemerous kind and found in retina ,
inner ear and olfactory pathway

30. 3. Unipolar neuron : single process
extending from the cell body, which
branches into central process
(towards CNS) and peripheral process
(away from CNS), process forms a
single axon and conducting impulse
away from dentrite, they are always
sensory neurons.

31. Functional Classification
Classified based on direction of
conduction of nerve impulse.
1. Afferent neuron:
to spinal cord or
brain
2. Efferent neuron:
away from brain
or spinal cord to
muscle or gland
3. Interneurons:
from afferent

34. Thank You!!!!