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Structure of neurons
Aswathi K S
1st MSc BCM
Roll No: 04
Central University of
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
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
•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
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
• 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
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
Neuron structure
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.
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
Oligodendroc
yte
Axon
Nucleus
Myelination in the
Central Nervous
System
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
• 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.
Node of
Ranvier
• 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
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
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
• 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
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
Neuron structure
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
• 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
Neuron structure
• Neurofibrills arebundles of
intermediate filaments called
neurofilaments extending through
cytoplasm of the neuron
• Microtubules and microfilaments also
present
• 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
• 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
Classification of Neuron
Structural classification
1. Multipolar
2. Bipolar
3. Unipolar
Functional Classification
1. Afferent neurons
2. Efferent neurons
3. Interneurons
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
2. Bipolar neurons: one axon and one
heavily branched dentrite, least
nemerous kind and found in retina ,
inner ear and olfactory pathway
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.
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
Neuron structure
Neuron structure
Thank You!!!!

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Neuron structure

  • 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
  • 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.
  • 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