The document provides an overview of neurons and neuroglia, detailing their structures, functions, and classifications, including the various types of neurons based on morphology and function. It also discusses neuronal injury, regeneration, and the roles of astrocytes and other neuroglial cells in the central nervous system. Clinical considerations regarding demyelination disorders and the transmission of diseases via axonal transport are addressed, along with references and example cases for further understanding.

1. Neuron & Neuroglia
Gowtham Padmanaban
Faculty of Medicine - Neuroscience
Texila American University

2. Learning Objectives
• Describe the composition and function of different
components of the neuron.
• Discuss the mechanism of axonal transport and its
application to the study of neuroanatomy.
• List the different types of neurons found within the
nervous system.
Explain the different types of neuroglia and their
functions.
• Discuss the nature of myelin formation.
• Explain the composition of peripheral nerve.
• Discuss the type of neuronal injury and the process of
regeneration.
2

3. NEUROSCIENCE
• Inside our heads, weighing
about 1.5 kg, is an
astonishing living organ
consisting of billions of
neurons
• It enables us to sense the
world around us, to think
and to talk and to act
• The human brain is the
most complex organ of the
body, and arguably the
most complex thing on
earth

4. Copyright
2013-2014
What is Neuron
• Human Body is coordinated by Nervous System
and endocrine system.
• Neurons – Structural & Function Unit of Nervous
System.
• Excitable cells specialized for reception of stimuli
and conduction of impulses.
• Neurons do not divide.

5. Types of Neurons
• Classified based on
1) Morphology
2) Size
3) Function

6. Morphology Classification
• Unipolar
• Multipolar
• Bipolars

7. Unipolar Neurons
• cell body - single
neurite that divides into
two branches,
– Peripheral structure.
– central nervous system.
• Examples -found in the
posterior root ganglion.

8. Multipolar neurons
• Many neurites arising from
the cell body .
• The axon – one & long.
• Remaining are dendrites.
• Most neurons of the brain
and spinal cord are of this
type.

9. Bipolar neurons
• Elongated cell body, from each
end of which a single neurite
emerges .
• Examples retinal bipolar cells
and the cells of the sensory
cochlear and vestibular ganglia.

11. Functional classification
• Sensory or afferent neuron.
• Motor or efferent neuron.
• Interneuron or association neuron.

12. Sensory neurons or Afferent neurons

13. Motor neurons or Efferent neurons

14. Interneurons or Association neurons

15. Structure of a Neuron
• Cell body (soma)
- Nucleus.
- Perikaryon (Cytoplasm).
- Neurolema (Plasma Membrane).
• Nerve Cell Processes
– Dendrites.
– Axon.
• Synapse.

16. Structure of a Neuron

17. Structure of a Neuron

18. Structures in a Nerve Cell
Structures Location Function
Nucleus Centrally placed, displaced to
periphery in cell injury
Controls cell activity
Cytoplasmic
organelles
Nissl substance
Throughout cytoplasm and
proximal part of dendrites, absent
in axon hillock and axon,
Synthesizes protein
Golgi complex Close to the nucleus products for transport to
nerve terminals; forms
cell membranes
Mitochondria Scattered Form chemical energy
Neurofibrils Run from dendrites through cell
body to axon
Determines the shape of
the neuron
Microfilaments &
Microfilaments
Beneath plasma membrane & all
over the cell
Cell transport
Lysosomes Throughout the cell Cell Scavangers
Lipofuction All over cytoplasm Metabolic by -product
Melanin Mid brain – substania nigra Dopa formation

19. Nerve Cell Processes
AXON Only one axon mostly.
Straighter .
Smoother than the dendritic.
Axon hillock is cone-shaped.
Myelinated & node of Ranvier present.
DENDRITIES Many branches.
Conducts nerve impulses from adjacent cells
inward toward the cell body.
Dendritic projections - dendritic spines.

20. Types of nerve fibers

21. Axon Transport
Anterograde
Transport -
towards axon
terminal
• 100 to 400 mm
/day
• Transport of
proteins &
transmitter
substances
Retrograde
Transport –
towards cell body
• 0.1 to 3.0 mm /day
• Transport of
axoplasm and
includes the
microfilaments and
microtubules.
• WALLERIAN DEGENERATION
• Anterograde degeneration.
• Damage at distal site of neuron.
• Disappearance of axons and myelin
sheaths .
• CNS and PNS.
• CHROMATOLYSIS
• Retrograde degeneration
• Damage closer to Soma.
• CNS & PNS.
• Soma swells & nucleus pushed to
corner.
• There is a loss of Nissl substance.

22. Transneuronal Degeneration
Anterograde
transneuronal
degeneration :
CNS – degeneration of
post synaptic neuron
related to same function.
EX; lateral geniculate
body of thalamus – optic
nerve
Retrograde transneuronal
degeneration:
Neuron sending inputs to
an injured neuron.
Processes withdrawn.

23. Neuronal Injury - Overview

24. Recovery of neuronal injury
• CNS :
• Damage is not severe,
sprouting of axons.
• Astrocytes proliferate
and forms scar.
• PNS:
• Regeneration of axons
occur if endothelial cells
are intact.

25. PNS: Regeneration

26. Synapse

27. Neuroglial cells

28. Neuroglial cells
• Astrocytes
– Fibrous – white matter ,Provide supporting framework,
are electrical insulators.
– Protoplasmic - Gray matter Store glycogen, have a
phagocytic function.
• Ependymal cells
– Ependymocytes – lines central canal ,ventricles,
circulates & absorbs CSF.
– Tanycytes – line floor of third ventricle , transports
subs. from CSF to hypophyseal – portal system.
– Choroid epithelial cells – surface of choroid plexus
secretes CSF.

29. Functions of Astrocytes
• Regulation of Extracellular potassium in CNS.
• Regulation of Glutamate concentration in CNS.
• Brain microcirculation.
• Help - metabolism of neurons.
• Involves in brain pathology : AIDS,
Alzheimer’s, Amyotrophic lateral sclerosis
,brain tumors

30. Regulation of Extracellular
potassium in CNS

31. Glucose & Glutamate
Metabolism

32. Alzheimer’s Disease

34. Astrocytes & Alzheimer’s
• Apolipoprotein E
• ( ApoE) is produced in
astrocytes
• ApoE is decreased in
alzhiemer’s.

35. ALS & Astrocytes
• Amyotrophic Lateral sclerosis - degeneration
of upper & lower motor neuron.
• Astrocytes expressing superoxide dismutase
exhibit of a loss of glutamate transporter
(EAAT 2).
• Increased excitotoxicity of glutamate –
neuronal damage.

36. Clinical Considerations

37. Disorders –Defective
Myelination
Disorder Defect Symptoms Treatment
Guillian – Barre
Syndrome
PNS , demyelination of
axons ,immunological
reaction
Progressive motor
weakness, motor &
sensory deficits
,respiratory weakness
Gamma globulin
/plasma exchange
Multiple
Sclerosis
CNS, demyelination of
axons, autoimmune
disorder
Sensory loss, loss of
vision ,speech
disturbances
Natalizumab,
interferon beta –
Ia,Ib
Charcot –
Marie – Tooth
Syndrome
Demyelination - PNS
by mutation in
connexin gene in
schwann cells, fails to
form gap junction
Motor and sensory
deficits and abnormal
gait
No cure

38. Traumatic lesions of peripheral
nerves

39. Axonal transport – Disease transmission
• Rabies – by both sensory & motor nerves
to CNS.
• Herpes simplex & herpes zoster.
• Poliomyelitis virus – from GIT to motor
neuron in spinal cord & brain stem.

40. Tumors of Neuron
• In CNS are rare,
• In PNS ,it is common,
• Neuroblastoma – starts from adrenal gland,
develop in neck, abdomen , spine.
• Ganglioneuroma – sympathetic ganglion.
• Pheochromocytoma –neuroendocrine tumor.

41. Tumors of Neuroglia
• Intracranial tumors – 40 -50 %.
• Gliomas – types,
• Astrocytomas.
• Glioblastomas.
• Ependymomas.

42. Neuromuscular blocking
agents
• D- tubocurarine – chondrodendron
tomentosum – arrow poisioning.
• Skeletal muscle relaxants- decamethonium,
benzoquinonium, doxacurium.
• Bacterial toxins – botulinum.

43. Reference
• Essential Neuroscience - Allan Seigel ,third
edition.
• Clinical Neuroanatomy – Richard.S.Snell.
Seventh edition

44. 1. A 30 year old man complained to neurologist of a
sudden onset of tremor, lack of coordination -motor,
blurred vision. The MRI results shows consistent changes
in white matter of brain and The associated diseases is ?
A. Guillian - Bare syndrome
B. ALS
C. Myasthenia gravis
D. Multiple sclerosis
E. Parkinson’s Disease

45. 2. What are the supporting cells in the central
nervous system called?
A. Schwann cells
B. Basket cells
C. Ganglion
D. Neuroglia
E. Satellite cells

46. 3. A 46 year old female admitted to emergency due
to 10 days of progressive numbness and weakness.
She developed increasing shortness of breath. The
neurological examination reveals hyporeflexia.
Choose the associated disease.
A. Guillian - Bare syndrome
B. ALS
C. Myasthenia gravis
D. Multiple sclerosis
E. Parkinson’s Disease

47. 4. In a case of rabies, a 23 year old male shows
changes in behavior. The rabies virus may have
reached the boy’s brain by which of the
following?
A. Phagocytosis
B. Pinocytosis
C. Transneuronal transport
D. Neuronal degeneration
E. Necrosis