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1. STRUCTURE OF NEURON
Dr. Faridullah Khan
Physiology Department
RMU Rawalpindi

2. NERVOUS SYSTEM
Is composed of Neurons and Glial cells which are supporting cells, help neurons in
maintaining their electrical potential and formation of BLOOD BRAIN BARRIER.
Neuroglia is made up of
1. Macroglia [oligodandrocytes , Astrocytes ]
2. Microglia [macrophages, mobile cells ]
3. Ependymal cells.

3. STRUCTURE
OF A TYPICAL NEURON

4. • NEURON is the name given to nerve cell with its
processes. Dendrites and axon/nerve fiber.
• Neurons are present in brain spinal cord and ganglia. In
adults they do not under go cell division.
• Histologically.
• Soma
• Axon
• Dendrites

6. SOMA
Unmylinated in humans. Surface is smooth may have
synaptic elevations contains organelles.

8. • Nucleus. endoplasmic reticulum. mitochondria. Golgi
apparatus. ribosomes. microtubules and neurofilaments.
Nucleus is large round pale staining with prominent
nucleoli. Binuclear cells in sympathetic and sensory
ganglia.

9. Polyribosome's often aggregate in groups associated with granular
Endoplasmic Reticulem. These are NISSL GRANULES.
these are RNA rich structures.
Nissl Granules are visible as basophilic granules under
light microscope.
Nissl Granules are not present in axon hillock.
Nissl Granules are more obvious in active nerve cells
[spinal motor neurons]

10. It shows high level of protein synthesis
[in soma & dendrites] for repair maintenance.
Injury to axon results in disappearance of Nissl granules.
this Is known as chromatolysis.
Granules containing melanin pigment are present
in substantia nigra.

11. With age senility pigment LIPOFUSCIN accumulates in
soma[partially degraded lipoprotenacious material by
lysosomes]
Glycogen and lipids are are also present in cytoplasm.

12. DENDRITES
Afferent processes which arise from cell body.
Principal site for signal reception.
Have small knobby projections called dendritic spines specially seen
in neurons of cerebellar and cerebral cortex.
Endoplasmic Reticulum, Nissl Granules,ribosomes are present
Always unmyelinated.

13. 12-13
Dendrites
• Conduct impulses towards the cell
body
• Typically
- numerous
- short
- highly branched
- unmyelinated
• Surfaces specialized for contact
with other neurons (synapses)
• Contain neurofibrils

14. AXON
Large single efferent process varies in length and diameter.
Arises from thickened part of cell body called axon hillock.
1st 100 micrometer or so part of axon is unmyelinated
called Initial segment is rich in voltage gated sodium channels.

15. 12-15
Axons
• Conduct impulses away from
cell body
• Single, long, thin cylindrical
process of cell, may be
myelinated
• Arises at axon hillock
• Impulses arise from initial
segment (trigger zone)
• Side branches (collaterals)
• End in fine processes called
axon terminals
• Swollen tips called synaptic
end bulbs contain vesicles
filled with neurotransmitters

16. • axon give rise to terminal branches and ends in synaptic
• knobs.
• These are presynaptic terminals having neurotransmitter vesicles
• Cytoplasm is known as axoplasm
• No Nissl Granules.GolgiApparatus . ribosomes. No synthetic activity.
• Axon survival depends upon transport of material from cell body.

17. NUCLEUS
• Large and round centrally located. Single prominent
• nucleolus.
• Nucleus is pale. finely dispersed chromatin Barr body
{compact X chromosome in females.
• Nuclear envelop is double layered and has fine nuclear
pores.

18. • Connective tissue layer covering each nerve fiber is called
ENDONEURIUM
• Fascicle covering is PERINEURIUM.
• Nerve trunk covering is called EPINEURIUM.

19. AXONAL TRANSPORT
Neurons are secretary cells in which proteins are synthesized in the
cell body and secreted from the axon terminal.{away from cell body}
Proteins and polypeptides are transported to axonal end by
axoplasmic flow.
Cell body thus maintains functional and structural integrity of the axon
by axon transport.
.

20. • Orthograde transport Fast 400mm/day.{proteins Transmitter
substances} Slow 0.5 to 10mm/day.{axoplasm. Microfilaments}
• Retrograde transport explains how cell body responds to changes
in distal end of axon. 200mm/day.
{Nissl Granules Fused vesicles Worn out organelles to be digested
by lysosomes}
• Axon transport is brought about by microtubules and
Require 2 molecular motors,Dynein and Kinesin.
RABIES/POLIOMYELITIS/TETANUS TOXIN.

22. MYELINATION
• Depending on manner of insulation Nerve fibers are of 2 types
myelinated and unmyelinated.
UNMYELINATED
Pain/post ganglionic axons of ANS.
• In PNS axons <1 micrometer in diameter.axons indent surface of schwaan cell
so it lies in trough.up to 15 axons share 1 schwann cell
• In CNS unmyelinated Nerve Fiber run in small groups and are not particularly
related to oligodandrocytes.

24. Myelination

27. Myelinated
• Axons of most of the neurons are covered by myelin which is
discontinuous layer interrupted at regular intervals by node of
Ranvier.
• Myelin consists of many layers of highly modified plasma membrane
wrapped around axon by supporting cells which are Schwann cells in
PNS . One schwann cell provide myelin around 0.5 to 1 mm long
segment of axon.
• Oligodandrocytes in CNS. One cell branch to provide myelin to 40 to
60 axons.

28. • Node of ranvier are situated in interval between adjacent
oligodandrocytes in CNS and in interval between adjacent schwann
cells in PNS.
• PNS Schwann cell rotates around axon many times
• CNS rotation of oligodandrocyte not possible , growth of cell
provides myelin

29. • Myelin formation starts before birth and continues during
1st year after birth.
• Myelin is compacted when extracellular portion of
membrane protein Po locks to same portion in opposing
membrane.
• NEUROPATHY results from defect in gene for Po.

30. • Defect in myelin leads to neurological defects.
• MULTIPLE SCLEROSIS .autoimmune,3 million people .20 to 50 yr.
more in female.
• WBC attack injured myelin and nerve.
• Potasium leakage through potassium channels. Hyperpolarization.
Failure to conduct action potential.

31. Conduction defects lead to
• SENSORY DEFECTS
• FATIGUE
• MUSCLE WEAKNESS
• SPEECH PROBLEMS
• VISUAL DEFECTS
• NCS confirms conduction defects.

32. Thank you