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Neuron Physiology
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Nerve
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Parts Of A Neuron
Cell body (soma) Axon Dendrites
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Neurons
Axon of anotherneuron
Axon of anotherneuron
Cell BodyCell BodyDendritesDendrites
AxonAxon
MyelinSheathMyelinSheath
Dendrites of another neuron
Dendrites of another neuron
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Cell Body
Soma or prikariyon Nucleus and cytoplamic organelles Nissels granules = RER Cytoskeletal proteins like
neurofilaments ,microtubules , actin microfilaments
Nucleus contain one or two nucleolus ,and no centriole
Terminally differentiated cells
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Contd
Soma extend into dendrites on one end and axon on the other
Membrane called plasmalemma
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Dendrites
Numerous short extensions from cell body
Increasing surface area Dendritic spines Receive incoming signals and
transmits them Helps in protein synthesis Helps in generating ACTION
POTENTIAL
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Axon
Axon fibers form the nerve Long cylindrical process extends away from
cell body Transmits output signals (Action Potential ) Contains organelles , cytoskeleton, axoplasm Axon hillock - initial segment portion of
neuron Axon terminal – axon divides into several
processes and has synaptic knobs Buttons contains neurotransmitters
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Myelination
It’s a protective insulator covering of the axon
Formed by schwann cells Double layer membrane of a single schwann
cell wraps itself several times around axon 1 mm in length , 8 -10 micrometer in
thickness Layers stick to each other due to protein p0 Schwann cell nucleus lies in the outermost
layer
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Contd
Nodes of Ranvier Internodal distance is 1-2mm and each
node is 0.5-1 micrometer
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Functions Of Myelination
Increases speed of conduction It reduces energy expenditure by the
cell Provides protective covering of the
axon
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Types Of Axon
Myleniated Axons Unmyelinated Axons
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Timing Of Myelination
Different neurons in body shows diff time of myelination
Starts early as 4th month of fetal life and completes by 2 years
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Axoplasmic Transport
Transfer of substances between cell body and axon terminal
For the development of neuron Bi-directional transport
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Types Of Axoplasmic Transport
Anterograde transport Retrograde transport Transneuronal transport
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Anterograde Transport
From ell body to axon terminal Mainly for neurotransmitters Two types – fast and slow Fast – 400mm/day by kinesin Slow- 0.5 – 2 mm/day Slow transport helps in nerve repair
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Retrograde Transport
From axon terminal to cell body 200mm /day done by dynin Keeps soma informed about synaptic
environment Transports viruses such as varicella
Zoster , rabies Transport toxins Transports nerve growth factor
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Neuronal Ion Channels
Voltage gated Na channels are mainly concentrated on nodes of ranvier
Voltage gated Ca channels are mainly present at the axon terminal for neurotransmitter secretion
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Classification Of Nerve Fibers
Based on function Myelination Erlanger and gasser classification
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Erlanger And Gasser Classification
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Applied Aspects
Demyelinating diseases 1) multiple
sclerosis 2) Gullian barre
syndrome
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Nerve Injury
Wallerian degeneration
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Grades Of Nerve Injury
5 grades 1st-transient loss of function 2nd- severe injury due to prolonged
pressure, intact endoneurium complete recovery but delayed
3rd- severe damage to endoneurial sheath
4th- disruption of nerve fasciculi 5th- complete transection
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Wallerian Degenration
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Factors Promoting Nerve Growth
Neurotrophins Other growth factors ( FGF,IGF-1,
PDGF , CNTF,GDNF)
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Neurotrophins
Nerve growth factor Brain derived neurotrophic factor Neurotrophin-3 Neurotrophin 4/5
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