Perph Nerv

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    Disorders of peripheral nerves

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    Symptoms and signs of

    disorders of nerves

    • Caused by changes in axons

     –Increased conduction time  –Increased temporal dispersion

    • Expression of neural plasticity causing

    changes in the function of CNS structures

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     Anatomy of peripheral nerves

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     Anatomy of peripheral nerves

    • eripheral nerves have

    different conduction

    velocity

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    Conduction velocity in nerves

    and fiber tracts

    • roportional to fiber diameter 

    • eripheral nerves! "#$ meter%sec

    cm%msec'

    • Spinal descending tracts! "($)*$$ m%sec

    • Cranial nerves! varies

    &Auditory nerve! +$ m%sec'

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     ,ig -./ From: Møller: Sensory Systems, 2003

    Nerve fibers with different

    diameter have different

    conduction velocity

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    Epineurium

    Perineurium

    Endoneurium

    Fascicles

    Nerve fber

    Node o Ranvier

    Schwann cell

    Myelin

    Axon

    From: Møller: Sensory Systems, 2003

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    0any nerves are mixed nerves

    • Contains nerve fibers 1ith different

    conduction velocity

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    Recording from a

    long nerve

    composed of fibers

    with different

    diameter thus

    different conduction

    velocity

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    Organization

    of the dorsal horn of the

    spinal cord

    ,230 423DA5 *667

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    0any nerves are bipolar nerves

    • Examples are dorsal roots

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      ,rom 4rodal *667

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    athologies of peripheral nerves

    Nerves! • Neurapraxia

    •  Axonotmesis • Neurotmesis   Nuclei!

    •  Altered discharge pattern &burst activity'

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    Causes of in8ury to peripheral

    nerves

    • 9rauma

    • Compression &entrapment'

    • Irritation

    • 0etabolic disorders

    • Inflammatory &neuritis'

    • :irus

    •  Age related changes

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    9rauma to peripheral nerves

    • Interruption of nerve trun; &neurotmesis'

    • Interruption of axons &axonotmesis'

    • 9otal conduction failure &neurapraxia'  • Impaired conduction &no morphologic

    change'

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    Normal

    Cenral porion Peripheral porion

    Sreched

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    Axon

    Epineurium

    Perineurium Endoneuriu

    Neurapraxia

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    9otal conduction failure

    &neurapraxia'

    • No function

    • 2ecovers spontaneously over days or

    1ee;s &1hen the cause is resolved'

    • 2esults of spontaneous recovery are

    almost al1ays good

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    Interruption of axons

    &axonotmesis'

    • No function

    • Ne1 axon gro1s from cell body

    &spontaneously'

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     Axonotmesis

    • Nerve may regenerate from in8ured

    location a1ay from the cell body

    • 2egeneration! * mm per day &approx. * inch per month'

    • 2esults of spontaneous recovery are good

    to moderate depending on distance

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    Interruption of nerve trun;

    &neurotmesis'

    • No function

    • Irreversible< grafting is re=uired

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    Neurotmesis

    • Does not regenerate spontaneously

    • >rafting is necessary to restore function

    • 2esults of grating are good to moderate to failures

    I 8 d

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    In8ured nerves

     Axon interrupted&?allerian

    degeneration'

    Interruption of axon and

    endoneurial sheet

    Interruption of 

    perineurial sheet

    Interruption of

    nerve trun;

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    Axon

    Epineurium

    Perineurium Endoneuriu

    9ype +

    9ype /

    9ype -

    9ype #

     Axonotmesis

    Neurotmesis

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    Interrupted axons

    • Degenerate distally &a1ay from cell body'

    • Wallerian degeneration • Interrupted axons regenerate from in8ury<

    provided that endoneural tube is intact

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    ?allerian degeneration means!

    9he degenerative changes the distal segment of a peripheral nerve

    fiber &axon and myelin' undergoes 1hen its continuity 1ith its cell body is interrupted by a focal lesion. Syn! orthograde degeneration<

    secondary degeneration.

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    S9A29 6%(%$#

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    2emaining symptoms after nerve

    healing of in8ury

    • Syn;inesis

    • @yperactivity

    &0ostly caused by effect on central nervous

    system structures'

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    Electrophysiological manifestations

    of pathologies of peripheral nerves

    Nerves! • Increased conduction times

    • Increased or decreased discharge activity

    • Dispersion of neural activity

    •  Altered discharge pattern &burst activity'

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    Cause of neural pathologies

    • 0echanical &compression< stretching'

    • @eat

    • 0etabolic • Inflammation

    • Iatrogenic &from medical treatment'

    • Idiopathic &un;no1n' •  Age

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    9rauma

    • >unshot to limbs

    •  Accidents

    • Surgery &iatrogenic'

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    Sprouting

    • Caused by in8ury

    • Caused by regeneration

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    ,ormation of neuroma

    • Sprouting of axons at cut of a nerve

    • In8ured perineurium

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    Neuroma are mechanically

    sensitive

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    Compression

    • No ;no1n cause

    • Scar tissue

    • Changes in bone formation

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    4loc; of axoplasmatic flo1

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    Irritation

    • Scar tissue

    • 4lood vessels

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    0etabolic and chemical induced

    peripheral neuropathy

    • Diabetes

    • remic< hepatic and vitamin &4*

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    Inflammatory &neuritis'

    • >uillain)4arre syndrome

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    :irus

     

    • @erpes simplex &causes severe pain'

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    Demyelination

    • Ephaptic transmission

    • 2eflection of neural activity

    • 0echanosensitivity

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    In8ury to a peripheral nerve can cause

    transneural degeneration of the target cell

    , ti l i li ti f l

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    ,unctional implications of neural

    in8uries

    • Change t