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Disorders of peripheral nerves

Disorders of peripheral nerves. 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. Anatomy of peripheral nerves.

Samuel
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Disorders of peripheral nerves

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  1. Disorders of peripheral nerves

  2. 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

  3. Anatomy of peripheral nerves

  4. Anatomy of peripheral nerves • Peripheral nerves have different conduction velocity

  5. Conduction velocity in nerves and fiber tracts • Proportional to fiber diameter • Peripheral nerves: ~50 meter/sec (5 cm/msec) • Spinal descending tracts: ~70-100 m/sec • Cranial nerves: varies (Auditory nerve: 20 m/sec)

  6. Nerve fibers with different diameter have different conduction velocity Fig 4.3 From: Møller: Sensory Systems, 2003

  7. From: Møller: Sensory Systems, 2003

  8. Many nerves are mixed nerves • Contains nerve fibers with different conduction velocity

  9. Recording from a long nerve composed of fibers with different diameter thus different conduction velocity

  10. Organization of the dorsal horn of the spinal cord FROM BRODAL 1998

  11. Many nerves are bipolar nerves • Examples are dorsal roots

  12. From Brodal 1998

  13. Pathologies of peripheral nerves Nerves: • Neurapraxia • Axonotmesis • Neurotmesis Nuclei: • Altered discharge pattern (burst activity)

  14. Causes of injury to peripheral nerves • Trauma • Compression (entrapment) • Irritation • Metabolic disorders • Inflammatory (neuritis) • Virus • Age related changes

  15. Trauma to peripheral nerves • Interruption of nerve trunk (neurotmesis) • Interruption of axons (axonotmesis) • Total conduction failure (neurapraxia) • Impaired conduction (no morphologic change)

  16. Neurapraxia

  17. Total conduction failure (neurapraxia) • No function • Recovers spontaneously over days or weeks (when the cause is resolved) • Results of spontaneous recovery are almost always good

  18. Interruption of axons (axonotmesis) • No function • New axon grows from cell body (spontaneously)

  19. Axonotmesis • Nerve may regenerate from injured location away from the cell body • Regeneration: 1 mm per day (approx. 1 inch per month) • Results of spontaneous recovery are good to moderate depending on distance

  20. Interruption of nerve trunk (neurotmesis) • No function • Irreversible, grafting is required

  21. Neurotmesis • Does not regenerate spontaneously • Grafting is necessary to restore function • Results of grating are good to moderate to failures

  22. Injured nerves Axon interrupted (Wallerian degeneration) Interruption of axon and endoneurial sheet Interruption of perineurial sheet Interruption of nerve trunk

  23. Axonotmesis Type 2 Neurotmesis Type 3 Type 4 Type 5

  24. Interrupted axons • Degenerate distally (away from cell body) • Wallerian degeneration • Interrupted axons regenerate from injury, provided that endoneural tube is intact

  25. Wallerian degeneration means: The degenerative changes the distal segment of a peripheral nerve fiber (axon and myelin) undergoes when its continuity with its cell body is interrupted by a focal lesion. Syn: orthograde degeneration, secondary degeneration.

  26. START 9/7/05

  27. Remaining symptoms after nerve healing of injury • Synkinesis • Hyperactivity (Mostly caused by effect on central nervous system structures)

  28. 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)

  29. Cause of neural pathologies • Mechanical (compression, stretching) • Heat • Metabolic • Inflammation • Iatrogenic (from medical treatment) • Idiopathic (unknown) • Age

  30. Trauma • Gunshot to limbs • Accidents • Surgery (iatrogenic)

  31. Sprouting • Caused by injury • Caused by regeneration

  32. Formation of neuroma • Sprouting of axons at cut of a nerve • Injured perineurium

  33. Neuroma are mechanically sensitive

  34. Compression • No known cause • Scar tissue • Changes in bone formation

  35. Block of axoplasmatic flow

  36. Irritation • Scar tissue • Blood vessels

  37. Metabolic and chemical induced peripheral neuropathy • Diabetes • Uremic, hepatic and vitamin (B1,B2,B12) deficits • Alcohol • Chemical

  38. Inflammatory (neuritis) • Guillain-Barre syndrome

  39. Virus • Herpes simplex (causes severe pain)

  40. Demyelination • Ephaptic transmission • Reflection of neural activity • Mechanosensitivity

  41. Injury to a peripheral nerve can cause transneural degeneration of the target cell

  42. Functional implications of neural injuries • Change the function of the target central neurons: • May cause expression of neural plasticity

  43. Abnormal activity in a peripheral nerve can cause changes in the function of the target cells

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