Peripheral nerve pathophysiology Traumatology course For 4th year medical students

Origin of peripheral nervous system disease These diseases can be broadly classified into four major categories: Spinal dystrophies (motor neuron body) Peripheral neuropathies (nerve: body+axon) Diseases of the myoneural junction Myopathies Groups one through three are primarily diseases of neural tissue and secondarily diseases of muscle. Myopathies are predominantly disorders of the muscle.

Peripheral nerve disorders The spectrum of peripheral nerve disorders includes Mononeuropathies (entrapment, trauma, etc) Mononeuritis multiplex (DM, vasculitis) Plexopathies (immune, neoplastic) Radiculopathies (discs, immune) Peripheral Neuropathies

Degeneration and Regeneration - Summary A deficiency of chemical messenger (due to denervation) generally produces an up-regulation of its receptors Acetyl choline receptors increase more than 10 folds in number and dispersed over the entire surface of the sarcolemma Sensitivity of the receptors towards acetylcholine increases Denervation also lowers the membrane potential  Muscles more prone to fibrillations After regeneration  functional innervation of the muscle is reestablished and sensitivity to acetyl choline decreases  resting membrane potential is restored (fibrillation disappears after regeneration) Smooth muscle does not atrophy when denervated becomes hyperresponsive to the chemical mediator that normally activates it Denervated exocrine glands [except sweat glands] become hypersensitive due to the synthesis or activation of more receptors A deficiency of chemical messenger generally produces an up-regulation of its receptors Lack of reuptake of secreted neurotransmitters because pre-synaptic nerve is not present Therefore excess neurotransmitters in the ‘synaptic space’ –> hyperreactivity of muscles