Because the sensory and motor cell bodies are in different locations within the PNS, nerve cell body disorders affect either the sensory or motor component, but usually not both.
Imbalances of
the PNS
Because the sensory and motor
cell bodies are in different locations within the PNS, nerve cell body
disorders affect either the sensory or motor component, but usually not both.
Demyelination or damage to the myelin sheath slows nerve conduction. This
affects mostly heavily myelinated fibers, causing buzzing or tingling
sensations, motor weakness, and reduced reflexes. Centrally located fascicles
are most vulnerable to vas-cular disorders such as vasculitis or ischemia,
which can cause sharp pain or burning sensations or motor weakness proportional
to atrophy. The distal two-thirds of a limb are usually affected.
Toxic-metabolic or genetic disorders are usually symmetrical when they begin.
Immune-mediated processes may be symmetric or asymmetric. Significant axon
dysfunction is caused by damage to the axon transport system, especially the
microtubules and microfilaments. Axonal degenera-tion slowly ascends, producing
sensory loss and weak-ness. Damage to the myelin sheath such as by injury or Guillain-Barre syndrome may be
repaired by surviving Schwann cells within 6–12 weeks. Regenera-tion is nearly
impossible when the cell body dies and is unlikely when axons are totally lost.
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