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Postural instability in individuals with akinetic-rigid Parkinson's disease is caused by which of the following?

A. Rigidity of postural flexor and extensor musculature
B. Disinhibition of the reticulospinal tracts
C. Loss of pedunculopontine cells
D. All of the above

  • #1
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Rationale: Postural instability occurs secondary to the extreme rigidity of postural flexors and extensors. The loss of pedunculopontine cells, combined with increased inhibition of the PPN, disinhibits the reticulospinal tracts, producing excessive contraction of postural and proximal limb muscles.

  • #2
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