Abstract
Changes in the neuromuscular system affecting the ageing motor unit manifest structurally as a reduction in motor unit number secondary to motor neuron loss, fiber type grouping due to repeating cycles of denervation-reinnervation, and instability of the neuromuscular junction that may be due to either or both a gradual perturbation in post-synaptic signaling mechanisms necessary for maintenance of the endplate acetylcholine receptor clusters or a sudden process involving motor neuron death or traumatic injury to the muscle fiber. Functionally, these changes manifest as a reduction in strength and coordination that precede a loss in muscle mass, as well as contribute to impairments in fatigue. Regular muscle activation in postural muscles or through habitual physical activity can attenuate some of these structural and functional changes up to a point along the aging continuum. On the other hand, regular muscle activation in advanced age (>75 y) loses its efficacy, and at least in rodents may exacerbate age-related motor neuron death. Transgenic mouse studies aimed at identifying potential mechanisms of motor unit disruptions in ageing muscle are not conclusive due to many different mechanisms converging on similar motor unit alterations, many of which phenocopy ageing muscle. Longitudinal studies of ageing models and humans will help clarify the cause and effect relationships and thus, identify relevant therapeutic targets in better preserving muscle function across the lifespan. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
AbstractChanges in the neuromuscular system affecting the ageing motor unit manifest structurally as a reduction in motor unit number secondary to motor neuron loss, fiber type grouping due to repeating cycles of denervation-reinnervation, and instability of the neuromuscular junction that may be due to either or both a gradual perturbation in post-synaptic signaling mechanisms necessary for maintenance of the endplate acetylcholine receptor clusters or a sudden process involving motor neuron death or traumatic injury to the muscle fiber. Functionally, these changes manifest as a reduction in strength and coordination that precede a loss in muscle mass, as well as contribute to impairments in fatigue. Regular muscle activation in postural muscles or through habitual physical activity can attenuate some of these structural and functional changes up to a point along the aging continuum. On the other hand, regular muscle activation in advanced age (>75 y) loses its efficacy, and at least in rodents may exacerbate age-related motor neuron death. Transgenic mouse studies aimed at identifying potential mechanisms of motor unit disruptions in ageing muscle are not conclusive due to many different mechanisms converging on similar motor unit alterations, many of which phenocopy ageing muscle. Longitudinal studies of ageing models and humans will help clarify the cause and effect relationships and thus, identify relevant therapeutic targets in better preserving muscle function across the lifespan. This article is protected by copyright. All rights reserved.This article is protected by copyright. All rights reserved.
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