THE NEUROMUSCULAR-JUNCTION - MUSCLE-FIBER TYPE DIFFERENCES, PLASTICITY AND ADAPTABILITY TO INCREASED AND DECREASED ACTIVITY

The neuromuscular junction (NMJ) of adult mammalian muscle is the site of the transduction of electrical stimuli, generated by the nervous s ystem, to the underlying muscle fibres, resulting in muscle action. It has been demonstrated that, in some ways, the morphology of the NMJ i s specific to muscle fibre type. It is also known that while the struc ture of the NMJ generally remains stable in young, healthy adults, a s ubtle form of remodelling continuously occurs at this synapse. The mor phology and physiology of the NMJ have been shown to adapt to both inc reased, and decreased use. Indeed, morphological changes of the NMJ ar e associated with functional alterations in neuromuscular transmission . Increased activity of the myoneural synapse results in adaptations t hat enhance neuromuscular transmission and, thus, muscle performance. Similarly to increased usage, decreased neuromuscular activity results in structural alterations of the NMJ. However, unlike those responses observed with enhanced activity, decreased recruitment of the myoneur al synapse can impair neuromuscular transmission and muscle performanc e. Thus, the NMJ demonstrates both anatomical and physiological adapta tions following substantial changes in its pattern of activity. These NMJ adaptations can affect the functional capacity of skeletal muscle in vivo.