Fatigue at the neuromuscular junction. Branch point vs. presynaptic vs. postsynaptic mechanisms.
There are several pre- and postsynaptic sites where neuromuscular transmission failure (NTF) can occur, leading to peripheral muscle fatigue. Presynaptic sites of NTF include: axonal branch point conduction block; a failure of excitation-secretion coupling at the presynaptic terminal; reductions in quantal release of ACh; and reductions in quantal size. Postsynaptic sites of NTF include: cholinergic receptor desensitization; and reduced sarcolemmal excitability. Susceptibility to NTF increases with stimulation frequency and is most prevalent in fatigable fast-twitch motor units. In addition, susceptibility to NTF varies with age and with conditions of altered use.
Sieck
G C
GC
Department of Anesthesiology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
Prakash
Y S
YS
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D018763:Muscle Fatigue / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology*