EVENTS LEADING TO
SKELETAL MUSCLE CONTRACTION
Muscular contraction is the result of a sequence of
chemical and physical events beginning with activity in
the central nervous system (CNS)(or sensory input to the
CNS). Failure or impairment at any site in this process
will result in a reduced contractile response of the
muscle. Fatigue and twitch fatigue, then, are results
of such failure. The identification of the site(s) of
failure in fatigue would provide a better understanding
of the mechanism(s) effecting the fatigue. Below, a
brief discussion of the normal sequence of events leading
to contraction is presented. CNS control of motor nerve
activity is complex and will not be described. For
simplicity, this discussion is based at the cellular level.
This sequence of events is described in a number of text
books (45, 62) and is illustrated in Figure 1. Following
the presentation of events leading to contraction, each
step in the sequence is considered as a potential site
for a mechanism of fatigue.
The sequence of events occurring at the nerve
terminal may be susceptible to failure. The arrival of
an action potential at the nerve terminal triggers the
release of acetylcholine from the terminal bouton.
Synaptic vesicles fuse to the terminal membrane and
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