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| How stress may affect chronic musculoskeletal head-neck disorders.
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Effects of sympathetic stimulation on the rhythmical jaw movements
produced by electrical stimulation of the cortical masticatory areas of
rabbits.
Roatta S, Windhorst U, Djupsjobacka M, Lytvynenko S, Passatore M.
Physiology Division, Department of Neuroscience, Medical School,
University of Turin, c.so Raffaello 30, 10125 Turin, Italy.
silvestro.roatta@unito.it
The somatomotor and sympathetic nervous systems are intimately linked.
One example is the influence of peripheral sympathetic fibers on the
discharge characteristics of muscle spindles. Since muscle spindles
play important roles in various motor behaviors, including rhythmic
movements, the working hypothesis of this research was that changes in
sympathetic outflow to muscle spindles can change rhythmic movement
patterns. We tested this hypothesis in the masticatory system of
rabbits. Rhythmic jaw movements and EMG activity induced by
long-lasting electrical cortical stimulation were powerfully modulated
by electrical stimulation of the peripheral stump of the cervical
sympathetic nerve (CSN). This modulation manifested itself as a
consistent and marked reduction in the excursion of the mandibular
movements (often preceded by a transient modest enhancement), which
could be attributed mainly to corresponding changes in masseter muscle
activity. These changes outlasted the duration of CSN stimulation. In
some of the cortically evoked rhythmic jaw movements (CRJMs) changes in
masticatory frequency were also observed. When the jaw-closing muscles
were subjected to repetitive ramp-and-hold force pulses, the CRMJs
changed characteristics. Masseter EMG activity was strongly enhanced
and digastric EMG slightly decreased. This change was considerably
depressed during CSN stimulation. These effects of CSN stimulation are
similar in sign and time course to the depression exerted by
sympathetic activity on the jaw-closing muscle spindle discharge. It is
suggested that the change in proprioceptive information induced by an
increase in sympathetic outflow (a) has important implications even
under normal conditions for the control of motor function in states of
high sympathetic activity, and (b) is one of the mechanisms responsible
for motor impairment under certain pathological conditions such as
chronic musculoskeletal head-neck disorders, associated with stress
conditions.
PMID: 15551082 [PubMed - indexed for MEDLINE]
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