Journal of Dental Research, Vol 72, 1503-1508, Copyright © 1993 by International & American Associations for Dental Research Online Journals
Sternocleidomastoid muscle inhibition induced by trigeminal stimulation
P. A. Browne, G. T. Clark, Q. Yang and M. Nakano
Division of Physical Therapy, Chapman University, Orange, California 92666.
Among numerous reports of anatomical and functional coupling between the
trigeminal and cervical systems is the demonstration that the
sternocleidomastoid (SCM) muscles may become activated along with the
masseter muscles during forceful abrupt biting maneuvers. Whether the
co-activated SCM is also inhibited by stimuli that produce masseter
inhibition is not known. This study evaluated the SCM for the presence of
inhibition during mechanically-elicited (chin or forehead tap) and
electrically-elicited (anterior maxillary gingiva stimulation) inhibition
of the masseter muscle in ten healthy men. Surface EMG data were recorded
bilaterally from the masseter and SCM muscles. The data for each muscle
were converted to ratios of the pre-stimulus maximum voluntary contraction
activity for each subject and averaged across subjects. Means of these
percentages were determined at several defined pre- and post-stimulus
intervals. The results indicate that masseter inhibition was clearly
elicited by the electrical and both forms of mechanical stimulation. SCM
co-inhibition could be evoked by electrical and chin tap stimulation but
not by forehead tap. The responses to these stimuli varied among subjects,
from trial to trial, and within subjects depending on the experimental
condition. The fact that it was possible for this co-inhibition to be
evoked is presented as further indication of the functional coupling of the
trigeminal and cervical systems.
