45 / 47
46
tone in the whole body, the other is red
nuclei to inhibit motorneurone activity.
(3) The cortical mechanism affects the
muscle tone by direct and indirect cortical
projection.
The human capacity to maintain a particular
isometric force in the presence of visual
feedback during a force-level, pursuit-
tracking experiment is less developed
for the jaw-closing muscles than for the
limb muscles. Therefore, this finding may
indicate that the projection on the trigeminal
motoneurone pool from visual inputs is poor,
or that the trigeminal effector system itself is
less finely tuned.
In the study, different posture may affect
on the velocity of mandibular movement
because of the muscle tonic. There are still
some doubtable factors could influence the
result of this experiment, such as the different
muscle activity from person to person. The
distance between the eyes of subject and
monitor is about 15 inches, however, we
do not sure if every subject can watch the
monitor very clearly, and how many people
of them are nearsighedness. Therefore, the
degree of the effect of visual factor is not
the same from one to another. The velocity
of mandibular movement can be influenced
of musc le force of each subject . The
physiological and clinical significance of the
value of mandibular movement acceleration
can be explained by Newton's Second law, F
= ma.
10
In this study, we find that not only the
maximum closing velocity was faster than
opening one but also the average closing
velocity was faster than opening one. It is
because the mastication activity of elevator
muscles is stronger than the depressor
muscles by the growth of age
11
.
The visual cues is transfer to mesencephalic
nuclei and then send the message to
trigeminal nerve to affect muscle tone and
activity
12,13
.
Conclusion
Although the effect of limb movement is very
conspicuous, the effect of jaw movement
is little. In our study, these data support
the concept that visual feedback has poor
influence on the velocity of mandibular
movement. Further research is needed to
explore it in longitudinal effect.
Reference
1. The precision of motor control in jaw and
limb muscles during isometric contraction
in the presence of visual feedback.
Van Steenberghe D., Bonte B., Schols
H.,Jacob R. and Schotte A.,Archs Oral
Biol. 1991 Vol.36, pp545-547
2. The importance of visual feedback on
the accuracy of jaw and finger position
in man .Jacob R.,Van Steenberghe D.,
and Schotte A., Archs Oral Biol. 1992
Vol.37,No.9, pp677-683
3. The e f f ec t s o f p r ac t i ce and v i sua l
f e e d b a c k o n ma n d i b u l a r b o r d e r
movementsJou-Song Wang and Yuh-
臺灣口腔醫學工程學會會誌
No.
13
Taiwan Oral