Craniofacial Muscles

70 V.E. Das
4.6 Summary
The oculomotor system is perhaps unique in that this motor control system is driving
a plant with little to no inertia. Further, the load is unchanging unlike in hand motor
control, for example, where the plant load can change if the subject picks up an
object of any weight. However, since poor vision is not well tolerated, there are
other stringent requirements for neural control of the oculomotor periphery including
precise calibration, fast response times, and high speeds of muscle contraction.
All of this is somehow achieved with a great deal of precision and accuracy by the
neural control of six pairs of EOMs. Although the framework of neural control was
laid out as early as in the 1960s and 1970s, it is apparent now that this framework is
not completely accurate in certain conditions (disjunctive eye movements for example).
Anatomical and biomechanical studies of muscle structure in recent years have
outpaced neurophysiological evaluation of how this complex system is controlled.
Perhaps the most important issues yet to be resolved would be to identify whether
the different fi ber types contribute differently to eye movements and to identify
whether their neural control from motoneurons is also distinct. Not only are these
questions important from the point of view of understanding oculomotor control,
but they are extremely important in understanding disease conditions such as strabismus
and nystagmus.
Acknowledgments This work was supported by NIH grant EY015312. I wish to thank Dr. Anand
Joshi and the editors for critically reading the manuscript and providing helpful comments.
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