A new transducer system for direct motor unit force measurement

Critical Reviews in Oral Biology & Medicine

2001

Self Cite

Motor unit territories in masticatory muscles appear to be smaller than territories in limb muscles, and this would suggest a more localized organization of motor control in masticatory muscles. Motor unit cross-sectional areas show a wide range of values, which explains the large variability of motor unit force output. The proportion of motor unit muscle fibers containing more than one myosin heavy-chain (MHC) isoform is considerably larger in masticatory muscles than in limb and trunk muscles. This explains the continuous range of contraction speeds found in masticatory muscle motor units. Hence, in masticatory muscles, a finer gradation of force and contraction speeds is possible than in limb and in trunk muscles. The proportion of slow-type motor units is relatively large in deep and anterior masticatory muscle regions, whereas more fast-type units are more common in the superficial and posterior muscle regions. Muscle portions with a high proportion of slow-type motor units are better equipped for a finer control of muscle force and a larger resistance to fatigue during chewing and biting than muscle portions with a high proportion of fast units. For the force modulation, masticatory muscles rely mostly on recruitment gradation at low force levels and on rate gradation at high force levels. Henneman's principle of an orderly recruitment of motor units has also been reported for various masticatory muscles. The presence of localized motor unit territories and task-specific motor unit activity facilitates differential control of separate muscle portions. This gives the masticatory muscles the capacity of producing a large diversity of mechanical actions. In this review, the properties of masticatory muscle motor units are discussed.

Section: Twitch and Tetanus Forcementioning

confidence: 99%

mentioning

confidence: 99%

Morphology and Physiology of Masticatory Muscle Motor Units

Eijden

Critical Reviews in Oral Biology & Medicine

2001

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“…For an extensive description of the methods used for anesthesia and recording of action potentials and twitch forces, we refer to earlier work. [10][11][12][13] In brief, preanesthesia was effected with a mixture of rompune and ketamine, applied intramuscularly, and atropine, applied subcutaneously. Further anesthesia was effected through halothane in a 1:3 oxygen-nitrous oxide mixture, provided through a tracheal cannula.…”

Section: Methodsmentioning

confidence: 99%

Action potential shape of rabbit masseter motor units and jaw angle

Eijden

2001

Muscle and Nerve

Action potentials of rabbit masseter motor units (n = 42) were registered at different jaw angles to examine whether the shape of the action potential is related to length of muscle fibers in motor units and depends on the intramuscular location of the motor unit. Twitches were elicited by stimulating motoneurons in the trigeminal motor nucleus. During jaw opening (0-21 degrees), the duration of the action potentials increased by about 10%. Anteriorly located motor units showed an increase in duration larger than that of more posteriorly located units, which was probably due to a larger stretching of the more anteriorly located units.

“…For an extensive description of the surgical procedures and the method of stimulating single motor units, the reader is referred to previous papers (Turkawski et al, 1996(Turkawski et al, , 1998. After the animals were pre-anesthetized with a mixture of Rompune and Ketamine applied intramuscularly, and Atropine applied subcutaneously, a tracheal cannula was provided for artificial ventilation.…”

Section: Surgical Proceduresmentioning

confidence: 99%

“…Motor units showing a large stimulus artifact Registration and Analysis of Motor Unit Force We used a force transducer, capable of measuring both the magnitude and the position of the line of action of forces in a single plane. Design and technical specifications of this transducer were described in detail by Turkawski et al (1996). Briefly, a motor unit force applied to the transducer is resolved into orthogonal force components.…”

Section: Surgical Proceduresmentioning

confidence: 99%

EMG Power Spectrum and Motor Unit Characteristics in the Masseter Muscle of the Rabbit

Eijden²

2000

J Dent Res

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Masticatory muscles contain a large variety of motor units with different physiological and morphological properties. In this study, we tested the hypothesis that a relationship exists between the mechanical and myo-electric properties of single motor units in the masseter muscle of the rabbit. It was expected that faster-contracting motor units, which usually have a relatively large number of fibers with large diameters, should have faster action potentials with larger amplitudes than slower motor units. Single motor units were stimulated. A two-dimensional force transducer registered mechanical parameters of the units. EMG electrodes were used to determine amplitude and frequency parameters of the action potentials of the same units. The results showed that faster-contracting motor units indeed produced action potentials with higher conduction velocities. However, faster motor units had no significant larger amplitude of the action potential. Small but significant positive correlations were found between the tetanic peak force and the amplitude of the action potentials. Little difference was found among the various frequency and amplitude parameters, respectively, making them equally suitable to describe the action potential. Surprisingly, a negative correlation between the amplitude and frequency parameters of the action potential was found, which may result from variability in arrival times of action potentials at the electrode site. Regional differences in the frequency parameters were found between the anterior and posterior parts of the superficial masseter.