AVERAGE BUT NOT CONTINUOUS SPEED MATCH BETWEEN MOTONEURONS AND MUSCLE UNITS OF RAT TIBIALIS ANTERIOR

被引:33
作者
BAKELS, R [1 ]
KERNELL, D [1 ]
机构
[1] UNIV AMSTERDAM,ACAD MED CENTRUM,GRAD SCH NEUROSCI AMSTERDAM,DEPT NEUROPHYSIOL,1105 AZ AMSTERDAM,NETHERLANDS
关键词
D O I
10.1152/jn.1993.70.4.1300
中图分类号
Q189 [神经科学];
学科分类号
071006 ;
摘要
1. Properties of single motoneuron/muscle-unit combinations were determined for tibialis anterior (TA) in rats anesthetized with pentobarbital. The TA observations were systematically compared with those obtained earlier by the use of the same techniques from rat medial gastrocnemius (MG). 2. TA motoneurons were investigated with regard to afterhyperpolarization (AHP; total duration 32-74 ms, amplitude 0.39-4.96 mV) and axonal conduction velocity (41-79 m/s). TA muscle-unit measurements included the time course of the isometric twitch (time-to-peak force 10.8-18.0 ms; total duration 42-92 ms), the maximum tetanic force (22-217 mN), and a measure of fatigue sensitivity (fatigue index 5-100%). The range of twitch and AHP durations (''speed range'') was markedly smaller in the present TA material than for MG. 3. The mean duration of the TA motoneuronal AHP (49 +/- 8 ms, mean +/- SD) was close to that of its muscle-unit twitch (56 +/- 12 ms). Thus an ''average'' speed match existed between TA motoneurons and their muscle fibers. 4. For TA there was no correlation between the time courses of AHP and twitch. Thus there was for TA no ''continuous'' speed match between the motoneurons and their muscle fibers. 5. For TA twitches or AHPs studied separately, there was a significant correlation between different time course measures. Furthermore, compared with TA units having relatively fast twitches, those with slower twitches tended to show 1) a smaller maximum tetanic force and 2) a greater AHP amplitude. Fatigue-resistant units tended to have slower twitches than fatigue-sensitive ones. 6. The findings suggest the presence, for TA, of a dissociation between two independently controlled aspects of the commonly occurring AHP versus twitch duration match: in TA there is only an ''average'' match, whereas for MG there is an ''average'' as well as a ''continuous'' match (true also within same speed range as TA). Comparisons between the tension-frequency relation for the TA muscle and the twitch and AHP durations for TA units suggested that, in a muscle with this limited range of speed variation among its units, the average match would suffice for ensuring an adequate fit between the motoneuronal frequency coding and the rate gradation of muscle-unit force.
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页码:1300 / 1306
页数:7
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