Hjortskov Nis, Skotte Jørgen, Hye-Knudsen Christian, Fallentin Nils
National Institute of Occupational Health, Dept. of Physiology, Lersø Parkallé 105, DK-2100 Copenhagen, Denmark.
J Appl Physiol (1985). 2005 Apr;98(4):1366-70. doi: 10.1152/japplphysiol.00955.2004. Epub 2004 Nov 12.
Animal experiments suggest that an increase in sympathetic outflow can depress muscle spindle sensitivity and thus modulate the stretch reflex response. The results are, however, controversial, and human studies have failed to demonstrate a direct influence of the sympathetic nervous system on the sensitivity of muscle spindles. We studied the effect of increased sympathetic outflow on the short-latency stretch reflex in the soleus muscle evoked by tapping the Achilles tendon. Nine subjects performed three maneuvers causing a sustained activation of sympathetic outflow to the leg: 3 min of static handgrip exercise at 30% of maximal voluntary contraction, followed by 3 min of posthandgrip ischemia, and finally during a 3-min mental arithmetic task. Electromyography was measured from the soleus muscle with bipolar surface electrodes during the Achilles tendon tapping, and beat-to-beat changes in heart rate and mean arterial blood pressure were monitored continuously. Mean arterial pressure was significantly elevated during all three maneuvers, whereas heart rate was significantly elevated during static handgrip exercise and mental arithmetic but not during posthandgrip ischemia. The peak-to-peak amplitude of the short-latency stretch reflex was significantly increased during mental arithmetic (P < 0.05), static handgrip exercise (P < 0.001), and posthandgrip ischemia (P < 0.005). When expressed in percent change from rest, the mean peak-to-peak amplitude increased by 111 (SD 100)% during mental arithmetic, by 160 (SD 103)% during static handgrip exercise, and by 90 (SD 67)% during posthandgrip ischemia. The study clearly indicates a facilitation of the short-latency stretch reflex during increased sympathetic outflow. We note that the enhanced stretch reflex responses observed in relaxed muscles in the absence of skeletomotor activity support the idea that the sympathetic nervous system can exert a direct influence on the human muscle spindles.
动物实验表明，交感神经输出增加会降低肌梭敏感性，从而调节牵张反射反应。然而，结果存在争议，人体研究未能证明交感神经系统对肌梭敏感性有直接影响。我们研究了交感神经输出增加对通过轻敲跟腱诱发的比目鱼肌短潜伏期牵张反射的影响。九名受试者进行了三种操作，导致腿部交感神经输出持续激活：以最大自主收缩的30%进行3分钟的静态握力运动，随后进行3分钟的握力后缺血，最后在3分钟的心算任务期间。在轻敲跟腱时，用双极表面电极测量比目鱼肌的肌电图，并连续监测逐搏心率和平均动脉血压变化。在所有三种操作期间，平均动脉压均显著升高，而心率在静态握力运动和心算期间显著升高，但在握力后缺血期间未升高。在心算期间（P < 0.05）、静态握力运动期间（P < 0.001）和握力后缺血期间（P < 0.005），短潜伏期牵张反射的峰峰值显著增加。以相对于静息状态的百分比变化表示时，心算期间平均峰峰值增加111（标准差100）%，静态握力运动期间增加160（标准差103）%，握力后缺血期间增加90（标准差67）%。该研究清楚地表明，在交感神经输出增加期间，短潜伏期牵张反射得到促进。我们注意到，在没有骨骼肌运动活动的放松肌肉中观察到的增强的牵张反射反应支持了交感神经系统可以对人体肌梭产生直接影响的观点。
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