Interactions in human quadriceps-triceps surae motoneuron pathways.
In an effort to more fully investigate spinal reflex pathways in humans, we measured the isometric force-time curve of the patellar (PTR) and Achilles (ATR) tendon-tap reflex in 12 college age subjects. We also conditioned the tendon jerk with a contralateral or ipsilateral tendon-tap stimulus, to ascertain the effects of segmental inputs on crossed-spinal reflex activity. The conditioning stimulus preceded the test reflex by 25, 40, 55, 70, 85, 100, 115, 130 or 145 ms. The results demonstrate that a tap to the contralateral patellar tendon produced long-latency excitation of quadriceps motoneurons, but a tap to the contralateral Achilles tendon produced short-latency facilitation and long-latency inhibition of the triceps surae motoneurons. Also, a conditioning tap to the contra- or ipsilateral patellar tendon produced a brief short-latency facilitation that was followed by a distinct, long-latency inhibition of triceps surae motoneurons. These results demonstrate that motoneuron excitability changes can be produced as a result of ispi- and contralateral segmental inputs. Moreover, these excitability changes may be long-lasting and only appear after a relatively long-latency. Several neurophysiological mechanisms are proposed to contribute to these changes.
Koceja
D M
DM
Department of Kinesiology, Indiana University, Bloomington 47405.
Kamen
G
G
D000125:Achilles Tendon / Q000502:physiology; D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D009470:Muscle Spindles / Q000502:physiology; D009132:Muscles / Q000294:innervation*; D009434:Neural Pathways / Q000502:physiology; D010329:Patella / Q000502:physiology; D010812:Physical Stimulation; D012026:Reflex, Stretch / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology