ISSN:
1432-1106
Keywords:
Golgi tendon organ
;
Group Ib input
;
Motor control system
;
Posture
;
Locomotion
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary 1. This report describes experiments on Ib afferents from tendon organs of the de-efferented soleus in acutely prepared cats in which: a) contrast was made of responses to passive forces generated by a dynamic stretch and to active forces generated by stimulating either the muscle nerve or small ventral root filaments; and, b) responses to static and dynamic stretch were related to physiological extents and rates of movement. 2. No significant differences were observed in tensions associated with threshold responses to active and passive inputs if rates of tension development were relatively similar and if the active force was generated by stimulation of the muscle nerve. Stimulation of small ventral rootlets revealed however that many motor units are “in parallel” and many “in series” with certain receptors. Thresholds of these receptors were much lower to active forces generated by “in series” motor units than to forces developed more randomly by graded stimulation of the muscle nerve. An absolute active force threshold was not gauged since it was estimated that at least some tendon organs can be driven by independent twitch contraction of 30–50 motor units. 3. Threshold responses to static stretch indicated that gradual flexion of the ankle joint (as for example on slow assumption of a crouched posture) would involve progressive recruitment of soleus Ib discharge with over 2/3rds of the units firing by the extreme of dorsi-flexion. Responses to dynamic stretch suggested that an even greater percentage of soleus tendon organs would be fired during ankle flexions associated with walking. During galloping the triceps surae undergoes an eccentric (lengthening) contraction at one phase of the step cycle and soleus Ib input to the spinal cord would then become even more pronounced. 4. In recent years the role of Golgi tendon organs in the reflex regulation of muscle has been reassessed with an emphasis on their ability to transmit continuously to the spinal cord information concerning the active force developed by muscle contraction and a de-emphasis of the significance of responses to muscle stretch. The present results emphasize however that soleus tendon organs are sufficiently sensitive to passive forces that muscle stretch can influence Ib input to the spinal cord in normal postural and locomotor activity. There is discussion of the functional significance of this finding and its relation to the central organization of Ib reflexes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00234263
