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  • 1
    Electronic Resource
    Electronic Resource
    Mechanical arrangement and transducing properties of Golgi tendon organs (1972)
    Springer
    Experimental brain research 14 (1972), S. 274-292 
    Details
    ISSN: 1432-1106
    Keywords: Golgi tendon organs ; Group Ib input ; Motor control system ; Posture ; Locomotion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. The mechanical arrangement and transducing properties of Golgi tendon organs in soleus and anterior tibial muscles of anesthetized cats have been studied by noting responses of their Ib afferents to muscle stretch (passive force) and contraction (active force) of small portions of the muscle including functionally isolated motor units. 2. Tendon organs were shown to be arranged both in-series and in-parallel with adjacent muscle fibers. There were gradations in these relations, the tightest arrangements involving the response to contraction of a single motor unit, brisk discharge from an in-series receptor and pause in the stretch-activated firing of an in-parallel receptor. Other arrangements included those in which groups of muscle fibers neither directly in-series nor in-parallel with a receptor were still found capable of influencing its firing pattern. If in-series muscle fibers maintained their contraction while in-parallel fibers were also contracting, the receptor usually responded slightly less actively than it did to the in-series force alone. 3. Tendon organs were found to have a very low threshold to in-series force developed by muscle contraction. Responses were observed to as little as 0.5 gm of twitch tension. Minimum active force thresholds were similar for the two muscles studied, but thresholds to dynamic stretch were lower for anterior tibial receptors. Division of the dynamic stretch threshold by the minimum active force threshold gave a measure of the extent to which each tendon organ was more sensitive to active than passive force. These values (generally less than 50) did not negate the physiological significance of responses to passive stretch. 4. The present data, together with those of Houk and his co-workers (1967, 1971) emphasize that tendon organs can participate in the moment to moment reflex control of normal muscle activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00816163
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  • 2
    Electronic Resource
    Electronic Resource
    Stretch responsiveness of Golgi tendon organs (1970)
    Springer
    Experimental brain research 10 (1970), S. 463-476 
    Details
    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
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  • 3
    Electronic Resource
    Electronic Resource
    Ankle flexor muscles in the cat: Length-active tension and muscle unit properties as related to locomotionSupported in part by the Institutional Studies and Research Committee of Northern Arizona University and by USPHS Grant Ns 07888 to D. G. Stuart. (1977)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 153 (1977), S. 23-37 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The mechanical properties of the whole muscle and fast-twitch muscle units of the cat hindlimb pretibial flexors have been explored and related to normal locomotion. Tibialis anterior (TA) is parallel-fibered and functionally crosses a single joint, the ankle, whereas extensor digitorum longus (EDL) is pinnate and spans the ankle, knee, metatarsophalangeal and interphalangeal joints. The active tetanic tension of TA remains near its peak value over a range of muscle lengths associated with normal ankle movement. In contrast, the length-tension curve of EDL is sharply peaked. However, normal corollary action of the knee, ankle and metatarsophalangeal joints during stepping minimizes EDL's excursion and maintains it at or near a length optimal for peak tension development. EDL is capable of producing synchronous but sterotyped digit and ankle movements while TA provides for independent ankle flexion at all relevant joint angles.The mechanical properties of 84 TA and 98 EDL fast-twitch muscle units were studied by measuring twitch contraction time (≤45 msec), peak tetanic tension, response to repetitive stimulation, and contractile fatigue resistance during electrical stimulation of single alpha axons, functionally isolated from ventral root filaments. These mechanical properties were essentially similar for both muscles with the exception of mean peak tetanic tension which was 30% lower for TA units (14 gm-wt) than for EDL units (20 gm-wt). A high proportion of units in both muscles demonstrated fatigue resistance which is reflective of the repetitive, phasic demand upon these muscles during locomotion.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051530103
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  • 4
    Electronic Resource
    Electronic Resource
    Digit flexor muscles in the cat: Their action and motor unitsSupported in part by USPHS grants NB 07888 and FR 05457. (1972)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 137 (1972), S. 335-352 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The relation between muscle action and the mechanical properties of motor units has been explored in the main digit flexors of the cat hind limb: plantaris (PL); flexor digitorum brevis (FDB); flexor hallucis longus (FHL); and, flexor digitorum longus (FDL). General observations on muscle action revealed that PL is an ankle extensor as well as a digit flexor. PL and FHL were shown to be the major force contributors to digit flexion with FDL playing a lesser but still significant role.The mechanical properties of PL, FHL and FDB motor units were studied by noting twitch and tetanic tensions produced by electrical stimulation of single alpha axons, functionally isolated from the ventral root filaments. These data were compared to similar data reported by Olson and Swett (1966) for flexor digitorum longus (FDL). Our sample (114 PL, 60 FDB and 124 FHL units) disclosed that PL, FDB and FHL have units of uniformly fast contraction times (means 22, 27 and 27 msec respectively). PL units developed the most tetanic tension (3 to 160, mean 62 gm-wt) followed by FHL (2 to 87, mean 31 gm-wt) with FDB units producing very little tension (1 to 20, mean 6 gm-wt). Swett and Olson's FDL sample (108 units) showed tensions ranging from 0.3 to 100 gm-wt (mean 10 gm-wt).A division of labor among the four muscles is proposed. The large PL units are advantageous for forceful phasic inputs to the digits during the locomotion and in keeping with PL's additional role as an ankle exstensor. The low output forces of FDB units are optimal for discrete input to the digits during subtle adjustments of posture. We propose that the larger fast contracting units of FHL are used primarily for forceful digit flexions required in locomotion and for phasic protrusion of the claws while the predominately small and slow contracting units of FDL are used for sustained claw protrusion.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051370305
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