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Sawada H, Kurimoto S, Tokutake K, Saeki S, Hirata H. Optimal conditions for graft survival and reinnervation of denervated muscles after embryonic motoneuron transplantation into peripheral nerves undergoing Wallerian degeneration. J Tissue Eng Regen Med 2021; 15:763-775. [PMID: 34030216 DOI: 10.1002/term.3223] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2020] [Revised: 05/16/2021] [Accepted: 05/17/2021] [Indexed: 12/26/2022]
Abstract
Motoneuron transplantation into peripheral nerves undergoing Wallerian degeneration may have applications in treating diseases causing muscle paralysis. We investigated whether functional reinnervation of denervated muscle could be achieved by early or delayed transplantation after denervation. Adult rats were assigned to six groups with increasing denervation periods (0, 1, 4, 8, 12, and 24 weeks) before inoculation with culture medium containing (transplantation group) or lacking (surgical control group) dissociated embryonic motoneurons into the peroneal nerve. Electrophysiological and tissue analyses were performed 3 months after transplantation. Reinnervation of denervated muscles significantly increased relative muscle weight in the transplantation group compared with the surgical control group for denervation periods of 1 week (0.042% ± 0.0031% vs. 0.032% ± 0.0020%, respectively; p = 0.009), 4 weeks (0.044% ± 0.0069% vs. 0.026% ± 0.0045%, respectively; p = 0.0023), and 8 weeks (0.044% ± 0.0029% vs. 0.026% ± 0.0008%, respectively; p = 0.0023). The ratios of reinnervated muscle contractile forces to naïve muscle in the 0, 1, 4, 8, and 12 weeks transplantation groups were 3.79%, 18.99%, 8.05%, 6.30%, and 5.80%, respectively, indicating that these forces were sufficient for walking. The optimal implantation time for transplantation of motoneurons into the peripheral nerve was 1 week after nerve transection. However, the neurons transplanted 24 weeks after denervation survived and regenerated axons. These results indicated that there is time for preparing cells for transplantation in regenerative medicine and suggested that our method may be useful for paralysed muscles that are not expected to recover with current treatment.
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Affiliation(s)
- Hideyoshi Sawada
- Department of Hand Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Shigeru Kurimoto
- Department of Hand Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Katsuhiro Tokutake
- Department of Hand Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Sota Saeki
- Department of Hand Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Hitoshi Hirata
- Department of Hand Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan
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2
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Kryściak K, Celichowski J, Krutki P, Raikova R, Drzymała-Celichowska H. Factors contributing to sag in unfused tetanic contractions of fast motor units in rat medial gastrocnemius. J Electromyogr Kinesiol 2018; 44:70-77. [PMID: 30529806 DOI: 10.1016/j.jelekin.2018.11.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Revised: 11/20/2018] [Accepted: 11/28/2018] [Indexed: 11/15/2022] Open
Abstract
The sag phenomenon can be observed in fast motor units (MUs) as a transitional decline in force during unfused tetanic contractions; however, its mechanisms are poorly understood. The study aimed to identify in the rat muscle factors that contribute to sag in two types of fast MUs: fast fatigable (FF) and fast resistant to fatigue (FR). First, we performed mathematical decomposition of sagging tetanic contractions of FF and FR MUs into twitch-like responses to consecutive stimuli. This process indicated an increase in the amplitudes of a few initial responses (up to the 2nd-3rd for FF and up to the 2nd-7th for FR MUs), followed by a decrease in the amplitudes of later responses. In comparison to the first twitch, the relative increase in force amplitudes of the several subsequent decomposed responses was smaller, and their contraction and relaxation times were shorter for FF than for FR units, which corresponded to observed differences in their sag profiles. Additionally, after occlusion of the blood circulation, sag disappeared, but it reappeared after restoration of the blood supply. This indicates that the presence of sag depends on the proper circulation in the muscle.
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Affiliation(s)
- K Kryściak
- Department of Neurobiology, Poznan University of Physical Education, Poland.
| | - J Celichowski
- Department of Neurobiology, Poznan University of Physical Education, Poland
| | - P Krutki
- Department of Neurobiology, Poznan University of Physical Education, Poland
| | - R Raikova
- Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Sofia, Bulgaria
| | - H Drzymała-Celichowska
- Department of Neurobiology, Poznan University of Physical Education, Poland; Division of Biochemistry, Poznan University of Physical Education, Poland
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Liu Y, Grumbles RM, Thomas CK. Electrical stimulation of transplanted motoneurons improves motor unit formation. J Neurophysiol 2014; 112:660-70. [PMID: 24848463 DOI: 10.1152/jn.00806.2013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Motoneurons die following spinal cord trauma and with neurological disease. Intact axons reinnervate nearby muscle fibers to compensate for the death of motoneurons, but when an entire motoneuron pool dies, there is complete denervation. To reduce denervation atrophy, we have reinnervated muscles in Fisher rats from local transplants of embryonic motoneurons in peripheral nerve. Since growth of axons from embryonic neurons is activity dependent, our aim was to test whether brief electrical stimulation of the neurons immediately after transplantation altered motor unit numbers and muscle properties 10 wk later. All surgical procedures and recordings were done in anesthetized animals. The muscle consequences of motoneuron death were mimicked by unilateral sciatic nerve section. One week later, 200,000 embryonic day 14 and 15 ventral spinal cord cells, purified for motoneurons, were injected into the tibial nerve 10-15 mm from the gastrocnemii muscles as the only neuron source for muscle reinnervation. The cells were stimulated immediately after transplantation for up to 1 h using protocols designed to examine differential effects due to pulse number, stimulation frequency, pattern, and duration. Electrical stimulation that included short rests and lasted for 1 h resulted in higher motor unit counts. Muscles with higher motor unit counts had more reinnervated fibers and were stronger. Denervated muscles had to be stimulated directly to evoke contractions. These results show that brief electrical stimulation of embryonic neurons, in vivo, has long-term effects on motor unit formation and muscle force. This muscle reinnervation provides the opportunity to use patterned electrical stimulation to produce functional movements.
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Affiliation(s)
- Yang Liu
- The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine, Miami, Florida; and
| | - Robert M Grumbles
- The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine, Miami, Florida; and
| | - Christine K Thomas
- The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine, Miami, Florida; and Department of Neurological Surgery, Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, Florida
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McNulty PA, Macefield VG. Intraneural microstimulation of motor axons in the study of human single motor units. Muscle Nerve 2005; 32:119-39. [PMID: 15880485 DOI: 10.1002/mus.20324] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Single motor unit activity has been studied in depth since the first intramuscular electrodes were developed more than 70 years ago. Many techniques have been combined or used in isolation since then. Intraneural motor axon microstimulation allows the detailed study of single motor units in awake human subjects in a manner most analogous to that used in reduced animal preparations. A microelectrode, inserted percutaneously into a peripheral nerve, stimulates the axon of a single alpha-motoneuron at a site remote from the contracting muscle, allowing detailed analyses of the contractile properties of a single motor unit in an otherwise quiescent muscle, that is, without interference of simultaneously active motor units or the presence of an electrode within the muscle. The methods and results obtained using this technique are described and compared to those of other studies of single motor units in human subjects. Differences have been found between human and animal motor units and between motor units of various muscles. Studying human and animal motor units using an analogous technique provides insight into the interpretation of human data when results differ from animal data, and when human motor units cannot be examined in the same way, or at a similar level of detail, as animal motor units.
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Affiliation(s)
- Penelope A McNulty
- Prince of Wales Medical Research Institute and University of New South Wales, Sydney, NSW, Australia.
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Fuglevand AJ, Macefield VG, Bigland-Ritchie B. Force-frequency and fatigue properties of motor units in muscles that control digits of the human hand. J Neurophysiol 1999; 81:1718-29. [PMID: 10200207 DOI: 10.1152/jn.1999.81.4.1718] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Modulation of motor unit activation rate is a fundamental process by which the mammalian nervous system encodes muscle force. To identify how rate coding of force may change as a consequence of fatigue, intraneural microstimulation of motor axons was used to elicit twitch and force-frequency responses before and after 2 min of intermittent stimulation (40-Hz train for 330 ms, 1 train/s) in single motor units of human long finger flexor muscles and intrinsic hand muscles. Before fatigue, two groups of units could be distinguished based on the stimulus frequency needed to elicit half-maximal force; group 1 (n = 8) required 9.1 +/- 0.5 Hz (means +/- SD), and group 2 (n = 5) required 15.5 +/- 1.1 Hz. Twitch contraction times were significantly different between these two groups (group 1 = 66. 5 ms; group 2 = 45.9 ms). Overall 18% of the units were fatigue resistant [fatigue index (FI) > 0.75], 64% had intermediate fatigue sensitivity (0.25 </= FI </= 0.75), and 18% were fatigable (FI < 0. 25). However, fatigability and tetanic force were not significantly different among groups. Therefore unlike findings in some other mammals, fast-contracting motor units were neither stronger nor more susceptible to fatigue than slowly contracting units. Fatigue, however, was found to be greatest in those units that initially exerted the largest forces. Despite significant slowing of contractile responses, fatigue caused the force-frequency relation to become displaced toward higher frequencies (44 +/- 41% increase in frequency for half-maximal force). Moreover, the greatest shift in the force-frequency relation occurred among those units exhibiting the largest force loss. A selective deficit in force at low frequencies of stimulation persisted for several minutes after the fatigue task. Overall, these findings suggest that with fatigue higher activation rates must be delivered to motor units to maintain the same relative level of force. Questions regarding classification of motor units and possible mechanisms by which fatigue-related slowing might coexist with a shift in the force-frequency curve toward higher frequencies are discussed.
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Affiliation(s)
- A J Fuglevand
- John B. Pierce Laboratory, New Haven, Connecticut 06519, USA.
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Bigland-Ritchie B, Fuglevand AJ, Thomas CK. Contractile Properties of Human Motor Units: Is Man a Gat? Neuroscientist 1998. [DOI: 10.1177/107385849800400413] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A major goal in neuroscience is to understand how the CNS controls posture and movement in humans. This requires an understanding of individual human motor unit properties and how they interact within the muscle to perform different tasks. This article describes differences and similarities between the contractile properties of human motor units and those of the cat prototype medial gastrocnemius (MG) muscle, on which so many studies have been conducted. The article describes the methods available for measuring human motor unit properties and their limitations, and it discusses how far the behavior of whole muscles can be predicted from their histochemistry. It questions the extent to which human motor units conform to the conventional criteria by which S (slow, fatigue resistant), FR (fast but fatigue resistant) and FF (fast, fatigable) unit types are usually classified. An important difference between human and cat MG data is that weak human motor units are not necessarily slow, nor strong ones fast; that is, generally, human unit force is not correlated with contractile speed. Also, unlike cat MG, the few human muscles studied so far contain few if any FF units but a high proportion of units with intermediate fatigue resistance (Flnt). These apparently aberrant human properties, however, are also found in other cat and rat muscles. Thus, cat MG may not be the best model for motor unit behavior generally. Finally, the influence of human motor unit properties on force output by recruitment and/or rate coding is discussed.
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Tension distribution of single motor units in multitendoned muscles: comparison of a homologous digit muscle in cats and monkeys. J Neurosci 1997. [PMID: 9030632 DOI: 10.1523/jneurosci.17-05-01734.1997] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
To determine whether single motor units (MUs) in multitendoned muscles distribute tension to multiple tendons or instead focus tension selectively on a single tendon, we examined the distribution of tension generated by single MUs in the cat extensor digitorum lateralis (EDLat), and in its macaque homolog, the extensor digiti quarti et quinti (ED45). General properties of MUs (maximal tetanic tension, axonal conduction velocity, and twitch rise time) were similar in these muscles to those reported for other limb muscles in cats and monkeys. Most cat EDLat MUs were found to exert tension rather selectively on one of the three tendons of the muscle. Fast fatigable MUs were slightly but significantly more selective than fast fatigue-resistant and slow MUs. In contrast, and contrary to expectation, the macaque ED45 contained a lower proportion of MUs that exerted tension selectively on one of the two tendons of the muscle, and a higher proportion of relatively nonselective MUs. These findings suggest that the cat EDLat may consist of three functional subdivisions, each acting preferentially on a different tendon, whereas the macaque ED45 is more likely to function as a single multitendoned muscle.
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Botterman BR. Task-dependent nature of fatigue in single motor units. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1995; 384:351-60. [PMID: 8585464 DOI: 10.1007/978-1-4899-1016-5_28] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The loss of force production during sustained activity presents the CNS a unique control problem. Different tasks stress the neuromuscular system at different sites and times, and involve different cellular mechanisms. The functional organization of muscles and their motor units has evolved to avoid fatigue processes that impair motor performance. The purpose of this brief review is to examine the fatigue properties of type-identified motor units and to speculate what these properties reveal about the organization and control of muscle.
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Affiliation(s)
- B R Botterman
- Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas 75235, USA
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Fritz N, Schmidt C, Yamaguchi T. Biochemical organization of single motor units in two multi-tendoned muscles of the cat distal forelimb. Exp Brain Res 1992; 88:411-21. [PMID: 1577113 DOI: 10.1007/bf02259116] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
In anesthetized cats single motor units (MUs) of the extensor carpi ulnaris (ECU) and extensor digitorum communis (EDC) muscles were selectively activated by stimulation of cervical ventral root filaments. The distribution of force developed by single MUs at the four distal tendons of the EDC muscle and at three portions of the distal tendon of the ECU muscle was analysed. In general, single MUs of both muscles distributed force over all tendons in a unimodal pattern, with the maximal force levels generated at one specific tendon which was termed the best-tendon. Distributions of force were quantitatively described by a parameter representing the mean direction of force output (output-index) and a further one representing the dispersion of force over the distal tendons (divergence). Generally, these parameters and the best-tendon remained stable when a MU was stimulated at different frequencies, but varied from MU to MU. Despite the general stability of the force distribution, slight systematic changes were regularly found in EDC MUs, when they developed a higher amount of force due to a higher frequency of stimulation: the relative amount of force at the best-tendon increased; e.g. the MUs got more selective for the best-tendon. These changes were partly due to overcoming mechanical cross-coupling between neighbouring compartments of the EDC muscle. Such changes of force distribution were only found in a part of the ECU MUs; other ECU MUs did not change their force distribution at all or became less selective for the best-tendon. The phenomenon that MUs of multi-tendoned muscles distribute their force output to the distal tendons in specific patterns is probably due to mechanical partitioning of the parent muscles: the localization of spatial territories of MUs within different anatomical muscle compartments should correspond to the best-tendon. Complex mechanisms allowing passive transmission of force from limited territories along the transverse axis of both muscles must be assumed in order to explain why most MUs act on all tendons and why force distributions change with increasing stimulus frequency. In addition, specific relations between unit type and force distributions were found within both muscles. Fatigue-resistant EDC MUs have broader force distributions than fatigue-sensitive EDC MUs and slow ECU MUs were found to act predominantly on the most ulnar part of the distal tendon. These biomechanical properties of MUs are discussed as supporting the specific functions of the respective muscles.
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Affiliation(s)
- N Fritz
- Physiologisches Institut, Universität München, Federal Republic of Germany
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Fritz N, Schmidt C. Contractile properties of single motor units in two multi-tendoned muscles of the cat distal forelimb. Exp Brain Res 1992; 88:401-10. [PMID: 1577112 DOI: 10.1007/bf02259115] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The contractile properties of motor units (MUs) in two multi-tendoned forelimb muscles were investigated. In anesthetized cats single MUs of the extensor carpi ulnaris (ECU) and extensor digitorum communis (EDC) muscles were selectively activated by stimulation of cervical ventral root filaments. MUs were characterized by various tests including single twitches, series of tetanic contractions providing a tension-frequency relation and a fatigue test. They were classified by the parameters contraction time (CT, time-to-peak within unpotentiated single twitches) and fatigue-index (RB, according to Burke). The ECU muscle is composed of 38% type FR MUs (fast, fatigue-sensitive; CT less than 38 ms; RB less than 0.5), 35% type FR MUs (CT less than 38 ms, RB greater than 0.5) and 27% type S MUs (slow; CT greater than 38 ms, RB greater than 0.5). 46% of the EDC MUs were classified as FF (RB less than or equal to 0.25), 29% as FI (fast, intermediately fatiguable; 0.25 less than RB less than 0.75) and 25% as FR/S (fatigue-resistant, fast or slow; RB greater than or equal to 0.75). The latter group was devised since most MUs appeared as fast and the unequivocal presence of slow MUs could neither be demonstrated nor excluded. Normalized tension-frequency relations of fast ECU and EDC MUs were nearly identical and similar to those reported for fast MUs of other muscles. In contrast to this, the tension-frequency relation of slow ECU MUs has a different shape supporting the use of this function to distinguish fast from slow MUs. The distribution of different types of MUs is discussed with regard to the structure and function of the parent muscles and in relation to hindlimb muscles of comparable architecture. As revealed by comparison to EMG data gained in behaving animals (Fritz et al. 1985; Hoffmann et al. 1986, Botterman et al. 1985), the three muscles of the cat distal forelimb investigated so far seem to be adapted to different tasks: the EDC to rapid movements with a high proportion of type FF MUs, flexor carpi radialis to sustained contractions during the body support with a high proportion of fatigue-resistant MUs; the ECU which changes synergism between both muscles has an intermediate composition.
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Affiliation(s)
- N Fritz
- Physiologisches Institut, Universität München, Federal Republic of Germany
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Gordon DA, Enoka RM, Stuart DG. Motor-unit force potentiation in adult cats during a standard fatigue test. J Physiol 1990; 421:569-82. [PMID: 2348403 PMCID: PMC1190102 DOI: 10.1113/jphysiol.1990.sp017962] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
1. The purpose of this study was to examine the time course of tetanic force during a standard fatigue test and to distinguish between the appearance of potentiation and fatigue among the four motor-unit types of a cat hindlimb muscle. 2. Motor units of the tibialis posterior muscle in the adult cat were assigned to four categories (i.e. types S, FR, FI, FF) based on conventional criteria (Burke, Levine, Tsairis & Zajac, 1973). The mean (+/- S.D.) time course of peak force was constructed for each motor-unit type and, within each type, for those units that potentiated (a greater than 3% increase in peak force compared to the initial value) and those that did not potentiate. 3. The average time courses of force differed between motor-unit types. There was, however, considerable variability within each motor-unit type. For the same relative force output, the forces exerted by slow-twitch units were less variable than those exerted by fast-twitch units. In addition, the variability among slow-twitch units was relatively constant during the fatigue test while variability among fast-twitch units either increased or decreased with time. 4. For a given motor-unit type, the average time course of force did not depend on whether force in each tetanus was expressed as a peak value, an average peak value, or a force-time integral. 5. Some motor units within each type exhibited potentiation. Most of the variability in the time course of the peak force for each motor-unit type could be accounted for by the potentiating units. Motor units that exhibited only force decline (i.e. fatigue), regardless of unit type, had less variable time courses of peak force. Since potentiation was transient in some unit types, it was assumed that at least two opposing processes (i.e. fatigue and potentiation) occurred simultaneously in these units (see also, Krarup, 1981; Rankin, Enoka, Volz & Stuart, 1988; Garner, Hicks & McComas, 1989). 6. It is concluded that the expression of force potentiation throughout a fatiguing regimen is variable among motor units and that this is not related to conventional motor-unit types. This dissociation suggests that the mechanisms that form the basis for the conventional distinction between motor-unit types are different from those which lead to force potentiation.
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Affiliation(s)
- D A Gordon
- Department of Physiology, University of Arizona, Tucson 85724
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Clamann HP, Schelhorn TB. Nonlinear force addition of newly recruited motor units in the cat hindlimb. Muscle Nerve 1988; 11:1079-89. [PMID: 3185603 DOI: 10.1002/mus.880111012] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The present experiments were designed to examine the interaction of simultaneously active motor units. Pairs of medial gastrocnemius (MG) or soleus (Sol) units were stimulated individually and then together with constant frequency trains of 5-40 pulses per second. Stimulating two units asynchronously produced a smoother contraction than synchronous stimulation, but rarely a force increase. This contrasts with similar experiments on whole muscle bundles. A force increase may require that adjacent muscle fibers be active. The combined force of two motor units exceeded the algebraic sum of their separate forces by 12% in MG and 5% in Sol on average. The force a unit could sustain after a second unit fell silent was greater than the force the unit produced alone (21% in MG and 8% in Sol). We conclude that motor units produce more force when interacting than alone. During derecruitment the units remaining active produce more force than when recruited.
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Affiliation(s)
- H P Clamann
- Department of Physiology, Medical College of Virginia, Richmond 23298
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Hamm TM, Nemeth PM, Solanki L, Gordon DA, Reinking RM, Stuart DG. Association between biochemical and physiological properties in single motor units. Muscle Nerve 1988; 11:245-54. [PMID: 3352659 DOI: 10.1002/mus.880110309] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Motor units from the cat tibialis posterior muscle were examined for an association between physiological and biochemical properties. Functionally isolated motor units were categorized on the basis of their physiological properties. This was followed by quantitative microbiochemical analysis of single muscle fibers from each unit, identified in cross sections using the glycogen-depletion method. The activities of malate dehydrogenase and beta-hydroxyacyl-CoA dehydrogenase distinguished between fatigable (type FF) and fatigue-resistant (types FR and S) units. The activities of both lactate dehydrogenase and adenylokinase were higher in fast- than in slow-contracting units. Cluster analyses, based on both physiological and biochemical properties or on biochemical properties alone, produced groupings identical to types FF, FR, and S. The association between physiological and biochemical properties substantiates the idea that biochemically distinct groups of motor units correspond to physiologically identifiable groups.
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Affiliation(s)
- T M Hamm
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ 85013
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Glenn LL, Whitney JF. Contraction properties and motor nucleus morphology of the two heads of the cat flexor carpi ulnaris muscle. J Morphol 1987; 191:17-23. [PMID: 3546705 DOI: 10.1002/jmor.1051910103] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Previous studies have examined the isometric contraction properties of the two heads of the cat flexor carpi ulnaris acting as a single unit. In this study, the contraction properties and fiber architecture of each head of the flexor carpi ulnaris were determined separately and related to previous reports on the histochemical characteristics of this muscle. The morphology of retrograde-labeled motor nuclei for the two heads of the muscle was also examined. The humeral head had a significantly longer contraction time (48 msec) than the ulnar head (36 msec) as well as a significantly lower tetanic fusion frequency (28 Hz vs. 35 Hz). The maximum tetanic tension per gram of muscle tissue was 71% greater in the ulnar head. Motoneurons of the flexor carpi ulnaris formed a column 12 mm long and 0.5 mm wide in the center of the ventral grey in spinal segments C8 and T1. The ulnar head had alpha-motoneurons with greater soma diameters than those in the humeral head. The smaller soma diameter, slower contraction time, and weaker contraction in the humeral head correlate with the preponderance of oxidative-metabolic muscle fiber types found in the humeral head by other workers. These correlations suggest that the humeral head plays a major role in maintaining a sustained antigravity tension that prevents the wrist from buckling during standing.
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