Rank order of motoneurons within a pool: law of combination.

Henneman, Elwood; Clamann, H. P.; Gillies, John; Skinner, R.D.

doi:10.1152/jn.1974.37.6.1338

Cited by 464 publications

(161 citation statements)

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“…A similar recruitment order exists for the excitatory interneurons that drive larval zebrafish swimming, but, interestingly, the opposite applies to the population of commissural inhibitory interneurons, with dorsal ones active at the lower frequencies. These authors showed that there is no particular correlation between soma size and recruitment order, seemingly at odds with Henneman's size principle (25), but input resistance and recruitment order are correlated, as we have also found.…”

Section: Discussioncontrasting

confidence: 44%

“…This suggests that, although there is no obvious dorsoventral spatial map in the spinal cord coding peripheral innervation, the innervation fields are indeed segregated into restricted areas of each muscle block. In addition, cell-body diameters spanned a relatively narrow range, ruling out the possibility that different regions of the myotome might be served by MNs with separate thresholds based exclusively on the size principle (25). An elegant recent study in zebrafish larvae on how neurons are recruited during different speeds of locomotion revealed a dorsoventral ordering of MNs (10), an organization that persists in the adult (26).…”

Section: Discussionmentioning

confidence: 99%

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Development of a spinal locomotor rheostat

Zhang

Issberner

Sillar

2011

Proc. Natl. Acad. Sci. U.S.A.

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Locomotion in immature animals is often inflexible, but gradually acquires versatility to enable animals to maneuver efficiently through their environment. Locomotor activity in adults is produced by complex spinal cord networks that develop from simpler precursors. How does complexity and plasticity emerge during development to bestow flexibility upon motor behavior? And how does this complexity map onto the peripheral innervation fields of motorneurons during development? We show in postembryonic Xenopus laevis frog tadpoles that swim motorneurons initially form a homogenous pool discharging single action potential per swim cycle and innervating most of the dorsoventral extent of the swimming muscles. However, during early larval life, in the prelude to a free-swimming existence, the innervation fields of motorneurons become restricted to a more limited sector of each muscle block, with individual motorneurons reaching predominantly ventral, medial, or dorsal regions. Larval motorneurons then can also discharge multiple action potentials in each cycle of swimming and differentiate in terms of their firing reliability during swimming into relatively high-, medium-, or low-probability members. Many motorneurons fall silent during swimming but can be recruited with increasing locomotor frequency and intensity. Each region of the myotome is served by motorneurons spanning the full range of firing probabilities. This unfolding developmental plan, which occurs in the absence of movement, probably equips the organism with the neuronal substrate to bend, pitch, roll, and accelerate during swimming in ways that will be important for survival during the period of free-swimming larval life that ensues.motor system | central pattern generator | ontogeny A dult vertebrates navigate through their environment with incredible agility and flexibility, a feature of locomotory behavior that is often critical for survival. During locomotion, sensory information interacts with central pattern generator (CPG) networks in the spinal cord, which in turn provide command signals to motorneurons (MNs) to sequence and guide movements appropriately (1). CPGs develop before locomotion is possible (2-4). Initially, however, the output of immature CPGs lacks the precision and flexibility that typifies adult locomotion. Therefore, postembryonic development must involve a period during which the central motor control circuitry is modified to accommodate the behavioral requirements of later stages. Much is known about the molecular mechanisms responsible for the differentiation of neuronal components of the motor system, motor axon trajectories, and innervation patterns (5-7). However, how this links to the functional development of these components has not been fully resolved, although there is ample evidence that activity itself is influential as a developmental signal (8, 9).Recent evidence has revealed a topographic recruitment order for dorsoventrally arranged spinal premotor interneurons and MNs during changes in swimming speed in larval ...

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Section: Discussioncontrasting

confidence: 44%

Section: Discussionmentioning

confidence: 99%

Development of a spinal locomotor rheostat

Zhang

Issberner

Sillar

2011

Proc. Natl. Acad. Sci. U.S.A.

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“…Because there is a one-to-one correspondence between firing of a motoneuron and generation of action potentials in the muscle fibers that it innervates, muscle responses are a surrogate measure of motoneuron responses. There is graded recruitment of motoneurons of increasing size by increasing synaptic input Henneman et al, 1974). Furthermore, corticospinal synapses onto motoneurons lack classical presynaptic inhibition (Nielsen and Petersen, 1994;Jackson et al, 2006).…”

Section: Test Stimulationmentioning

confidence: 99%

Voluntary Motor Output Is Altered by Spike-Timing-Dependent Changes in the Human Corticospinal Pathway

Taylor¹,

Martin²

2009

J. Neurosci.

129

167

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Repeated pairs of timed presynaptic and postsynaptic potentials cause lasting changes in efficacy of transmission at many synapses. The corticospinal tract is the major pathway controlling voluntary movement in humans, and corticospinal neurons have monosynaptic connections to motoneurons of many muscles. We hypothesized that corticospinal transmission in humans could be altered by delivering, to the corticospinal-motoneuronal synapses, timed pairs of presynaptic volleys (produced by cortical stimulation) and antidromic postsynaptic volleys (by peripheral nerve stimulation). To test corticospinal transmission, electrical cervicomedullary stimuli evoked motor responses [cervicomedullary motor-evoked potentials (CMEPs)] in biceps brachii before and for 1 h after conditioning with 50 paired cortical and peripheral nerve stimuli. Seven interstimulus intervals (ISIs) of conditioning stimulus pairs were tested on different days. With one ISI (ϩ3 ms; cortical before peripheral nerve stimulation), CMEPs were significantly increased in size by 33 Ϯ 30% (mean Ϯ SD; n ϭ 7) from 4 until 32 min after conditioning. With two other ISIs (Ϫ13 ms, ϩ22 ms), CMEPs were decreased from ϳ30 until 60 min after conditioning (by 25 Ϯ 23% and 27 Ϯ 32%; n ϭ 8). The remaining ISIs produced no changes. In a second study, subjects performed weak bilateral voluntary elbow flexion contractions before and after conditioning of the right elbow flexors. Conditioning ISIs that increased or decreased CMEPs similarly increased or decreased voluntary force and EMG on the right. Thus, depending on their timing, repeated paired stimuli can potentiate or depress corticospinal transmission, and these changes are functionally relevant. We suggest that bidirectional spike-timing-dependent plasticity can be induced at corticospinal-motoneuronal synapses and can influence voluntary motor output.

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“…No entanto, é fato que, se o objetivo for melhorar ou manter o desenvolvimento da força, é necessário manter, durante o exercício, a mais elevada ou a máxima velocidade de execução [62][63][64][65][66][67][68][69] . Esta forma de trabalho é baseada em dois critérios 70 : a) efeito direto sobre a melhora da força [62][63]66,[71][72] ; b) associação da intensidade da carga sobre o tipo de fibra recrutada, principalmente as fibras de contração rápida [73][74][75][76] e as respostas adaptativas correspondentes 64,68,72,[77][78][79] .…”

Section: Comportamento Mecânico Durante O Trabalho De Repetição Da Forçaunclassified

Capacidade de repetição da força: efeito das recuperações interséries

Silva-Grigoletto

Valverde-Esteve²,

Brito

et al. 2013

Rev. bras. educ. fís. esporte

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ResumoPara estimular uma melhor resposta adaptativa aos objetivos específi cos do treinamento de força, a sobrecarga progressiva é a estratégia mais utilizada. A quantidade de trabalho realizada no treino com sobrecarga é aspecto determinante para a melhora do rendimento. Porém, a sobrecarga resulta em desgaste muscular mecânico, o que desencadeia o aparecimento da fadiga. A fadiga é proporcional à característica das cargas (volume, intensidade e recuperação). Neste sentido, a manipulação do intervalo de recuperação é fundamental para evitar a fadiga excessiva, possibilitando uma menor infl uência do desgaste mecânico na execução da série, auxiliando, assim, na manutenção do volume e intensidade adequadas. A estratégia frequentemente empregada é aumentar o tempo de recuperação entre séries. No entanto, evidências existentes na literatura científi ca indicam que a maneira mais efi ciente de conseguir estes objetivos (diminuir a fadiga e manter o volume de treinamento necessário) é incorporar curtas recuperações no interior da série ("intra-set" ou ISR). Pode-se alcançar tal objetivo, incorporando a recuperação entre repetições ("inter-repetition rest" ou IRR), ou a cada bloco de repetições (agrupamento ou "cluster"). Estas estratégias metodológicas permitem conservar as características mecânicas do gesto (velocidade, força e potência) durante as repetições por série. PALAVRAS-CHAVE: Treinamento de resistência; Força muscular; Contração muscular; Fadiga muscular.Diversas modalidades esportivas, especialmente aquelas de caráter cíclico (ciclismo de estrada, remo, natação, etc.), o desempenho está associado à capacidade de repetir eficientemente um gesto motor que, frequentemente, demanda elevada quantidade de força 1 . Assim, solicita-se no treino a repetição de ações musculares de elevada intensidade, cuja magnitude pode variar de acordo com as características da atividade, o trabalho a se desenvolver, ou o objetivo almejado no treinamento planejado.Volume (total e parcial), intensidade, descanso e a ordem de realização dos exercícios são as variáveis de treinamento que, habitualmente, são manipuladas e ajustadas para conseguir os objetivos almejados 2 . Estes aspectos são aqueles que melhor definem e caracterizam a magnitude das cargas de treinamento. Entende-se como carga de trabalho, a variável descritiva que caracteriza os esforços ou estímulos exigidos ao atleta durante a realização do exercício ou sessão de treinamento. As cargas consideradas ideais variam de acordo com a contração muscular desenvolvida (concêntricas, excêntricas, isométricas, controladas ou explosivas) e a utilização de exercícios com perfil mecânico distinto que envolvam uma ou mais articulações.Após considerar todos os aspectos determinantes do desempenho, os treinadores planificam seus protocolos de trabalho maximizando, assim, a busca por melhor resposta adaptativa, ou as respostas que resultem em melhor benefício ao rendimento do atleta. Ou seja, estabelecem estratégias de treinamento com o objetivo de adaptar-se cada vez mais as carac...

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Rank order of motoneurons within a pool: law of combination.

Cited by 464 publications

References 0 publications

Development of a spinal locomotor rheostat

Development of a spinal locomotor rheostat

Voluntary Motor Output Is Altered by Spike-Timing-Dependent Changes in the Human Corticospinal Pathway

Capacidade de repetição da força: efeito das recuperações interséries

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