Motor Unit Distribution of the Dorsal Longitudinal Flight Muscles in Locusts

1963 ◽  
Vol 40 (1) ◽  
pp. 123-136
Author(s):  
A. C. NEVILLE
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Average Diameter ◽  
Fast Response ◽  
Muscle Fibres ◽  
Recurrent Nerve ◽  
Motor Axons ◽  
Flight Muscles ◽  
Large Motor ◽  
Longitudinal Muscles

1. The peripheral pathways of the ‘fast’ motor fibres to the locust dorsal longitudinal flight muscles are described at the single unit level, from electrophysiological and histological studies. This is summarized in a diagram on Pl. 1. 2. Both pterothoracic dorsal longitudinal muscles consist of five anatomically distinct motor units, arranged in layers from dorsal to ventral. Each of the four more ventral units of both muscles receives a motor axon from the segment in front via the recurrent nerve, whereas the uppermost motor unit is innervated in each case from the segment containing the muscle. The motor units are nearly equal both in size and capability for work. 3. Each of the five ‘fast’ motor axons innervates one topographically distinct bundle of muscle fibres. There is no overlap between muscle motor units. 4. Even within a single muscle, motor units are capable of vibrating at independent frequencies. This indicates that the coupling of units which occurs during flight is neither structurally nor functionally rigid. 5. With respect to peripheral features, the motor units within each dorsal longitudinal muscle are designed for fast response which improves the synchronization when the relevant neurons fire simultaneously (large motor axons, 15-25 µ in average diameter with high propagation velocity, 8 m./sec. at flight temperature). 6. It is suggested that a tonic motor output, containing at least three units, which was recorded from mesothoracic nerve IBa, travels to the small lateral dorsal muscles.

scholarly journals Chromatophore Motor Units in Eledone Cirrhosa (Cephalopoda: Octopoda)

1985 ◽  
Vol 117 (1) ◽  
pp. 415-431 ◽  
Author(s):  
F. DUBAS ◽  
P.R. BOYLE
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Video Camera ◽  
Muscle Fibres ◽  
Motor Axons ◽  
Individual Muscle ◽  
Nerve Bundles ◽  
Suction Electrode ◽  
Electrical Impulses

Innervation of chromatophore muscles of the octopus Eledone cirrhosa was investigated by stimulating nerve bundles in the skin with a suction electrode and monitoring chromatophore movements with a photo-cell or a video camera. Attention was focused on the organization of the chromatophore muscle fibres into motor units. Individual muscle fibres respond to single electrical impulses with twitch-like contractions that do not facilitate with repetition, but summate to a smooth tetanus at about 10–15 Hz. At tetanic frequency, the degree of expansion of single chromatophores is always maximal. However, the number of expanded chromatophores can be graded by variations of either the stimulus voltage or frequency. Individual chromatophores and probably individual muscle fibres are part of several motor units. Chromatophores forming a given motor unit are found among chromatophores served by other motor axons. The motor units apparently form precise parts of natural patterning.

scholarly journals Neuromuscular organization of avian flight muscle: architecture of single muscle fibres in muscle units of the pectoralis (pars thoracicus) of pigeon (Columba livia)

1999 ◽  
Vol 354 (1385) ◽  
pp. 917-925 ◽  
Author(s):  
A. J. Sokoloff ◽  
G. E. Goslow
Keyword(s):  
Motor Unit ◽  
Cross Sections ◽  
Unit Length ◽  
Muscle Length ◽  
Motor Units ◽  
Columba Livia ◽  
Muscle Fibres ◽  
Cross Sectional ◽  
Total Length ◽  
Fast Twitch

The M. pectoralis (pars thoracicus) of pigeons ( Columba livia ) is comprised of short muscle fibres that do not extend from muscle origin to insertion but overlap ‘in-series’. Individual pectoralis motor units are limited in territory to a portion of muscle length and are comprised of either fast twitch, oxidative and glycolytic fibres (FOG) or fast twitch and glycolytic fibres (FG). FOG fibres make up 88 to 90% of the total muscle population and have a mean diameter one-half of that of the relatively large FG fibres. Here we report on the organization of individual fibres identified in six muscle units depleted of glycogen, three comprised of FOG fibres and three comprised of FG fibres. For each motor unit, fibre counts revealed unequal numbers of depleted fibres in different unit cross-sections. We traced individual fibres in one unit comprised of FOG fibres and a second comprised of FG fibres. Six fibres from a FOG unit (total length 15.45 mm) ranged from 10.11 to 11.82 mm in length and averaged (±s.d.) 10.74±0.79 mm. All originated bluntly (en mass) from a fascicle near the proximal end of the muscle unit and all terminated intramuscularly. Five of these ended in a taper and one ended bluntly. Fibres coursed on average for 70% of the muscle unit length. Six fibres from a FG unit (total length 34.76 mm) ranged from 8.97 to 18.38 mm in length and averaged 15.32 ±3.75 mm. All originated bluntly and terminated intramuscularly; one of these ended in a taper and five ended bluntly. Fibres coursed on average for 44% of the muscle unit length. Because fibres of individual muscle units do not extend the whole muscle unit territory, the effective cross-sectional area changes along the motor unit length. These non-uniformities in the distribution of fibres within a muscle unit emphasize that the functional interactions within and between motor units are complex.

The motor unit

2016 ◽  
Author(s):  
David Burke ◽  
James Howells
Keyword(s):  
Motor Unit ◽  
Neuromuscular Junctions ◽  
Discharge Rate ◽  
Motor Units ◽  
Motor Unit Action Potential ◽  
Muscle Fibres ◽  
Reflex Gain ◽  
Active Motor ◽  
Motor Unit Action ◽  
Fast Twitch

The motor unit represent the final output of the motor system. Each consists of a motoneuron, its axon, neuromuscular junctions, and muscle fibres innervated by that axon. The discharge of a motor unit can be followed by recording its electromyographic signature, the motor unit action potential. Motoneurons are not passive responders to the excitatory and inhibitory influences on them from descending and segmental sources. Their properties can change, e.g. due to descending monoaminergic pathways, which can alter their responses to other inputs (changing ‘reflex gain’). Contraction strength depends on the number of active motor units, their discharge rate, and whether the innervated muscle fibres are slow-twitch producing low force, but resistant to fatigue, fast-twitch producing more force, but susceptible to fatigue, or intermediate fast-twitch fatigue-resistant. These properties are imposed by the parent motoneurons, and the innervated muscle fibres have different histochemical profiles (oxidative, glycolytic, or oxidative-glycolytic, respectively).

Interspike interval relationship among flight muscle fibres in Drosophila

1980 ◽  
Vol 87 (1) ◽  
pp. 137-147 ◽  
Author(s):  
J. H. Koenig ◽  
K. Ikeda
Keyword(s):  
Interspike Interval ◽  
Flight Muscle ◽  
Motor Units ◽  
Muscle Fibres ◽  
Interspike Intervals ◽  
Neural Input ◽  
Flight Muscles ◽  
Bilateral Pair ◽  
Left And Right ◽  
Driving Source

Simultaneous intracellular recordings were made from the 10 motor units (12 fibres) comprising the bilateral pair of dorsal longitudinal flight muscles in Drosophila melanogaster while in stationary flight. The neural input which commonly drives these units was characterized by observing the influence which this input has on the interspike intervals of the various units. It was observed that the intervals of these units (both ipsilateral and contralateral), when considered collectively (that is, as a series of successively occurring intervals without regard for which unit represents which interval), fluctuate in a serially correlated manner. These interval fluctuations collectively define a fluctuation of complex waveform. The characteristics of this waveform suggest that two (or more) oscillating inputs are involved in commonly driving these units. In addition, a coupling in frequency and timing was observed between certain pairs of ipsilateral units, as well as between the units of one side relative to those of the other side. This coupling suggests that the neural pathway leading from the oscillating driving source might diverge, first to left and right sides, and then at a more peripheral level into three separate pathways, one leading to units 1 and 2, another to units 3 and 4, and a third to unit 5/6.

scholarly journals Numbers and contraction-values of individual motor-units examined in some muscles of the limb

1930 ◽  
Vol 106 (745) ◽  
pp. 326-357 ◽  
Keyword(s):  
Motor Unit ◽  
Motor Nerve ◽  
Motor Units ◽  
Muscle Fibres ◽  
Total Potential ◽  
Quantitative Statement ◽  
Effector Organ ◽  
Quantum Reaction ◽  
The Individual ◽  
Individual Motor

“The muscle with its nerve may be thought of as an additive assemblage of motor-units, meaning by motor-unit an individual motor nerve-fibre with the bunch” [or “squad” (E. L. Porter, 1929 (1))]“ of muscle-fibres it activates.” (2) The components of such a unit can claim sufficiently close and sufficiently analysed interrelation to warrant acceptance for many purposes as a single functional entity. In application to reflexes, the unit thus resulting favours brevity and directness of quantitative statement. Its correspondence with a so-to-say quantum reaction, which forms the basis, by combinations temporal and numerical, of all grading of the muscle as effector-organ, fits it for measuring that grading. It is, moreover, applicable centrally as well as peripherally, since the motor-units active number the motoneurones discharging. Such mensuration, the total of the pool of motoneurones being known, evaluates per se the given reaction in terms of the total potential reaction. 1. Contraction-Tension of the Individual Motor-Unit. In the following experiments it was therefore sought to find the physiological size of the motor-unit, i. e. , to measure its contraction-tension. The muscles examined (cat) have been gastrocnemius (median head) soleus, semitendinosus, extensor longus digitorum , and, less fully, tibialis anticus and crureus.

Motor unit area in a rat muscle

1961 ◽  
Vol 200 (5) ◽  
pp. 944-946 ◽  
Author(s):  
Forbes H. Norris ◽  
Richard L. Irwin
Keyword(s):  
Motor Unit ◽  
Unit Area ◽  
Muscle Fibers ◽  
Motor Units ◽  
Ventral Root ◽  
Motor Axons ◽  
Single Motor ◽  
Peroneus Longus ◽  
Rat Muscle ◽  
Stimulation Of

Single motor axons to rat peroneus longus were isolated in the ventral root. The muscle was then explored with a microelectrode during stimulation of the axon. The muscle fibers supplied by the axon were identified by the intracellular depolarization potentials evoked by axon stimulation. In ten experiments the muscle fibers of a motor unit were rather widely scattered. This indicates that in certain motor units all the muscle fibers are not grouped together within one area of the muscle.

scholarly journals Metabolic cost underlies task-dependent variations in motor unit recruitment

2018 ◽  
Vol 15 (148) ◽  
pp. 20180541 ◽  
Author(s):  
Adrian K. M. Lai ◽  
Andrew A. Biewener ◽  
James M. Wakeling
Keyword(s):  
Cost Function ◽  
Motor Unit ◽  
Metabolic Cost ◽  
Motor Units ◽  
Recruitment Strategy ◽  
Muscle Fibre Types ◽  
Muscle Fibres ◽  
Recruitment Strategies ◽  
Size Principle ◽  
Low Intensity

Mammalian skeletal muscles are comprised of many motor units, each containing a group of muscle fibres that have common contractile properties: these can be broadly categorized as slow and fast twitch muscle fibres. Motor units are typically recruited in an orderly fashion following the ‘size principle’, in which slower motor units would be recruited for low intensity contraction; a metabolically cheap and fatigue-resistant strategy. However, this recruitment strategy poses a mechanical paradox for fast, low intensity contractions, in which the recruitment of slower fibres, as predicted by the size principle, would be metabolically more costly than the recruitment of faster fibres that are more efficient at higher contraction speeds. Hence, it would be mechanically and metabolically more effective for recruitment strategies to vary in response to contraction speed so that the intrinsic efficiencies and contraction speeds of the recruited muscle fibres are matched to the mechanical demands of the task. In this study, we evaluated the effectiveness of a novel, mixed cost function within a musculoskeletal simulation, which includes the metabolic cost of contraction, to predict the recruitment of different muscle fibre types across a range of loads and speeds. Our results show that a metabolically informed cost function predicts favoured recruitment of slower muscle fibres for slower and isometric tasks versus recruitment that favours faster muscles fibres for higher velocity contractions. This cost function predicts a change in recruitment patterns consistent with experimental observations, and also predicts a less expensive metabolic cost for these muscle contractions regardless of speed of the movement. Hence, our findings support the premise that varying motor recruitment strategies to match the mechanical demands of a movement task results in a mechanically and metabolically sensible way to deploy the different types of motor unit.

Organization of skeletal muscle in the urodele Triturus cristatus : muscle fibre types and motor units

1985 ◽  
Vol 223 (1233) ◽  
pp. 495-510 ◽  
Keyword(s):  
Succinate Dehydrogenase ◽  
Motor Unit ◽  
Muscle Fibre ◽  
Lucifer Yellow ◽  
Motor Units ◽  
Fibre Types ◽  
Differential Staining ◽  
Muscle Fibre Types ◽  
Muscle Fibres ◽  
Dehydrogenase Reaction

Four muscle fibre types are described in the biceps and extensor digitorum communis muscles of the newt forelimb. The histological criteria forming the basis for the distinctions include differential staining with p -phenylenediamine and succinate dehydrogenase histochemistry and electron microscopy. In addition, three distinctive motor unit types are described for the biceps muscle. These are fast units, slow units and intermediate units. The structure of muscle fibre and the physiological characteristics of muscle fibres belonging to each motor unit, have been correlated by using iontophoretic passage of Lucifer yellow into muscle fibres belonging to physiologically characterized motor units and their subsequent histological identification by the succinate dehydrogenase reaction. The three motor unit types correspond to slow muscle fibres, intermediate muscle fibres and two classes of fast muscle fibres.

Collateral Innervation of Muscle Fibres by Motor Axons of Dystrophic Motor Units

Nature ◽  
1973 ◽  
Vol 246 (5434) ◽  
pp. 500-501 ◽  
Author(s):  
JOHN E. DESMEDT ◽  
S. BORENSTEIN
Keyword(s):  
Motor Units ◽  
Muscle Fibres ◽  
Motor Axons

Reflex Control of Abdominal Flexor Muscles in the Crayfish

1965 ◽  
Vol 43 (2) ◽  
pp. 211-227 ◽  
Author(s):  
DONALD KENNEDY ◽  
KIMIHISA TAKEDA
Keyword(s):  
Giant Axon ◽  
Muscle Fibres ◽  
Motor Axons ◽  
Giant Fibre ◽  
Optimal Interval ◽  
Flexor Muscles ◽  
Muscle Types ◽  
Giant Fibres ◽  
Large Motor ◽  
Almost All

1. The flexor musculature of the crayfish abdomen is divided into two systems: a set of tonic superficial muscles, and a complex series of massive flexor muscles that produce powerful twitches but never exhibit tonic contractions. The muscle types are histologically differentiated, and also separately innervated: the main flexors receive ten large motor axons, and the slow superficial muscles six smaller ones. 2. Fibres of the main flexor muscles studied are almost all triply innervated; each receives endings from (a) the ‘motor giant’ axon, (b) one of several specific non-giant motor axons, and (c) a common inhibitor. 3. Excitatory junctional potentials (e.j.p.s) due to motor giant and non-giant axons are similar and large; each may trigger secondary, active ‘spikes’, thus often producing post-junctional responses of 100 mV. or more. The responses differ in that the motor giant e.j.p. shows a dramatic decrease upon repetitive stimulation, whereas that due to non-giant motor axons exhibits some facilitation. 4. Activity in the central giant fibres drives both motor axons. The response to both, when the motor giant system is fully rested, is slightly larger than that to either alone; when activated by stimulation of the central giant fibre the junctional potentials are evoked asynchronously due to differences in central reflex time, and double spiking in the muscle fibres sometimes results. Upon repeated stimulation the response to the giant is reduced to a very low level; this is accompanied by a decrease in the tension developed in successive reflexly evoked twitches. The motor giant system thus apparently functions to provide additional tension for the first few ‘flips’ in a series of swimming movements during escape. 5. Impulses in the inhibitor axon, even at the optimal interval, reduce the amplitude of excitatory post-junctional potentials by only a small amount; their effect in shortening duration is more notable. It is postulated that the peripheral inhibitor functions to cut short excitatory depolarizations and hence to terminate lingering tension that might oppose subsequent reflex actions.

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