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.

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 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).

Compartmentalization of motor units in the cat neck muscle, biventer cervicis

1988 ◽  
Vol 60 (1) ◽  
pp. 30-45 ◽  
Author(s):  
J. B. Armstrong ◽  
P. K. Rose ◽  
S. Vanner ◽  
G. J. Bakker ◽  
F. J. Richmond
Keyword(s):  
Motor Unit ◽  
Muscle Fibers ◽  
Motor Units ◽  
Neck Muscle ◽  
Nerve Bundle ◽  
Glycogen Depletion ◽  
Nerve Bundles ◽  
In Series ◽  
C3 Segment ◽  
Stimulation Of

1. The neck muscle biventer cervicis is supplied by five separate nerve bundles that originate from segments C2-C5 and enter the muscle at different rostrocaudal levels. We have used the glycogen-depletion method to investigate the distribution of muscle fibers supplied by each nerve bundle and also the extent of motor-unit territories supplied by single motoneurons in the C3 segment. 2. Prolonged intermittent stimulation of each nerve bundle produced glycogen depletion in a compartment of muscle fibers that ran only a fraction of the whole-muscle length. The depleted compartment was separated by tendinous inscriptions from adjacent, serially arranged compartments that were supplied by different nerve bundles. Thus the muscle was divided into five in-series compartments, arranged in the same rostrocaudal sequence as the nerves by which they were supplied. 3. Six fast, glycolytic (FG) and five fast, oxidative-glycolytic (FOG) motor units were depleted by repetitive intracellular stimulation of their antidromically identified motoneurons in the C3 segment. The fibers of each motor unit were confined to a striplike subvolume whose cross-sectional area was only 20-40% of that for the whole compartment in which it was located. Single motor units contained an average of 408 extrafusal fibers (range: 262-582 fibers), and these were distributed with an average density of 20 fibers/mm2 in cross sections through their motor domains. No significant differences were found between the numbers or densities of fibers in FG and FOG motor units. 4. The specialized in-series organization of compartments has functional implications because the forces generated by one compartment of motor units must be transmitted through other in-series compartments of muscle fibers rather than directly onto skeletal attachments. The confined distribution of muscle fibers belonging to a single motor unit suggests that an additional level of organization may exist within individual compartments. The implications of these features for the physiological behavior and neural control of biventer cervicis are discussed.

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.

Motor units and histochemistry in rat lateral gastrocnemius and soleus muscles: evidence for dissociation of physiological and histochemical properties after reinnervation

1987 ◽  
Vol 57 (4) ◽  
pp. 921-937 ◽  
Author(s):  
M. J. Gillespie ◽  
T. Gordon ◽  
P. R. Murphy
Keyword(s):  
Motor Unit ◽  
Muscle Fibers ◽  
Motor Units ◽  
Slow Muscle ◽  
Muscle Fiber Types ◽  
Fiber Types ◽  
Lateral Gastrocnemius ◽  
Fast And Slow Muscle ◽  
Individual Muscle ◽  
Significant Change

A reexamination of the question of specificity of reinnervation of fast and slow muscle was undertaken using the original "self" nerve supply to the fast lateral gastrocnemius (LG) and slow soleus muscles in the rat hindlimb. This paradigm takes advantage of the unusual situation of a common nerve branch, which supplies both a fast and slow muscle, and of the opportunity to keep the reinnervating nerve in its normal position. In addition it provides a test of the effects of cross-reinnervation among muscles of the same functional group. The properties of soleus and LG muscles and of individual muscle units were characterized in normal rats and in rats 4-14 mo after cutting the lateral gastrocnemius-soleus (LGS) nerve and suture of the proximal stump to the dorsal surface of the LG muscle. Individual muscle units were functionally isolated by stimulation of single motor axons to LG or soleus muscle contained in teased filaments in the L4 and L5 ventral roots. Motor units were classified as fast contracting fatiguable (FF), fast contracting fatigue resistant (FR), and slow (S) on the basis of criteria described in the cat by Burke et al. and applied to rat muscle units by Gillespie et al. Muscle fibers were classified as fast glycolytic (FG), fast oxidative glycolytic (FOG), and slow oxidative (SO) on the basis of histochemical staining for myosin ATPase, nicotinamide-adenine dinucleotide diaphorase (NADH-D), and alpha-glycerophosphate (alpha-GPD). Reinnervated muscles developed less force and weighed less in accordance with having fewer than normal motor units and having lost denervated muscle fibers. Normal LG contained a small proportion of S-type motor units (9%), whereas the majority (80%) of control soleus units were S type. After reinnervation, each muscle contained similar proportions of fast and slow motor units with S-type units constituting 30% of units in both muscles. When compared with the normal motor-unit sample, there was no significant change in average twitch and tetanic force in reinnervated muscles for each type of motor unit. However, the range within each type was greater, and there was considerable overlap between types. Twitch contraction time was inversely correlated with force in normal and reinnervated muscles as shown previously in self- and cross-reinnervated LGS in the cat. Changes in proportions of motor units in reinnervated LG were accompanied by corresponding changes in histochemical muscle types. This contrasted with reinnervated soleus in which the proportion of muscle fiber types was not significantly changed from normal despite significant change in motor-unit proportions.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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