Malleability of the motor system: a comparative approach

The various ways in which the power output of muscles can be changed are described. As a result of exercise and growth, force production is increased by an increase in the cross-sectional area of the fibres. This is associated with changes in the rate of synthesis and degradation of muscle proteins which lead to build up of the myofibrils. These then split longitudinally when they reach a critical size. This process is repeated so that the number of myofibrils increases very considerably. Also, during growth, the displacement is increased by increasing the length of the muscles. To do this more sarcomeres are produced in series along the length of the fibres. This is induced by stretch which also encourages fibre growth in girth as well as in length. Yet another way of changing the power output of a muscle is to change the types of muscle fibres (motor units) within the muscle. Fibre type transformation has been fibres (motor units) within the muscle. Fibre type transformation has been shown to occur with cross innervation and stimulation but it does not usually occur with exercise training. It has been possible, however, to change the fibre type proportions in young animals. Also, by combining stretch with stimulation, it has been possible for instance to make the fast glycolytic fibres add on fast oxidative type sarcomeres or even slow oxidation type sarcomeres. Interestingly, fibre transformation also occurs in some species of fish during acclimation to low temperatures in that the specific myofibrillar ATPase activity is increased. This means that the reduction in power output due to decreased temperature is to some extent compensated for by an increase in the intrinsic rate of shortening. EMG studies of fish swimming at different temperatures have shown that the acclimated fish can swim faster and can derive more aerobic sustainable power as a result of this change.

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Cardiomyoplasty — Improvement of Muscle Fibre Type Transformation by an Anabolic Steroid (Metenolone)

Journal of Molecular and Cellular Cardiology ◽

10.1006/jmcc.1997.0543 ◽

1997 ◽

Vol 29 (11) ◽

pp. 2989-2996 ◽

Cited By ~ 11

Author(s):

Markus Czesla ◽

Gaby Mehlhorn ◽

Dirk Fritzsche ◽

Gerhard Asmussen

Keyword(s):

Muscle Fibre ◽

Anabolic Steroid ◽

Fibre Type ◽

Muscle Fibre Type ◽

Type Transformation

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Post-synaptic morphology of mouse neuromuscular junctions is linked to muscle fibre type

10.1101/2020.04.04.025106 ◽

2020 ◽

Author(s):

Aleksandra M. Mech ◽

Anna-Leigh Brown ◽

Giampietro Schiavo ◽

James N. Sleigh

Keyword(s):

Motor Neuron ◽

Muscle Fibre ◽

Fibre Type ◽

Neuromuscular Junctions ◽

Fibre Diameter ◽

Neuromuscular Diseases ◽

Neuronal Morphology ◽

Muscle Fibre Type ◽

Muscle Membrane ◽

Muscle Fibres

AbstractThe neuromuscular junction (NMJ) is the highly specialised peripheral synapse formed between lower motor neuron terminals and muscle fibres. Post-synaptic acetylcholine receptors (AChRs), which are found in high density in the muscle membrane, bind to acetylcholine released into the synaptic cleft of the NMJ, ultimately facilitating the conversion of motor action potentials to muscle contractions. NMJs have been studied for many years as a general model for synapse formation, development and function, and are known to be early sites of pathological changes in many neuromuscular diseases. However, information is limited on the diversity of NMJs in different muscles, whether muscle fibre type impacts NMJ morphology and growth, and the relevance of these parameters to neuropathology. Here, this crucial gap was addressed using a robust and standardised semi-automated workflow called NMJ-morph to quantify features of pre- and post-synaptic NMJ architecture in an unbiased manner. Five wholemount muscles from wild-type mice were dissected and compared at immature (post-natal day, P7) and early adult (P31-32) timepoints. Post-synaptic AChR morphology was found to be more variable between muscles than that of the motor neuron terminal and there were greater differences in the developing NMJ than at the mature synapse. Post-synaptic architecture, but not neuronal morphology or post-natal synapse growth, correlates with fibre type and is largely independent of muscle fibre diameter. Counter to previous observations, this study indicates that smaller NMJs tend to innervate muscles with higher proportions of fast twitch fibres and that NMJ growth rate is not conserved across all muscles. Furthermore, healthy pre- and post-synaptic NMJ morphological parameters were collected for five anatomically and functionally distinct mouse muscles, generating reference data that will be useful for the future assessment of neuromuscular disease models.Graphical Abstract

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Form and classification of motor endings in mammalian muscle spindles

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1985.0058 ◽

1985 ◽

Vol 225 (1239) ◽

pp. 195-212 ◽

Cited By ~ 5

Keyword(s):

Muscle Fibre ◽

Fibre Type ◽

Muscle Spindles ◽

Muscle Fibre Type ◽

Motor Axon ◽

Muscle Fibres ◽

Intrafusal Muscle ◽

Axon Terminals ◽

Hindlimb Muscle

The presynaptic features of 234 motor endings supplied to cat hindlimb muscle spindles have been studied in teased, silver preparations, and the postsynaptic features of a further 27 endings have been studied in serial, 1 μm thick, transverse sections. In the presynaptic study motor endings received by the three types of intrafusal muscle fibre were compared with the endings supplied to spindles by the various functional categories of motor axon. Three forms of motor ending were found that had significantly different presynaptic features. These forms correspond closely to those previously identified in the literature as p 1 (β), p 2 (dynamic γ) and trail (static γ). The results of the postsynaptic study showed that the degree of indentation of the intrafusal muscle fibres by motor axon terminals increases with greater distance from the primary ending, irrespective of muscle-fibre type. We conclude that the postsynaptic form of intrafusal motor endings is determined by distance from primary ending and muscle-fibre type. It is not determined by type of motor axon, and cannot be correlated with presynaptic form so as to produce a unified classification of intrafusal motor endings.

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The effect of maternal undernutrition on muscle fibre type in the newborn lamb

Proceedings of the British Society of Animal Science ◽

10.1017/s1752756200012199 ◽

2003 ◽

Vol 2003 ◽

pp. 60-60

Author(s):

A.J. Fahey ◽

J.M. Brameld ◽

T. Parr ◽

P.J. Buttery

Keyword(s):

Muscle Fibre ◽

Meat Quality ◽

Fibre Type ◽

Muscle Development ◽

Nutrient Supply ◽

Muscle Fibre Type ◽

Growth Potential ◽

Muscle Fibres ◽

General Hypothesis ◽

Maternal Undernutrition

Muscle fibre type can influence meat quality (Maltinet al1997). Muscle fibre formation occurs during gestation and in the sheep the total number of fibres in a muscle is essentially fixed at birth. (Ashmereet al1972). Postnatal growth of muscle is entirely due to elongation and widening of the existing muscle fibres. Therefore the gestational period is important in the long-term growth potential of the animal. By investigating changes in muscle fibre type, the aim of this study was to test the general hypothesis that the poor carcass quality sometimes seen in ruminant animals may be due to poor nutrition at strategic time points during the animal’s development. As agricultural practices continue to become more extensive, variation in the nutrient supply to the animal is becoming more common. Therefore it is important to understand the effect of any changes in nutrient supply to the mother, during gestation on the subsequent muscle development of the fetus and ultimately the effects on meat quality.

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