Fibre type composition of single motor units during synapse elimination in neonatal rat soleus muscle

Nature ◽  
1984 ◽  
Vol 309 (5970) ◽  
pp. 709-711 ◽  
Author(s):  
Wesley J. Thompson ◽  
Lee A. Sutton ◽  
Dan A. Riley
Keyword(s):  
Soleus Muscle ◽  
Fibre Type ◽  
Motor Units ◽  
Neonatal Rat ◽  
Synapse Elimination ◽  
Fibre Type Composition ◽  
Single Motor ◽  
Single Motor Units ◽  
Type Composition ◽  
Rat Soleus Muscle

Influence of 12 weeks of hypobaric hypoxia on fibre type composition of the rat soleus muscle

1995 ◽  
Vol 154 (3) ◽  
pp. 417-418 ◽  
Author(s):  
K. ITOH ◽  
M. ITOH ◽  
A. ISHIHARA ◽  
C. HIROFUJI ◽  
H. HAYASHI
Keyword(s):  
Soleus Muscle ◽  
Fibre Type ◽  
Hypobaric Hypoxia ◽  
Fibre Type Composition ◽  
Type Composition ◽  
Rat Soleus Muscle

Muscle Regionalization

1998 ◽  
Vol 23 (1) ◽  
pp. 1-22 ◽  
Author(s):  
Daniel Kernell
Keyword(s):  
Early Development ◽  
Fibre Type ◽  
Fiber Type ◽  
Motor Task ◽  
Motor Units ◽  
Metabolic Enzyme ◽  
Fibre Type Composition ◽  
Single Motor Units ◽  
Key Words Skeletal Muscle ◽  
Type Composition

In this review, the term muscle fibre regionalization signifies the presence of regional intramuscular differences in fibre type composition. As is well known, highly regionalized muscles commonly have greater concentrations of slow fibres deep than superficially. However, the degree of regionalization varies markedly between muscles and is not confined to deep vs. superficial locations. Fibres of the same myosin type may show regionalized differences in their metabolic enzyme activity, even within single motor units (Larsson, 1992). Regionalization of fibre type composition occurs also within single neuromuscular partitions. The intraspinal position of motoneurones is often coarsely related to the intramuscular sites of their muscle units. Muscles with a marked fibre type regionalization tend to show a corresponding regionalization of activity; in several muscles, however, the activity regionalization may vary depending on the motor task. During early development, fibre type regionalization emerges even under aneural conditions. The mechanisms are still unknown; relevant aspects of early development are briefly reviewed. Key words: skeletal muscle, fiber type, topography, activity, development

Spontaneous Electromyographic Activity in Adult Rat Soleus Muscle

1998 ◽  
Vol 80 (1) ◽  
pp. 365-376 ◽  
Author(s):  
Torsten Eken
Keyword(s):  
Motor Unit ◽  
Soleus Muscle ◽  
Motor Units ◽  
Firing Frequency ◽  
Electromyographic Activity ◽  
Single Motor Unit ◽  
Single Motor ◽  
Adult Rat ◽  
Single Motor Units ◽  
Rat Soleus Muscle

Eken, Torsten. Spontaneous electromyographic activity in adult rat soleus muscle. J. Neurophysiol. 80: 365–376, 1998. Single-motor-unit and gross electromyograms (EMG) were recorded from the soleus muscle in six unrestrained rats. The median firing frequencies of nine motor units were in the 16–25 Hz range, in agreement with previous studies. One additional motor unit had a median firing frequency of 47 Hz. This unit and one of the lower-frequency units regularly fired doublets. Motor-unit firing frequency was well correlated to whole-muscle EMG during locomotion. Integrated rectified gross EMG revealed periods of continuous modulation, phasic high-amplitude events, and tonic low-amplitude segments. The tonic segments typically were caused by a small number of motor units firing at stable high frequencies (20–30 Hz) for extended periods of time without detectable activity in other units. This long-lasting firing in single motor units typically was initiated by transient mass activity, which recruited many units. However, only one or a few units continued firing at a stable high frequency. The tonic firing terminated spontaneously or in conjunction with an episode of mass activity. Different units were active in different tonic segments. Thus there was an apparent dissociation between activity in different single motor units and consequently between single-motor-unit activity and whole-muscle EMG. It is proposed that the maintained tonic motor-unit activity is caused by intrinsic motoneuron properties in the form of depolarizing plateau potentials.

scholarly journals Selective innervation of types of fibres in developing rat muscle

1987 ◽  
Vol 132 (1) ◽  
pp. 249-263
Author(s):  
W. J. Thompson ◽  
L. C. Soileau ◽  
R. J. Balice-Gordon ◽  
L. A. Sutton
Keyword(s):  
Motor Units ◽  
Neonatal Rat ◽  
Muscle Fibre Types ◽  
Muscle Fibres ◽  
Glycogen Depletion ◽  
Fibre Type Composition ◽  
Type Composition ◽  
Motor Neurones ◽  
Developing Rat ◽  
Polyneuronal Innervation

The technique of glycogen depletion has been used to identify the types of muscle fibres innervated by individual motor neurones in the neonatal rat. This analysis shows that neonatal motor units are highly biased in their fibre type composition, even at times when the fibres receive extensive polyneuronal innervation. This finding suggests that the innervation of muscle fibres is somehow sorted according to type during early development. This sorting does not appear to occur during the removal of the polyneuronal innervation because little, if any, increase in the bias of unit compositions occurs as the number of synapses present in the muscle is reduced 2- to 3-fold. To determine whether the sorted innervation might be explained by a selective synaptogenesis, a study was made of the type compositions of units formed by reinnervation of neonatal soleus muscle. Glycogen depletion of single units 2 weeks following crush of the soleus nerve at postnatal day 2 showed that most of them (10/12) had biased type compositions which could not be explained by a random reinnervation. The location of fibres in the reinnervated motor units suggests that the regenerating axons innervated a novel set of fibres. The differentiation of fibres into types was apparently not changed during their reinnervation. These results imply that regenerating motor neurones in the neonatal rat selectively reinnervate muscle fibre types. These and other studies further imply that the organization of fibres into motor units during normal development does not occur, as is widely believed, by a random innervation of naive fibres and their subsequent differentiation under the influence of innervation.

MUSCLES WITHIN MUSCLES: A MECHANOMYOGRAPHIC ANALYSIS OF MUSCLE SEGMENT CONTRACTILE PROPERTIES WITHIN HUMAN GLUTEUS MAXIMUS

2006 ◽  
Vol 10 (01) ◽  
pp. 23-35 ◽  
Author(s):  
D. McAndrew ◽  
M. Gorelick ◽  
J. M. M. Brown
Keyword(s):  
Fibre Type ◽  
Lateral Displacement ◽  
Gluteus Maximus ◽  
Motor Units ◽  
Isometric Tension ◽  
Contractile Properties ◽  
Laser Sensor ◽  
Contraction Time ◽  
Fibre Type Composition ◽  
Type Composition

The aim of this investigation was to determine the contractile properties of motor units within 3 segments of the gluteus maximus utilizing a laser-based mechanomyographic (MMG) technique. The intention was to determine whether there were segmental differences in motor unit contractile properties and whether these differences may be related to the muscle segment's function and its fibre type composition. Ten subjects were recruited from the student population at the University of Wollongong. Maximal percutaneous neuromuscular stimulation (PNS) was delivered to the medial and lateral portions of three (cranial, middle, caudal) muscle segments of the gluteus maximus by an MMG stimulator. An MMG laser sensor measured the lateral displacement of the muscle segment belly resulting from the development of maximal isometric tension. Parameters characterizing the MMG waveforms were statistically compared to determine variations in contractile properties both within (medial to lateral) and between segments. Our results indicated that the contractile properties of motor units varied significantly (p < 0.05) between, but not within (medial to lateral), the three segments of the gluteus maximus. Most the gluteus maximus. Most notably, segment contraction time (t c ) decreased significantly (p < 0.05) in a cranio to caudal direction suggesting a variation in muscle fibre type composition within the three segments of the muscle. Even when corrected for differences in muscle belly displacement between subjects, the cranial segment was found to have a significantly (p < 0.05) longer contraction time than the two more caudal segments. The results suggest that the gluteus maximus was composed of muscle segments that were physiologically, as well as anatomically, designed to fulfil particular roles during everyday motor tasks. Based upon these results, the MMG technique appears to have considerable utility for the non-invasive assessment of muscle segment contractile properties for both laboratory and clinical applications.

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