ISSN:
1432-1106
Keywords:
Muscles
;
Muscle contraction
;
Motor unit
;
Contractile properties
;
Cat
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The active length-tension curves of identified single motor units (MUs) belonging to peroneus longus muscle (PL) of anaesthetized adult cats were obtained by eliciting isometric single twitches and tetani. The recorded responses were evaluated by measuring the peak tension amplitude and the tension-time area at muscle lengths extending throughout the physiological length range of the muscle (mean 5.5 mm, standard deviation ±0.8). The muscle lengths at which each tested MU developed its maximal twitch (L tw) and tetanic (L te) tensions were determined and compared with the muscle length (L o) at which the stimulation of all the α-axons, innervating PL and contained in L7 ventral root, developed their maximal twitch tension. The mean of single MU L tw values was at L o+1.08±1.1 mm. Slow MUs showed the longest values of L tw(L o+1.6±1.0 mm). Single MUs stimulated at tetanic frequencies presented their L te at values shorter than L o (L o−2.8±1.7 mm). Slow MUs had the shortest L te (L o−3.4±1.5 mm). For all the units L te was shorter than L tw. L tw and L te were, respectively, negatively and positively correlated with the developed tension. Optimal length values also appeared to be related to the MU types. The possibility is discussed that the muscle and tendon compliances and the high non-linearities to the applied forces are the main factors which can determine the differences among L o, L tw and L te values. The relationships between MU type and optimal length values are suggested to be, at least partly, an epiphenomenon due to the different contraction strengths of the various MU types. However, the heterogeneous distribution of the MU types is brought into account to explain the dependence of L tw and L te values on MU type.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00227334
