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Isometric contractions of motor units and immunohistochemistry of mouse soleus muscle.
Author(s) -
Lewis D M,
Parry D J,
Rowlerson A
Publication year - 1982
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1982.sp014157
Subject(s) - isometric exercise , motor unit , myosin , population , soleus muscle , anatomy , axon , chemistry , motor unit recruitment , reciprocal inhibition , biophysics , biology , electromyography , skeletal muscle , endocrinology , neuroscience , biochemistry , medicine , inhibitory postsynaptic potential , physiology , environmental health
1. Isometric contractions of motor units, isolated functionally by ventral root splitting in vivo, were recorded from mouse soleus muscle. 2. Motor unit tensions varied over a narrow symmetrical range and averaged 4.7% of whole muscle tension, corresponding to twenty‐one motor units per muscle. 3. There was considerable variation between muscles in isometric twitch times‐to‐peak and even greater variation for the motor units. The distribution of motor unit times‐to‐peak was apparently unimodal and could be fitted by a single normal population. A slightly better fit was, however, obtained with two normal populations, as suggested by the histochemistry. 4. Twitch time‐to‐peak decreased in proportion to axonal conduction velocity in individual animals. The whole population of motor units could be fitted by a linear relation between time‐to‐peak and the reciprocal of conduction time in the motor axon. Motor unit tension was also linearly related to the reciprocal of conduction time. 5. Histochemistry showed clear division between Type I and Type IIa fibres. Type I fibres reacted strongly with antibody against slow myosin of cat soleus muscle; Type IIa gave a reaction no stronger than the background. The division was as clear as in the cat or rat.