Functional Specialization in the Motor Unit Population of Cat Medial Gastrocnemius Muscle
The population of motor units making up the medial gastrocnemius (MG) muscle in the cat has been studied as a representative example of a very heterogeneous motor pool. The wide range in physiological and histochemical characteristics of MG muscle units, and the details of their interrelation, suggest that the different motor unit types in the population are specialized for particular functions and particular patterns of activity. However, it is clear that the functional activity of a given muscle unit is controlled by the properties of its innervating motoneurone, and by the organization of synaptic input to that cell. In order to provide a clear picture of the motor unit pool in a heterogeneous muscle, it is thus necessary to study in detail the interrelations between motoneurone and muscle unit. The evidence presently available from such studies indicates that the properties intrinsic to MG motoneurones, and the spatial and functional organization of synaptic input to them, are quite consistent with the patterns of functional usage for which the different types of muscle units seem best suited. For example, type S muscle units are slowly-contracting and extremely resistant to fatigue, the latter associated with their high oxidative enzyme capacity.
KeywordsFatigue Depression Resis Posite Stein
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