The number and distribution of muscle spindles in human intrinsic postvertebral muscles

Abstract

Analyses of human patterns of movement have shown that a large number of daily activities require movement of the head and trunk as a basic component. The control of postvertebral muscles is obviously of importance in these movements as well as in the maintenance of posture, particularly that of the head. Electromyographic evidence in subjects studied by Zuk (1962), Hoogmartens & Basmajian (1973), Monticelli, Ascani, Salsano & Salsano (1975) and Hoogmartens & Stuyck (1977) shows that asymmetry of stretch reflexes in spinal muscles may play a part in the causation and progression of many cases of idiopathic scoliosis. Spencer & Eccles (1976), Spencer & Zorab (1976) and Spencer (1977) have produced morphological and histochemical evidence to show that there are relatively more tonic (Type I) fibres on the convex side of the scoliotic curve than on the concave side, although it is not clear from their report whether this asymmetry in the distribution of muscle fibre types is a predisposing factor or a result of idiopathic scoliosis. Nevertheless, earlier work by Cooper (1960, 1966) showed that long, complex spindles were particularly numerous in tonic muscles.