The response to stretch of muscle spindle afferents of baboon's tibialis anticus and the effect of fusimotor stimulation

Abstract

SUMMARY1. Systematic studies of the response of baboon's tibialis anticus muscle spindles to stretch were undertaken. Most of the spindle afferents studied had conduction velocities between 72 and 78 m/sec with a range from 39 to 93 m/sec. There was no clear bimodality in the histogram of the conduction velocity. Measurements were made of the axon diameters of the nerve to tibialis anticus. The largest number of the larger axons had diameters from 11 to 13 It. The largest axon diameter measured 17 ,t and there were very few of these.2. The dynamic index for any given afferent tended to be greater for the more rapidly conducting afferents and lower for the more slowly conducting afferents. However, a statistically significant regression line of this relationship could only be drawn for a stretch velocity of 64 mm/sec.3. The spindle afferent response to stretch was studied from different muscle lengths. It was found that the velocity sensitive portion of the response to phasic stretch decreased when the stretch extended up to or beyond the maximum physiological length of the muscle.4. Dynamic and static fusimotor fibres were isolated. The response of the spindle afferent to stretch, while the dynamic fusimotor fibre was being stimulated, was the same as that reported for the cat by P. B. C. Matthews (1962). During static fusimotor stimulation the response of the spindle afferent to stretch was usually like that reported for the cat. In a single case, however, static fusimotor stimulation resulted in a lowering of the peak frequency of the response of the spindle afferent to the phasic portion of stretch.

The mammalian muscle spindle and its central control

“…There is considerable scatter in the relationship between axonal conduction velocity and dynamic response (Matthews 1963;Koeze 1968Koeze , 1973a Cheney and Preston 1976a), which is partly due to the existence of spindle afferents with intermediate response properties (Rack and Westbury 1966;Browne 1975;Dutia 1980;Inoue et al 1981 (Richmond and Abrahams 1979a;Abrahams 1981). Differences in size of locally effective stretch may further account for some of the scatter at issue (Meyer-Lohmann et al 1974;Windhorst et al 1975Windhorst et al , 1976Banks et al 1981b).…”

“…Given the existence of bag1 fibres in human spindles (Sect. 2.3.1) and of static and dynamic neurones in monkey (Koeze 1968;Cheney and Preston 1976b,c), one should also expect to find separate static and dynamic fusimotor effects in man. However, the crucial tests, relying on the observation of decreased or increased dynamic sensitivity in responses to sufficiently large stretches (see Sect.…”

A functional analysis of the components of the mesencephalic nucleus of the fifth nerve in the cat

“…This is important in determining whether primary and secondary afferents form two distinct groups separable by physiological means, or are a single continuous population. Evidence for such a division has been presented for the hind-limb muscles (Matthews, 1963), but classification has been unsuccessful in other situations (Koeze, 1968;Bach-y-Rita & Ito, 1966).…”

“…A widely held view is that they also are present in the MeNV (Cooper & Fillenz, 1955;Fillenz, 1955). On the other hand, evidence from the pig and sheep (Manni, Bortolami & Desole, 1966, 1968 places them in the trigeminal ganglion. Recordings from more than five hundred single units in the nucleus have permitted us to check some of these possibilities in the cat.…”

The independence of corticomotoneuronal and fusimotor pathways in the production of muscle contraction by motor cortex stimulation

“…This procedure had the disadvantage of uncertainty, since a few of the extensor digitorum afferents and efferents probably survived and a few tibialis anticus afferents and efferents may have been cut. Observations on the extensor digitorum longus spindle afferent response, when tibialis anticus was stretched, suggested criteria which could be used to detect the spindle afferents from extensor digitorum longus (Koeze, 1968).…”