The effect of sinusoidal stretching upon the activity of stretch receptors in voluntary muscle and their reflex responses

Abstract

Voluntary muscle in most human subjects shows a periodicity in the discharge of groups of motor units, at a frequency about 9-10 c/s. These periodic 'bursts' of action potentials are accompanied by a corresponding mechanical oscillation. Under normal conditions this rhythmic activity is responsible for only a small fraction of the total tension being exerted by a muscle and, as shown by Lippold, Redfearn & Vuco (1957), produces a tremor which can be regarded as physiological. We argued that the effect was peripherally determined by self-oscillation in the stretch-reflex servo-loop, since the frequency of oscillation could be altered by cooling or stretching the muscle. The abolition of the rhythm by de-afferentation and by ischaemia of the muscle provides additional evidence for this hypothesis.These facts do not, however, rule out the possibility of a central contributory factor. Continuous medullary stimulation is known to produce rhythmical activity in motoneurones at about 10 c/s independently of the frequency of stimulation (Bernhard, Skoglund & Therman, 1947). The 10 c/s precentral cortical rhythm might also contribute to such a central driving tendency, although Lindqvist (1941) has shown that the slowing of the alpha rhythm as a result of overbreathing is not accompanied by any change in the frequency of tremor.The influence of any such central pace-maker upon the stretch reflex should be revealed by a study of the relationship between input to and output from the reflex centre. If there were a central rhythmical drive, then this relationship would be expected to vary in time with this rhythm.

Oscillation in the stretch reflex arc and the origin of the rhythmical, 8–12 c/s component of physiological tremor

“…tivity to stretch. Observations made during other experiments on mammalian muscle spindles (Lippold, Redfearn & Vuco, 1958;Lippold, Redfearn & Nicholls, 1960a, b) lend support to the view that cessation of the circulation to a muscle spindle will, in fact, almost abolish its response to stretch. If the foregoing assumptions are true, the imposition of ischaemia in a limb and its resultant effects on the spindles are equivalent to altering the loop gain at its peripheral part.…”

The response of de‐efferented muscle spindle endings in the cat's soleus to slow extension of the muscle

“…The difference in phasic behaviour of the primary and secondary endings, if existing under a wide range of conditions, is likely to be of great functional significance. The phasic sensitivity of the primary ending is somewhat similar to the 'phase advance' or 'velocity feedback' used to stop oscillation in some inanimate control systems, and is thought to be of similar importance in the reflex stabilization of muscle contraction (Merton, 1951;Pringle & Wilson, 1952;Lippold et at. 1958 (Leksell, 1945;Kuffler et al 1951;Whitteridge, 1959).…”

“…Thus the values of slope already given must have depended upon the choice of 2-3 mm/sec as the standard rate of stretch, but the results obtained would not have been markedly different if a slightly higher or a slightly lower rate of stretch had been used. At higher rates of stretch than were available for the present experiments large effects would be expected on increasing the velocity of stretch, at any rate for the primary endings (Matthews, 1933;Lippold, Redfearn & Vu6o, 1958;Granit & Homma, 1959b;S. Cooper, unpublished).…”

Oscillation of the human ankle joint in response to applied sinusoidal torque on the foot

“…In this subject, a quick dorsiflexion of the foot by the motor produces a (Halliday & Redfearn, 1956;Lippold, 1970), the partially flexed forearm (Fox & Randall, 1970), the abducted index finger (Stephens & Taylor, 1974), and the soleus during quiet standing (Lippold et al 1958;Mori, 1973). Mori (1973) has found a tendency toward synchronization of contiguous motor units in the soleus during quiet standing and found motor units to fire synchronously at about 9 spikes/sec.…”

“…The response of stretch receptors to sinusoidal stretching or to vibration has been investigated by Lippold, Redfearn & Vuco (1958), Bianconi & Van der Meulen (1963), Stuart, Ott, Ishikawa & Eldred (1965), Brown, Engberg & Matthews (1967), Matthews & Stein (1969), Rosenthal, McKean, Roberts & Terzuolo (1970), Poppele & Bowman (1970), and WVestbury (1971). (See Matthews (1972) for a comprehensive review.)…”