Fusimotor after‐effects on responses of primary endings to test dynamic stimuli in cat muscle spindles.

Abstract

SUMMARY1. Conditioning stimulation of individual dynamic fusimotor axons, either y or , leaves after-effects which enhance the responses ofprimary endings to test stimulation of the same axon applied during slow ramp stretch. These after-effects have a long duration, persisting well over 5 min, but are abolished by stretch of large amplitude.2. The dynamic after-effects also enhance frequencygrams elicited by lowfrequency repetitive stimulation during slow ramp stretch, causing single stimuli to become much more effective.3. When several dynamic axons to the same spindle are isolated, conditioning stimulation of one leaves an after-effect to test stimulation of itself and of all other dynamic axons. When two dynamic axons are used for conditioning stimulation, facilitation or occlusion can be demonstrated in their interaction, indicating that they converge on the same intrafusal element.4. Dynamic after-effects persist during background static fusimotor activity of considerable amplitude, suggesting that static and dynamic actions are quite independent.5. Dynamic after-effects appear to result from residual changes in the bag, fibre, probably from a persistent increase in the number of cross-bridges between thick and thin filaments. These after-effects produce a large increase in the response of primary endings to dynamic fusimotor activity and probably have an important functional role.

Effects of stretch on dynamic fusimotor after‐effects in cat muscle spindles.

“…Such after-effects are abolished by a large stretch of the muscle. As shown in the preceding paper (Emonet-Denand, Hunt & Laporte, 1985), the after-effect of dynamic fusimotor stimulation enhances the response of primary endings to test stimulation of dynamic axons during slow ramp stretch. This effect, reflecting residual changes in the bag1 fibre, is also destroyed by a large muscle stretch.…”

“…Preliminary reports of a portion of this work have appeared (Emonet-Denand & Hunt, 1984; Emonet-Denand, Hunt & Laporte, 1983). METHODS The methods were the same as reported in the previous paper (Emonet-DIenand et al 1985).…”

Modulation of Human Muscle Spindle Discharge by Arterial Pulsations - Functional Effects and Consequences

“…However, more subtle fusimotor related enhancement of muscle spindle afferent sensitivity, which is more likely to facilitate the detection of weak stimuli, are known as fusimotor after-effects [40]–[42]. The advantage of this mechanism is that it can increase sensitivity of muscle spindle endings in the absence of noise inducing fusimotor contraction.…”

“…Fusimotor activation is the key factor regulating the sensitivity and dynamic range of muscle spindle operation [39] , however, for detection of very weak stimuli this mechanism may not be always efficient because weak activation and twitches of intrafusal muscle fibres below their fusion frequency generate twitch induced spiking activity that may mask the effects of very weak stimuli. However, more subtle fusimotor related enhancement of muscle spindle afferent sensitivity, which is more likely to facilitate the detection of weak stimuli, are known as fusimotor after-effects [40] – [42] . The advantage of this mechanism is that it can increase sensitivity of muscle spindle endings in the absence of noise inducing fusimotor contraction.…”

Propriomuscular coding of kinaesthetic sensation

“…They combine information on both position and velocity in signals which, in addition, depend on the efferent activities of ~, /3 or 7 fibers (Crowe and Matthews 1964;Hulliger 1984;Emonet-Denand et al 1985;Ribot et al 1986). These two complementary aspects (coding and decoding) are closely linked and need to be approached in a combined study.…”