Abstract
Over the past three decades, neurophysiologists studying the neural circuitry responsible for control of skeletal muscles have developed several different general theories of sensorimotor control. These have usually invoked one or more of the sources of proprioceptive signals (e.g. muscle spindle and Golgi tendon organ afferents) in positive or negative feed-back loops to the homonymous alpha motoneurones. In this paper we consider to analyze the role of posi-tive feedback in combination of negative feedback due to important role of them in stabilizing the neu-romuscular system.
Highlights
The stretch reflex differs in decerebrate and intact animals and since Sherrington’s time it has come to be realized that several CNS mechanisms may contribute components of different latency to the stretch reflex response
In the simple reflex model the muscle contractile element is modeled as a first-order low-pass filter with a cutoff frequency of 8 Hz, somewhat higher than the isometric frequency response characteristic of cat triceps surae muscles of Rosenthal that positive force feedback may be appropriate in some et al 1970
A force increment of 10 N represents the mean force developed by triceps surae during the stance phase of slow gait [11]
Summary
The stretch reflex differs in decerebrate and intact animals and since Sherrington’s time it has come to be realized that several CNS mechanisms may contribute components of different latency to the stretch reflex response. Muscle spindle Ia afferents activated by muscle lengthening monosynaptically excite homonymous alpha motoneurons which in turn cause the muscle to resist the stretch. In static postures Ib input generally results in homonymous inhibition, but it has been shown that this switches to longer-latency homonymous excitation during locomotion [1], at least in cat extensor muscles. Group II input from muscle spindles has been implicated in long latency components of stretch reflexes [2,3,4]. Ia homonymous excitation represents negative displacement feedback, which augments the intrinsic stiffness of active muscles in the face of length perturbations. Positive feedback is synonymous with instability and oscillation in engineering systems, but when muscles are the actuators; their nonlinear lengthtension properties turn out to stabilize the positive feedback loop [5]
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