muscle spindles


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Related to muscle spindles: Golgi tendon organs, joint receptors
Simplified diagram of a muscle spindle.

muscle spindles

specialized sensory structures within skeletal muscles, consisting of small intrafusal muscle fibres which do not contribute to load-bearing or power generation, but participate in control of the working (extrafusal) fibres. The intrafusal fibres are innervated towards their ends by gamma motor neurons, but are also invested more centrally by both primary and secondary sensory endings; these signal changes in length, and also rates of change in length of the muscle, to the central nervous system. The gamma motor neurons control the sensitivity of the sensory endings to stretching. They also compensate for the shortening of muscle spindles during extrafusal contraction by causing additional intrafusal contraction; this ensures that sensory feedback continues during muscle contractions. The overall system mediates both the stretch reflex and, in voluntary movement, appropriate adjustment of force-generation to load, provided the load is not varying too rapidly. See also gamma motor system, tendon jerk reflex.
References in periodicals archive ?
Paraspinal muscle spindle responses to the duration of a spinal manipulation under force control.
Muscle spindles that detect change in muscle fibre length and rate of change in length.
Apart from what this evident, acceleration-associated, contractile power-rate restriction may demonstrate about the protective functions of muscle spindles, the restriction may affect functional muscle contractions more often than the evident, maximum force restriction.
1978) Muscle spindle responses in man to changes in load during accurate position maintenance.
Yet there remains the possibility that, even with a profound reduction in afferents from muscle spindles or tendon organs, weight discrimination can still be performed on the basis of corollary discharges associated with the active-lifting movements.
Such a system would control the prosthetic hand via muscle contraction and would sense the tension and length changes transmitted from the prosthetic hand via muscle spindles and skin sensors, allowing more natural sensory feedback and control of the prosthetic device.
Future research should investigate the interaction between balance and muscle spindles, which play a part in both ankle and hip strategies of postural control.
Spinal manipulation has been shown to stimulate the muscle spindle and Golgi tendon organ afferents evoking paraspinal reflexes that can inhibit motorneuron excitability and, thus, relax skeletal muscle (8).
Muscles themselves are stimulated by the 'challenge' in a Bowen move, which activates the muscle spindles in response to the stretch on the muscle fibres.
Kulkarni V, Chandy MJ and Babu KS (2001): Quantitative study of muscle spindles in suboccipital muscles of human foetuses.
The rationale stated for the increased abdominal musculature endurance also applies to results obtained for this variable, namely that the muscle spindles activated a larger fraction of the motor neuron pool and recruited previously inactive motor units into contraction, thus resulting in a more efficient use of the force production potential of the muscle groups involved.