فعالیت فیبرهای گاما در وضعیت استراحت و هنگام کشش های فازیک و تونیک در دوک عضلانی دم Rat

Background and Purpose: Basically, The muscle spindle is innervated by γ – fibers, γ – fibers are divided into phasic and tonic groups on the basis of their function. Ït is believed that phasic one γ innervate all the muscle spindle fibers where as tonic one innervate only tonic muscle spindle fibers and phasic of type two. The purpose of this study was to observe the fiber activity during phasic and tonic stretches in muscle spindle of rat tail and their effect on the sensory afferent fibers. Ând more knowing about physiologic mechanisms of γ-fibers, afferents and the way of controlling them will provide significant help in control of patients with rigidity and distonic move ments. Materials and Methods: Ïn this study, 15 normal male Sprague-Dawely rats with mean 500 gram weight were selected. General anaesthesia urethane (30 g/100 ml) with the dose of 170 mg/100g body weight and laminectomy was done in part of lumbosacral. Results: During severe stimulation of external ear of anaesthetized rat, γ fibers activity increases and affect afferent spindle fibers, so that, La fiber showed more activity compare to group ÏÏ afferent fibers. Stretches in muscle spindle first inhibits the activity of γ neuron fibers, after releasing of stretches physic and tonin γ fiber will be active. Ïn phasic stretches activity of la afferents of muscle spindle will be more and more while than group ÏÏ afferent fibers while the tonic of amplitude of Depolarized la decreases. However two sensory fibers are active. Çonclusion: Following γ-mononeuron activity, muscle afferent fibers shown the depolarized amplitude in the same spindle segment or even one or two segments upper. Ïn a way, always muscle spindle activity had stimulfaneous fluctuation with time. Âny way both the afferent fibers are controlled by γ ring. γ is under control of nuclear activity of central nerve. Ând in continual resting position La activity was not clear.