These changes are supported by observed increases in reflex amplitude 10 minutes post-conditioning contraction (Trimble and Harp, 1998), and the possible 30% contribution of the motoneuron excitation to the discharge frequency from Ia afferents of the intrafusal
stretch receptors (Gandevia, 1998).
Standardized measurements were made of the area and diameter of the muscle spindle, mean cross-sectional area of intrafusal
fibers, number of intrafusal
fibers and thickness of the spindle capsule in the muscle spindle with the largest diameter.
Tissue engineering the mechanosensory circuit of the stretch reflex arc: Sensory neuron innervation of intrafusal
Gamma motor neurons innervate intrafusal
muscle fibers and provide the maintenance of sensitivity of the muscle spindle at the time when muscle is shortened during the contraction.
The EMG activity during a stretch is triggered by impulses from the intrafusal
fibers of the muscle spindles.
In 1986, Laskin and Block hypothesized that the source of electrical activity was intrafusal
fibers inside the muscle spindle .
The therapeutic effects of BTX-A seemed to be due not only to partial denervation of extrafusal muscles but also to fusimotor denervation of intrafusal
fibers that tonically control the sensitivity of spindle sensory afferents [19-21].
Murakami et al., "Glycogen depletion of the intrafusal
fibers in a mouse muscle spindle during prolonged swimming," American Journal of Physiology, vol.
Gamma [chi] motorneurons, which transmit impulses to special skeletal muscle fibres, called intrafusal
fibres, part of the muscle spindle.
Gamma motor neurons can adjust the sensitivity of the intrafusal
fibers by innervating these intrafusal
fibers of the muscle spindle (41).
The phenomenon of muscle history is thought to arise from the spontaneous formation of stable, non-recycling intrafusal
cross-bridges between actin and myosin filaments when muscle is held at constant length.
Its are composed of 3-12 intrafusal
muscle fibers, of which there are three types: