İnsan tibialis anterior motor ünitelerinde germe refleksi

OBJECTIVES: Reflex responses of the tibialis anterior motor units to stretch stimulus were investigated to pinpoint synaptic connections of muscle spindle afferents to tibialis anterior moto7neurons in human.

MATERIALS & METHODS: Three types of stretch stimuli were applied and results were analysed using two different methods. The stimuli were simple tap-like stretch; ramp-and-hold stretch; and half-sine stretch. Stimulus induced responses in single motor units were analysed using averaged surface electromyogram (SEMG) and peristimulus time histograms (PSTH) and peristimulus frequencygram (PSF).

RESULTS: Using SEMG and PSTH, we found that the tap-like stretch stimulus induced five reflex responses. Using the same data, the PSF technique indicated only two excitatory reflex responses. The PSF displayed that the first two of the excitatory reflexes in the PSTH induced significant increase in the discharge rate of the related unit. The silent periods in the PSTH were actually continuations of the net excitatory effects as the discharge rate of the low number of occurrence during these ‘silent’ periods were higher than the prestimulus discharge rates. Stretch stimuli in the shape of ramp-and-hold induced several peaks and troughs in the SEMG and PSTH. PSF analyses displayed increase in discharge rates in the most of related peaks and troughs. Halfsine stretch stimulus induced a long-lasting excitation followed by a long-lasting inhibition in SEMG and PSTH. The increase in the discharge rate however lasted for the entire duration of the stimulus and continued through the ‘inhibitory’ phase as indicated in SEMG and PSTH.

CONCLUSION: The results are discussed in the light of the fact that the discharge rate of a motoneuron has a strong positive linear relationship with the effective synaptic input it receives.