Figure 6. Reflex response of a single human soleus motor unit to the Achilles tendon tap. This Fig. shows two different approaches to estimating the synaptic potential in humans. The reflex response of a soleus motor unit to 838 tap stimuli is expressed by PSTH and PSF. PSTH records confirmed the classic belief that a tap to a tendon generates three different reflexes: tendon jerk reflex, inhibitory (refractory, silent) period, and long-latency excitation. The tendon jerk reflex is signified by a large number of counts in the PSTH at a latency of about 44 ms. This reflex response lasted for 5 ms and was followed by a silent period of about 60 ms. The silent period is signified by a small number of counts in the PSTH. There was also a 'long-latency' reflex starting around 120 ms after the stimulus. Alternatively, the PSF record showed only one reflex response, a single long-lasting excitation. There was a rapid increase in the discharge frequency coincident with the tendon jerk reflex latency. This increase lasted for about 65 ms, after which the discharge rate returned to the pre-stimulus level. Time zero (arrows) indicates the timing of the tendon tap. Adapted from Türker et al. (1997b) with permission from Springer-Verlag.
