Figure 3. Effects of sympathetic activation on a spindle secondary ending.

Recording from a silent secondary muscle spindle ending in extensor digitorum longus. A, the ending was activated by vibrating the tendon at 20 Hz, firing with every second cycle. B, the the unit's entrainment pattern did not change during an end-expiratory apnoea. Multi-unit sympathetic activity was also recorded concurrently from the same microelectrode, illustrated in the RMS-processed nerve signal.