Modulation of Human Muscle Spindle Discharge Figure 2. Pulse-wave driven muscle spindles. Each panel shows post stimulus time histogram at the bottom and raster sweeps of single cardiac cycles on top. A–C, Afferents typically responded with one single spike phase-locked to the cardiac cycle. D–F, Afferents responding with two spikes at the time corresponding to the pulse wave upbeat. A third spike corresponding to the time of dicrotic notch is generated by afferents depicted in E and F (see also B&D). Each bar indicates total count of spikes falling within corresponding 0.02 s time bin. Each dot in raster plot indicates one spike. doi:10.1371/journal.pone.0035091.g002 PLoS ONE | www.plosone.org 5 April 2012 | Volume 7 | Issue 4 | e35091