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Figure 2. Typical examples of responses from single masseter muscle spindle units to cyclic sinusoidal stretching. Vertical lines indicate the start of a stretch stimulation (continuous) and the first spike of a spindle unit response (dashed). Muscle spindle units were classified as primary or secondary according to their response patterns. Primary endings (A) discharged during stretch and were silent during release, while secondary endings (B) responded with tonic discharges in proportion to the change of muscle length during the entire stimulation period. Lower tracings show typical primary and secondary unit responses after 15 days of iOVD. Cycle histograms show averaged unit responses over 5 consecutive cycles (bins of 100 ms).
