Figure 3. The relationship between the 'stretch' stimulus and the first excitatory response. All records are from trials during the local anesthetic block of the stimulated tooth. Thick lines represent the CUSUM of the ipsilateral masseter SEMG; thin lines represent the bite force. Note that the unload stimulus induces a reduction in the force record, and the tap stimulus induces an increase, followed by a decrease in the force record. Since there was no change in the electrical activity of the jaw muscles preceding these changes in the bite force, they are labeled as mechanical artifacts of the stimuli. This subtle yet consistent mechanical artifact is used for eliciting and studying the muscle spindle stretch reflex responses. Note also that the latency of the early excitatory reflex response is shorter in the trials with the unload stimuli, since the 'stretch' arrives earlier with the unload stimulus.
