Figure 2. Cumulative sum (CUSUM; Ellaway, 1978) of the ipsilateral masseter surface electromyography (SEMG) and bite force responses to mechanical stimulation of an upper incisor tooth. Calibration was in 'k' (average pre-stimulus background activity) for the CUSUM and in Newtons (the calibration bar for the force data indicates 1 N) for the bite force. Thick lines are the pre-local-anesthetic records, and thin lines are the records taken during the local anesthetic block. Stimulus delivery was at 0 ms. The response to unloading stimulus (2 N load taken off within 5 ms; 400 N/s) is shown at the top; the response to the tap stimulus (2 N load is delivered within 5 ms; 400 N/s) is shown at the bottom. The vertical dotted lines indicate the minimum reaction time for the subject. The relationship between the change in the load and the reflex response is illustrated in an expanded time scale in Fig. 3. Note that the inhibitory reflex disappears but the excitatory reflex stays the same or increases in size during the local anesthetic block of the stimulated tooth. Therefore, both unload and tap stimuli activated not only the PMRs but the spindles as well. Spindle response became obvious once the PMRs were blocked by the local anesthesia. See text for details.
