Abstract: An inexpensive apparatus for sensing and displaying the duration of the Silent Periods of masticatory muscles, which is suitable for diagnostic applications made in a doctor's office. The apparatus includes electrode means to be applied to the skin overlying a masticatory muscle and for sensing electrical activity within the muscle, and means providing an electrical signal representative of the sensed electrical activity. The apparatus further includes means receiving the representative electrical signal and sensing therein the onset of a Silent Period. Further means rejects those Silent Periods which have a duration less than a predetermined time interval, which time interval is selected to establish a minimum Silent Period of interest. Finally, the apparatus determines and displays the duration only of those Silent Periods longer than the predetermined time interval.