Investigating synaptic connections of human jaw muscle

Investigating synaptic connections of human jaw muscle Electromyography is an electrophysiological method used to investigate the human nervous system and its connections. In this study, electromyography measurement of masseter muscle by applying mechanical and transcranial magnetic stimuli at different levels was aimed to reveal synaptic connections and possible connectivity changes between cortex, masseter muscle and receptors in different muscle contraction conditions. Twenty healthy adult volunteers (22-39 years of age) who did not have any dental, neurological, psychiatric, allergic or muscular diseases and pregnancy status participated in the study. Right incisor was stimulated by mechanical stimuli in different intensity. The left motor cortex innervating the right jaw muscles was stimulated using a stimulator via a figure of-eight shaped transcranial magnetic stimulation coil. Surface EMG was recorded from the right masseter muscle with disposable adhesive Ag-AgCl electrodes. Motor evoked potentials, inhibitions and excitations of the electromyographic activity and reflex parameters were investigated. The present study demonstrates that the reflex responses during chewing were different from the responses during the isometric contraction of the jaw. When all stimulus types were considered together, the amplitude of the reflex increased with the increase of the stimulus intensity (p<0,05). The reflex connections of the periodontal mechanoreceptors and muscle spindles during the chewing functions were shown after mechanical stimulation of the incisor via local anesthesia to the perioral region. As a result of transcranial magnetic stimuli in different intensities, the contribution of the cortex to the jaw muscles during chewing was revealed. Main findings of this study is electromyography recording during different levels of mechanical and transcranial magnetic stimulation is an effective method to investigate the synaptic connections from masticatory motor cortex to masseter muscle in different chewing conditions. Key Words: Mechanical stimulation, transcranial magnetic stimulation, electromyography, masseter muscle, periodontal mechanoreceptors, muscle spindles, motor cortex.