Related Experiment Video
Updated: Jun 19, 2026
In Vivo Functional Assessment of Rat Masseter Muscle Following Surgical Creation of a Volumetric Muscle Loss (VML) Injury
Published on: November 15, 2024
Effect of stimulus parameters and contraction level on inhibitory responses in human jaw-closing muscles:
F Jadidi1, K Wang, L Arendt-Nielsen
1Department of Clinical Oral Physiology, University of Aarhus, Denmark. fjadidi@odont.au.dk
Objective:
Examine the effect of stimulus duration, intensity and level of muscle contraction on the inhibitory responses evoked by electrical stimuli in human jaw-closing muscles applied to the right mental nerve.
Design:
The inhibitory jaw-reflexes, short-latency (ES1) and long-latency (ES2), were recorded in the surface electromyogram (EMG) of masseter and temporalis muscles in 16 healthy subjects. Three stimulus durations (1ms single square-wave pulse, 10 and 450ms square-wave pulse train), two stimulus intensities adjusted to perceived intensity of 3 (non-painful) and 7 (distinct painful) on a 0-10 verbal rating scale were applied to the right mental nerve while the subject was biting at 25% and 50% of the maximal voluntary contraction (MVC).
Results:
The magnitude of suppression in the ES2 evoked by 1 and 10ms stimuli was dependent on stimulus intensity (P<0.002 and P<0.001, respectively) but not contraction level. However, ES1 could not be observed in most of the recordings. There were significant decreases evoked by the 450ms stimuli in RMS-EMG values in the 400-500ms compared with the pre-stimulus interval (P<0.001) which was dependent on contraction level (P<0.01) but not on stimulus intensity (P=0.486).
Conclusions:
The present results suggest that the ES2 reflex response is associated with the duration of the electrical stimuli, the intensity level but not the contraction level. In contrast, the inhibitory effects of ultra-long stimuli (450ms) are not specifically related to the intensity level suggesting that this is a non-nociceptive response.
Related Concept Videos
01:20Motor Unit Stimulation
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
01:22Muscle Stimulation Frequency
Wave summation
At low firing rates, motor neurons induce individual twitch contractions in muscle fibers. These twitches...
01:14Design Example: Frog Muscle Response
When the switch connecting the RL circuit is closed, a brief muscle contraction is observed. This is because, at a steady state, the inductor acts like a short circuit,...
01:20Excitation-Contraction Coupling in Skeletal Muscles
When an action potential...
01:25Smooth Muscle Contraction
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...
01:29Relaxation of Skeletal Muscles
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.