Invited reviewReflex responses of masseter muscles to sound
Section snippets
Sound as a stimulus activating cochlear as well as vestibular receptors
Although the primary receptor specialised for the detection of sound is the cochlea, it has been known for many years that sound can also affect the vestibular system. For instance, in humans intense sound is well known to produce vestibular symptoms and illusions of movement (Parker et al., 1975). These probably arise from stimulation of otolith organs in the saccule since this is reported to be the most sensitive part of the vestibular system to sound (Young et al., 1977, Cazals et al., 1983,
Masseter responses to vestibular stimulation
There are many investigations into the vestibular interactions with muscles controlling the neck and eye. However, it seems possible that motoneurones innervating the masseter muscles might also be a possible target of vestibular inputs since these muscles, in addition to their role in mastication, phonation, respiration and swallowing, are also involved in maintaining the posture of the jaw against gravity (Lund and Olsson, 1983, Miralles et al., 1987). To date this question has only been
Masseter responses to acoustic stimulation
Responses to loud sounds were first recorded in the average surface EMG of voluntarily contracted masseter muscles using acoustic click stimuli (Deriu et al., 2005). Unilateral stimulation evokes a bilateral and symmetrical short-latency response that consists of two overlapping components distinguished by their threshold, latency and by their appearance in the rectified EMG, as summarized in Table 1. Responses to bilateral stimulation are similar, but larger.
The lower threshold response is a
Possible role for the vestibulo-masseteric reflex pathways in trigeminal motor control
In addition to mastication, the masseter muscle is involved in speech, swallowing, respiration and maintenance of the position of the mandible, by bringing it back to its physiological axis. Each of these functions require jaw muscles to perform motor tasks that differ in force produced, as well as rapidity, shape and precision of mouth movements. Furthermore, they are often required to perform these multiple and very different actions simultaneously, so that we are able, for instance to speak
Clinical prospects
The study of the vestibulo-masseteric reflex and of the acoustic masseteric reflex in people with selective lesion of vestibular or cochlear receptors definitely demonstrated that these end organs originate the p11/n15 and the p16/n21 waves, respectively (Deriu et al., 2007). This study also shows that masseter responses to sound can be used as additional tools to test saccular and cochlear function in human otological investigations. However, it seems unlikely that these responses will replace
Acknowledgements
This work was supported by grants from the Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR) and from Fondazione Italiana Sclerosi Multipla (FISM 2008/R/9). Dr. Elena Giaconi was supported by a grant from MIUR (PRIN).
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2022, Clinical NeurophysiologyCitation Excerpt :In addition to the corticobulbar projections that control voluntary movement of masticatory muscles, a further circuit in the brainstem recruits masticatory muscles for chewing movements, i.e., the brainstem central pattern generator. The brainstem central pattern generator activates bilateral, rhythmic, and alternating activity in jaw opening and closing muscles and is strongly modulated by sensory feedback from the jaw, tongue, and face, thus adapting movements to the hardness of food or to unexpected perturbations (Deriu et. al., 2010; Morquette et al., 2012). In this regard, cortical and sensory input integration is crucial in triggering or correcting the pattern.
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2019, Clinical NeurophysiologyCitation Excerpt :Based on these findings, we suggest that, to ensure the highest detection rate, both electrode configurations be used when recording the VMR and the AMR. The difference in activation threshold of cochlear and vestibular receptors to sound may explain the different characteristics of the low-threshold, longer-latency AMR (p16/n21 potential), which is cochlear in origin, and of the high-threshold, short-latency VMR (p11/n15 potential), which is of vestibular origin (Deriu et al., 2003, 2005, 2007, 2010). The overlap between these masseter responses makes it important to define which range of click intensity allows a clear detection and distinction between them.
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2015, Clinical NeurophysiologyCitation Excerpt :When the VMR is elicited by loud clicks, it partially overlaps with the acoustic-masseteric reflex (p16/n21 wave) so that, in normal hearing people, the n15 wave is not detectable and a p11/21 complex is visible (Deriu et al., 2005). Neurophysiologic criteria to discriminate the vestibular- and the cochlear-induced masseter responses have been defined and their inhibitory nature and origin clarified (Deriu et al., 2005, 2007, 2010). The neural pathway from vestibular receptors to the SCM is not characterised in humans, although the existence of monosynaptic projections from the vestibular complex to masseter motoneurons has been demonstrated in experimental animals (Giaconi et al., 2006; Cuccurazzu et al., 2007).