Excitatory and Inhibitory Controls of the Masseter and Temporal Muscles Elicited from Teeth in the Rat.

Yamamura, Chie; Shimada, Kyuhachiro

doi:10.2170/jjphysiol.42.283

Cited by 11 publications

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“…This may be due to the differential activation of motor units by PMRs, where small motor units receive excitatory input and large motor units receive inhibitory input (Yamamura and Shimada, 1992). Therefore, at low bite-force levels, reflex activation of small-sized motor units would be relatively intense, which will help keep the food between the teeth (Trulsson and Johansson, 1995).…”

Section: Slow Loading Of a Toothmentioning

confidence: 99%

“…Reflex work where slowly rising mechanical stimuli were applied to the incisor teeth in the orthogonal direction suggested that, at low levels of background activity, the stimulus generates a net closing force, whereas at high levels of background activity, it induces a net reduction of the closing force (Yang and Türker, 1999). This may be due to the differential activation of motor units by PMRs, where small motor units receive excitatory input and large motor units receive inhibitory input (Yamamura and Shimada, 1992). Therefore, at low bite-force levels, reflex activation of small-sized motor units would be relatively intense, which will help keep the food between the teeth (Trulsson and Johansson, 1995).…”

Section: Slow Loading Of a Toothmentioning

confidence: 99%

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Reflex Control of Human Jaw Muscles

Türker

2002

Critical Reviews in Oral Biology & Medicine

137

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Introduction The main function of the masticatory muscles is to break food down into pieces small enough to be swallowed. These are strong muscles that generate very large forces across very short distances and apply themvia rigid teeth. Such large forces can easily damage the teeth and their supporting tissues, tongue, cheeks, and the joints unless they are controlled precisely and effectively. There is evidence that the masticatory forces are controlled very precisely and that these forces change from bite to bite, depending on the consistency of the bolus. However, we do not fully understand this control mechanism. Unless the details of the mechanism that controls the masticatory forces in health and disease are thoroughly understood, the diagnosis and treatment of masticatory-related dysfunctions (such as temporomandibular dysfunction) will remain at the present "symptomatic" state.The aim of this review is to discuss what is known about the control of the human masticatory system and to propose a method for standardized investigation. This review is divided into six parts. The first part discusses the activation of human jaw muscle motoneurons by the central and peripheral sources. The second part discusses the receptors that are thought to contribute to the control of human mastication. In part 3, the reflexes elicited in human subjects are discussed. In part 4, simulated chewing experiments are discussed. In part 5, recording and analyzing methods are discussed, and a new method for estimating synaptic potential in human motoneurons is introduced. Finally, in part 6, three frequently asked questions are used to discuss the issues put forward in this review.Presently, our knowledge of mastication and its control by various receptors is patchy. Most of the work in this area comes from animal species with which investigators have used widely varying reduction techniques (anesthetization, decerebration, curarization, etc.). In these preparations, when nerve pathways are the subject of the study, the nerve to be stimulated is dissected free and teased so that one or a few identified nerve fibers are stimulated. The synaptic potential that is induced by this stimulation is recorded by means of microelectrodes that are placed within the central nervous system (reviewed in Lund, 1991;Linden, 1990). It is also possible for investigators to initiate "chewing" in animal preparations, and to study the effects of various receptor systems on the development of force (Lavigne et al ., 1987;.In humans, one must establish the connections of various afferents to the motoneurons that innervate the masticatory muscles under static or dynamic conditions to begin to understand the mechanism and control of mastication. The human work is challenging, since direct recording from motoneurons is not yet possible and precise stimulation of nerves is not easily controlled. Therefore, various indirect measurements have been used for the study of synaptic potential in human subjects. In most of these studies, afferent nerves are stimul...

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Section: Slow Loading Of a Toothmentioning

confidence: 99%

Section: Slow Loading Of a Toothmentioning

confidence: 99%

Reflex Control of Human Jaw Muscles

Türker

2002

Critical Reviews in Oral Biology & Medicine

137

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show abstract

“…In particular, repetitive excitatory inputs of the largeamplitude ON spikes from the bursttype TG -RA neuron would be the most advantageous to evoke the early transient excitation in the masseteric motoneurons. On the other hand, the existence of the inhibitory P M R w a s d i s c l o s e d f r o m t h e f i n d i n g t h a t labiolingual pressing on the rat maxillary incisor induced an inhibition of ongoing spontaneous EMG activity in the ipsilateral masseter muscle 23) . This phenomenon could be explained from our finding that the labiolingually applied toothpressing completely depressed the spontaneous spike discharge in the three spontaneously active TG -SA neurons, in contrast to the linguolabially applied toothpressing, which resulted in a facilitation of the spontaneous spike activity.…”

mentioning

confidence: 98%

“…The direction in which a rat maxillary incisor is pressed has been reported to determine the production of the excitatory or inhibitory periodontalmasseteric reflex (PMR) 22,23) . In the excitatory PMR, a linguolabial tapping on the maxillary incisor induced a fast transient e l e c t r o m y o g r a p h i c ( E M G ) a c t i v i t y a n d a subsequent tonic EMG activity in the ipsilateral masseter muscle 22) .…”

mentioning

confidence: 99%

Response characteristics of primary periodontal mechanoreceptive neurons simultaneously recorded in the trigeminal ganglion and mesencephalic trigeminal nucleus of the rat in response to trapezoidal and rectangular mechanical stimulation of a single tooth

Miyata

2013

J Kyushu Dent Soc

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Periodontal mechanoreceptors are dually innervated by primary neurons whose cell bodies exist in the trigeminal ganglion (TG) and the mesencephalic trigeminal nucleus (MTN) . We obtained simultaneous recordings of singleunit responses of primary periodontal mechanoreceptive neurons located in the TG and MTN of the same animal to controlled experimental forces applied to a single tooth. Simultaneous singleunit recordings of electrophysiologically identified primary periodontal mechanoreceptive neurons in a rat's TG and MTN were performed while isosceles trapezoidal or rectangular mechanical stimuli were being applied in either the linguolabial or the labiolingual direction to the ipsilateral maxillary incisor. Fiftyfour single units were recorded in 27 rats and classified as rapidly adapting (RA) or slowly adapting (SA) periodontal neurons on the basis of their responses to a decisive rectangular mechanical stimulus applied in the linguolabial direction. Significantly more RA neurons existed in the MTN than the TG (P < 0.05) . The response characteristics of the SA and RA periodontal neurons were quite similar between the TG and MTN. The trapezoidal and rectangular stimuli applied in the linguolabial direction elicited a vigorous sustained spike discharge in SA periodontal neurons in both the TG and MTN, whereas both stimuli applied in the opposite (labiolingual) direction did not elicit any SA responses. Rectangular stimuli applied in both directions elicited highthreshold ON -OFF spike responses in the RA periodontal neurons in both the TG and MTN. We also found an unreported bursttype periodontal neuron; its responsiveness was characterized by a brief repetitive

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Response of human jaw muscles to axial stimulation of a molar tooth

Brinkworth¹,

Male²,

Türker³

2004

Exp Brain Res

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The reflexes of the main jaw-closer muscles (masseter and anterior temporalis) on both sides of the jaw were investigated using surface electromyography to observe reflex activity following mechanical stimulation of the 1st right upper-molar tooth at various forces under a number of levels of jaw-muscle activity. As with analogous studies performed on the incisor, three distinct reflex events were identified in the EMG before the earliest conscious subject reaction: early excitation, inhibition and late excitation. However, contrary to observations found during studies on the incisor, excitation, not inhibition was the primary reflex response. The application of a local anaesthetic block around the stimulated molar showed that the primary agents in eliciting the observed reflexes were not contained within the periodontium of the stimulated tooth. A diminished representation of periodontal mechanoreceptors around the molar teeth and more elaborate root structures, hence a more solid connection to the jaw and consequently less tooth movement, were deemed the likely reason for the distinction between the reflex responses of the incisal and molar regions. In addition to the reflex studies, the minimum reaction time of a number of subjects was determined to permit the distinction of a reflex event and an event that could be a conscious subject reaction. It was found that the reaction time of the temporalis muscles was significantly shorter than those of the masseter, while no significant difference was found between the left and right sides. Overall, the data showed that the presence or absence of background muscle activity and subject variability were the main causes of changes in the reflex response, provided the level of the stimulus was greater than 3 N. The application of local anaesthetic had no impact on the reflexes evoked.

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Excitatory and Inhibitory Controls of the Masseter and Temporal Muscles Elicited from Teeth in the Rat.

Cited by 11 publications

References 0 publications

Reflex Control of Human Jaw Muscles

Reflex Control of Human Jaw Muscles

Response characteristics of primary periodontal mechanoreceptive neurons simultaneously recorded in the trigeminal ganglion and mesencephalic trigeminal nucleus of the rat in response to trapezoidal and rectangular mechanical stimulation of a single tooth

Response of human jaw muscles to axial stimulation of a molar tooth

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