Copies of author's previously published articles inserted. / Bibliography: leaves 172-204. / xi, 211 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / H-relexes are used to determine the reflex connections of muscle spindle afferents, the exitability of the motorneuron pool and the integrity of the reflex pathways. However, H-relexes are small and can be difficult to elicit in the masseter, limiting their use in the investigation of the masticatory system. This study investigated the recruitment of masseter motorneurons into the H-reflex, compared to the recruitment occuring during voluntary isometric biting, to determine the distribution of the effective muscle spindle input. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physiology, 1999

Thesis (Ph. D.)--University of Adelaide, 1989. / Typescript (Photocopy). Copy of published paper co-authored by author, in back. Includes bibliographical references (leaves 209-228).

There is a dearth of knowledge on the functional organization of the anatomically complex human masseter muscle. Limited physiological studies suggest a functional organization which may differ significantly from human limb muscles. The present studies aimed to examine the putative relationship between structure and function in the human masseter muscle as a basis for understanding function and dysfunction in human jaw muscles. In the first experiment single motor unit (SMU) activity was recorded from pairs of recording sites distributed throughout the masseter muscle. In each case SMU activity at a chosen location was used as a reference to search for synchronized SMU activity at another selected site. The locations of the needle tips were estimated in 3-dimensions (3-D) by means of an optical system, then transferred to 3-D reconstructions derived from Magnetic Resonance images. This approach permitted calculation of the linear distances between verified muscle recording sites. The mean separation of the sites from which synchronous SMU activity could be recorded was 8.8±3.4mm. The putative territories had a preferred orientation in the antero-posterior axis. Motor unit territories were larger than described previously, and appeared to be related to anatomical compartments. The second experiment involved recording activity from stereotactically mapped masseter SMUs. In each case, the lowest sustainable firing frequency (LSFF) was reached by slow increases and decreases in voluntary firing rate, followed by sustained firing at the lowest possible rate. Pulse-discrimination and digital sampling of consecutive inter-spike intervals (ISIs) were then used to measure LSFF for 2-6 separate occlusal and postural tasks to which each unit contributed. There were significant differences between mean ISIs for the tasks performed by most units, which suggests descending drive to masseter units is highly task-dependent. There were also regional differences in unit task specificities. In the third paradigm, reflex SMU activity was recorded from units in the masseter muscle and the inferior head of the lateral pterygoid muscle. Bipolar electrodes fixed to the gingiva near the maxillary canine delivered single pulses of 1ms duration at sub-noxious levels of intensity. At constrained firing frequencies (10, 15Hz), pulses were injected sequentially, with increasing delays, after preselected spikes. More profound inhibition occurred in units firing at 10 than 15Hz. There were significant differences in masseter inhibitory responses when the unit task varied. Reflex inhibition in masseter and lateral pterygoid SMUs is highly frequency-dependent, and also task-dependent in masseter units. The fourth study involved recording activity from SMUs in the masseter muscle. A midline load cell was fixed to the incisor teeth and aligned either perpendicular (P) or 30 degrees anterior (A) to the occlusal plane, without altering jaw position. A rigid spike-triggered averaging (STA) paradigm was used to extract the contribution of individual SMUs to the overall force at load cell orientations P and A. Spikes preceded or followed by an interval of less than 100ms were rejected prior to averaging. At background bite forces from 0.06-8N, the isometric forces apparently developed by individual units varied randomly with load cell orientations, (P range 36.2±19.6mN; A range 38.2±28.4mN). All units could be fired slowly with varying degrees of muscle coactivation, in some instances without contact on the load cell. The use of STA as a method for determining SMU tension in the masseter muscle appears to be task-dependent and in the presence of coactivation may be inappropriate. The findings collectively indicate the heterogeneous nature of SMU behaviour in the human masseter muscle which is consistent with internal muscle compartments based on anatomical features and functional behaviour. There thus appear to be both physiological and anatomical substrates for differential motor control of selected regions of the human masseter muscle. / Dentistry, Faculty of / Graduate

Headache is a common complaint in society and is related to personal, biomechanical and socioeconomic circumstances. In current literature trigger-points (TrPs) in the majority of the muscles of the face and neck contributing to tension-type headache (TTH) have been evaluated, except the TrPs of the masseter muscles. The aim of this studyis to determine the association between myofascial (TrPs) in the masseter muscle group and episodic tension-type headache (ETTH). Fourteen subjects with ETTH were matched with same sex and same age subjects not suffering from headache acting as the control group. The diagnostic criteria as described by Simons and Travel (1999) were used in the objective tests to diagnose the TrPs in the masseter muscles. Subjective tests included a disability questionnaire, National stress awareness day stress questionnaire, (NSAD stress questionnaire), a precipitating and aggravating factors questionnaire. Active TrPs were found in 92.86% of ETTH group and 7.14% had latent TrPs. Within the control group 7.14% had active TrPs, 14.29% latent TrPs and 78.37% had no TrPs.Differences in the presence of masseter TrPs between the ETTH and control group were significant with p-value <0.001. All the questions asked in the headache disability questionnaire evaluating headache frequency, intensity and severity were significantwith p-value<0.005. The NSAD stress questionnaire revealed statistical significant values for questions pertaining to muscular aches and pains and subjectively subjects claimed that theyfelt tension at work. The precipitating questionnaire showed that physical activity, stress / tension and reading were significant precipitating factors for developing a tension-type headache. The aggravating questionnaire only showed light as an aggravating factor. Stress and tension had 100% “yes”answers in the ETTH group.Weather as an aggravating factor had 100% “no” answersfrom the control group.Physical activity, driving and noise had relative high percentages of “yes”answers from the ETTH group and higher probability scores for being an aggravating factor whencomparing the ETTH and control group, but were not found to be statistically significant. Myofascial TrPs in the masseter muscle group contribute to the origin and or maintenance of ETTH.

Thesis (M.S.)--University of Michigan, 1985.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains viii, 88 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 62-66).

Copies of author's previously published articles inserted. / Bibliography: leaves 121-137. / ix, 138 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates the pattern of reflexes evoked by stretch in a human jaw-closing muscle (masseter) at the level of the whole muscle and individual motor units. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physiology, 1994

The human masseter muscle is a structurally complex jaw elevator with the capability of generating high, multidirectional forces. The invasiveness of current anatomical and physiological methods has, however, limited both the number and scope of studies of human masseter muscle structure and function. Therefore the aim of this work was to apply in vivo magnetic resonance (MR) techniques to elucidate the three-dimensional internal architecture of the human masseter muscle and its metabolic response to exercise in order to gain a better understanding of the jaw muscles in health and disease. In the first of these experiments, five adult subjects were selected and examined using cephalometric radiography, magnetic resonance imaging (MRI) and three-dimensional rotational and reconstructive computer graphics to describe the organization of tendon planes within the masseter muscle. Planar quadrilaterals representing putative tendon planes were fitted to the surfaces of the three-dimensional muscle reconstructions, and these were related to the mid-sagittal plane in the coronal and axial views. To confirm whether putative planes disclosed by MRI represented true anatomic entities, a fresh human cadaver head was imaged by MRI and then cryosectioned at millimetre intervals. Planar sections through the reconstructed muscle generated from the cadaver cryosections were correlated with the actual MR images in the same planes. Tendon plane angulation appeared to be related to ramal length and lower face height measured cephalometrically. In the axial view, the tendon planes appeared roughly to follow the angulations of the zygomatic arch and the lateral face of the mandibular ramus. Our results suggest that the angulation of tendon planes, and possibly pennation angles are different depending on the viewing angle, and infer that muscle fibres inserting on either side of a central tendon may need to develop different tensile forces if translation is to occur directly along the tendon axis. In the second, 31P magnetic resonance spectroscopy (MRS) was utilized to examine the masseter muscles of six adult males at rest and performing stereotyped isometric clenching exercises. 31P MR spectra were acquired from three locations within the muscle using a 2cm by 3cm, single-turn, copper receiver coil. The spectra were quantified on the basis of relative peak area and position. The organic phosphate (Pi) to creatine phosphate (PCr) ratio (Pi/PCr), which has been shown to be proportional to free ADP concentration and hence, the metabolic activity, as well as the normalized Pi concentration ([Pi]) and pH, were calculated for each site and exercise. The mean resting Pi/PCr ratio and [Pi] were greater for the deep part of the muscle than for the superficial and intermediate parts. These differences were significant to p<0.01. The mean pH however, was similar in all parts of the muscle at rest. During exercise, a significant increase in mean Pi/PCr was found in the superficial and intermediate parts of the muscle. Both these differences were significant to p<0.05. An accompanying decrease in mean pH was observed in all parts of the muscle during exercise. In the superficial part of the muscle, this decrease was significant to the p<0.05 level, and in the deep part, the decrease was significant to the p<0.001 level. No significant differences were found for these parameters between left and right molar clenching. These results suggest that metabolic activity may be monitored in the masseter muscle using 31P MR spectroscopy and that task-dependent and regional variations in metabolic activity may be demonstrated both at rest and during exercise. They are promising enough to encourage future studies of muscle metabolism in subjects with jaw muscle disorders. These experiments demonstrate the novel application of magnetic resonance techniques for studying craniomandibular morphology and function non-invasively. Collectively, they reveal the anatomical and functional heterogeneity which exist in the human masseter muscle. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

Typescript (Photocopy) / Copy of published paper co-authored by author, in back / Bibliography: leaves 209-228 / xiv, 232 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1989

Thesis--Göteborg. / Extra t.p. with thesis statement inserted. Includes reprints of the author's articles. Includes bibliographical references.