Biomedical subjects

G M Murray

Publications and source records attributed to G M Murray.

At least 37 records · Page 2Linked to original sources

PubMed2000

The involvement of the styloid process in head and neck pain--a preliminary study.

The styloid process and associated structures have been implicated in a variety of craniomandibular dysfunctions and pain complaints. There have been anecdotal reports that treatment directed at this area can result in a dramatic reduction in referred symptoms, somatic pain and autonomic signs as well as an increase in mandibular range of motion. In the past, an elongation of the styloid process was considered necessary for pain and dysfunction symptoms to arise from this area. The patients in this study did not have elongated styloid processes, yet had orofacial pain and dysfunction symptoms seemingly referred from this area. An injection of local anaesthetic and corticosteroid in the area of the styloid process significantly reduced lateral head pain and improved mandibular function in spite of an absence of any demonstrable pathology at the styloid process.

Adolescent↗

PubMed2000

The effect of nitrous oxide on hearing.

There is a belief that the administration of nitrous oxide (N2O) increases hearing acuity. This increase can be interpreted as hearing low intensity sounds more loudly. This study examined auditory threshold levels, acoustic impedance, acoustic perception, memory, and discrimination to determine if hearing was altered by end-tidal 10% or 20% nitrous oxide. Subjects also qualitatively interpreted three intensity levels using a subjective intensity test. Observations were made in the breathing mediums of room air in the control stages (Stages 1 and 4), compared to N2O and supplemental oxygen (Stages 2 and 3), in 16 human subjects in a quiet room. Breathing end-tidal 10% and 20% N2O significantly increased middle ear pressure, and produced a significant effect on the subjective interpretation of a sound's intensity. There was no significant effect on auditory threshold at a range of frequencies. It appears that 10% or 20% N2O inhalation does not lead to the commonly held view of increased hearing acuity as measured in terms of auditory threshold. Rather, at these levels of N2O inhalation, subjects experience a state similar to a pre-sleep stage, whereby the hearing diminishes but remains active for loud intensity sounds.

Acoustic Impedance Tests↗

PubMed1999

Polymer-based lanthanide luminescent sensor for detection of the hydrolysis product of the nerve agent Soman in water.

The techniques of molecular imprinting and sensitized lanthanide luminescence have been combined to create the basis for a sensor that can selectively measure the hydrolysis product of the nerve agent Soman in water. The sensor functions by selectively and reversibly binding the phosphonate hydrolysis product of this agent to a functionality-imprinted copolymer possessing a coordinatively bound luminescent lanthanide ion, Eu3+. Instrumental support for this device is designed to monitor the appearance of a narrow luminescence band in the 610-nm region of the Eu3+ spectrum that results when the analyte is coordinated to the copolymer. The ligand field shifted luminescence was excited using 1 mW of the 465.8-nm line of an argon ion laser and monitored via an optical fiber using a miniature spectrometer. For this configuration, the limit of detection for the hydrolysis product is 7 parts per trillion (ppt) in solution with a linear range from 10 ppt to 10 ppm. Chemical and spectroscopic selectivities have been combined to reduce the likelihood of false positive analyses. Chemically analogous organophosphorus pesticides tested against the sensor have been shown to not interfere with determination.

Chemical Warfare Agents↗

PubMed1999

Electromyographic activity of the human lateral pterygoid muscle during contralateral and protrusive jaw movements.

Understanding of the normal function of the lateral pterygoid muscle is limited. The principal aim here was to determine whether there is a progressive increase in lateral pterygoid activity as the mandibular condyle moves downwards and forwards as would be expected if the muscle is concerned with the precise horizontal positioning of the mandible. In eight humans, recordings were made of the activity of the superior (SHLP) and inferior (IHLP) heads of the lateral pterygoid and the masseter, anterior temporal, posterior temporal and digastric muscles, together with the movement of the palpated lateral condylar pole (JAWS-3D tracking system) during trials of a contralateral and a protrusive jaw movement. Recording sites in SHLP and, in one participant, IHLP were verified by computed tomography. In each participant there was a progressive increase in the rectified and smoothed SHLP and IHLP activity in association with condylar movement during the contralateral and protrusive jaw movement. Further, irregularities in condylar movement, which reflected variations in the rate at which the jaw was moved, were correlated in time with prominent bursts of SHLP and IHLP activity. In all participants there was a consistently high correlation coefficient between the rectified and smoothed SHLP and IHLP activity and condylar displacement during the contralateral or protrusive jaw movements. For example, the mean (+/-SD) correlation between anterior condylar translation during contralateral excursion and SHLP activity was 0.91+/-0.09, and for IHLP 0.96+/-0.02. For the masseter, anterior temporal, posterior temporal and digastric muscles, mean r-values were, respectively, 0.10+/-0.77; -0.14+/-0.72; 0.24+/-0.78; 0.54+/-0.47. When treated as a group the correlation coefficients for SHLP and IHLP were statistically significantly different from the correlation coefficients for the other muscles treated as a group (ANOVA; p < 0.002 for correlation with anterior translation). These observations support the notion that the lateral pterygoid provides the principal driving force for moving the jaw forwards or laterally in protrusive or lateral excursive condylar movements. Further, the data suggest that the muscle plays a part in the fine control of jaw movements.

Adult↗

PubMed1999

Simultaneous recording of mandibular condylar movement and single motor-unit activity at verified sites in the human lateral pterygoid muscle.

In recent years, understanding of normal jaw-muscle function has been enhanced by detailed descriptions of their complex internal architecture and of the functional activity of single motor units (SMUs). The lateral pterygoid muscle, however, has been poorly studied, although it is thought to play an important part in the control of jaw and jaw-joint movement. The present study is the first of a series of SMU studies to clarify the normal function of this muscle. The aims were to demonstrate (a) the unequivocal isolation of SMU activity from one or two verified recording sites within the lateral pterygoid, and (b) that these SMUs can be recorded reliably together with condylar movement during simple command jaw movements. Recordings of SMU activity were made with fine-wire electrodes from sites within the superior and inferior heads of the right lateral pterygoid during biting or command lateral jaw movements and combined with recordings of condylar and mid-incisor point movement. Recording sites were verified by computed tomography. In four young adults, the activities of 17 SMUs were reliably discriminated at seven recording sites within the lateral pterygoid. The units could be recorded during repeated trials of the same movement throughout a recording session with no appreciable change in amplitude or waveform. Units could also be discriminated simultaneously at separate recording sites--one in the superior head and the other in the inferior head. These data demonstrate that SMU activity can be recorded from verified sites within the lateral pterygoid simultaneously with condylar movement during command jaw movements.

Action Potentials↗

PubMed1999

Trajectories of condylar points during nonworking side and protrusive movements of the mandible.

STATEMENT OF PROBLEM: During lateral excursive and protrusive jaw movements, condylar points are distant from any instantaneous rotational center. Therefore, it is likely that different condylar points would follow similar trajectories during these movements. PURPOSE: This study evaluated the effect of changes in condylar point location on trajectories of condylar points on the nonworking side and during a protrusive jaw movement and compared these changes with the effects described for open-close and working-side condylar movements in the same group of subjects. METHODS: The movements of 5 clinically determined condylar points were recorded in 44 subjects during a contralateral excursion and during protrusion (7 radiographically determined condylar points in 2 subjects). RESULTS: During any single jaw movement, the trajectory of each condylar point was similar in form and dimension to the other condylar points within that subject. CONCLUSION: Changes in condylar point location had little effect on the trajectories of condylar points on the nonworking side and during protrusive jaw movement.

Adult↗

PubMed1999

Trajectories of condylar points during working-side excursive movements of the mandible.

STATEMENT OF PROBLEM: Trajectories of different condylar points provide different interpretations of condylar movement during open-close jaw movements. Movement of the working-side condyle is often assessed clinically by recording the trajectory of a single arbitrary condylar point. PURPOSE: This study examined the effect of the differences in condylar point location on condylar point movement trajectories during a working-side movement. METHODS: Different points exhibited different trajectories during a single working-side movement in each of 44 subjects. RESULTS: Up to 40% of a point's displacement could be attributed simply to the location of the point. CONCLUSIONS: Interpretation of condylar movement on the working side within a subject depends on the point chosen.

Adult↗

PubMed1999

Electromyographic evidence for functional heterogeneity in the inferior head of the human lateral pterygoid muscle: a preliminary multi-unit study.

OBJECTIVE: Functional heterogeneity, i.e. regional or selective activation of subpopulations of fibres within a muscle, has been described in some jaw and limb muscles. Each head of the lateral pterygoid muscle may also be functionally heterogeneous. The aims of this investigation were to develop a technique to test this hypothesis, and to use this technique to determine whether there is any multi-unit electromyographic (EMG) evidence for functional heterogeneity within the inferior head of the lateral pterygoid (IHLP). METHODS: In 3 human subjects without craniomandibular disorders, recordings were made of condylar movement and multi-unit EMG activity from two sites in the IHLP during repeated trials of a contralateral (n = 21) and a protrusive (n = 26) jaw movement. The recording sites within IHLP were approached extraorally (labelled IHLP-extra) and were verified by computer tomography (CT); the other (IHLP-intra) were from sites in IHLP approached intraorally. RESULTS: In each subject, the time of occurrence of the peak filtered signal from IHLP-extra was significantly different (P<0.05) from IHLP-intra for all protrusion trials but not for contralateral trials. CONCLUSIONS: The data suggest a task-dependent change in motor unit recruitment order within IHLP and that IHLP is functionally heterogeneous.

Adult↗

PubMed1999

Organization of somatosensory areas I and II in marsupial cerebral cortex: parallel processing in the possum sensory cortex.

Organization of somatosensory areas I and II in marsupial cerebral cortex: parallel processing in the possum sensory cortex. Controversy exists over the organization of mammalian thalamocortical somatosensory networks. An issue of particular contention is whether the primary and secondary somatosensory areas of cortex (SI and SII) are organized in a parallel or serial scheme for processing tactile information. The current experiments were conducted in the anesthetized brush-tail possum (Trichosurus vulpecula) to determine which organizational scheme operates in marsupials, which have taken a quite different evolutionary path from the placental species studied in this respect. The effect of rapid reversible inactivation of SI, achieved by localized cortical cooling, was examined on both evoked potential and single neuron responses in SII. SI inactivation was without effect on the amplitude, latency, and time course of SII-evoked potentials, indicating that the transient inputs responsible for the SII-evoked potential reach SII directly from the thalamus rather than traversing an indirect serial route via SI. Tactile responsiveness was examined quantitatively before, during, and after SI inactivation in 16 SII neurons. Fourteen were unchanged in their responsiveness, and two showed some reduction, an effect probably attributable to the loss of a facilitatory influence exerted by SI on a small proportion of SII neurons. The temporal precision and pattern of SII responses to dynamic forms of mechanical stimuli were unaffected, and temporal dispersion in the SII response bursts was unchanged in association with SI inactivation. In conclusion, the results establish that, within this marsupial species, tactile inputs can reach SII directly from the thalamus and are not dependent on a serially organized path through SI. A predominantly parallel organizational scheme for SI and SII operates in this representative of the marsupial order, as it does in a range of placental mammals including the cat and rabbit, the tree shrew and prosimian galago, and at least one primate representative, the marmoset monkey.

Animals↗

PubMed1999

Features of cortically evoked swallowing in the awake primate (Macaca fascicularis).

Although the cerebral cortex has been implicated in the control of swallowing, the output organization of the cortical swallowing representation, and features of cortically evoked swallowing, remain unclear. The present study defined the output features of the primate "cortical swallowing representation" with intracortical microstimulation (ICMS) applied within the lateral sensorimotor cortex. In four hemispheres of two awake monkeys, microelectrode penetrations were made at </=1-mm intervals, initially within the face primary motor cortex (face-MI), and subsequently within the cortical regions immediately rostral, lateral, and caudal to MI. Two ICMS pulse trains [35-ms train, 0.2-ms pulses at 333 Hz, </=30 microA (short train stimulus, T/S); 3- to 4-s train, 0.2-ms pulses at 50 Hz, </=60 microA (continuous stimulus, C/S)] were applied at </=500-micron intervals along each microelectrode penetration to a depth of 8-10 mm, and electromyographic (EMG) activity was recorded simultaneously from various orofacial and laryngeal muscles. Evoked orofacial movements, including swallowing, were verified by EMG analysis, and T/S and C/S movement thresholds were determined. Effects of varying ICMS intensity on swallow-related EMG properties were examined by applying suprathreshold C/S at selected intracortical sites. EMG patterns of swallows evoked from various cortical regions were compared with those of natural swallows recorded as the monkeys swallowed liquid and solid material. Results indicated that swallowing was evoked by C/S at approximately 20% of 1,569 intracortical sites where ICMS elicited an orofacial motor response in both hemispheres of the two monkeys, typically at C/S intensities </=30 microA. In contrast, swallowing was not evoked by T/S in either monkey. Swallowing was evoked from four cortical regions: the ICMS-defined face-MI, the face primary somatosensory cortex (face-SI), the region lateral and anterior to face-MI corresponding to the cortical masticatory area (CMA), and an area >5 mm deep to the cortical surface corresponding to both the white matter underlying the CMA and the frontal operculum; EMG patterns of swallows elicited from these four cortical regions showed some statistically significant differences. Whereas swallowing ONLY was evoked at some sites, particularly within the deep cortical area, swallowing was more frequently evoked together with other orofacial responses including rhythmic jaw movements. Increasing ICMS intensity increased the magnitude, and decreased the latency, of the swallow-related EMG burst in the genioglossus muscle at some sites. These findings suggest that a number of distinct cortical foci may participate in the initiation and modulation of the swallowing synergy as well as in integrating the swallow within the masticatory sequence.

Animals↗

PubMed1998

Signalling of static and dynamic features of muscle spindle input by cuneate neurones in the cat.

1. The capacity of cuneate neurones to signal information derived from muscle spindle afferent fibres about static stretch or vibration of forearm extensor muscles was examined electrophysiologically in anaesthetized cats. 2. Static stretch (>= 2 mm in amplitude) and sinusoidal vibration (at frequencies of 50-800 Hz) were applied longitudinally to individual muscle tendons by means of a feedback controlled mechanical stimulator, and responses were recorded from individual cuneate neurones and from individual spindle afferent fibres. 3. Cuneate neurones sampled were located caudal to the obex and displayed a sensitivity to both vibration and static stretch of forearm muscles that was consistent with their input arising from primary spindle endings. In response to static muscle stretch, they displayed graded and approximately linear stimulus-response relations, and a stability of response level at fixed lengths that was consistent with these neurones contributing discriminative information about static muscle stretch. 4. In response to sinusoidal muscle vibration the cuneate neurones also showed graded stimulus-response relations (in contrast to spindle afferents which at low vibration amplitudes attain a plateau response level corresponding to a discharge of 1 impulse on each vibration cycle). Lowest thresholds were at 100-300 Hz and bandwidths of vibration sensitivity extended up to approximately 800 Hz. 5. Temporal precision in cuneate responses to muscle vibration was assessed by constructing phase scatter and cycle histograms from which measures of vector strength could be calculated. Cuneate responses displayed somewhat poorer phase locking (and lower vector strengths) than spindle afferent responses to vibration (a reflection of uncertainties associated with synaptic transmission). Nevertheless, the remarkable feature of cuneate responses to muscle vibration is the preservation of tight phase locking at frequencies up to 400-500 Hz, which presumably enables these central neurones to contribute accurate temporal information for the kinaesthetic sense in a variety of circumstances involving dynamic perturbations to skeletal muscle.

Animals↗

PubMed1998

Effects on non-human primate mastication of reversible inactivation by cooling of the face primary somatosensory cortex.

Rhythmical jaw movements can be evoked by intracortical microstimulation within four physiologically defined regions, one of which is the primary face somatosensory cortex (face SI). It has been proposed that these regions may be involved in the selection and/or control of masticatory patterns generated at the brainstem level. The aim here was to determine if mastication is affected by reversible, cooling-induced inactivation of the face SI. Two cranial chambers were chronically implanted in two monkeys (Macaca fascicularis) to allow access bilaterally to the face SI. A thermode was placed on the dura or pia overlying each SI that had been shown with micro-electrode recordings to receive intraoral inputs. A hot or cold alcohol-water solution was pumped through the thermodes while the monkey chewed a small piece of apple or a sultana during precool (thermode temperature, 37 degree C), cool (2-4 degrees C), and postcool (37 degrees C) conditions. Electromyographic (EMG) activity was recorded intramuscularly from the masseter, genioglossus, and anterior digastric. Cooling of SI impaired rhythmical jaw and tongue movements and EMG activity associated with mastication in one monkey (H5), and modified the pattern of EMG activity in the other (H6). The total masticatory time (i.e., time taken for chewing and manipulation of the bolus before swallowing) was increased. This was due principally to an increase in the oral transport time (i.e., time taken for manipulation of bolus after chewing and before swallowing: monkey H6, control, 2.7 sec; cool, 5.2 sec, p < 0.05); the bolus was manipulated by the tongue during this period before swallowing. Within the chewing time (i.e., time during which chewing occurred), cooling resulted in a significant increase in anterior digastric muscle duration, a significant delay in the onset of masseter EMG activity, and a significant increase in the variance of genioglossus EMG duration. The data support the view that the face SI plays a part in modulating the central pattern generator for mastication.

Afferent Pathways↗

PubMed1997

The effects of neonatal median nerve injury on the responsiveness of tactile neurones within the cuneate nucleus of the cat.

1. The capacity of cuneate neurones to attain normal functional properties following neonatal median nerve injury was investigated with single neurone recording in anaesthetized cats, 12-24 months subsequent to a controlled crush injury. Effectiveness of the peripheral nerve injury was confirmed by the abolition of the median nerve compound action potential following the crush. 2. Cuneate recording was carried out after denervation of the forearm, apart from the median nerve, to ensure that neurones studied had receptive fields within the distribution zone of the regenerated median nerve. Controlled and reproducible tactile stimuli were used to evaluate the functional capacities of neurones to determine whether they were consistent with those reported earlier for cuneate neurones in cats that had normal peripheral nerve development. 3. Twenty-two cuneate neurones with well-defined tactile receptive fields within the distribution zone of the regenerated median nerve were classified according to their adaptation characteristics and functional properties. Slowly adapting neurones responded throughout static skin indentations and had graded and approximately linear stimulus-response relations over indentation ranges up to 1.5 mm. Rapidly adapting neurones responded to the dynamic phases of skin indentations and could be divided into two broad classes, one most sensitive to vibrotactile stimuli at 200-400 Hz which appeared to receive a predominant input from Pacinian corpuscle receptors, and a non-Pacinian group that included neurones most sensitive to skin vibration at 5-50 Hz which appeared to receive glabrous skin input from the rapidly adapting class of afferent fibres. 4. Based on the stimulus-response relations and on measures of phase locking in the responses to vibrotactile stimuli, it appears that the functional properties of cuneate neurones activated from the field of a regenerated median nerve subsequent to a neonatal nerve crush injury were consistent with those reported previously for 'control' cuneate neurones. The results indicate that cuneate neurones can acquire normal tactile coding capacities despite the disruption caused by prior crush injury to their peripheral nerve source.

Animals↗

PubMed1997

Micellar electrokinetic capillary chromatography with laser-induced fluorimetric detection of amines in beer.

Capillary electrophoresis with simultaneous ultraviolet absorbance and laser-induced fluorescence detection is applied to identify and quantify selected amines in beer following derivatization with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole. Quantitation was performed using the method of standard addition in order to avoid pH-dependent variations in the reactivity of the derivatizing agent with the added benefit of verifying peak identity. An inexpensive and "easy-to-use" on-column fiber optic fluorescence detection cell is described and implemented in the analysis.

Amines↗

PubMed1997

The variability of condylar point pathways in open-close jaw movements.

STATEMENT OF PROBLEM: Clinical assessments of condylar movement often rely on the movement of a single clinically determined or average value condylar point. PURPOSE: The aim of this investigation was to study the effect of differences in condylar point location on recorded movement trajectories with an open-close jaw movement. METHODS: Recordings were made of the movements of various condylar points in 44 subjects. The points were identified clinically (average value points) and radiographically. RESULTS: The trajectory of each condylar point, whether average value or radiographically determined, was different in form and dimension from any other condylar point within a subject for the same open-close jaw movement. CONCLUSIONS: Depending on the point chosen in the vicinity of the condyle, quite different interpretations of condylar movement within a subject could be made. The data underscore the caution that must be exercised when interpreting condylar movement from the movement of a single condylar point.

Adult↗

PubMed1997

The effect of posterior tooth guidance on non-working side arbitrary condylar point movement.

Occlusal form is frequently modified in clinical practice and yet we do not have detailed knowledge of the possible effects of these changes on condylar movement. The aim of this study was to quantify the effects of an alteration in the occlusion on condylar movement during a lateral excursive jaw movement. Posterior tooth guidances (i.e. metal overlays) were attached to both maxillary first molars. The movement of arbitrary condylar points on the non-working side was recorded in seven subjects during lateral excursion under natural tooth guidance (control) and was compared with that after placement of the overlays (guidance). The guidance resulted in statistically significant changes to the displacement of the arbitrary condylar points on the non-working side. For example, at a standardized (3 mm) displacement along the mid-incisor point trajectory during the lateral excursion for both control and guidance in all subjects, the corresponding displacements of the condylar points were statistically significantly decreased under the guidance situation in comparison with the control situation. These data suggest that, for the same magnitude of mandibular displacement during lateral excursion, the introduction of a posterior tooth guidance limits condylar displacement on the non-working side.

Adult↗

PubMed1997

Functional properties of neurons in the primate tongue primary motor cortex during swallowing.

Recent studies conducted in our laboratory have suggested that the tongue primary motor cortex (i.e., tongue-MI) plays a critical role in the control of voluntary tongue movements in the primate. However, the possible involvement of tongue-MI in semiautomatic tongue movements, such as those in swallowing, remains unknown. Therefore the present study was undertaken in attempts to address whether tongue-MI plays a role in the semiautomatic tongue movements produced during swallowing. Extracellular single neuron recordings were obtained from tongue-MI, defined by intracortical microstimulation (ICMS), in two awake monkeys as they performed three types of swallowing (swallowing of a juice reward after successful tongue task performance, nontask-related swallowing of a liquid bolus, and nontask-related swallowing of a solid bolus) as well as a trained tongue-protrusion task. Electromyographic activity was recorded simultaneously from various orofacial and laryngeal muscles. In addition, the afferent input to each tongue-MI neuron and ICMS-evoked motor output characteristics at each neuronal recording site were determined. Neurons were considered to show swallow and/or tongue-protrusion task-related activity if a statistically significant difference in firing rate was seen in association with these behaviors compared with that observed during a control pretrial period. Of a total of 80 neurons recorded along 40 microelectrode penetrations in the ICMS-defined tongue-MI, 69% showed significant alterations of activity in relation to the swallowing of a juice reward, whereas 66% exhibited significant modulations of firing in association with performance of the trained tongue-protrusion task. Moreover, 48% showed significant alterations of firing in relation to both swallowing and the tongue-protrusion task. These findings suggest that the region of cortex involved in swallowing includes MI and that tongue-MI may play a role in the regulation of semiautomatic tongue movement, in addition to trained motor behavior. Swallow-related tongue-MI neurons exhibited a variety of swallow-related activity patterns and were distributed throughout the ICMS-defined tongue-MI at sites where ICMS evoked a variety of types of tongue movements. These findings are consistent with the view that multiple efferent zones for the production of tongue movements are activated in swallowing. Many swallow-related tongue-MI neurons had an orofacial mechanoreceptive field, particularly on the tongue dorsum, supporting the view that afferent inputs may be involved in the regulation of the swallowing synergy.

Animals↗

PubMed1996

Placement and verification of recording electrodes in the superior head of the human lateral pterygoid muscle.

Previous studies in man have relied only on electromyographic (EMG) activity patterns and anatomical landmarks to confirm electrode placement in the superior head of the lateral pterygoid. Computed tomography (CT) was used here to determine whether indwelling fine wires could be visualized in that muscle head in man and thus provide evidence for correct placement before EMG. Two imaging sessions were conducted in six individuals. First, a series of contiguous axial CT slices was obtained to calculate the trajectory of insertion of fine wire electrodes into the superior head. For each individual, the trajectories for the location of the fine wires in the approximate mediolateral and anteroposterior centre of the superior head were different. Further axial CT slices were taken after electrode insertion; in each case, these slices clearly showed the wire ends located within the muscle. It was concluded that fine wires in the lateral pterygoid can be imaged by CT. Furthermore, imaging is necessary to accommodate interindividual anatomical variations and to confirm the position of the electrodes within the muscle.

Adult↗