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At least 307 records · Page 17Linked to original sources
PubMed2000

Neck muscle vibration alters visually-perceived roll after unilateral vestibular loss.

Unilateral sternocleidomastoid muscle vibration was applied to 21 normal and six unilateral vestibular deafferented (uVD) human subjects at head erect and during 30 degrees left and right whole body roll-tilt. In normal subjects, neck vibration had no effect upon the settings of a visual bar to subjective visual horizontal (SVH) in any roll-tilt condition. In uVD subjects settings to SVH were significantly altered by neck vibration, with ipsilesional neck vibration increasing the SVH bias at head erect. Further, during contralesional roll-tilt, ipsilesional neck vibration in uVD subjects significantly increased the E-effect. These results suggest that compensation after vestibular loss allows cervical signals to influence visual perception of roll-tilt.

Adult↗
PubMed1997

The functional effectiveness of neck muscle reflexes for head-righting in response to sudden fall.

Reflex head-righting in normal and labyrinthine-defective (LD) subjects was compared to identify the relative functional effectiveness of vestibular-collic and cervico-collic myotactic reflexes. To restrict stimuli largely to the head and neck, subjects lay supine, supported up to the shoulders on a horizontal bed with their head supported in a sling over the edge. The head fell freely as the sling was released with an electromagnetic catch. Head drops were delivered with the subjects instructed to relax and accept the fall passively or to actively right the head as fast as possible. With both instructions, righting responses in normal subjects commenced with electromyographic (EMG) bursts in the sternocleidomastoid (SCM) at 24.5 ms latency, which was reflected in a deceleration of the downwards head velocity. The latency of the earliest EMG responses in LD subjects was 67.4 ms, accompanied by similar deceleration. It is assumed that the earliest response in normal subjects is vestibular, whereas in LDs the SCM stretch reflex is the earliest response. These reflexes are followed at circa 100 ms by more intense EMG activity due to voluntary movement, but braking of head fall is evident before voluntary activity takes effect. Righting was more effective in normal subjects than in LDs, and when "active" normal subjects made more vigorous righting responses than when "passive"; whereas active righting in LDs was no better than passive. The results demonstrate that reflex responses contribute significantly to head-righting. The vestibular contribution gives an advantage over stretch reflexes alone and also assists in voluntary enhancement of reflex responses.

Acceleration↗
PubMed1990

[Extensive fibromatosis of the neck muscles].

Extensive fibromatosis, also called desmoid tumor, is a histologically benign tumor, which is nonetheless serious due to its recurrent character and to its potential for infiltration of neighboring tissues. Extensive surgery is the only effective means of treatment, radiation therapy being used only as a complement. The authors describe an elective location of the lesion in the sheaths of the scalenus muscles. This development is usually observed in young women, as is the case in the observation reported here.

Adult↗
PubMed2005

Differential effect of sleep-wake states on lingual and dorsal neck muscle activity in rats.

Postural tone is reduced during slow-wave sleep (SWS) and absent during rapid eye movement sleep (REMS). In obstructive sleep apnea subjects, upper airway dilating muscles, including those of the tongue, show a similar pattern; this contributes to sleep-related airway obstructions. However, in healthy subjects, state-dependent changes in the activity of pharyngeal muscles are variable. In seven chronically instrumented Sprague-Dawley rats, an animal model used to study sleep and sleep-disordered breathing, we quantified lingual and postural muscle activity across the sleep-wake states by measuring the root mean square levels of the electromyograms (EMG) in successive 10s intervals collected during 2h of recording at a constant circadian time (1-3p.m.). The nuchal EMG was low and steady during SWS and further reduced with occasional twitches during REMS. In contrast, the mean lingual EMG during SWS was only 5.9+/-1.6% (S.E.) of its mean in wakefulness, and during REMS, it increased to 46+/-15% (S.E.) (p<0.03) due to the appearance of phasic bursts, the intensity of which progressively increased. The lingual and nuchal activities also had different time courses during state transitions. In obstructive sleep apnea subjects, the sleep-wake changes in the activity of pharyngeal muscles may become similar to those in postural muscles as a result of pharyngeal tone adaptations to the disorder.

Animals↗
PubMed2004

Neck muscle activity and perceived pain and discomfort due to variations of head load and posture.

BACKGROUND: The increasing use of helmet-mounted displays in aviation raises issues of head-supported weight and neck musculoskeletal function, especially during acceleration. OBJECTIVES: This study aimed to quantify musculoskeletal stress as weight was added to the front of the head in different head positions and determine the effectiveness of a counterbalance in reducing stress. METHODS: There were 20 subjects who participated. The study required that the subject move his head every 10 s for 10 min to one of five positions that were assumed to represent those readily adopted in everyday situations: neutral, 30 degrees extended, 30 degrees flexed, 35 degrees left rotated, and 35 degrees right rotated. Of the subjects, 10 repeated the test while wearing a GSMK6 helmet, and when 0.5 kg, 1.0 kg, or 2.0 kg was added to the front of the helmet. The other 10 subjects repeated the test but with counterbalances. During testing, EMG was recorded from the neck extensors and sternocleidomastoid muscle. Pain levels were recorded using the Borg-CR10 scale. RESULTS: Changes in head position from neutral resulted in significant increases of EMG amplitude (mean +/- SD) in the neck extensors of up to 18 +/- 13% (p < 0.05), and due to head load by 46 +/- 33% (p < 0.05) with a frontal load of 2 kg. Sternocleidomastoid EMG showed little change due to increases in load but increased significantly by up to 265 +/- 227% of the neutral position (p < 0.05) when the head was rotated. CONCLUSIONS: The use of head-mounted displays presents the risk of detrimental effects to the musculoskeletal system. Determining the effect of added weight requires a knowledge of working head postures.

Adult↗
PubMed1999

Neck muscle activity after unilateral labyrinthectomy in the alert guinea pig.

In the guinea pig, lateral deviation of the head is a cardinal symptom of the vestibular syndrome caused by unilateral labyrinthectomy. In the course of recovery from this syndrome (vestibular compensation), lateral deviation of the head disappears completely in 2-3 days. Because this symptom is known to be due to the lesion of the horizontal semicircular canal system, and since obliquus capitis inferior (OCI) muscle is activated predominantly by yaw rotation (horizontal vestibulocollic reflex), we hypothesized that changes in the activity of this muscle could be at least in part responsible for the lateral head deviation caused by unilateral labyrinthectomy. In order to test this hypothesis, electromyographic (EMG) activities of the right and left OCI muscles, as well as eye movements, were recorded in 12 head-fixed alert guinea pigs at various times after left surgical labyrinthectomy (performed with the animals under halothane anesthesia). After the operation, a decrease in tonic EMG activity was observed in the right (contralateral to the lesion) OCI muscle while an increase in tonic EMG activity was detected in the left (ipsilateral) OCI muscle. In addition, phasic changes in EMG activity associated with ocular nystagmic beats occurred in the OCI muscles. These phasic changes were in the opposite direction to those of the tonic changes. There were bursts of activity in the right OCI and pauses in the left OCI. From measurements of rectified averaged EMG activities which took into account both parts (tonic and phasic) of the phenomenon, it was concluded that the labyrinthectomy-induced asymmetry between the activities of the left and right OCI muscles was high enough and lasted long enough to be an important mechanism in the lateral deviation of the head caused by unilateral labyrinthectomy.

Animals↗
PubMed1997

[Registration of average potentials from neck muscles after the acoustic stimulation of the vestibule in patients with impaired function of the internal ear and in healthy subjects].

Electrophysiological studies of human perceptive functions are displayed in last years. The vestibular evolved myogenic potentials (VEMP) seems to represent a new and promising technique for assessment of vestibulo-spinal reflex function. In this study we have measured VEMP in patients with disturbed function of inner ear. We have studied 6 patients with unilateral sensorineural deafness and normal excitability of vestibular organs; 6 patients with unilateral weakness of vestibular function and 19 healthy subjects. We have found that in patients with unilateral weakness of estibular function VEMPs had diminished amplitudes whereas in patients with unilateral deafness VEMPs were unchanged. These data strongly suggest that VEMPs were generated by stimulation of vestibular end-organ. VEMPs are highly objective, simple, secure and comfortable technique to assess the vestibulo-spinal connections.

Adult↗
PubMed1992

Activation of the neck muscles from the ipsi- or contralateral hemisphere during voluntary head movements in humans. A reaction-time study.

Reaction times (RTs) of EMG onset of agonist right and left sternocleidomastoid (SCM) and splenius (SPL) muscles in response to acoustic (AC) or unilateral somatosensory (SS) stimulation were measured in normal subjects, during head rotation (to the right or to the left) and flexion. No significant difference was present in the AC-RT of SCM muscles of the two sides between rotations or flexion. The same was true for the SPL. Under the tactile condition, in which the stimulus was delivered to one index finger, the RTs of both agonist muscles were shorter during head rotation toward the stimulus than away from it: the SCM contralateral to the stimulated finger was faster than the ipsilateral SCM, while the reverse was true for the SPL. During flexion, the SS-RTs of the SCM of both sides were similar, and similar in turn to the SCM-RT during rotation away from the stimulus. When the stimulus was delivered to the shoulder, the RT difference between the agonist SCMs disappeared. The delay in the activation of the SCM ipsilateral to the stimulated finger is compatible with the interhemispheric transmission time in the absence of callosal connection between the hand areas of the primary somatosensory cortex. The data favour the hypothesis that SCM activation during voluntary head rotation is controlled by the ipsilateral hemisphere.

Adult↗
PubMed1999

[Electromyographic activity of neck muscles during the production of inspiratory pressure].

The differential inspiratory EMG activities of the scalene (SCLN), sternocleidomastoid (STERNO), and trapezius (TRAPEZ) muscles were studied in 6 awake and healthy men (mean age, 22 years; and mean weight, 62.4 kg). Pairs of fine wire EMG electrodes were inserted into each of these muscles using a guide needle and high-resolution ultrasonography. With subjects on a mouthpiece, inspiratory effort against an occluded airway was recorded at end expiratory position in the standing position. Mouth pressure and integrated EMG signals were sampled to a computer during the gradual production of maximal static inspiratory pressure (PImax) over 10 s. Maximum EMG activity (EMGmax) was obtained for each muscle during specific respiratory and postural maneuvers. Mouth pressures and integrated EMG activities were expressed as percentages of PImax and EMGmax, respectively. As mouth pressure increased, SCLN, then STERNO, and finally TRAPEZ EMGs were sequentially activated in 5 subjects. In one subject, STERNO preceded SCLN EMG activation. Group mean (+/- SE) mouth pressures at the onset of SCLN, STERNO, and TRAPEZ EMG were 10.3 +/- 5.8% PImax. 30.8 +/- 8.2% PImax, and 79.3 +/- 9.6% PImax, respectively. TRAPEZ mouth pressures differed from SCLN and STERNO values (p < 0.05). At 90% PImax, group mean (+/- SE) SCLN, STERNO, and TRAPEZ EMG activity reached 69.7 +/- 9.0% EMGmax, 51.5 +/- 11.1% EMGmax, and 5.1 +/- 2.4% EMGmax, respectively. TRAPEZ EMG at 90% PImax differed from both SCLN and STERNO values (p < 0.05). These results suggest that SCLN has strong, STERNO intermediate, and TRAPEZ weak, inspiratory activities.

Adult↗
PubMed1995

Neck muscle responses to abrupt free fall of the head: comparison of normal with labyrinthine-defective human subjects.

1. EMG responses from sternocleidomastoid (SCM) and orbicularis oculi were recorded in subjects who lay supine with their heads cradled in a sling. When the sling released abruptly, their heads fell freely. Normal and bilateral labyrinthine-defective subjects (LDs) were studied. 2. The normal response in SCM was a small burst of excitation at 22-25 ms latency, of 18 ms duration. This merged into a larger, later burst. The drop also produced eye blinks at 22-38 ms. 3. The onset of the SCM response in LDs was delayed (56-73 ms) even though the latency of their eye blinks was normal. 4. We conclude that the early response at approximately 22 ms in normal subjects is mediated by a vestibulocollic reflex. The delayed activity in LDs may be a stretch reflex. This is the first demonstration of the latency of the vestibulocollic pathway to natural stimulation in man.

Acceleration↗
PubMed1998

[Examination of averaged EMG potentials from the neck muscles after vestibular organ activation by acoustic stimulus (VEMPs)].

Electrophysiological examination of the function of perceptive organs, like eye or cochlea, works up more and more interest in scientists to look for an objective method of vestibular end organ investigation. In many papers authors attempt to estimate the efficiency of vestibular organs after using angular or linear acceleration as stimulus, which required special and expensive apparatus. Papers that described vestibular evoked myogenic potentials (VEMPs) seem to be very promising. In this study an attempt was taken to obtain VEMPs with own modification of stimulus and response register. Preliminary examinations in 14 healthy volunteers were performed. Two subjects with sensorineural deafness on one side and symmetric, normal excitability of vestibular organs and 4 with bilateral hearing loss and unilateral weakness of vestibular excitability were examined. There were also 6 patients with only weakness of vestibular excitability. On the basis of practical observations, there is a possibility that evoked potentials were a result of stimulation of vestibular part of the inner ear--sacculus. The method of the study is objective, simple, secure and comfortable for patients.

Adult↗