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PubMed1984

Sites in the rabbit flocculus specifically related to eye blinking and neck muscle contraction.

In alert rabbits, the cerebellar flocculus was mapped for effects of local stimuli delivered through glass microelectrodes. Triple-barreled glass microelectrodes were used, each barrel of which was filled with solution containing one of three different dyes (Fast Green FCF, Pontamine Sky Blue and Nigrosine) for differentially labeling the sites exhibiting different stimulus effects. In addition to eye movements reported earlier, eye blinking and contraction of dorsal neck muscles were elicited from limited areas of the flocculus. Eye blinking sites were concentrated rostroventrally and neck muscle contraction sites caudoventrally within the flocculus. The present results suggest that the rabbit flocculus contains specific sites devoted to the control of eye blinking and neck posture.

Animals↗

PubMed1988

Vestibular disturbances after neck muscle sectioning in rat.

The nystagmus response to rotatory acceleration was investigated in rats. The stimulus was exerted by a turntable accelerated 13.3%/sec2 for 9 seconds and after 1-2 minutes decelerated accordingly. Eye movements were recorded using the search coil technique. The duration of postrotatory nystagmus and speed of slow component velocity gain were recorded. After unilateral neck muscle sectioning no change appeared. After bilateral sectioning the nystagmus response was increased with a remaining high gain and prolonged response duration. The experiments show the influence by the muscles on the velocity storage mechanism.

Acceleration↗

PubMed1979

[Neural mechanisms of group I fibers of neck muscles (author's transl)].

Afferent projection of upper cervical dorsal roots C2 and C3 upon spinal cord and brain stem was investigated on cats using both histological and electrophysiological methods. 1. Degenerated terminals, stained by Fink-Heimer's methods, were found in Rexed's laminae III and IV, intermediate nucleus and ventral horn of the spinal cord and nucleus cuneatus and spinal trigeminal nucleus. 2. Monosynaptic reflex responses were obtained from motor nerves innervating dorsal neck muscles by stimulating the dorsal roots in some decerebrated cats. However, this reflex responses could be unable to elicite in the spinal preparation. 3. The neurons responding exclusively to the ventral rami located in cranial parts of the nucleus and those responding to dorsal rami located in the caudal region. Neurons responding to both rami were also found.

Animals↗

PubMed1996

Reflex (unloading) and (defensive capitulation) responses in human neck muscle.

1. We studied unloading and stretch responses in human neck muscle during manoeuvres in which the head pulled against a 2-3 kg weight which could be abruptly released or applied electromagnetically. 2. During head tracking in pitch, unloading of the weight induced inhibition of EMG in the contracting sternocleidomastoid at a mean latency of 24.9 ms in normal subjects and at 41 ms in bilateral labyrinthine-defective subjects, with antagonist (trapezius) excitation at 30.5 and 41.3 ms, respectively. During tracking in yaw, unloading induced inhibition in the contracting splenius capitis (SpC) at a mean latency of 20.4 ms in normal subjects and 25 ms in labyrinthine-defective subjects, with excitation in the antagonist SpC at 22.2 and 24 ms, respectively. 3. If subjects tried to resist an unexpected sideways tug on the head a burst occurred in the stretched SpC at a mean latency of 53.5 ms. When subjects relaxed there was excitation of the shortening of SpC at 75.9 ms, which assisted the imposed motion and is possibly a "defensive reflex".

Adult↗

PubMed2002

Three-dimensional spatial tuning of neck muscle activation in humans.

The complex structure of the neck musculoskeletal system poses challenges to understanding central nervous system (CNS) control strategies. Examining muscle activation patterns in relation to musculoskeletal geometry and three-dimensional mechanics may reveal organizing principles. We analyzed the spatial tuning of neck muscle electromyographic (EMG) activity while subjects generated moments in three dimensions. EMG tuning curves were characterized by their orientation (mean direction) and focus (spread of activity). For the four muscles that were studied (sternocleidomastoid, splenius capitis, semispinalis capitis and trapezius), EMG tuning curves exhibited directional preference, with consistent orientation and focus among 12 subjects. However, the directional preference (orientation) of three of the four neck muscles did not correspond to the muscle's moment arm, indicating that maximizing a muscle's mechanical advantage is not the only factor in determining muscle activation. The focus of muscle tuning did not change with moment magnitude, demonstrating that co-contraction did not increase with load. Axial rotation was found to have a strong influence on neck muscle spatial tuning. The uniform results among subjects indicate that the CNS has consistent strategies for selecting neck muscle activations to generate moments in specific directions; however, these strategies depend on three-dimensional mechanics in a complex manner.

Adult↗

PubMed2006

Evaluation of repeatability of pressure algometry on the neck muscles for clinical use.

Neck and shoulder pain is a common disorder which is often associated with a low-pressure pain threshold (PPT) of muscle tissues as manifested by hyperalgesia on palpation or the use of a pressure algometer. The objective of the present study was to evaluate the intratester repeatability of pressure algometer (Force-Five) on the neck and shoulder area in women with neck pain. The study was cross-sectional with single-group repeated measurements. PPT measurements in 20 women with chronic non-specific neck pain were measured on consecutive days at the levator scapulae, at two points on the trapezius muscles on each side and at the sternum as the only non-muscular site. The intratester repeatability of the PPT measurements was satisfactory or good (Intraclass correlation coefficient (ICC 0.78-0.93). The coefficient of repeatability ranged from 16.8 to 24.4N/cm2 and the coefficient of variation ranged from 10% to 22%, depending on the site tested. Considerable individual variation was observed when consecutive measures were analysed against their mean. On the group level the repeatability of the measurements allows the pressure algometer to be used for research purposes. However, on the individual level, due to the considerable variation found in the PPT results, caution is advised when interpreting the results in clinical practice.

Chronic Disease↗

PubMed1995

Muscle cell death during the development of head and neck muscles in the chick embryo.

Degenerating myofibers have been reported in the embryos and neonates of a number of birds and mammals, but neither the pervasiveness of the phenomenon nor the spatio-temporal patterns of degeneration has been examined in detail. Using transmission electron microscopy, we determined the patterns of muscle cell death in the chick biventer cervicis, a head extensor muscle. Cell death is most pronounced at incubation days 10 through 15, and occurs throughout the muscle. This is the period during which many myofiber clusters segregate into individual fibers, each with a separate basal lamina, and secondary myofibers become demarcated. Cells of largest diameter, presumably the primary myofibers, are preferentially affected. Degenerating cells exhibit a cohort of cytological features consistent with apoptosis, including the presence of dense, darkly-staining, hypercontracted myofibrils, misshapen nuclei with irregular chromatin condensations along the nuclear envelope, and scores of cytoplasmic vesicles and vacuoles. In cross section some large diameter muscle cells are characterized by sparse, flocculent cytoplasm that is devoid of myofibrils and organelles. Some show disintegrating cell membranes. In longitudinal section 200-300 microns long regions of hypercontracted myofibrils alternate with areas devoid of fibrils; this arrangement suggests that the myofibrils break into segments that are in register along one part of a muscle fiber and entirely absent from the adjacent length of fiber. We have observed similar patterns of muscle cell degeneration in the complexus, splenius cervicis, depressor mandibulae, and branchiomandibularis muscles. By day 18 of incubation most signs of degeneration are absent and by hatching (day 21) the muscle fibers all appear healthy. Many of these cytological changes in embryonic head muscle cells are characteristic of programmed cell death. We hypothesize that large-scale death of myocytes is a normal part of avian myogenesis and an important mechanism for affecting the transformation from embryonic to hatching muscle patterning.

Animals↗

PubMed2005

Surface electromyographic response of the neck muscles to maximal voluntary clenching of the teeth.

The purpose of this study was to evaluate the activity of digastric, sternocleidomastoid, upper trapezius, lower trapezius and cervical muscles in response to maximum voluntary clenching (MVC) of the teeth. Twenty healthy subjects aged 24-31 years were divided into two groups of 10: a resting group and a clenching group. The resting group simply maintained the mandible at rest with teeth apart for two 1-min periods, whereas the clenching group underwent an initial resting period followed after 1-min by a clenching period during which they were required to perform MVC. The electromyography (EMG) responses of each muscle were recorded during all periods, and means and standard deviations of the root mean square EMG were calculated. Within-group and between-group comparisons of EMG activity were made using, respectively, the Sign two-tailed test for two related samples and the Kolmogorov-Smirnov two-tailed test for two independent samples (significance level 0.05). Data indicated a significant increase of EMG activity of the anterior neck muscles (digastric and sternocleidomastoid) during MVC as compared with EMG recorded during resting periods. If confirmed by further research, our findings suggesting an involvement of anterior neck muscles during isometric contraction of the jaw elevator muscles may have clinical implications.

Bite Force↗

PubMed2004

Anticipatory modulation of neck muscle reflex responses induced by mechanical perturbations of the human forehead.

The aim of this study was to test whether anticipation of upcoming head blow stimuli, which elicit reflex responses in the neck muscle, makes the reflex responses greater or not. In nine healthy subjects the reflex responses were elicited in the sternocleidomastoid (SCM) muscle in the eyes-open (EO) and eyes-closed (EC) conditions, which corresponded to the predictable and unpredictable conditions, respectively. The subjects were instructed not to resist the perturbations after the impact. The results demonstrated that the reflex response of the SCM muscle was significantly smaller in the predictable EO condition than in the unpredictable EC condition (P < 0.05), although no significant differences were observed in either the background EMG activities or the head accelerations. Further, this effect of anticipation was observed only in the later reflex EMG component, which most probably mediated the stretch reflex pathway. In contrast, no significant difference was observed in the early component, which was presumed to be the vestibular-collic reflex. The reduced stretch reflex response was suggested to be functionally relevant to the task requirement, i.e., to let the neck extension movement occur, and not to resist after the impact of the head blow. It was concluded that the anticipation has an effect on reducing the stretch reflex responses in the neck muscle, but does not have any effect on the presumed vestibular-collic reflex under the present experimental paradigm. It is suggested that the gain of the stretch reflex pathway is modulated by anticipatory information of upcoming mechanical event.

Adult↗

PubMed1997

Distribution of motoneurons supplying feline neck muscles taking origin from the shoulder girdle.

A combination of fluorescent retrograde tracers and horseradish peroxidase (HRP) was used to compare the spinal distributions of motoneurons supplying shoulder muscles with attachments to the skull and cervical spinal cord that suggest a significant role in head movement. Two muscles, the rhomboideus and the levator scapulae, were innervated by multiple segmental nerve bundles that entered the muscles at different rostrocaudal locations. Motoneurons that were labelled retrogradely from rhomboideus nerve bundles formed a single, long column in the ventral horn from C4 to C6, lateral to previously studied motor nuclei supplying deep neck muscles. When different tracers were used to differentiate motoneurons supplying specific nerve bundles, discrete subnuclei could be identified that were organized in a rostrocaudal sequence corresponding to the rostrocaudal order of the nerve bundles. Levator scapulae motoneurons formed a second elongate column immediately lateral to the rhomboidues motor nucleus. Three other muscles, that trapezius, sternomastoideus, and cleidomastoideus, were supplied by cranial nerve XI. Labelled motoneurons from these muscles formed a single column from the spinomedullary junction to middle C6. Within this column, the three motor nuclei supplying the sternomastoideus, cleidomastoideus, and trapezius were laminated mediolaterally. Sternomastoideus and cleidomastoideus motoneurons were confined to upper cervical segments, whereas trapezius motoneurons were found from C1 to C6. In C1 and C6, the motoneuron column was located centrally in the gray matter, but, between C2 and C5, the column lay on the lateral wall of the ventral horn in a position dorsolateral to motor nuclei supplying the rhomboideus and the deeper neck muscles. The findings in this study suggest that descending and propriospinal systems responsible for coordinating head movement may have to descend as far caudally as C6 if they are to project onto muscles controlling the mobility of the lower neck.

Accessory Nerve↗

PubMed1987

Modulation by eye position of neck muscle contraction evoked by electrical labyrinthine stimulation in the alert cat.

Modulation of vestibulo-spinal reflexes by gaze is a model system for studying interactions between voluntary and reflex motor activity. In the alert cat, the EMG of Splenius and Obliquus capitis muscles increases with ipsilateral gaze eccentricity during spontaneous eye movements. Labyrinth stimulation by current pulses evokes EMGs with latencies consistent with a three neuron vestibulocollic pathway. The amplitude of evoked activity increases with eye position. The directions in which eye movements increase EMG was usually the same for both spontaneous and induced EMG activity, namely, horizontal and ipsilateral. However, sometimes the increase in spontaneous EMG occurred with horizontal eye position, whereas the induced EMG changed with vertical eye position. Spontaneous and evoked EMG are then modulated by different eye position signals. Command signals reflecting eye position probably reach two different types of neurons in the vestibulo-collic pathway, most likely secondary vestibular neurons and neck muscle motoneurons.

Animals↗

PubMedDate not supplied

[The correlation of the bioelectrical activity of the archistriatum and the neck muscles of chickens in ontogeny].

Experiments have been carried out on 14-, 18-day chick embryos and 1-day chicks. Studies were made on amplitude-frequency, temporal, integral parameters of EEG in archistriatum and EMG in neck muscles, as well as on their crosscorrelation. It was shown that archistriatum EEG may be recorded from the 14th day of incubation. From the 14th to the 18th day, rapid changes in the frequency were observed, from the 18th day--in the amplitude. EMG had a pattern of bursts of the bioelectrical activity which consists of both high and low amplitude action potentials. Between the 14th and the 18th day of incubation, more significant changes were observed in the duration of these bursts, after the 18th day--in the interval between the latter. Reliable correlation between the integral parameters of EEG in archistriatum and EMG in neck muscle was found in 18-day chick embryos and 1-day chicks. Bilateral coagulation of archistriatum resulted in significant increase in total bioelectrical activity of the muscle.

Action Potentials↗

PubMed2003

Attenuation of human neck muscle activity following repeated imposed trunk-forward linear acceleration.

It has been suggested that, after a passive linear acceleration of a seated subject which resembles a small, rear-end car impact, sensory information from proprioceptive, vestibular, and visual systems elicit stabilizing neck muscular responses. These neck muscular responses are presumably reflex based and are modified with the magnitude of the perturbation. A key issue that remains is to determine whether the neck and head postural responses can be modulated by a previous experience of the acceleration and not only by the magnitude of the acceleration. This question is of interest because, contrary to cadaver studies, one could expect that humans apprehending a rapid trunk acceleration would adopt a bracing behavior to minimize head movements. The aim of the present experiment was to verify whether neck-muscle activities can be modulated when prior knowledge about whole-body acceleration onset, direction, and magnitude are unknown compared with when only acceleration onset is unknown. Nine seated subjects were submitted to 11 imposed, forward linear accelerations (1.1 g). For the first trial, subjects were completely unaware of the platform acceleration characteristics (onset, direction, amplitude, and acceleration magnitude). For the subsequent ten trials, subjects knew they would be submitted to a forward linear acceleration, but the onset of the acceleration was unknown. Head kinematics and EMG responses of the neck muscles to the first perturbation were similar for all subjects (6.2 degrees head extension, EMG activity starting from 55 to 72 ms after platform onset). Following the first trial, however, all subjects showed a decreased neck EMG activity. Moreover, subjects responded in one of two ways across trials: one group of subjects ( n=5) maintained a constant head angular position and velocity, whereas the other group ( n=4) showed an increased head angular position (up to 12.6 degrees ) and velocity. This suggests that the first perturbation trial revealed a completely reactive response. After this initial trial, the responses observed may present a mixture of feedforward and feedback control. It is likely that whiplash injuries occur under conditions resembling those observed for the first trial only. If this is the case, the behavior for the following trials cannot be representative of injury mechanisms occurring in whiplash-like motion. Altogether, our results strongly suggest that, following repeated trunk linear accelerations of a constant magnitude, the nervous system prefers to minimize muscle stress instead of adopting a bracing strategy.

Acceleration↗

PubMed2003

Intramuscular injection of antigens and adjuvant preferentially decreases 18:2n-6 and 18:3n-3 in pig neck muscle.

Linoleic (18:2n-6) and alpha-linolenic acids (18:3n-3) have many important physiological functions including immunomodulation. We tested how immunization influences the metabolism of 18:2n-6 and 18:3n-3 in the neck muscle of pigs. At 35 d old, pigs received either an intramuscular neck injection containing hen egg white lysozyme (HEWL), killed Mycobacterium tuberculosis, and Freund's complete adjuvant (immunized) or PBS (control). At 49 d old, immunized pigs received a booster injection of HEWL and Freund's incomplete adjuvant, and the control pigs received PBS into the neck. At 56 d old, all pigs received an intradermal injection of Mycobacterium bovis into the hind leg to induce a delayed-type hypersensitivity (DTH) reaction. At 57 d old, immunized pigs had a twofold increase in serum haptoglobin, a 10-fold increase in antibodies to HEWL, and the skinfold at the DTH reaction site was 10 times thicker than the controls. Both 18:2n-6 and 18:3n-3 (% composition) were approximately 25% lower in muscle TG, 40% lower in FFA, 50% lower in phospholipids, but not different in cholesteryl esters of the neck muscle of immunized pigs. The antigens in this model induce an increased response in the innate (haptoglobin), humoral (antibodies), and cellular (DTH) immune systems as well as a preferential decrease of 18:2n-6 and 18:3n-3 in the inflamed neck muscle. It appears that 18:2n-6 and 18:3n-3 are preferentially metabolized (possibly beta-oxidized) in response to antigens.

Animals↗

PubMed2002

Differences in the fatigue of masticatory and neck muscles between male and female.

The purpose of this study was to investigate the nature of fatigue and recovery of masticatory and neck muscles and the differences between sexes in normal subjects during experimentally induced loading. Subjects consisted of eight males (mean age: 27.6 years) and eight females (mean age: 24.2 years) selected from the volunteers in the Faculty of Dentistry, Hiroshima University. The inclusion criteria for the subjects were as follows: (1) good general health, (2) normal horizontal and vertical skeletal relationships, (3) no severe malocclusions and (4) no complaints of temporomandibular disorders. Each subject was requested to bite an occlusal-force meter with 98, 196 and 294 N forces on the first molar region per side for 45 s. Activities of the masseter and sternocleidomastoid (SCM) muscles were recorded during these performances. Fatigue and recovery ratios were calculated with mean power frequency of power spectrum using a fast Fourier transform algorithm. Significant differences in the fatigue ratios between both sexes were found for the masseter muscle with 98, 196 and 294 N bite forces. Meanwhile, the SCM presented a significant difference between both sexes only at 98 N biting. Significant differences in the recovery ratios between both sexes were more prominent in the masseter muscle than in the SCM. These results suggest that the differences in muscle endurance between sexes may have some association with higher susceptibility of craniomandibular disorders in females than in males.

Adult↗

PubMed1988

On neck muscle activity and load reduction in sitting postures. An electromyographic and biomechanical study with applications in ergonomics and rehabilitation.

In this study of the biomechanics and muscular function of the cervical spine, skilled women workers simulated standardized electromechanical assembly work in eight sitting postures. Normalized electromyography was used to quantify activity in neck-and-shoulder muscles. With the whole spine flexed, muscle activity in the cervical erector spinae, trapezius and thoracic erector spinae muscles was higher than when the whole spine was straight and vertical. The posture with the trunk slightly inclined backward and neck vertical gave the lowest activity levels. Flexed neck compared to vertical neck gave higher activity in the cervical erector spinae. Work with abducted arm gave high neck muscle activity. Work postures can thus be optimized to diminish neck muscle load. Two ergonomic acids were studied during the work cycle. Elbow support reduced the activity in the trapezius and thoracic erector spinae/rhomboids muscles in the posture with the whole spine flexed and in the posture with the whole spine vertical. Arm suspension gave mainly similar reduction in these postures, and also a reduction in the cervical erector spinae. In the position with the trunk slightly inclined backward, arm suspension gave a reduction in the trapezius. These findings indicate that arm support or arm suspension can be used to reduce neck muscle load. Three methodological studies related to neck muscle load and normalization were included. 1) Examination of the effect of different isometric maximum test contractions on neck muscles showed that all contractions activated all muscles studied, including those on the contralateral side, to some extent and at various levels. The highest frequency of attained maximum levels was: for neck extension, in cervical erector spinae; for cervical spinae lateral flexion, in splenius and levator scapulae; for arm abduction, in trapezius, and, for shoulder elevation and scapular retraction/elevation, in thoracic erector spinae/rhomboids. Proximal resistance gave higher activity than distal. 2) The relationship between EMG activity and muscular moment was studied in women during submaximal and maximum isometric neck extension. The relationship found was non-linear, with greater increase in activity at high moments in the posterior neck muscles studied. The slightly flexed cervical spine position induced a higher level of activity in erector spinae cervicalis than did the neutral position for a given relative muscular moment. 3) Muscular activity was related to cervical spine position during maximum isometric neck extension. Peak activity in the cervical erector spinae was found in the slightly flexed lower-cervical spine position.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed2004

Long-lasting body leanings following neck muscle isometric contractions.

Our objective was to investigate the neural mechanisms and the functional relevance of motor effects that develop involuntarily following the release of a sustained isometric muscle contraction. The few data available in the literature deal only with post-contractions occurring in a body segment. Although these data emphasise the role of proprioceptive input, the question as to whether this phenomenon is of central or peripheral origin remains unclear. Given the leading role of neck muscle proprioceptive input in body orientation and posture regulation, we designed two experiments to test for postural posteffects after voluntary and involuntary neck muscle contraction. The spatiotemporal characteristics of the posteffects were analysed by means of stabilometric recordings following 30-s isometric contraction of splenius, trapezius and levator muscle groups, and 30-s electrically-induced contraction of the levator muscle group. Results show that a postural response occurred after voluntary contraction of each muscle group tested, which was oriented in the plane of action of the muscle, and lasted 14 min at least. In contrast, no clearly oriented body leanings were found after electrical stimulation of the levator muscle, except for a slight increase in natural postural instability. Data are interpreted as a change in the postural reference resulting from an increase in proprioceptive inflow accompanying mainly the voluntary muscle contraction.

Adult↗

PubMed2002

Dynamic modeling of the neck muscles during horizontal head movement.

This paper presents modeling and simulation of superficial neck muscle movement in the horizontal plane (yaw). The parametric muscle model was constructed using Pro/Engineer 2000i Student Edition, Parametric Technologies Corp, and simulated using Pro/Mechanica. Pennation angles, force-tension, force-generation and rate of muscle activation data were obtained from anatomic and physiological studies. Saccadic eye movement models developed by G. Alexander Korentis and John Enderle also provided the basis for this model.

Biomechanical Phenomena↗