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At least 199 records · Page 11Linked to original sources
PubMed2001

Startle response of human neck muscles sculpted by readiness to perform ballistic head movements.

1. An acoustic startle stimulus delivered in place of a 'go' signal in a voluntary reaction time (RT) task has been shown previously to advance the onset latency of a prepared distal limb movement without affecting the amplitude of the muscle response or movement kinematics. The primary goal of this study was to use muscles with a larger startle response to investigate whether the startling stimulus only triggered the RT movement or whether some form of interaction occurred between a startle response and a temporally advanced RT movement. 2. Twenty healthy male or female subjects were instructed to react as quickly as possible to an acoustic 'go' stimulus by performing a ballistic head flexion or right axial rotation. The 'go' stimulus was periodically replaced by an acoustic stimulus capable of eliciting a startle reflex. Separate startle-inducing stimuli under relaxed conditions before and after the movement trials served as control trials (CT trials). Bilateral surface electromyography of the orbicularis oculi, masseter, sternocleidomastoid and cervical paraspinal muscles, and head-mounted transducers were used to measure the muscle response and movement kinematics. 3. Muscle activation times in startled movement trials (ST trials) were about half those observed in RT trials, and were not significantly different from those observed in the startle CT trials. The duration of head acceleration was longer in ST trials than in RT trials and the amplitude of both the neck muscle electromyogram (EMG) and head kinematics was larger during ST trials than during RT trials. The EMG amplitude of ST trials was biased upward rather than scaled upward compared with the EMG amplitude of RT trials. 4. Over the 14 ST trials used in this experiment, no habituation of the reflex response was observed in the muscles studied. This absence of habituation was attributed to a combination of motor readiness and sensory facilitation. 5. The results of this experiment indicated that the neck muscle response evoked by a startling acoustic stimulus in the presence of motor readiness could be described as a facilitated startle reflex superimposed on a temporally advanced, pre-programmed, voluntary RT movement. Parallel reticular pathways to the neck muscle motoneurones are proposed as a possible explanation for the apparent summation of the startle and voluntary movement responses.

Adult↗
PubMed1990

[Histological and histochemical changes in the neck muscles of spontaneously occurring scoliosis in a special strain of Japanese quail, SQOHM].

A strain of Japanese quail, SQOHM, is known as a model of idiopathic scoliosis in humans. It shows hereditary scoliotic deformities occurring in the cervical region. Histological, histochemical and serological studies were performed in 51 scoliotic and 109 non-scoliotic quail. Histological study revealed internal nuclei and tiny groups of small fibers in the neck muscles. The incidence of these, however, was only 19% in the scoliotic and 7% in the non-scoliotic quail. Histochemical observation with adenosine triphosphatase, phosphorylase and succinic dehydrogenase stains was made on the dorsal neck muscles. An increase in the number of beta-fibers, and a decrease in the number and hyperplasia of alpha-fibers were observed on the concave side of the scoliosis. The increase in number of beta-fibers on the concave side can play a role in promoting the deformity was suggested.

Adenosine Triphosphatases↗
PubMed1988

Activation of neck muscles from the human motor cortex.

Percutaneous stimulation of the motor cortex has been used to assess directly the supranuclear projection to the sternomastoid, trapezius and splenius capitis muscles. The projection to sternomastoid had a mean latency of 6.5 ms for the contralateral electromyographic response. A smaller and more variable response, usually with a longer latency (mean 9.5 ms), occurred in the ipsilateral sternomastoid. Electromyographic responses on both sides were potentiated by voluntary contraction or strong inspiratory efforts. They were evoked at lower stimulus intensities in the contralateral sternomastoid. Short-latency responses were recorded from the contralateral but not the ipsilateral trapezius and splenius capitis muscles. These results indicate that weakness of head rotation towards the hemiplegic limb following a supranuclear lesion may reflect reduced power of dorsal neck muscles rather than of sternomastoid.

Electric Stimulation↗
PubMed1979

Neck muscle and trigeminal input to the upper cervical cord and lower medulla of the cat.

Experiments on chloralose-anaesthetized cats have shown that low-threshold neck muscle afferents project to laminae IV and V in the dorsal horn of the upper cervical cord, to lamina VI including the region which encompasses the central cervical nucleus, as well as to extensive regions of the ventral horn. At posterior medullary levels projections also exist to laminae IV, V, and VI of the spinal nucleus of V (although those to lamina IV are circumscribed), to the deep layers and lateral margin of the cuneate nucleus, and to the inferior olive. These projections are both from low- and high-threshold afferents. Evidence of a functional relationship between the trigeminal and neck muscle afferent system was found both in the upper cervical cord and lower medulla. About 40% of units in both regions receive a convergent input and when convergence could not be demonstrated, prior stimulation of one modality in some instances affected the responsiveness of the unit to the other modality. A motor role was found for some trigeminal afferent projections to the upper cervical cord. Trigeminal afferents consistently activated antidromically identified motoneurons of splenius, biventer cervicis, and complexus.

Action Potentials↗
PubMed2007

Electromyography of superficial and deep neck muscles during isometric, voluntary, and reflex contractions.

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41 years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45 deg intervals) from the neutral posture; (ii) 50 N isometric contractions with a slow sweep of the force direction through 720 deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular-kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models' muscle geometry, physiology, and feedforward/feedback neuromechanics.

Adult↗
PubMed1991

Torque vectors of neck muscles in the cat.

Anatomical texts describe the neck musculature without measurements of muscle locations or quantitative estimates of pulling actions (torques). This study is based on measurements in stereotaxic coordinates of cat neck muscle origins and insertions, and neck intervertebral rotation axes. Torque vectors in three dimensions were calculated for 14 pairs of dorsal and ventral muscles that insert on the skull or first cervical vertebra. Predicted torque vectors were in general agreement with qualitative statements in the literature. Biventer cervicis and the rectus capitis major, medius, and minor muscles act mainly to raise the head, and longus capitis acts almost exclusively to lower the head. Longissimus capitis, sternomastoid, and cleidomastoid act mainly to roll the head. Complexus acts about equally to raise the head and rool it. Splenius and occipitoscapularis have torque in all three coordinate directions. Torques were altered by changing the pitch of the head with respect to the neck. The calculated neck muscle torques did not correspond to previously reported directions of neck muscle excitation during the vestibulocollic reflex. The neck musculature appears to be a complex, multidimensional system that presents interesting problems in motor control.

Animals↗
PubMed2000

Neck muscle vibration makes walking humans accelerate in the direction of gaze.

We studied the effect of the continuous vibration of symmetrical dorsal neck muscles in seven normal subjects during (a) quiet standing, (b) stepping in place movements and (c) walking on the treadmill. The experiments were performed in a darkened room and the subjects were given the instruction not to resist the applied perturbation. In one condition the velocity of the treadmill was controlled by feedback from the subject's current position. Head, trunk and leg motion were recorded at 100 Hz. In normal standing, neck vibration elicited a prominent forward body sway. During stepping in place, neck vibration produced an involuntary forward stepping at about 0.3 m s-1 without modifying the stepping frequency. If the head was turned horizontally 45 and 90 deg to the right or to the left, neck muscle vibration caused stepping approximately in the direction of the head naso-occipital axis. For lateral eye deviations, the direction of stepping was roughly aligned with gaze direction. In treadmill locomotion, neck vibration produced an involuntary step-like increase of walking speed (by 0.1-0.6 m s-1), independent of the initial walking speed. During backward locomotion, the walking speed tended to decrease during neck vibration. Thus, continuous neck vibration evokes changes in the postural reference during quiet standing and in the walking speed during locomotion. The results suggest that the proprioceptive input from the neck is integrated in the control of human posture and locomotion and is processed in the context of a viewer-centred reference frame.

Acceleration↗
PubMed1981

Responses of cat mesencephalic reticulospinal neurons to stimulation of superior colliculus, pericruciate cortex, and neck muscle afferents.

Neurons were recorded extracellularly in the mesencephalic reticular formation outside the interstitial nucleus of Cajal in cerebellectomized cats anesthetized with alpha chloralose. Reticulospinal neurones were identified by antidromic stimulation of the upper cervical segments. Stimulation in the deep layers of the ipsilateral superior colliculus evoked firing in 36% of reticulospinal neurons. For many neurons thresholds for activation were high in the intermediate tectal layers and declined as the electrodes entered the underlying tegmentum. However, low threshold points were found above the deep fiber layer within the superior colliculus for some cells. Stimulation of the contralateral superior colliculus excited 10% of neurons and thresholds for activation were high above the deep fiber layer for all neurons. Stimulation of the ipsilateral and contralateral pericruciate cortex excited 39 and 21% of neurons, respectively. The lowest threshold area was found in the frontal eye fields. Sixteen percent of neurons received excitation from neck muscle afferents (C2 biventer-cervicis) bilaterally. Comparison of responses between mesencephalic reticulospinal neurons and interstitiospinal neurons (Fukushima et al. 1981) showed that responses of the two groups of neurons were similar when the pericruciate cortex and neck muscle afferents were stimulated. However, a difference was observed in tectal responses. since low threshold points were rarely observed above the deep fiber layer for interstitiospinal neurons.

Afferent Pathways↗
PubMedDate not supplied

[Temperature changes in the neocortex, posterior hypothalamus and neck muscles in the wakefulness-sleep cycle of white rats].

In chronic experiments on male relatively unrestrained rats, simultaneous studies have been made on the behaviour during wake-sleep cycle and on changes in the temperature of the neocortex, posterior hypothalamus and neck muscles. Interaction of two mechanisms at the hypothalamic level is discussed, namely the development of various stages of the wake-sleep cycle and thermoregulation. Special attention is paid to the phase of rapid sleep, when the transition of an animal from homoiothermic to heterothermic conditions presumably takes place.

Animals↗
PubMed1988

Location of motoneurons supplying upper neck muscles in the chicken studied by means of horseradish peroxidase.

The distribution of motoneurons innervating the upper cervical muscles, biventer cervicis, splenius capitis, complexus, rectus capitis dorsalis, rectus capitis lateralis, and rectus capitis ventralis in the chicken was examined by retrograde transport of horseradish peroxidase. Labeled motoneurons supplying upper neck muscles ranged from 30 to 60 micron in diameter and were located within two subnuclei in the brainstem. The rostrocaudal distributions of motoneurons projecting to individual cervical muscles ranged from 3 to 9 mm in length, both rostral and caudal to the obex. Detailed analysis of the data showed that the more dorsally positioned subnucleus projected mainly to the hypaxial muscles, i.e., the rectus capitis ventralis and lateralis, whereas the ventral subnucleus supplied chiefly the epaxial muscles, i.e., the biventer cervicis and splenius capitis. The complexus and rectus capitis dorsalis were innervated by both of these subnuclei. Historically these dorsal and ventral subnuclei, respectively, have been called the nucleus hypoglossus ventralis and the nucleus hypoglossus ventralis ventrolateralis. In view of the observation that these nuclei do not undergo retrograde degeneration following section of the hypoglossal nerves, this older nomenclature is misleading. In agreement with other authors, we suggest that these motoneuron groups should be collectively referred to as the nucleus supraspinalis.

Animals↗
PubMed1991

Illusions of head and visual target displacement induced by vibration of neck muscles.

Vibration of the posterior muscles of the neck in human subjects induces illusions of displacement and movement of a visual target when there is no visual reference (Biguer et al., 1988). Although illusions of head movement are rarely reported by subjects, when they point to the location of the nose they demonstrate an alteration of the perceived position of the head. The kinaesthetic illusion is in a direction consistent with the visual illusion but is of smaller magnitude.

Head↗
PubMed2004

Dorsal neck muscle vibration induces upward shifts in the endpoints of memory-guided saccades in monkeys.

Producing a movement in response to a sensory stimulus requires knowledge of the body's current configuration, and spindle organs embedded within muscles are a primary source of such kinesthetic information. Here, we sought to develop an animal model of kinesthetic illusions induced by mechanically vibrating muscles as a first step toward a mechanistic understanding of how kinesthesia is integrated into neural plans for action. We elected to examine the effects of mechanical vibration of dorsal neck muscles in head-restrained monkeys performing memory-guided saccades requiring them to look to the remembered location of a flashed target only after an imposed delay. During the delay on one-half of all trials, mechanical vibration (usually 1,500 ms in duration, 200 microm in amplitude, 100 Hz in frequency) was applied to the dorsal aspect on one side of the monkey's neck. We compared the metrics of such vibration saccades to control saccades without vibration during the delay interval. Relative to control saccades, the endpoints of vibration saccades were shifted consistently upward, even though the variability in saccadic endpoints was unaltered. Although the stability of the eye was compromised during the delay interval of vibration trials, as evidenced by an increased incidence of upward drifts and downward microsaccades, vibration saccades displayed different metrics than control saccades, including an upwardly deviated radial direction and increased vertical amplitude. The influence of variations in the duration (500-2,500 ms), amplitude (100-300 microm), or frequency (75-125 Hz) of vibration scaled well with the presumed change in spindle activity entrained by vibration. Comparisons of the profile of these results are made to the human literature. We conclude that neck muscle vibration induces alterations in oculomotor performance in monkeys consistent with a central interpretation of illusory neck flexion and downward gaze deviation due to increased activation in the spindles of neck extensor muscles.

Animals↗
PubMed1985

Vestibular control of neck muscles in acute and chronic hemilabyrinthectomized cats.

Reflex activity evoked in neck extensor muscles by head movements in the sagittal plane (the sagittal vestibulocollic reflex (v.c.r.), Dutia & Hunter, 1985), was studied in decerebrate cats with acute or chronic loss of one vestibular labyrinth. After acute hemilabyrinthectomy, tonic electromyographic (e.m.g.) activity in the biventer cervicis muscle ipsilateral to the lesion was normal, while that in the contralateral muscle was abolished. Sinusoidal head movements in the sagittal plane (0.1-5 Hz, 1-10 deg peak to peak) caused reflex modulation of e.m.g. activity in the ipsilateral muscle, but did not evoke any response in the contralateral muscle. The phase (re head position) of the reflex response in the ipsilateral muscle was similar to that in a normal cat with intact labyrinths, while reflex gain was lowered by 2-8 dB below its value before hemilabyrinthectomy. Removal of the remaining labyrinth in acutely hemilabyrinthectomized animals restored bilaterally symmetrical tonic e.m.g. activity in the neck extensors. There was no e.m.g. modulation during head movements after bilateral labyrinthectomy. In chronic hemilabyrinthectomized cats (four to seven weeks), tonic e.m.g. activity in the neck muscles on both lesioned and intact sides was similar to normal. The gain and phase of the sagittal v.c.r. were also normal over a wide range of frequencies of head movement on both lesioned and intact sides. Interruption of the medial longitudinal bundle approximately 1 mm rostral to the obex did not abolish the bilaterally symmetrical compensated reflex response in either muscle, indicating that the descending axons in the medial vestibulospinal tract are not essential in mediating the normal v.c.r. response in compensated animals.

Action Potentials↗
PubMed2004

Spatio-temporal evaluation of neck muscle activation during postural perturbations in healthy subjects.

The purpose of this study was to examine the spatio-temporal activation of the sternocleidomastoid (SCM) and cervical extensor (CE) muscles with respect to the deltoid muscle onset during rapid voluntary upper limb movement in healthy volunteers. The repeatability and reliability of the spatio-temporal aspects of the myoelectric signals were also examined. Ten subjects performed bilateral and unilateral rapid upper limb flexion, abduction and extension in response to a visual stimulus. EMG onsets and normalised root mean square (nRMS) values were calculated for the SCM and CE muscles. Subjects attended three testing sessions over non-consecutive days allowing the repeatability and reliability of these measures to be assessed. The SCM and CE muscles demonstrated feed-forward activation (activation within 50 ms of deltoid onset) during rapid arm movements in all directions. The sequence and magnitude of neck muscle activation displayed directional specificity, however, the neck flexor and extensor muscles displayed co-activation during all perturbations. EMG onsets demonstrated high repeatability in terms of repeated measure precision (nSEM in the range 1.9-5.7%). This was less evident for the repeatability of nRMS values. The results of this study provide a greater understanding of cervical neuromotor control strategies. During bilateral and unilateral upper limb perturbations, the SCM and CE muscles demonstrate feed-forward co-activation. It seems apparent that feed-forward activation of neck muscles is a mechanism necessary to achieve stability for the visual and vestibular systems, whilst ensuring stabilisation and protection of the cervical spine.

Adult↗
PubMed2005

Electromyographic activity of dorsal neck muscles in squirrel monkeys during rotations in an upright or upside down posture.

Electromyographic (EMG) activity was recorded from occipitoscapularis, semispinalis, and splenius neck muscles in five alert squirrel monkeys during 0.25-Hz rotations about horizontal axes oriented at 22.5 degrees intervals, including pitch, roll, and intermediate axes. The animals were oriented in either upright or upside down posture. In the upright posture, all monkeys exhibited compensatory EMG activity with maximal activation during rotations about axes between pitch in the pitch forward direction and contralaterally directed roll. Response timing varied across animals with EMG peaks ranging from near pitch forward head velocity to near pitch forward head position. When the head was upside down, response dynamics and directionality were altered to varying degrees in different monkeys. The greatest change in response to head inversion was seen in the monkey that had response phases closest to head position, the least in the animal with phases closest to head velocity. The monkey with EMG response peaks closest to position phase showed nearly 180 degrees inversion of responses when the head was upside down, suggesting that in this monkey a righting reflex mediated by utricular signals was activated in the upside down posture. The monkey with EMG response peaks closest to velocity phase may have lacked a righting response and exhibited only a canal-mediated compensatory vestibulocervical reflex in both upright and upside down postures. The results suggest that reflex contraction of neck muscles in response to passive head rotation includes an interplay of compensatory and righting responses that varies from animal to animal.

Animals↗
PubMed1996

Source document position as it affects head position and neck muscle tension.

Measurements of head position, mechanical load at C7, and level of muscle EMG activity in the muscles of the neck were compared across six document positions in both a reading task and a typing (word processing) task. Source documents, identified as a primary visual task, were placed in two positions in front of the subject, flat on the table to each side of the keyboard, and on a document stand at each side of the keyboard. Each of the 20 subjects performed both a reading task and a typing task in each of these document positions while measurements were taken. It was found that the greatest variations in head position occurred in head rotation with documents flat on the table. This document position on each side also produced the greatest level of muscle tension in both the neck extensors and, to a lesser degree, the sternocleidomastoid muscles. In addition, greater variability between document position measures was found in the typing condition.

Adult↗