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PubMed1996

The medullary reticular formation is a site of muscle relaxant action of diazepam on deep back and neck muscles in the female rat.

We tested the hypothesis that the effect of systemic injections of diazepam (DZ, 125 mg/kg) to reduce the quality of the reproductive behavior, lordosis, and to reduce the EMG of lumbar back muscles involved in lordosis (Schwartz-Giblin et al., 1984) is exerted through a reticulospinal pathway with cells of origin in the nucleus gigantocellularis that excites lumbar motoneurons indirectly (Robbins et al., 1990, Robbins et al., 1992). In contrast, DZ facilitates lordosis behavior when infused into the midbrain central gray (McCarthy et al., 1995). Direct deposits of crystalline mixtures of DZ (20-80 ng) in dextrose were delivered to the medullary reticular formation (MRF) by diffusion from a cannula inserted through a guide to which a bipolar stimulating electrode was attached. The multiunit EMG response evoked by 20 (300 ms long) stimulus trains was recorded in back and neck muscles, lateral longissimus and splenius before and 5, 15, 30 and 60 min after local DZ deposits. There was a significant reduction in EMG response over this time period when stimulus intensities were within the range of 1.2-1.5 times threshold (Friedman two-way non-parametric test, P < 0.002). Large amplitude motor units that provide large tensions were the most sensitive to DZ-induced inhibition. Control deposits of dextrose had no significant effect. Systemic injections of progesterone (1 mg, i.p.) 60 min after DZ deposits, but not after dextrose deposits, further reduced the MRF-evoked EMG responses over the course of 1 h. As predicted, DZ infusions into the midbrain central gray did not reduce the reticulospinal-evoked axial muscle response, consistent with the facilitatory effect of midbrain central gray infusions of DZ on the lordosis quotient. The results suggest that benzodiazepine agonists (if endogenous) acting at sites in the MRF would be effective muscle relaxants during pregnancy, prior to the fall in progesterone that precedes labor.

Animals↗

PubMed2006

Effect of muscle wrapping on model estimates of neck muscle strength.

Of the computational models of the cervical spine reported in the literature, not one takes into account the changes in muscle paths due to the underlying vertebrae. Instead, all model the individual muscle paths as straight-line segments. The major aim of this study was to quantify the changes in muscle moment arm, muscle force and joint moment due to muscle wrapping in the cervical spine. Five muscles in a straight-line model of the cervical spine were wrapped around underlying vertebrae, and the results obtained from this model were compared against the original. The two models were then validated against experimental and computational data. Results show that muscle wrapping has a significant effect on muscle moment arms and therefore joint moments and should not be neglected.

Cervical Vertebrae↗

PubMed1981

The nature of afferents from the large dorsal neck muscles that project to the superior colliculus in the cat.

1. A 3.5-5 mm passive stretch of dorsal neck muscles at velocities of 50 mm/sec, a stimulus adequate to excite most neck muscle spindles, was usually ineffective in eliciting unit discharge in the superior colliculus. The sudden release of muscle tension was effective and excited fifty-seven of sixty-seven units tested. 2. When electrical stimulation of neck muscle nerves was used, a stimulus strength sufficient to excite Group III muscle afferents was usually required to elicit unit discharge in the superior colliculus. 3. It is concluded that the projection from neck muscles to the superior colliculus largely takes origin in Group III afferent whose function remains to be determined. Some contribution to the projection to the superior colliculus from proprioceptive afferents served by larger fibres cannot be ruled out.

Action Potentials↗

PubMed2006

Repeatability of electromyography and force measurements of the neck muscles in adolescents with and without headache.

BACKGROUND: Reliable measurements are needed to study the dysfunction of the neck muscles. The aim of this study was to determine the intra-tester repeatability of EMG and isometric force measurements of the neck muscles in adolescents with headache and headache-free controls. METHODS: A group of 30 adolescents with migraine-type headache, 29 with tension-type headache, and 30 headache-free controls were recruited. Maximal isometric neck muscle force with simultaneous recording of surface EMG from the cervical erector spinae and the sternocleidomastoideus muscles was measured twice during one day. FINDINGS: For all groups, intra-class correlation coefficients (ICC) and coefficients of variation (CV) showed acceptable repeatability of all measurements. (Force measurements: ICC 0.98-0.99, CV 0.7-3.7%; EMG measurements: ICC 0.95-0.99, CV 4.9-10.1%.) On the individual level, variation between the consecutive measurements was found to be low in all groups. INTERPRETATION: The present EMG and force measurements of neck muscles indicate acceptable intra-tester repeatability in adolescents. The repeatability was comparable in migraine- and tension-type headache and headache-free groups. The EMG and the force measurements offer the possibility to investigate neck muscle dysfunction in adolescent headache.

Adolescent↗

PubMed2003

Lasting amelioration of spatial neglect by treatment with neck muscle vibration even without concurrent training.

OBJECTIVE: It has been shown recently that neck muscle vibration in combination with an exploration training leads to lasting amelioration of spatial neglect. The present study evaluated whether vibration of the left posterior neck muscles alone has the potential to induce lasting reduction in spatial neglect. DESIGN: A multiple baseline design was used to control for spontaneous recovery or uncontrolled change caused by external events. PATIENTS: Six patients with spatial neglect following right hemisphere stroke. METHODS: Daily vibration treatment of the left posterior neck muscles for 20 minutes on 10 consecutive days. During vibration, patients did not perform any specific activities. RESULTS: We observed significant amelioration of spatial neglect after terminating the vibration therapy. The improvement was found to be stable at follow-up testing about 1.4 years later. CONCLUSION: Vibration of the left posterior neck muscles is a useful, non-invasive tool supplementing the established methods of spatial neglect treatment. It does not necessarily require the patient's co-operation, which is an important advantage especially in the early phases of rehabilitation.

Activities of Daily Living↗

PubMed1988

Growth changes in the skull and upper cervical skeleton after partial detachment of neck muscles. An experimental study in the rat.

The influence of altered neck muscle function on the morphology of the craniocervical area was studied in the rat. The neck muscles were detached from their cranial attachments at 14 days of age and the skulls subjected to macroscopic, radiological and microscopic examination at 180, 360 and 450 days of age. Visual observations only were made on the three upper cervical vertebrae. As compared with the situation in the unoperated control animals, the occipital area of the experimental skull was flattened, the superior margin of the foramen magnum was irregularly curved, the sutural serration appeared less accentuated in the posterior lambdoid suture, the normally smooth curvature of which had a caudal flexture in the middle. The spheno-occipital synchondrosis was structurally similar to that in the controls, and no obliteration was seen. The angular relations between the basicranial components changed following the operation in that the posterior basicranial components at first were bent downwards while the situation was later reversed. To compensate for the upward inclination of the posterior part of the basi-occipital bone, the anterior rim of the foramen magnum had become reshaped. The downward flexion of the basicranium was considered to be the result of the decreased nuchal muscle tension whereas the reversed angle phenomenon was possibly brought about by tissue scarring. The dorsal arch of the first cervical vertebra was wider craniocaudally than in the controls and its cranial border was bent ventrally. The second vertebra differed from the controls in that the spinous process was longer and in some cases was directed upwards.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1997

Changes in dorsal neck muscle activity related to imposed eye movement in the decerebrate pigeon.

Movements of the head and eyes are known to be intimately related. Eye position has also been shown to be closely related to the electromyographic activity of dorsal neck muscles; however, extraocular muscle proprioception has not generally been considered to play a part in the control of such movements. We have previously shown that, in the pigeon, imposed movements of one eye modify the vestibular responses of several dorsal neck muscles in ways that are dependent on stimulus parameters such as the amplitude and velocity of imposed eye movement. The present study examines more closely the interactions between imposed eye movements and different muscle pairs. The three neck muscle pairs studied each responded to afferent signals from the extraocular muscles in discrete and specific ways which appeared to be correlated with their different actions. Complementary effects of imposed eye movements in the horizontal plane were seen for both the complexus and splenius muscle pairs, with imposed eye movements in one direction producing the largest inhibition of the ipsilateral muscle's vestibular response and imposed eye movements in the opposite direction the largest inhibition of the contralateral muscle's vestibular response. During roll tilt oscillation (ear-up/ear-down) in the frontal plane, similar complementary effects of imposed eye movement were seen in the complexus muscle pair, but the splenius muscle pair showed little tuning, with similar inhibition for imposed eye movement directed either upwards or downwards. In contrast to these complementary effects, the biventer cervicis muscle pair showed no vestibular modulation during vestibular stimulation in the horizontal plane and their spontaneous activity was not altered by imposed eye movement. During roll-tilt oscillation (ear-up/ear-down) in the frontal plane imposed eye movement directed vertically upwards increased both muscles' vestibular responses and imposed eye movement directed vertically downwards inhibited both muscles' vestibular responses. Section of the ophthalmic branch of the trigeminal nerve (deafferenting the eye muscles) abolished the effects of imposed eye movement on the neck muscle pairs. In conjunction with further control experiments these results provide compelling evidence that proprioceptive signals from the extraocular muscles reach the neck muscles and provide them with a functionally significant signal. We have previously shown that signals from the extraocular muscles appear to be involved in the control of the vestibulo-ocular reflex. It follows from the experiments reported here that proprioceptive signals from the extraocular muscles are also likely to be involved in the control of gaze.

Animals↗

PubMed2004

Decreased neck muscle strength is highly associated with pain in cervical dystonia patients treated with botulinum toxin injections.

OBJECTIVES: To compare the isometric neck muscle strength of cervical dystonia patients treated with botulinum toxin injections with that of healthy control subjects and to evaluate the association between neck strength, neck pain, and disability in these patients. DESIGN: Clinical cross-sectional study. SETTING: Outpatient rehabilitation and neurology clinics in a Finnish hospital. PARTICIPANTS: Twenty-three patients with cervical dystonia with botulinum toxin-treated neck muscles and 23 healthy control subjects. INTERVENTIONS: Not applicable. Main outcome measures Isometric neck strength was measured by a special neck strength measurement system. Disability was measured by the Neck Disability Index, and pain and symptoms of cervical dystonia by a visual analog scale. RESULTS: Isometric neck strength in all directions measured was significantly lower (25%-44%) in the cervical dystonia patients than in the healthy controls. Neck pain levels reported during the strength tests (r range, -.36 to -.70) and neck pain experienced during the preceding week (r range, -.52 to -.63) were inversely associated with isometric strength results. The difference between sides in rotation strength was 35% in the patient group (P<.001), whereas no significant difference between sides was found in the healthy controls. Fifty-one percent of the patients reported moderate or severe disability. Pain, stiffness, and incorrect position of the head were the most prominent symptoms. CONCLUSIONS: Cervical dystonia patients with botulinum toxin-treated neck muscles showed significantly lower maximal neck strength than healthy controls. The patients also had a statistically significant difference between sides in neck rotation strength. Thus, strength measures may be useful to detect disturbance in the function of the neck muscles.

Botulinum Toxins, Type A↗

PubMed1996

Effect of neck posture on patterns of activation of feline neck muscles during horizontal rotation.

The electromyographic (EMG) patterns of neck muscles were recorded during whole-body horizontal rotation in head-free, alert cats and head-restrained, decerebrate cats. In some trials the cervical column of the animal was oriented vertically, whereas in others it was oriented more horizontally. In alert cats making head movements that compensated for the motion of the platform, neck muscles with modulated patterns of activity could be divided into a subset whose individual EMG patterns changed significantly when the neck posture was altered (including longissimus capitis, obliquus capitis superior and scalenus anterior) and a subset whose individual EMG patterns were invariant regardless of neck posture (including obliquus capitis inferior, levator scapulae and complexus). In head-restrained, decerebrate cats, electromyograms from all implanted muscles were modulated similarly in phase with the platform position. Changing the orientation of the neck had little effect upon these EMG patterns evoked by the horizontal vestibulocollic reflex. One decerebrate cat with strong extensor tone was tested further under head-free conditions. There was very little compensatory head movement, but individual neck muscles displayed patterns of activity that were more similar to those observed in alert, head-free animals.

Adaptation, Physiological↗

PubMed1995

Transcutaneous electrical stimulation and vibration of neck muscles in neglect.

Four neglect patients without visual field defects, one with a lesion of the right basal ganglia and three with a right, predominantly parietal lesion, were examined with a cancellation and a copying task before, during and after neck muscle vibration, during transcutaneous electrical stimulation of neck muscles and during vibration of hand muscles on the left side. In all patients, neck muscle vibration improved task performance, while transcutaneous electrical stimulation and hand vibration had little or no effect. The present results demonstrate that the effect of neck muscle vibration cannot be explained as arousal and activation due to unspecific sensory stimulation on the contralesional side of the body. They rather argue for the assumption that the compensatory effect of neck muscle vibration on neglect is an effect induced by the predominant activation of afferent Ia nerve fibres and their specific contribution to the central representation of egocentric space.

Afferent Pathways↗

PubMed1995

Eye movements in normal subjects induced by vibratory activation of neck muscle proprioceptors.

Versional eye movements, induced by neck muscle vibration at 70 Hz in 8 normal subjects, were recorded with infrared reflection technique in each eye separately with one eye fixating a target and the other covered. The direction of eye movements was horizontal when the sternocleidomastoid muscle on one side of the neck and the splenius on the other side were activated, and downward when both splenii muscles were vibrated. The direction was the same as that of the illusory movements of the target also induced by the vibration. These findings would imply that the proprioceptive messages originating in the neck muscles are processed together with visual information of eye position in determining gaze direction.

Eye Movements↗

PubMed1987

Changes in neck muscles in Swedish reindeer bucks during rutting season.

Three neck muscles in Swedish reindeer bucks have been studied before and during the rutting season. These were M. splenius, M. sternocephalicus and M. brachiocephalicus. For comparison, M. longissimus dorsi was chosen. Fibre composition and fibre size were studied in the four muscles as also was the metabolic potential of three enzymes, representing respiratory chain (cytochrome oxidase), beta-oxidation of fatty acids (3-hydroxyacyl-CoA dehydrogenase) and anaerobic glycolysis (lactate dehydrogenase). The extreme increase in size of certain muscles in the neck in connection with the rutting season (e.g. sternocephalicus, which increases from 250 g to 1,500 g) was to a great extent due to an increase in fibre size. In splenius, all three fibre types studied increased (I, IIA, IIB); in brachiocephalicus, mainly IIA and IIB; and in sternocephalicus, only the IIB. No corresponding fibre increase could be found in longissimus dorsi. In splenius and sternocephalicus from bucks older than 54 months, 60-70% of the fibres were of type I, and in brachiocephalicus, only about 40%. In all muscles but one, oxidative capacity (cytochrome oxidase) and beta-oxidation of fatty acids (3-hydroxyacyl-CoA dehydrogenase) decreased significantly during the rutting season. This indicates that purposes other than the enhancement of energy production by fatty acid oxidation must account for the enlargement of the neck muscles.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2000

Head movements and neck muscle activities associated with the jaw movement during mastication in the rabbit authors.

Rhythmical head movements and neck muscle activities associated with the masticatory jaw movement were investigated in rabbits. In natural mastication, head movements and neck muscle activities showed a rhythmical feature synchronized with jaw movement. During cortically induced rhythmical jaw movements, some neck muscle showed rhythmical activity induced by biting a wooden stick. Neck muscles may contribute to the rhythmical head movement after loading the tooth with food.

Animals↗

PubMed1989

Neck muscle spindle activity in the decerebrate, unparalyzed cat: dynamics and influence of vestibular stimulation.

1. Using floating electrodes, we recorded from neck-muscle spindle afferents in the C2 dorsal root ganglion of the decerebrate cat. Nerves to dorsal neck muscles were cut so that the afferents presumably originated mainly from ventral and ventrolateral perivertebral muscles and sternocleidomastoid. One goal of our experiments was to study possible vestibular influence exerted on these spindles via the fusimotor system. Unparalyzed preparations were therefore used. 2. Stimuli consisted of sinusoidal rotations in vertical planes. Neck tilt stretched neck muscles, whereas whole-body tilt stimulated vestibular receptors. 3. For each afferent we first determined the most effective direction of neck tilt, then used stimuli oriented close to this direction to study response dynamics, particularly gain of responses to stimuli of different amplitudes (0.5-7.5 degrees). 4. Three-quarters of the afferents failed to respond to 0.5 degrees, 0.2-Hz neck rotations. Stimuli that were effective usually elicited responses that had low gain and were linear over the whole range of amplitudes. Only a few afferents had behavior typical of spindle primary afferents: high-gain responses to small sinusoidal stimuli, gain decreasing as stimulus amplitude increases. This prevalence of static spindle responses in the unparalyzed cat is in striking contrast to results obtained on neck-muscle spindles in paralyzed, decerebrate cats, and on hindlimb extensor muscle spindles in decerebrate, unparalyzed cats. 5. Paralysis produced by injection of Flaxedil changed the behavior of 2/4 spindle afferents tested, causing the appearance of high-gain responses to 0.5 degrees stimuli and of nonlinear behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed2000

Effect of prolonged neck muscle vibration on lateral head tilt in severe spasmodic torticollis.

UNLABELLED: Short term vibration of the dorsal neck muscles (10-35 s) is known to induce involuntary movements of the head in patients with spasmodic torticollis. To investigate whether neck muscle vibration might serve as a therapeutic tool when applied for a longer time interval, we compared a vibration interval of 5 seconds with a 15 minute interval in a patient with spasmodic torticollis with an extreme head tilt to the right shoulder. Head position was recorded with a two camera optoelectronic motion analyzer in six different test conditions. Vibration regularly induced a rapid change of head position that was markedly closer to a normal, upright posture. After 5 seconds of vibration, head position very quickly returned to the initial position within seconds. During the 15 minute interval, head position remained elevated. After terminating vibration in this condition, the corrected head position remained stable at first and then decreased slowly within minutes to the initial tilted position. CONCLUSIONS: (1) In this patient, muscle vibration was the specific sensory input that induced lengthening of the dystonic neck muscles. Neither haptic stimulation nor transcutaneous electrical stimulation had more than a marginal effect. (2) The marked difference in the change of head position after short and prolonged stimulation supports the hypothesis that spasmodic torticollis might result from a disturbance of the central processing of the afferent input conveying head position information-at least in those patients who are sensitive to sensory stimulation in the neck region. (3) Long term neck muscle vibration may provide a convenient non-invasive method for treating spasmodic torticollis at the central level by influencing the neural control of head on trunk position.

Female↗

PubMed2004

Neck muscle strength and endurance in fighter pilots: effects of a supervised training program.

INTRODUCTION: Cervical discomfort is common among pilots of high performance aircraft. An exercise program was introduced to increase the strength and endurance of the neck muscles. The purpose of this study was to analyze whether coaching or reinforcement strategies by a physical therapist was associated with improvement in neck muscle strength, endurance, and neck complaints in two cohorts of fighter pilots performing regular neck muscle exercises. METHODS: A reinforced group (RG) of 20 pilots (24-40 yr) at an Air Force base received weekly encouragement to perform their standardized exercise program three times per week. A non-reinforced reference group (NRG) of 20 pilots (23-37 yr) from another Air Force base carried out the same program without any supervision. Both groups performed the training program for 6-8 mo. Before and after the training period, isometric measurements of the neck flexors and neck extensors were performed in both groups. RESULTS: After the completion of the 6-8 mo training period, the RG pilots significantly increased their neck muscle strength (flexors: M = 3.9 nm, p = 0.000 and extensors: M = 5.0 nm, p = 0.001) as well as endurance in their neck extensors (M = 53 s, p = 0.000). The NRG pilots significantly decreased both strength (M = 11.5 nm, p = 0.0001) and endurance (M = 33 s, p = 0.003) of their neck extensors. Furthermore, the NRG pilots did not show any significant change of their neck flexor strength. No significant changes in the frequency of neck complaints were reported in either group throughout the entire study period. CONCLUSION: The reinforced training program increased the strength and endurance of the appropriate muscle groups. In order to draw any further conclusions concerning reducing neck complaints, a longer observation period with a larger group of pilots might be needed. However, it is likely that there is an individual correlation between strength and endurance of the neck muscles and neck pain, which means that any rehabilitation program should be tailored for each individual.

Accidents, Occupational↗

PubMed1987

Properties of cat neck muscle spindles and their excitation by succinylcholine.

The sensitivity to sinusoidal stretching and small-amplitude vibration, and the variability of the resting discharge rate of de-efferented muscle spindles in the neck extensor muscle biventer cervicis (b.c.) of the cat have been studied. The effects of intra-arterial infusion of succinylcholine (SCh) on the response of the receptors to ramp stretches of the muscle were also determined. When activated by SCh, one group of afferents showed only a slow facilitation of their discharge rate, similar to that of spindle secondary sensory endings in hind-limb muscles. A second group of afferents developed a large dynamic response and a marked increase in their static discharge rate and were presumed to originate in "normal" b1b2 c spindles in the b.c. muscle. A third group of afferents developed only a marked increase in static discharge, without potentiation of the dynamic response, suggesting an origin in the b2c units of tandem spindles which are relatively common in the neck muscles. On the basis of their passive characteristics alone, afferents from b1b2c units could not be readily distinguished from those from b2c units. The characteristics of these receptors, and their differences from the well-studied hind-limb spindle afferents, are discussed.

Afferent Pathways↗

PubMed1999

The effect of muscle-tone-reducing procedures in athetotic head movements: partial nerve block by lidocaine and surgical release of the neck muscles.

OBJECTIVE: To investigate the effect of muscle-tone-reducing procedures (MTRPs), i.e. partial nerve block by lidocaine (PNB) and surgical release of muscle attachment to bone (SRMAB), on incessant involuntary head movements in athetotic patients. METHODS: Pre/post-MTRP changes in neck-muscle activities, glabella movement and maximum isometric forces of the head were measured in six athetotic patients with severe spondylotic myelopathy resulting from incessant involuntary head movements. RESULTS: Pre/post-MTRP changes in neck-muscle activities resembled those after gamma-block. In four patients, PNB reduced the maximum isometric force by no more than 40% of pre-PNB force, while decreasing the amount of involuntary head movements to 37-65% of the pre-PNB value in the frontal plane. MRSAB reduced the force by less than 40% of pre-SRMAB force in 4 MRSAB tested patients, while decreasing the amount of involuntary head movements to 12-45% of the pre-SRMAB value in all 6 patients. CONCLUSION: MTRPs reduced involuntary head movements significantly while preserving voluntary muscle forces relatively well. PNB and SRMAB procedures have in common the effect of reducing gain in the myotatic reflex pathway by decreasing the excitatory inflows to alpha-motoneurons via muscle spindle Ia-afferents, which resulted from blocking mainly gamma-efferent conduction by PNB, and reducing background tension in muscle spindles by SRMAB.

Adult↗