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PubMed1994

Longus colli has a postural function on cervical curvature.

To determine the postural role of longus colli (LC) and dorsal neck muscles, we have studied the relationship between their cross-sectional areas related to their force of contraction and the lordosis and the length of the cervical spine. This study was carried out in 36 healthy subjects. Muscle cross-sectional areas were measured by computerized tomography. The index of lordosis and the length of the cervical spine were measured on an X-ray profile. The cross-sectional area of LC was correlated to the lordosis index (R = -0.432, p < 0.02) whereas all the other parameters were not correlated. The authors conclude that LC counteracts the lordosis increment related to the weight of the head and to the contraction of the dorsal neck muscles. Postural functions of LC and postcervical muscles are complementary. They form a sleeve which encloses and stabilizes the cervical spine in all positions of the head.

Adult↗
PubMed1991

Plasticity mechanisms in vestibular compensation in the cat are improved by an extract of Ginkgo biloba (EGb 761).

The effects of administration of an extract of Ginkgo biloba (EGb 761) on vestibular compensation was studied in unilateral vestibular neurectomized cats. This experimental model of CNS plasticity was investigated by using behavioral tests (postural disorders compensation, locomotor balance recovery), electrophysiological (spontaneous and evoked neck muscle activity) and neurophysiological (spontaneous firing rate recovery of deafferented vestibular cells) recordings, and immunocytochemical methods (synaptic loss and synaptic reoccupation within the deafferented vestibular nuclei). In all experiments, EGb 761 was administered over 30 days at daily doses of 50 mg/kg IP. The results showed a faster recovery in the EGb-treated group of cats as compared to an untreated control group. EGb administration strongly accelerated postural and locomotor balance recovery. Concomitantly, spontaneous neck muscle activity, vestibulo-collic reflexes and spontaneous firing rate of vestibular units located on the lesioned side were restored earlier. Morphological correlates characterized by a more rapid synaptic reoccupation were found in the deafferented medial vestibular nucleus by means of immunoreactive labelling using an antibody against a synaptic vesicle-associated protein (synaptophysin), but they displayed a longer time-constant in comparison with the behavioral and neurophysiological data. These results clearly demonstrate that EGb 761 acts on recovery mechanisms considered as key processes in vestibular compensation. They suggest that this substance would possess neurotrophic and/or neuritogenic properties improving functional recovery after CNS injury.

Animals↗
PubMed2000

Gravity cue has implicit effects on human behavior.

Gravity modifies us without our knowing it. Possible functional disabilities of eye, head and body movements were investigated under 1 G and microgravity environments to evaluate the gravity cue for human behavior. The system for visual stability might be explained from the viewpoint of ordination between eye and head under microgravity. It is important ascertain the significance of gravity in the maintenance of human visual stability. Coordination of eye position and head motion behavior by neck muscle discharge was examined in the mission SL-J, as well as a subjective evaluation of visual stability during spaceflight. The results shows that: 1) poor performance of eye movement can be observed; 2) unusual neck muscle activity can be observed; 3) there is decreased visual stability in microgravity; and 4) egocentric body axis is emphasized under microgravity conditions.

Eye Movements↗
PubMed1993

The control of slow orienting eye movements by tectoreticulospinal neurons in the cat: behavior, discharge patterns and underlying connections.

The activity of tectoreticulospinal neurons (TRSN) during orienting gaze shifts was studied in alert, head-fixed cats by intra-axonal recordings. The scope of the study was to evaluate the role of this class of superior colliculus neurons in the generation of slow eye movements (drifts) which often follow main-sequence saccades and sometimes appear as an independent motor event of orienting. The parameters of such movements are described in the first part of the paper. The organization of underlying pathways in the lower brainstem has been studied by intra-axonal horseradish peroxidase (HRP) tracing. The mean amplitude of postsaccadic drifts (PSD) is 1.21 degrees (SD 0.63), but it can eventually reach 6-8 degrees. PSDs have mean velocity of 14.9 degrees/s (SD 4.28) and mean duration of 104.2 ms (SD 50.8). These two parameters are positively correlated with PSD amplitude. The presence of PSDs is usually associated with an increased neck muscle activity on the side toward which the eyes move. The durations of these two motor events show a reliable positive correlation. PSDs appear to occur when gaze error persists after a saccade and a correction is attempted by means of a slow eye movement and a head turn. The durations of TRSN bursts are, on average, longer than the sum of the lead time and the saccade duration. Bursts associated with combinations of saccades and PSD are significantly longer than those recorded in the absence of PSDs. The probability of occurrence of PSDs is higher when firing of TRSNs continues after saccade termination. Such prolonged discharges usually coincide with a combination of PSDs and phasic activation of the neck electromyogram. The mean firing rate of TRSNs during PSDs is 62% of that during saccade-related portions of the burst and declines to 45% after the end of PSDs. According to its timing and intensity, postsaccadic firing of TRSNs is appropriate as a signal underlying slow, corrective eye movements and later portions of phasic neck muscle contractions during orienting. Intra-axonal HRP labeling showed that visuomotor TRSNs of the X type (n = 3) terminate in the abducens nucleus, with 145-331 boutons terminaux and en passant. Average bouton densities in the nucleus are lower than in the periabducens reticular formation, but higher than in more rostral paramedian pontine reticular formation (PPRF) regions. Terminal fields in the PPRF match the locations of "eye-neck' reticulospinal neurons (RSNs) and exitatory burst neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Abducens Nerve↗
PubMed1993

Gravity load related asymmetries in the sagittal vestibulo-collic reflex.

EMG recordings of the neck muscles (biventer cervicis, complexus, splenius, longus capitis) of decerebrate cats were obtained during pitch and roll stimulations (sinusoidal stimulation: 30 degrees p-p amplitude, 0.2 Hz frequency). Most of the EMG responses to pitch showed activation peaks leading the position stimuli by 56 degrees and inhibition peaks leading by 11 degrees. Conversely, in response to roll the activation peak led by 16 degrees and the inhibition peak by 10 degrees. The activation peaks of the pitch responses were, thus, more asymmetric and more leading than those of the roll responses. Consequently, the harmonic distortion coefficient was significantly higher in pitch than in roll. Moreover, when the vertical semicircular canals were activated in absence of otolithic modulation, the pitch and roll responses maintained the same difference in timing observed in the presence of otolithic coactivation. It appeared that the simultaneous stimulation of both anterior semicircular canals (pitch) induces a greater lead than that of combined anterior and posterior canals (roll). Thus the timing of neck muscle responses to vestibular stimulation depends on the pair of activated vertical semicircular canals.

Animals↗
PubMed1984

Dendritic distribution of motoneurons innervating the three heads of the trapezius muscle in the cat.

The organization of the nuclei and dendritic architecture of motoneurons innervating the three heads of the trapezius muscle, clavotrapezius (CT), acromiotrapezius (AT), and spinotrapezius (ST), have been examined by using intracellular staining techniques. CT, AT, and ST motoneurons were found in the spinal accessory nucleus and were arranged in three overlapping subnuclei. CT motoneurons were primarily found in C2 and C3. In contrast, most AT motoneurons were found in C3, C4, and C5 and ST motoneurons were found in C4, C5, and the rostral parts of C6. Most dendrites of CT motoneurons, located in rostral C2, extended dorsally and many of these dendrites spread medially and laterally to encompass all of lamina VIII and the dorsolateral part of lamina VII. When viewed in the horizontal plane these motoneurons had a stellate appearance. The dendritic tree structure of CT motoneurons changed abruptly between rostral C2 and mid-C2. The majority of dendrites of CT motoneurons located in the central and caudal parts of C2 projected rostrally and caudally to form a complex bundle of dendrites in the motoneuron nucleus. Small numbers of dendrites were also found ventromedial and dorsal to the soma. The dendritic trees of CT motoneurons in C3 and C4 and AT and ST motoneurons located in C4 and the rostral parts of C5 also followed this fusiform distribution pattern. The dendritic trees of AT and ST motoneurons in caudal C5 were not fusiform but instead had a complex distribution pattern which consisted of dendrites projecting in several directions. Many dendrites projected rostrally and caudally, and in addition, there were major dendritic projections ventrolateral and dorsolateral to the soma. These results indicate that each head of the trapezius muscle is innervated by two structurally dissimilar groups of motoneurons which occupy different spinal segments. Trapezius motoneurons at the same segmental level, regardless of which head of the trapezius muscle they innervated, have similar dendritic trees whose structure differs from those of neighbouring dorsal neck muscle motoneurons in C2, C3, and C4. Thus, the organization of motoneuron dendritic trees appears to be governed by several factors including the muscle innervated by the motoneuron and the transverse and segmental position of the motoneuron's soma.

Animals↗
PubMed1990

Adaptation of craniofacial muscles in subjects with craniomandibular disorders.

The purpose of this study was to examine muscle function in subjects with muscle pain. Forty-three subjects with pain in the craniomandibular muscles, clinically determined by manual palpation, were studied for alteration in recruitment of temporalis, masseter, and suprahyoid muscles during a series of phasic movements. Seventeen normal subjects were used as controls. The subjects with muscle pain were divided into three subgroups: (1) those with pain in both mandibular and neck muscles; (2) those with pain in these two muscle groups with joint degeneration; and (3) those subjects with pain only in mandibular muscles. Surface electromyographic (EMG) recordings were taken as each subject performed 16 different responses in which mandibular incisor movement was tracked simultaneously. The results show that the subjects with muscle pain use their anterior temporalis muscles with less frequency (i.e., probability) and with less intensity in several responses than normal subjects. These responses include rapid vertical closing movements, retrusion, ipsilateral laterotrusion, and natural as well as contralateral mastication. The masseter muscle is impaired much less in its function, and the recruitment of the suprahyoid muscles is not affected in the patients with muscle pain. Comparison of the bilateral activity in the anterior temporalis muscles during intercuspal clenching shows that the subjects with muscle pain often demonstrate a more severe asymmetrical recruitment of these muscles than the more symmetrical recruitment seen in normal subjects. Similar observations were made for the masseter muscle. These studies demonstrate that subjects with muscle pain in craniomandibular muscles alter the recruitment of their jaw muscles, thus supporting the concept that the neuromuscular system is altered in patients with craniomandibular disorders.

Adult↗
PubMed1993

Oral motor disorders in humans.

Motor disorders affecting the orofacial musculature include bruxism, chronic orofacial muscle pain affecting the jaw and neck muscles and the involuntary waking period disorders such as orofacial dyskinesia, oral mandibular dystonia, tremor and others. Research at UCLA has touched these and many other areas. Current results have indicated the usefulness of contingent afferent electrical stimulation of the lip to control bruxism; provided information regarding the fatigue, endurance and recovery faculties of the protrusive jaw muscles; explored the issue of chronic muscle hyperactivity inducing headache pain; and worked with botulin toxin as a method to treat orofacial dystonia and dyskinesia.

Bruxism↗
PubMedDate not supplied

[Role of the telencephalon in regulating the electrical activity of skeletal muscles in chick embryos].

On 18-day chick embryos, studies have been made of functional properties of hyperstriatum accesorium (HA) of the telencephalon and that of neck muscles. To investigate the relationship between the HA structure and the EMG in muscles, the former was subjected to unilateral coagulation. Specific levels were established of the energy of oscilatory processes--EEG in the HA and EMG of neck muscles--as well as the relationship between them and possible role of HA structure in regulation of fast movements.

Animals↗
PubMed1995

Orienting-related eye-neck neurons of the medial ponto-bulbar reticular formation do not participate in horizontal canal-dependent vestibular reflexes of alert cats.

Ponto-bulbar reticular formation neurons, including identified reticulospinal neurons, were studied in alert, head-fixed cats. Orienting-related neurons of "eye-neck" type (ENNs) were selected on the basis of qualitative correlations of their discharges with visually triggered eye saccades and electromyographic activity (EMG) of dorsal neck muscles. It was tested whether ENNs participate both in visually triggered gaze shifts requiring eye-head coordination and in gaze-stabilizing movements, such as vestibulo-ocular and vestibulo-collic reflexes (VOR, VCR). Firing patterns were studied during passive sinusoidal rotation (0.2-1.0 Hz; 2.0-21.5 deg peak-to-peak) in the horizontal plane. Responses to electrical stimulation of the superior colliculus and the vestibular nerve were recorded to assess the convergence of tectal and vestibular synaptic inputs. The same methods were applied to a control sample of neurons with discharges apparently "unrelated" to orienting movements. ENNs did not show any modulation of firing rate correlated to compensatory VOR or VCR during passive sinusoidal rotations. Among "unrelated" cells, the fraction of modulated units was close to that reported for reticular neurons projecting in the medial reticulospinal tract. Phasic and sustained components of ENN bursts were associated with anticompensatory movements induced by rotation, such as quick phases, ocular beating field shift, and the increase of EMG activity in neck muscles acting in the direction of passive rotation. Monosynaptic excitation from the contralateral superior colliculus was observed in 92.3% of ENNs, but only 2 out of 17 tested showed an excitatory response to vestibular nerve stimulation. In the control group of "unrelated" neurons the proportions of monosynaptic tectal and excitatory vestibular nerve inputs were, respectively, 75.6 and 71.4%. It is concluded that ENNs are specifically related to active gaze shifts, derived from either visual or from head velocity inputs. Rhombencephalic connections of vestibular nuclei to these neurons appear to be quite weak. Parallel inputs from the mid- or forebrain must be assumed to explain their firing patterns during rotation-induced anticompensatory gaze shifts. Within the studied range of frequencies and amplitudes of passive rotation, ENNs did not participate in the vestibulo-collic reflex. It is therefore unlikely that reticular neurons controlling orienting eye-neck synergies act also as a premotor pathway for gaze-stabilizing movements.

Animals↗
PubMed1987

Quantitative analysis of cervical musculature in rats: histochemical composition and motor pool organization. I. Muscles of the spinal accessory complex.

In this paper we characterize the architecture and segmental innervation, histochemical composition, muscle spindle populations, and motor pool organization of rat spinal accessory (SA) muscles: sternomastoid (SM), cleidomastoid (CM), cleidotrapezius (CT), and acromiotrapezius (AT). We also consider whether individual rat neck muscles are supplied by more than one population of motor neurons as they are in turtles and cats and whether in SA muscles motor neuron size scales with target muscle fiber type. SM, CM, and CT are ventral, parallel strap muscles. Each can be divided into grossly visible white and red compartments. AT is a dorsolateral sheetlike muscle that shows no gross compartmentalization. All four muscles are dominated by fast-twitch glycolytic (FG) and fast oxidative glycolytic (FOG) fibers, and FG fibers are significantly more numerous than the FOG type in three out of four muscles. Thus SA muscles in rats appear to be specialized for rapid, phasic head movements. Topographical analyses revealed that there is a striking compartmentalization of fiber types in the ventral muscles that corresponds to the red and white segments seen grossly. Spindles are found only in regions containing slow-twitch oxidative (SO) fibers. Cross-muscle comparisons indicate that there are significant differences between SA muscles in their fiber type composition. The motor pools of SA muscles form a single column from lower medulla to C5. Rostral cells lie dorsomedially in the ventral horn and, at the C1/C2 junction, the column shifts ventrolaterally. Within this column, each motor pool occupies a characteristic rostrocaudal position in the order SM:CM:CT:AT. Thus SM and (in part) CM motor neurons lie more medially than cells supplying the trapezius complex, suggesting that they may be under different patterns of synaptic drive. We saw no evidence that rat SA muscles are supplied by more than one population of motor neurons. Direct comparisons between the soma sizes of motor neurons that supply muscles or parts of muscles with significantly different histochemical compositions indicate that these size differences are in the direction predicted from their histochemical profiles, thus suggesting that in these muscles motor neuron soma size may scale with muscle fiber type.

Accessory Nerve↗
PubMed2003

Hypoalgesia to pressure pain in referred pain areas triggered by spatial summation of experimental muscle pain from unilateral or bilateral trapezius muscles.

Animal and human experimental studies have suggested the importance of spatial summation in the nociception processing and in the activation of descending inhibition. However, the relationship between the areas (size) of muscles stimulated and the recruitment of descending inhibition has not been addressed. Consequently, we tested whether bilateral versus unilateral injection of hypertonic saline into trapezius muscles caused hypoalgesia to pressure pain (pressure pain thresholds, PPTs) in the local pain areas (the trapezius muscles) and the referred pain areas (the posterolateral neck muscles). Two groups of volunteers participated. One group received a unilateral injection (one injection) and the other group bilateral injections (two injections). In the bilateral group, hypertonic saline was injected in one trapezius first, and 45 s later, while pain was still present from the first injection, a second injection was performed into the contralateral trapezius muscle. The saline-evoked time to maximal pain was significantly shorter after the second injection than after the first injection. More subjects developed referred pain after the bilateral compared with the unilateral injection. In the referred pain areas, the PPTs 7.5 and 15 min after the second injection were significantly increased compared with the first injection, while no changes in the PPT were observed in local and referred pain areas after unilateral injection. This suggests that the induction of descending inhibition was triggered by spatial summation during the later phase of experimentally induced muscle pain. The present experimental model might be used for further investigation of descending inhibition related to the spatial characteristics of nociceptive stimuli in humans.

Adult↗
PubMed1998

Encoding target-trunk relative position: cervical versus vestibular contribution.

The contribution of cervical and vestibular cues in signaling the changes in target-trunk relative positions during self-motion was investigated. Normal subjects (Ss) were shown a LED flashed in the peripheral visual field in a dark room. Ss were then passively rotated about the vertical axis in one of three different conditions: (1) head chair-fixed (vestibular condition); (2) head earth-fixed (relaxed neck condition); and (3) head earth-fixed, but with the Ss actively attempting to turn it (activated neck condition). The Ss were then required to indicate, with their unseen index finger, the position of the previously flashed target. It was found that pointing at the memorized target was similarly accurate in the relaxed neck condition and in the activated neck condition. In the vestibular condition, pointing accuracy dropped significantly. These results suggest that neck proprioceptive signals are more effective than vestibular ones in signaling relative changes in the position of stationary objects with respect to the body during head-trunk motion. The finding that cervically mediated estimates were unchanged during active contraction of the neck muscles may suggests that efference copy signals may help interpret the change in the afferent signals caused by voluntary neck muscle activation.

Adult↗
PubMed2004

Glutamate evoked neck and jaw muscle pain facilitate the human jaw stretch reflex.

OBJECTIVE: Although pain and neuromuscular function are clearly linked in several clinical conditions manifested in the craniofacial and cervical regions, it is unclear if pain in these regions influences reflexly evoked activity in the jaw or neck muscles in humans. The aim of the present study was to test the effects of glutamate-evoked jaw or neck muscle pain on the jaw stretch reflex recorded in both jaw and neck muscles. METHODS: Nineteen healthy men participated in the study. Electromyographic (EMG) recordings were made from the left masseter (MAL) and right masseter (MAR) muscles and the right sternocleidomastoid (SCM) and splenius (SP) muscles. Glutamate (1 M) or isotonic saline was injected into the MAR or right SP in random order and then the other solution was injected 1-3 weeks later. Pain intensity was scored on a 10 cm visual analogue scale. Stretch reflexes were evoked by standardized jaw stretches before, during and 15 min after the end of the experimental muscle pain. Twenty trials were averaged in each condition. RESULTS: Pain evoked by MAR or SP glutamate injections was associated with a significant increase in the stretch reflex amplitude recorded in both MAR and SCM. The onset and offset times and duration of the stretch reflex did not change in any muscle during the various pain conditions. Injection of isotonic saline into the MAR or SP did not produce any significant change in the reflex parameters in any of the muscles. CONCLUSIONS: The results indicate the close interplay between the craniofacial and cervical regions in the neuromuscular changes that may result from musculoskeletal pain in either region. SIGNIFICANCE: The changes in neuromuscular activity documented in this study may be involved in the clinical occurrence of altered muscle activity in the orofacial and cervical regions as a result of deep tissue trauma and pain.

Adult↗
PubMed1998

A model for evaluation of gastric sensitivity in awake rats.

We developed a model for the evaluation of gastric sensitivity to distension in awake rats. A balloon made from a latex condom was chronically placed in the stomach and three stainless steel electrodes were implanted in the neck muscles. Isobaric distensions were performed with a barostat by step of 5 mmHg with 10 min inflation and 2 min deflation. Gastric pressure, integrated neck electromyogram (EMG) and gastric volume were continuously monitored on a potentiometric recorder. Gastric distension at 15 or 20 mmHg induced a typical posture associated with contractions of the neck muscles. Pain threshold was defined as the pressure inducing an increase of integrated neck EMG greater than 100%. The mean pain threshold was 18.5 +/- 0.7 mmHg and was not modified 2, 4 and 7 days after the first experiment. However, gastric volumes were significantly higher on the 4th and the 7th days. Morphine at the doses of 0.4 and 4 mg kg-1 i.p. significantly increases the pain threshold. At the doses of 0.04 and 0.4 mg kg-1, morphine significantly increased gastric volume for the distending pressure of 10 mmHg. Naloxone (2.5 mg kg-1 i.p.) reversed the effects of morphine. In conclusion, our model permits simultaneous evaluation of pain threshold and gastric compliance associated with gastric distension in conscious rats.

Animals↗
PubMed1990

Differential sensitivities of fetal muscle groups to d-tubocurarine.

Nine fetal lambs were instrumented for long-term intrauterine recording of electrocorticogram electrooculogram, electyromyogram of the dorsal neck muscle, the quadriceps femoris, and the diaphragm, monitoring of blood pressure, and measurement of heart rate. d-Tubocurarine (0.1 to 0.8 mg) was administered intravenously to the fetus over a 1-minute interval. Increasing doses of d-tubocurarine selectively blocked various muscle groups, with the extraocular muscles being the most sensitive. Comparison of the median effective dose for neuromuscular blockade of the extraocular muscles/nuchal muscle/diaphragm was 1:2.5:6. The duration of action of d-tubocurarine was directly related to the relative sensitivities of the different muscle groups, which are ranked from most sensitive to least sensitive as extraocular muscles, nuchal muscle, and diaphragm. Fetal electrocorticogram continued to cycle despite total neuromuscular blockade. However, there was an increase in synchronized and mixed activity, which was predominantly due to an increase in cycle numbers, and a decrease in desynchronized activity, which was predominantly due to shorter cycle lengths. During total neuromuscular blockade, there was also a significant decrease in heart rate during synchronized and mixed electrocorticogram states but not during a desynchronized electrocorticogram state, thus resulting in a loss of the heart rate difference normally seen between synchronized and desynchronized states. Fetal blood pressure did not change with total neuromuscular blockade.

Animals↗
PubMed1997

Neurophysiological investigations in patients with head tremor.

We studied 30 patients whose primary complaint was head tremor in an attempt to characterize neurophysiological aspects of their abnormal movement. Based on family medical history and physical examination, 23 patients had definite or probable essential tremor (essential head tremor, EHT). The remaining seven had mild dystonic signs accompanying their head tremor (head tremor plus dystonic signs, HT + DS). We recorded head movement and the electromyographic (EMG) activity of the sternomastoid and splenius capitis muscles, determined the spontaneous blinking rate, and measured the excitability recovery curve of the blink reflex and of the masseteric inhibitory reflex. All patients had tremor bursts at a frequency ranging between 3 and 9 Hz in at least one of the muscles examined. The predominant pattern seen when patients were sitting relaxed and facing forward was that of synchronized EMG bursts in both splenius capitis muscles. Maintenance of extreme head postures demonstrated two types of additional abnormalities: type 1 (enhancement of tremor), which was observed in 11 patients (47.8%) with EHT and in two (28.5%) with HT + DS; and type 2 (activation of neck muscles not required for maintenance of the posture), which was observed in two patients (8.7%) with EHT and in five (71.5%) with HT + DS (chi 2 = 26.4; p < 0.001). Mean blinking rate per minute was 24.9 +/- 14.6 in patients with EHT and 42.3 +/- 10.5 in patients with HT + DS (paired t test, p = 0.001). The blink reflex and masseteric inhibitory reflex excitability recovery curves showed an abnormal interneuronal excitability enhancement in seven (30.4%) of the 23 patients with EHT and in two (28.5%) of the seven with HT + DS (chi 2 = 3.1; p > 0.05). Abnormal patterns of EMG activity of the neck muscles correlated well with the presence of mild dystonic signs. However, the analysis of brainstem interneuronal excitability did not enable recognition of those patients with head tremor who could potentially develop cervical dystonia. The enhancement of brainstem interneuronal excitability found in approximately 30% of patients with head tremor could be related to plastic changes triggered by increased activity of the cranial muscles.

Adult↗