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At least 1,783 records · Page 99Linked to original sources
PubMed1998

Stumbling reactions in man: influence of corticospinal input.

The aim of this study was to evaluate the degree of contribution of supraspinal input to the generation of the compensatory leg muscle activation following stance perturbation. Therefore, evoked motor response (EMR) input-output relations of two different motor tasks were compared at 3 distinct periods: (1) the basic period of muscular activity during standing, i.e. when no additional cortical or spinal activity due to the different tasks is to be expected, (2) the pre-movement period with low background activity, when different spinal and cortical inputs to the motoneuronal pool can be assumed and (3) the period of plateau EMG activity of compensatory and voluntary motor task. Transcranial magnetic stimulation (TMS) just below the motor threshold was applied randomly at 19 different time-intervals before and during the onset of stance perturbation and for comparison during an equivalent voluntary foot-dorsiflexion task. Recordings of electromyographic (EMG) activity from the tibialis anterior (TA) and corresponding ankle-joint movements were made from both legs. Forward-directed displacements were induced by randomly-timed ramp impulses of constant acceleration upon a moveable platform. For comparison, leg muscle EMG was recorded during isometric foot dorsiflexion during stance while leaning back against a support. The stance perturbations were followed by a compensatory response (CR) in the TA with a mean onset time of 81 ms. During the basic period of muscular activity and the period of plateau EMG activity there was no significant difference of the input-output relation between stance perturbation and the voluntary motor task. However, in the voluntary task compared with the CR, there was significantly greater input-output relation (facilitation) of the EMR in the TA following TMS, which may be related to an increased cortical influence. In contrast to this result of the CR following stance perturbation, a facilitation of the EMR was described for hand muscles under corresponding conditions of automatic compensation for muscle stretch, suggesting a transcortical reflex loop. This difference in the results from upper and lower extremity muscles favors the assumption of a predominantly spinal generation of the TA-CR following stance perturbation.

Adult↗
PubMed1983

Cardiopulmonary mechanoreceptors and renin release in humans.

We investigated the hemodynamic determinants of the reflex release of renin to changes in posture and blood volume distribution in healthy humans to determine the relative contribution of arterial and cardiopulmonary mechanoreceptors to the reflex release of renin under physiological circumstances. In the first experiments, we induced a selective decrease of right atrial pressure by inflation of cuffs around the thighs. Renin increased and returned toward baseline on decompression. The renin increase was neurogenic because plasma norepinephrine increased, the response was abolished by beta blockade, and renin did not increase in patients with denervated transplanted kidneys. The second experiments were performed with tilting and later filling a pressure suit to counteract the effect of tilting on gravitational pooling of the blood. Tilting elicited increases of renin and norepinephrine; filling the suit abolished these increases. Right atrial pressure fell with tilting and rose after filling the suit. Because the neck was elevated above the heart equally in both conditions, it is concluded that the increase and decrease of renin reflected decrease and increase of the stretch of cardiopulmonary receptors. The third experiments were performed by elevating the upper trunk with the legs remaining in a horizontal position (sitting). This caused a heart-to-neck pressure difference and an increased sympathetic outflow through unloading arterial baroreceptors. Norepinephrine increased but renin did not. Cardiopulmonary receptors exhibit an important influence on the reflex release of renin.

Blood Pressure↗
PubMed1995

The effect of transcutaneous electrical nerve stimulation (TENS) on autonomic cardiovascular reflexes.

Transcutaneous electrical nerve stimulation (TENS) has been shown to have an anti-ischaemic effect in patients with angina and peripheral vascular disease that appears to be additional to any analgesic action. The mechanism for this anti-ischaemic effect is not known but it is possible that TENS interferes with the autonomic responses to ischaemia. To determine if TENS has any direct action on autonomic reflexes we have assessed the effect of high frequency TENS on a variety of standard tests of autonomic cardiovascular reflexes in 10 normal subjects. Tests were done on four consecutive days at the same time and TENS therapy or placebo was randomly allocated on 2 days each. Results of the tests were assessed by one person 'blinded' to the randomization order. These showed that TENS was associated with a significant reduction in the rise of the diastolic blood pressure (21.8 +/- 2.3 v. 17.6 +/- 17 mmHg; p < 0.05) during isometric exercise, using sustained Handgrip. There was no significant effect discernible on the changes of heart rate and blood pressure during the Valsalva manoeuvre, cold face stimulus or head-up tilt. Transcutaneous electrical nerve stimulation appears, therefore, to have a mild inhibitory action on those reflexes mediated predominantly by the sympathetic nervous system and this is more apparent when the stimulation may be greater, as during isometric exercise.

Adult↗
PubMed1995

Uniform characterization of potentiation in simple and complex situations when agents bind to different molecular sites.

There is general agreement about potentiation in dose-response studies, characterized by a left shift of the dose-response curve of A by a fixed dose of B when B is causing no effect by itself (simple situation). When B causes an effect similar to A (complex situation) by binding to different molecular sites, we propose an analogous analysis. This approach is based on comparison of experimental effects of A and B in combination with theoretical, independent effects, representing an effect of A that is not affected by B. We argue here that comparison of experimental effects with those of dose-additive (additive) combinations is inappropriate. Theoretical considerations and several practical examples show that the magnitude of effects due to additive combinations widely varies with the slope of dose-response curves of A. Consequently, it is also shown that one and the same theoretical effect may appear overadditive, additive, or underadditive. These situations are demonstrated by the experimental examples: inhibition of cytopathic effects in virus-infected cells, loss of righting reflex in mice, and smooth muscle relaxant effects of organic solvents.

Animals↗
PubMed1993

Relative contributions of cardiopulmonary and sinoaortic baroreflexes in causing sympathetic activation in the human skeletal muscle circulation during orthostatic stress.

The aim of this study was to reexamine the hypothesis that cardiopulmonary baroreflexes are more important than sinoaortic baroreflexes in causing vasoconstriction in the skeletal muscle circulation during orthostatic stress. We recorded muscle sympathetic nerve activity (MSNA) with microelectrodes in the peroneal nerve (and forearm blood flow with venous occlusion plethysmography) in normal subjects (innervated ventricles) and in heart transplant recipients (denervated ventricles) during graded lower body negative pressure (LBNP) performed alone and in combination with intravenous infusion of phenylephrine, which was titrated to eliminate the orthostatically induced fall in blood pressure and thus the unloading of both carotid and aortic baroreceptors. The principal new findings are as follows: (1) The increases in both MSNA and forearm vascular resistance during multiple levels of LBNP were not attenuated by heart transplantation, which causes ventricular but not sinoaortic deafferentation. (2) In heart transplant recipients, a small increase in MSNA during mild LBNP was dependent on a decrease in arterial pressure, but in normal subjects, a similar increase in MSNA occurred in the absence of any detectable decrease in the aortic pressure stimulus to the sinoaortic baroreceptors. (3) In normal subjects, the large increase in MSNA during a high level of LBNP was dependent on a decrease in arterial pressure and could be dissociated from the decrease in central venous pressure. Taken together, the findings strongly suggest that sinoaortic baroreflexes are much more important and ventricular baroreflexes are much less important than previously thought in causing reflex sympathetic activation and vasoconstriction in the human skeletal muscle circulation during orthostatic stress.

Female↗
PubMed1994

Flexibility of lower limb reflex responses to painful cutaneous stimulation in standing humans: evidence of load-dependent modulation.

1. In six human subjects standing without support, the reflex response of the tibialis anterior muscle (TA) was elicited by painful electrical stimulation (500 Hz, 20 ms) of the anterior sole of the foot and analysed by post-stimulus averages of rectified electromyography. The threshold intensity for the reflex response was very close to the subjective pain sensation (mean value, 1.05 times). Estimation of the afferent conduction velocity gave a mean value of 26.5 m s-1, suggesting that a contribution from A delta fibres was necessary to evoke the reflex response. The TA reflex response was then used as the pain test reflex. 2. Changes in the TA excitatory pain reflex response (elicited at 1.2 times the pain threshold) were investigated while the subjects maintained different postures in upright stance. Standing on the ipsilateral leg produced a significant decrease in the reflex response with respect to its value in symmetrical stance (standing on both legs), whereas a significant facilitation was observed when the subject was standing on the contralateral leg. A parallel depression of the response in both limbs was present when the subject maintained an upright stance with the lower limbs abducted. Thus, it was apparent that the TA pain responses decreased as the supporting function of the leg increased. 3. A significant inverse correlation between the load to which the limb was subjected and the size of the reflex response was observed in all subjects. We propose that the load to which the limb is subjected, measured from peripheral mechanoreceptors, is used as a measure of the current supporting function of the limb, on the basis of which the reflex is regulated.

Adult↗
PubMedDate not supplied

A study of normal baby movements.

Twenty-five normal newborns aged between 3 and 6 days had their movements recorded by clinical observation in a controlled environment, chart recording from an automatic movement mattress over 4 hours, and cine photography triggered by the movement mattress. Over 80 different individual types of movement were grouped into six categories: progression movements (obligatory reciprocal movements), symmetrical movements (slower flexion or extension movements), startle movements, asymmetrical tonic neck reflex and 'Moro', facial movements and athetoid movements. The normal newborn's motor activity is significantly related to the level of arousal, gestational age, and environmental variables such as position, temperature, light and noise.

Arousal↗
PubMedDate not supplied

Volume displacement of the tympanic membrane in the sitting position as a function of middle ear muscle activity. A quantitative microflow method.

An open microflow meter system has been worked out for quantitative recording of the volume displacement of the tympanic membrane and its movement direction at stapedius reflex. An acoustically elicited M. stapedius contraction can be recognized by the characteristic response and latency time. The stapedius reflex contraction causes an outward or inward movement of the tympanic membrane. The magnitude of the volume displacement of the tympanic membrane is influenced by the middle ear pressure and in some ears the movement direction of the tympanic membrane changes.

Adult↗
PubMed2005

Parallel reflex pathways from flexor muscle afferents evoking resetting and flexion enhancement during fictive locomotion and scratch in the cat.

Reflex actions of muscle afferents in hindlimb flexor nerves were examined on ipsilateral motoneurone activity recorded in peripheral nerves during midbrain stimulation-evoked fictive locomotion and during fictive scratch in decerebrate cats. Trains of stimuli (15-30 shocks at 200 Hz) were delivered during the flexion phase at intensities sufficient to activate both group I and II afferents (5 times threshold, T). In many preparations tibialis anterior (TA) nerve stimulation terminated ongoing flexion and reset the locomotor cycle to extension (19/31 experiments) while extensor digitorum longus (EDL) stimulation increased and prolonged the ongoing flexor phase activity (20/33 preparations). The effects of sartorius, iliopsoas and peroneus longus muscle afferent stimulation were qualitatively similar to those of EDL nerve. Resetting to extension was seen only with higher intensity stimulation (5T) while ongoing flexor activity was often enhanced at group I intensity (2T) stimulation. The effects of flexor nerve stimulation were qualitatively similar during fictive scratch. Reflex reversals were consistently observed in some fictive locomotor preparations. In those cases, EDL stimulation produced a resetting to extension and TA stimulation prolonged the ongoing flexion phase. Occasionally reflex reversals occurred spontaneously during only one of several stimulus presentations. The variable and opposite actions of flexor afferents on the locomotor step cycle indicate the existence of parallel spinal reflex pathways. A hypothetical organization of reflex pathways from flexor muscle afferents to the spinal pattern generator networks with competing actions of group I and group II afferents on the flexor and extensor portions of this central circuitry is proposed.

Adaptation, Physiological↗
PubMed2003

Lumbar paraspinal muscle function, perception of lumbar position, and postural control in disc herniation-related back pain.

STUDY DESIGN: A follow-up study evaluating postural control, lumbar movement perception, and paraspinal muscle reflexes in disc herniation-related chronic low back pain (LBP) before and after discectomy. OBJECTIVES: To assess the effect of discectomy on postural control, lumbar perception, and reflex activation of paraspinal muscles during sudden upper limb loading. SUMMARY OF BACKGROUND DATA: Impaired muscle function, postural control, and lumbar proprioception have been observed in LBP. However, they have not been studied in sciatica patients after surgery. METHODS: The study included 20 patients selected for an operation for chronic LBP caused by disc herniation and 15 controls without chronic LBP. The paraspinal muscle responses for upper limb loading during unexpected and expected conditions were measured by surface electromyography. The ability to sense lumbar rotation was assessed in a previously validated motorized trunk rotation unit in the seated position. The postural control was measured with a vertical force platform. Pain, disability, and depression scores were recorded. RESULTS: Patients had poorer lumbar perception (P = 0.012) and postural control (P < 0.05) than did healthy controls. The postural control remained unchanged, but lumbar perception (P = 0.054) and the lumbar feed-forward control (P = 0.043) improved after the surgery. CONCLUSIONS: The results demonstrate impaired lumbar proprioception and postural control in sciatica patients. During short-term follow-up after operative treatment, postural control does not seem to change, but impaired lumbar proprioception and feed-forward control of paraspinal muscles seem to recover.

Chronic Disease↗
PubMed1989

[Cooperation and substitution of the saccadic system and the reflexes of vestibular origin: should the "reflex" concept be revised?].

Neuronal mechanisms of production of ocular saccadic movements are discussed, together with stabilizing movements of vestibular origin, and descriptions given of several neuronal elements constituting the tecto-reticulo-spinal system, the generator of horizontal saccadic movements in the brain stem, the vestibulo-ocular pathway, etc... Analysis of these pathways and of the signals travelling through them suggests that the overall apparatus is not constituted of isolated reflex modules but acts as a true functional unit for cooperation between orientation and stabilization mechanisms. In addition, coordination of synergies between eye and head movements appear to be based on the activity of clearly identifiable neurons. This neuronal implementation of the concept of synergy is completed further by a remarkable functional flexibility. The latter allows substitution by the brain, for example, fo saccades instead of vestibular reflex movements when the latter are deficient because of lesions or disturbances in the coherence of sensory information. The principal conclusion reached is that cognitive factors, which imply representations of body movements in space activated as a function of the subject's goals, must be considered when ocular movement, and gaze control is described.

Animals↗
PubMed1995

A dorsal light reflex in a squid.

A dorsal light reflex is described in the squid Lolliguncula brevis. When illuminated from the side in visually homogeneous surroundings, a free-swimming squid rolls the dorsal side of its head and trunk 10-20 degrees towards the light. With the trunk restricted in a holder, the squid rolls its head 4-5 degrees towards the light; this reaction increases by about 50% when the statocysts are bilaterally removed and increases further when the neck receptor organ is also destroyed. The results indicate a multi-modal interaction of visual, statocyst and proprioceptive inputs during postural control.

Animals↗
PubMed1979

[Psychotropic effect of sodium hydroxybutyrate].

A conclusion was drawn on the qualitative features of the spectrum of sodium hydroxybutyrate psychotropic activity from its effect on the conditioned motor-defensive reflex, behaviour in the conflict situation, active avoidance without discriminative control in rats as well as from the lateral position test The results obtained allow the effect of sodium hydroxybutyrate in non-narcotic doses to be characterized as a hypnotic one showing elements inherent in neuroleptics and tranquilizers.

Animals↗
PubMed1983

Abnormal neurohumoral response to nitroprusside infusion in congestive heart failure.

Vasodilator drugs produce tachycardia and an increase in circulating plasma norepinephrine in normal subjects. In contrast, heart rate does not change when the same drugs are given to patients with congestive heart failure. To assess if this difference could be related to a different reflex activation of the sympathetic nervous system, the response of plasma norepinephrine to nitroprusside infusion and to head-up tilt was studied in 5 normal subjects and in 46 patients with chronic congestive heart failure. Norepinephrine and heart rate increased significantly during both stimuli in normal subjects but were unchanged during nitroprusside infusion for the entire group of patients with heart failure, with considerable variability in individual responses. In 21 patients (Group I) norepinephrine increased during nitroprusside infusion, while in the remaining 25 (Group II) norepinephrine decreased. The hemodynamic response to nitroprusside was similar in the two groups, thus suggesting that the different changes in plasma norepinephrine could not be explained on the basis of a different hemodynamic response to the drug. Plasma norepinephrine also did not change significantly in Group II during tilt, although the decrease in intracardiac pressure and the increase in peripheral resistance were similar to those in Group I who increased norepinephrine normally by 56%. These data indicate that a subset of patients with severe ventricular dysfunction have an abnormal humoral, reflex sympathetic response to changes in arterial or intracardiac pressure, or both. The higher mortality in Group II suggests that this alteration in the sympathetic response may be a marker of the severity and prognosis of heart failure.

Adult↗
PubMed2005

An internal model of head kinematics predicts the influence of head orientation on reflexive eye movements.

Our sense of self-motion and self-orientation results from combining information from different sources. We hypothesize that the central nervous system (CNS) uses internal models of the laws of physics to merge cues provided by different sensory systems. Different models that include internal models have been proposed; we focus herein on that referred to as the sensory weighting model. For simplicity, we isolate the portion of the sensory weighting model that estimates head angular velocity: it includes an inverse internal model of head kinematics and an 'idiotropic' vector aligned with the main body axis. Following a post-rotatory tilt in the dark, which is a rapid tilt following a constant-velocity rotation about an earth-vertical axis, the inverse internal model is applied to conflicting vestibular signals. Consequently, the CNS computes an inaccurate estimate of head angular velocity that shifts toward alignment with an estimate of gravity. Since reflexive eye movements known as vestibulo-ocular reflexes (VOR) compensate for this estimate of head angular velocity, the model predicts that the VOR rotation axis shifts toward alignment with this estimate of gravity and that the VOR time constant depends on final head orientation. These predictions are consistent with experimental data.

Adaptation, Physiological↗
PubMed2004

Effects of loading and unloading of lower limb joints on the soleus H-reflex in standing humans.

OBJECTIVE: To investigate the effects of loading and unloading of the lower limb joints on the soleus H-reflex in standing humans. METHODS: H-reflexes were elicited in the soleus muscle in subjects standing on a force platform in a water tank under the following loading conditions of the ankle and knee joints: control condition; reduced loads of -10 and -20 N; imposed loads of 10 and 20 N. The joint loading was altered by changing the combinations of buoys and weights attached to the lower limb segments, while total body weight was kept constant. RESULTS: As the ankle- or knee-joint load was reduced, the H-reflex was significantly enhanced compared to that under the control condition. In contrast, the H-reflex was decreased as the ankle- or knee-joint load was increased. In both cases, similar levels of background activity were recorded. CONCLUSIONS: The present results suggest that joint afferents might mediate the suppression of the soleus H-reflex in standing humans. However, the identification of the receptors and/or the mechanisms cannot be addressed under the current experimental set up. SIGNIFICANCE: The results of this study give some basic insights into reflex control in an upright posture.

Adult↗
PubMed1980

Balancing as a clinical test in the differential diagnosis of sensory-motor disorders.

During balancing on a seesaw normal individuals have a mean sway oscillation of 4.3 Hz, which is significantly lower (3.3 Hz) in patients with peroneal muscular atrophy. It is assumed that the oscillations in both cases are generated by spinal stretch reflexes and that the lower frequency in patients with peroneal muscular atrophy is due to their slower nerve conduction velocity. The balancing movements are altered when spinal stretch reflex activity is reduced by ischaemia but are normal in patients with a dorsal column lesion despite a similar sensory loss. The analysis of balancing movements can be a diagnostic tool in differentiating several sensory-motor disturbances.

Adolescent↗
PubMed1990

Regulation of sympathetic nerve activity in mild human hypertension.

There is substantial evidence for increased sympathetic nerve activity in young, mildly hypertensive humans. This evidence has been derived mainly from measurements of plasma catecholamines and from responses to adrenergic antagonists and agonists in normotensive and mildly hypertensive subjects. In addition, in recent studies direct measurements of sympathetic nerve activity to the muscle circulation have been obtained by microneurography. These data also indicate that sympathetic nerve activity is increased in young, mildly hypertensive humans. The present paper reviews this work with microneurographic measurements and highlights several concepts. (1) The increases in sympathetic nerve activity to the muscle in mild hypertension are not a result of impairment in the inhibitory influence of arterial baroreceptors; presumably, they reflect a heightened central nervous system sympathetic drive. (2) In the supine position the inhibitory influence of cardiopulmonary baroreceptors on sympathetic nerve activity is increased in mild hypertension. This increase in cardiopulmonary baroreflex control buffers the heightened sympathetic neural drive in mildly hypertensive subjects in the supine position, but withdrawal of this increase during orthostatic stress produces exaggerated reflex sympathetic vasoconstrictor responses to orthostasis in mildly hypertensive subjects. (3) Arterial chemoreceptor reflexes are increased in mildly hypertensive subjects and lead to exaggerated increases in sympathetic nerve activity during hypoxia. (4) There is increasing evidence that two humoral agents, epinephrine and insulin, exert excitatory effects on sympathetic neural outflow, which may contribute to the increased sympathetic activity and arterial pressure in human hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemoreceptor Cells↗