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PubMed1976

Responses of cats to sudden falls: an otolith-originating reflex assisting landing.

A short-latency electromyographic response has been demonstrated in the human gastrocnemius during unexpected falls (11). The hypothesis that it is a form of otolith-spinal reflex has been tested in the cat. Electromyographic activity was measured in four muscles while suddenly and unexpectedly dropping a series of six cats from 50 cm above the ground. In normal animals, electrical activation of all muscles tested occurred in two distinct phases. An early burst commenced as early as 15 ms from the instant of release, was usually spindle shaped, and often but not always disappeared by 100 ms. This burst was totally and permanently abolished by bilateral labyrinthectomy, but not by selective inactivation of the relevant semicircular canals. A later phase of muscle activity commenced 75-140 ms after release and gradually built up and then subsided, rougly centered about the movement of landing on the ground. This activity was not greatly altered by labyrinthectomy. The present results appear to confirm that the early electromyographic response to sudden falls is due to an otolith-spinal reflex. A later component is nonlabyrinthine in origin, however. Smooth landings from short falls are not possible in the absence of either phase of the response.

Animals↗

PubMed1986

Spatial organization of neck and vestibular reflexes acting on the forelimbs of the decerebrate cat.

EMG recording was used to study the spatial organization of vestibular and tonic neck reflexes acting on forelimb and shoulder muscles of the decerebrate cat. Neck reflexes were studied in preparations with intact labyrinths as well as those with acute or chronic labyrinthectomies. Reflexes were described by response vectors whose orientation component is aligned with the optimal excitatory direction of tilt or head rotation. A muscle's vector orientation remained reasonably stable over a period of hours, although there was sometimes drift at the beginning or end of an experiment. Orientation of muscle response vectors did not change systematically with stimulus frequency of 0.05-2.0 Hz. For vestibular reflexes this is so, although their dynamics are consistent with convergent input from semicircular canals and otolith organs. Regardless of the preparation, a consistent reflex pattern emerged. Vestibular reflexes are characterized by response vector orientation near ear-down roll. Neck vector orientation lies in the opposite direction from the vestibular vector but typically lies further from the roll plane: Nose-up pitch is excitatory for the shoulder muscles supra- and infraspinatus, and for the medial and lateral heads of triceps, whereas nose-down pitch excites the long head of triceps. Our results generally agree with the pattern proposed by Roberts (28) for neck reflexes but disagree in part with his proposed pattern of vestibular reflexes; we did not see the expected consistent excitation by nose-down pitch.

Animals↗

PubMed1995

Extreme blood pressure fluctuations in a patient with intact autonomic reflexes and intact sodium conservation.

A patient who had episodes of profound hypotension alternating with severe hypertension without an obvious precipitating cause is reported. The hypotensive episodes were accompanied by tiredness, syncope, bradycardia, and a low norepinephrine concentration while supine or standing. In contrast, the hypertensive episodes were associated with marked tachycardia, sweating, anxiety, abdominal pain, and very high levels of plasma norepinephrine concentration. Extensive investigations failed to support a diagnosis of pheochromocytoma. The testing of baroreceptor function and autonomic reflexes was normal. Blood pressure was not salt sensitive. It was concluded that this patient has a unique clinical syndrome of extreme fluctuation of blood pressure and sympathetic nervous activity yet intact cardiovascular reflexes and normal sodium conservation. The abnormal blood pressure regulation most likely has a central origin.

Aged↗

PubMed1979

[Organization of reflex responses elicited in man by muscle stretch applied to uni- and bi-functional muscles].

The organization of human forearm reflexes following the application of extension torque perturbations has been studied in three flexors of the elbow: brachioradialis (BR), biceps (B), and pronator teres (PT). Two of these flexors are also involved in wrist supination: (B) and pronation (PT). During the perturbation, the wrist was fixed at various angles: from full supination to full pronation. The results show that the amplitude of the reflex responses of B and PT is highly dependent on wrist position. By eliminating biceps length changes as a source of observed reflex variation, it has been shown that the normalized reflex amplitude of B increases by 300% when the wrist position is varied from full pronation to full supination. In contrast, the BR muscle has a reflex response which is independent of wrist position. These results are discussed in relation to the role of reciprocal innervation and the possible action of receptors encoding wrist angle.

Humans↗

PubMed1975

Reflex patters initiated by the secondary sensory fiber endings of muscle spindles: a proposal.

Muscle spindles have two kinds of sensory fibers, each with stretch-sensitive endings on the nuclear bag muscle fibers and the nuclear chain muscle fibers within the spindle. The stretch reflex responses initiated by the primary sensory fibers have been well defines. There are other stretch reflexes of poorly defined origin and distribution. Clinical studies on spastic patients indicate that these stretch reflexes show regional responses or regional synergies. Stretch of flexor muscles of proximal joints of an extremity causes slowly recruiting, prolonged, reflex flexion in that extremity, in the contralateral extremity and also in the ipsilateral extremity, producing the crossed extension-flexion reflex and long spinal reflex. Likewise, stretch of extensor muscles of the proximal joints initiates a similar extension reflex in the same distribution. Stretch of the distal flexors of an extremity reflexly spreads flexion through that extremity. Stretch of the distal extensors of an extremity spreads extension throughout that extremity. These reflexes can be abolished by intramuscular neurolysis with phenol. They have long internuncial pathways and involve both alpha and gamma motoneurons. The demonstration that these reflex patterns are initiated by stretch of the muscle and show characteristics similar to those shown in physiological studies by the secondary sensory spindle reflexes suggests that they are initiated by stretch of the endings of the secondary sensory fibers of muscle spindles.

Humans↗

PubMed1979

Role of the asymmetrical tonic neck reflex in hand visualization in normal infants.

Fourteen infants were each videotaped 7 times within the first 12 weeks of life to determine whether or not the asymmetrical tonic neck reflex had a role in placing their hands within their fields of vision. Infants' arms were more frequently out of the reflex position. Hands were within the peripheral visual field more often than in the focal visual field or not within the visual field. The proportion of observations that hands were in a particular visual field varied in accordance with the presence or absence of the reflex. A higher proportion of reflex observations occurred in the focal visual field, whereas a higher proportion of observations made when the infants were not in the reflex position occurred in the peripheral visual field. Further, the proportion of focal field observations in the reflex position was greater than the proportion of observations out of the reflex position for the first six of the seven ages. This study confirms that when infants are in the asymmetrical tonic neck reflex position, their hands are more likely to be in a position in which they can be visualized.

Age Factors↗

PubMed1979

Muscular hypertonia: quantitative analysis.

By a statistical method of analysis, the force applied to move a limb passively can be translated into physiologically relevant parameters relating to the muscle. The parameters identified and measured are the dynamic and static activity of the muscle and their interactions with the varying length of the muscle during stretch. This method of analysis has been shown to be of assistance in evaluating the reflex status of persons with central nervous system disorders in preparation for treatment and in measuring the effects of treatment.

Humans↗

PubMed1988

Influence of gravity on cat vertical vestibulo-ocular reflex.

The vertical vestibulo-ocular reflex (VOR) was recorded in cats using electro-oculography during sinusoidal angular pitch. Peak stimulus velocity was 50%/s over a frequency range from 0.01 to 4.0 Hz. To test the effect of gravity on the vertical VOR, the animal was pitched while sitting upright or lying on its side. Upright pitch changed the cat's orientation relative to gravity, while on-side pitch did not. The cumulative slow component position of the eye during on-side pitch was less symmetric than during upright pitch. Over the mid-frequency range (0.1 to 1.0 Hz), the average gain of the vertical VOR was 14.5% higher during upright pitch than during on-side pitch. At low frequencies (less than 0.05 Hz) changing head position relative to gravity raised the vertical VOR gain and kept the reflex in phase with stimulus velocity. These results indicate that gravity-sensitive mechanisms make the vertical VOR more compensatory.

Animals↗

PubMed2006

[Electromyographic study of stretch reflexes in the normal and prosthetic hip].

PURPOSE OF THE STUDY: Several studies have been devoted to the effect of proprioception on joint function. Modifications in feedback control from the cord have been observed in unstable joints due to capsule and ligament laxity. A few studies have examined the effect of knee and hip arthroplasty on proprioception, but none have established whether stretch reflexes affect function of a prosthetic joint. The purpose of the present study was to demonstrate the electromyographic characteristics of stretch reflexes of the normal hip joint and to compare them with those observed in the prosthetic hip. MATERIAL AND METHODS: Two groups of patients were studied. The first included eleven subjects free of neurological disorders whose studied limb was healthy. The second group included ten subjects with a total hip prosthesis who had undergone extensive capsulectomy during the arthroplasty. Voluntary muscle contraction was noted in each subject. In addition, electromyographic recordings were made to note response of the ipsilateral and contralateral quadriceps crural and tensor of the fascia lata during changes in joint position. Recordings were made with the subject in the supine position, the limb suspended, hip flexed at 45 degrees and knee extended. Three series of ten recordings were made in random order to measure the latency of muscle response to free fall of the limb, accelerated fall of the relaxed limb, and accelerated fall associated with calibrated contraction of the quadriceps. Mean latency of muscle response was calculated for each trial. RESULTS: In the conditions of this study, there was no statistically significant difference (p = 0.05) in the reflex time course between natural and prosthetic hips. DISCUSSION: Changes due to joint replacement and capsulectomy do not appear to affect the stretch reflexes of the hip joint.

Aged↗

PubMed1992

Head nodding is compensatory in spasmus nutans.

BACKGROUND: Spasmus nutans is defined as asymmetric nystagmus with associated head nodding in childhood. It is not clear whether head nodding is a compensatory mechanism to control the nystagmus or an involuntary movement of pathologic origin. METHODS: The authors analyzed the relation between head and eye movements by simultaneous eye and head movement recordings of 35 patients with spasmus nutans. RESULTS: In 21 of these patients, the fine, fast, dissociated nystagmus changed during head nodding to larger and slower symmetric eye movements with both eyes oscillating at the same amplitude in phase and 180 degrees out of phase to the head movements, corresponding to a normal compensatory vestibulo-ocular reflex. CONCLUSION: These findings indicate that head nodding is compensatory in spasmus nutans.

Child, Preschool↗

PubMed1988

Skin microvascular circulation in the sympathetic dystrophies evaluated by videophotometric capillaroscopy and laser Doppler fluxmetry.

Finger-skin microcirculation and its reactions to sympathetic stimuli were investigated in 12 patients with sympathetic dystrophies, secondary to trauma or other diseases. Nailfold-skin capillary blood cell velocity (CBV) was measured by videophotometric capillaroscopy. Laser Doppler fluxmetry was used to provide an index of skin circulation in vessels in addition to the superficial capillaries. Both CBV and laser Doppler flux (LDF) values were significantly lower in the patients, compared with the healthy controls (P less than 0.05), despite the fact that skin temperature was the same in both groups. During cooling of the contralateral hand, CBV and LDF decreased markedly (22-60%) in the control group but not in the patients (0-13%). The decrease in skin perfusion normally seen upon lowering of the hand was also impaired in the patient group (7%) compared with controls (42%) (P less than 0.05). These impaired vasomotor reflex responses are consistent with sympathetic dysfunction and may well explain some of the typical features of the syndrome, e.g. limb oedema.

Aged↗

PubMed1993

Isoproterenol induced cerebral hypoperfusion in a heart transplant recipient.

To determine the effect of tilt isoproterenol provocation on cerebral perfusion in a patient with denervated heart, transcranial Doppler sonography was used to assess changes in cerebral blood flow velocity during upright tilt test. A 51-year-old man with history of syncopal spells after heart transplantation was evaluated by using upright tilt test with and without isoproterenol for 30 minutes, respectively, at 80 degrees inclined. Mean cerebral blood flow was measured in the main stem of the right middle cerebral artery. Blood pressure and heart rate were noninvasively monitored. Tilt isoproterenol provocation but not tilt alone induced a significant reduction in cerebral blood flow velocity, without remarkable hypotension. There was no change in respiratory activity. This may indicate that vagal reflexes are not implicated in the mechanism of isoproterenol to induce cerebral hypoperfusion and hence neurally mediated syncope.

Blood Flow Velocity↗

PubMed1985

Spatial and temporal response properties of the vestibulocollic reflex in decerebrate cats.

Vestibulocollic reflex responses of several neck muscles in decerebrate cats were studied during angular rotations of the whole body in a large number of vertical and horizontal rotation planes, at frequencies from 0.07 to 1.6 Hz. Vestibulocollic responses were compared to eye muscle and forelimb muscle vestibular responses. Electromyographic activity was recorded by fine wires inserted in biventer cervicis, complexus, longus capitis, obliquus capitis inferior, occipitoscapularis, rectus capitis major, splenius, lateral rectus, and triceps brachii. At frequencies of approximately 0.5 Hz and above, neck muscle electromyographic response gains were sinusoidal functions of stimulus orientation within a set of vertical or horizontal planes, and a muscle's response phase remained constant across rotation planes, or reversed by 180 degrees. Response patterns at high frequencies were consistent with vestibulocollic reflex activation by semicircular canals through brain circuitry that modifies canal dynamics. At frequencies of approximately 0.5 Hz and above, the stimulus orientation in which a given neck muscle's response was maximal remained nearly constant across frequencies. Thus, we used responses to rotations at high frequencies to calculate axes of maximal response of each muscle in three-dimensional space. Lateral rectus, obliquus, and to a lesser extent, splenius and longus capitus were activated predominantly by horizontal rotations. Biventer was activated predominantly by pitch, triceps predominantly by roll, and complexus, occipitoscapularis, and rectus major significantly excited by rotations in all three coordinate planes. In some cases, at frequencies less than 0.5 Hz, neck muscle response phase varied depending on the vertical plane in which the cat was rotated, and the optimal response plane was poorly defined and varied with frequency. These responses indicated that, at some frequencies, neck muscle activity can result from summation of inputs with differing spatial orientation and dynamics (spatial-temporal convergence). Differences between responses to vertical and horizontal rotations suggested that low-frequency spatial-temporal convergence behavior of the vestibulocollic reflex during vertical rotations was due to convergent semicircular canal and otolith receptor inputs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1984

A comparative study on the presence of the asymmetrical tonic neck reflex in adult hemiplegia.

In this study, the intensity of the asymmetrical tonic neck reflex (ATNR) was measured in post-cerebrovascular accident (CVA) adults with hemiplegia and in neurologically intact adults to determine if the reflex exaggerated following CVA. Fourteen subjects with right and left hemiplegia were matched to neurologically intact subjects by age and sex and tested for the ATNR. Intensity of the reflex was measured using electromyography (EMG) biofeedback. The results indicate that no difference exists between the two groups in intensity of the reflex. The method of rotation used to elicit the reflex did significantly affect the strength of the muscle response. A possible explanation for observation of the reflex in the hemiplegic individual's movement and its significance in neuromuscular re-education programs is discussed.

Aged↗

PubMed1990

[Parkinsonian rigidity: clinical and physiopathologic aspects].

Neurophysiologic mechanisms responsible for parkinsonian rigidity are poorly understood. In any case, they have to fit all the clinical data which are first reviewed before discussing 2 theories which are proposed to interpret rigidity. The first theory postulates that increased resistance to mobilization is due to hyperactivity in a long loop reflex pathway which originates at the neuromuscular spindles and relays in the motor cortex. This theory is based on the largely accepted finding that, in parkinsonian patients, M2 response is increased when a voluntary movement is abruptly stopped. Although popular this hypothesis is far from explaining all the clinical facts, namely that rigidity is equal in extensor and flexor, proximal and distal muscles. Based on a reflex set by primary afferent discharges, it is incompatible with the lack of rigidity reinforcement after faster passive mobilization. The second theory rests on data obtained from electrophysiological studies of some spinal interneurones. Both IA and IB inhibitory interneurones are functionally modified but not in the same direction. While the IA inhibitory interneurone is facilitated, the IB inhibitory interneurone is less active. Disappearance of autogenic inhibition can explain rigidity at rest and the tonic stretch reflex. In addition, interneurones intervening in the flexor reflex disclose a modified excitability. It is possible to interpret these facts by postulating an abnormal influence transmitted through descending reticulospinal pathways. This abnormal influence would result from modified activation of reticular nuclei by afferents projecting from the basal ganglia. Such a hypothesis is open to experimental testing through the startle reaction. The latter facilitates the H reflex by the reticulospinal pathways, the influence of cortex--if any--being negligible.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiology↗

PubMedDate not supplied

[Results of a study of vestibular function and space perception in cosmonauts].

The results of studying the vestibular function and the function of spatial perception in 26 cosmonauts before and after 30 space flights are discussed. The typical postflight changes in these functions were: an increase in the reactivity of the otolith organ, a decrease in the sensitivity of semicircular canals, a decline in the accuracy of perception of spatial coordinates, asymmetry of most parameters, development of illusionary reactions inflight. The cosmonauts also showed individual variations with respect to the degrees of the above responses, the dynamics and length of adaptation, the development of the motion sickness symptom-complex, etc. At R+O some cosmonauts exhibited a change in the direction of the eye counter-rotation, i. e., the negative otolith reflex or at turn towards the tilt direction. Possible mechanisms of these vestibular changes are discussed.

Adult↗

PubMed1986

Somatosympathetic reflex unilateral sweating and pupillary dilatation in a paraplegic man.

Sympathetic spinal reflex responses to painful stimuli have been studied in experimental animals, but have rarely been demonstrated in human beings. We report the case of a paraplegic man with a high thoracic sensory level to pain, who developed unilateral pupillodilatation and sweating from the head to the midthoracic region as a response to rib fractures below the sensory level. This regional sympathetic reflex response was similar in many ways to that seen in spinally transected animals. Regional sympathetic reflex responses may provide a clinically useful sign of a painful and perhaps dangerous condition which is located below the analgesic level in spinal cord-injured patients.

Adult↗

PubMed1986

Phasic stretch reflex of the abdominal muscles.

This analysis of the abdominal stretch reflex (ASR) evoked by a tap to the abdomen was designed to explore how abdominal motoneurons process signals from respiratory and nonrespiratory sources. We recorded surface EMGs from the external and internal oblique muscles in standing subjects. Amplitudes of the abdominal stretch reflex varied despite constant tap forces, but strong taps evoked a larger reflex than weak taps. Trunk rotation toward the recording side, or voluntary contraction of the external and internal oblique muscles increased the reflex amplitudes, whereas contralateral rotation reduced their occurrence. An abdominal stretch reflex during a voluntary contraction was followed by a silent period of 40 to 80 ms. Often a late wave followed a reflex by 20 to 40 ms. Amplitudes during breathholds at residual lung volume were larger than those evoked during a breathhold at functional residual capacity, suggesting that abdominal stretch reflex amplitudes are inversely proportional to static lung volume. During quiet breathing the reflex amplitude reached a maximum slightly before end-expiration and decreased progressively to a minimum close to end-inspiration. During rebreathing, background abdominal activity was augmented with highest activity in late expiration. Abdominal stretch reflex amplitudes continued to wax and wane in phase with respiration, and the maximal reflex occurred progressively earlier in expiration. In summary, the abdominal stretch reflex reflects strong control from abdominal muscle spindles, lung proprioceptors, and chemoreceptors. The relative contributions of these inputs need to be determined.

Abdominal Muscles↗