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PubMed1986

Conditioning of crossed extensor reflex pathways by independent natural stimulation of labyrinth, neck and elbow joint afferents.

The present experiments demonstrated that labyrinth, neck and elbow joint afferents interact to influence the excitability of crossed extensor reflex pathways projecting to triceps brachii in decerebrate cats. Reflex excitability was dependent on head, neck and elbow position such that it was increased when the elbow was held at full flexion and either the head maintained side down or the neck rotated side up. Such interaction between these afferents is likely to be important in postural control.

Animals↗
PubMed1993

Microneurography and applications to issues of motor control: Fifth Annual Stuart Reiner Memorial Lecture.

Among the hypotheses regarding fusimotor functions based on earlier animal experiments some are inconsistent, others are in conformity with microneurographic observations in man. The human data provide evidence against the following two theories: (1) the length follow-up servo theory; and (2) the theory that fusimotor neurons can be selectively activated to produce spindle sensitization and stretch reflex reinforcements. The human data support the theory of alpha-gamma coactivation. In particular, in the early phase of isometric voluntary contractions fusimotor-driven afferent spindle activity assists in autogenetic activation of alpha motoneurons and in reciprocal relaxation of antagonists. As muscle fatigue develops, the autogenetic reflex drive via the fusimotor route declines. The fusimotor bias during contraction provides for maintenance of spindle sensitivity to minute perturbations and for load-compensating reflex adjustments to such perturbations. Reflex overcorrections may lead to uncontrollable oscillations of the type seen in enhanced physiological tremor.

Afferent Pathways↗
PubMed1982

The effect of elbow joint afferent discharge on transmission in forelimb flexion reflex pathways to biceps and triceps brachii in decerebrate cats.

The present experiments were performed to investigate the influence of elbow joint afferent discharge on the excitability of reflex arcs mediating flexion withdrawal and crossed extensor reflexes in the forelimb muscles of decerebrate cats. The excitability of flexion withdrawal and crossed extensor reflexes in forelimb muscles was shown to be modulated by elbow joint position. Flexion withdrawal reflexes were most easily elicited when the elbow was extended and crossed extensor reflexes were most easily elicited when the elbow was flexed. This modulation of transmission was not confined to reflex pathways projecting to muscles acting at the elbow but also included pathways to muscles acting at the wrist and shoulder in addition to muscles in the contralateral forelimb. The changing excitability of reflex pathways caused by elbow movement was unaltered by degloving the skin covering the joint and tenotomy of the medial head of triceps and the long head of biceps. However, modulation of reflex excitability by joint movement was totally abolished by local anaesthesia of the joint in an otherwise intact limb. Thus, the present experiments indicate that transmission in forelimb flexion reflex pathways can be powerfully influenced by elbow joint afferent discharge.

Animals↗
PubMed2006

Motor and reflex testing in GM1-gangliosidosis model mice.

A large number of genetic disease model mice have been produced by genetic engineering. However, phenotypic analysis is not sufficient, particularly for brain dysfunction in neurogenetic diseases. We tried to develop a new assessment system mainly for motor and reflex functions in G(M1)-gangliosidosis model mice. Two genetically engineered model mouse strains were used for this study: the beta-galactosidase-deficient knockout mouse representing infantile G(M1)-gangliosidosis (severe form), and transgenic mouse representing juvenile G(M1)-gangliosidosis (mild form). We modified human child neurology techniques, and selected eleven tests for motor assessment and reflex testing. The test results were scored in four grades: 0 (normal), 1 (slightly abnormal), 2 (moderately abnormal), and 3 (severely abnormal). Both disease model mouse strains showed high scores even at the apparently pre-symptomatic stage of the disease, particularly with abnormal tail and hind limb postures. Individual and total test scores were well correlated with the progression of the disease. This method is simple, quick, and reproducible. The testing is sensitive enough to detect early neurological abnormalities, and will be useful for monitoring the natural clinical course and effect of therapeutic experiments in various neurogenetic disease model mice, such as chemical chaperone therapy for G(M1)-gangliosidosis model mice.

Age Factors↗
PubMed1999

Characteristics of the VOR in response to linear acceleration.

The primate linear VOR (LVOR) includes two forms. First, eye-movement responses to translation [e.g., horizontal responses to interaural (i.a.) motion] help maintain binocular fixation on targets, and therefore a stable bifoveal image. The translational LVOR is strongly modulated by fixation distance, and operates with high-pass dynamics (> 1 Hz). Second, other LVOR responses occur that cannot be compensatory for translation and instead seem compensatory for head tilt. This reflects an otolith response ambiguity--that is, an inability to distinguish head translation from head tilt relative to gravity. Thus, ocular torsion is appropriately compensatory for head roll-tilt, but also occurs during IA translation, since both stimuli entail IA acceleration. Unlike the IA-horizontal response, IA torsion behaves with low-pass dynamics (with respect to "tilt"), and is uninfluenced by fixation distance. Interestingly, roll-tilt, like IA translation, also produces both horizontal (a translational reflex) and torsional (a tilt reflex) responses, further emphasizing the ambiguity problem. Early data from subjects following unilateral labyrinthectomy, which demonstrates a general immediate decline in translational LVOR responses, are also presented, followed by only modest recovery over several months. Interestingly, the usual high-pass dynamics of these reflexes shift to an even higher cutoff. Both eyes respond roughly equally, suggesting that unilateral otolith input generates a binocularly symmetric LVOR.

Acceleration↗
PubMed1986

Diaphragmatic responses to body position changes in obese patients with obstructive sleep apnea.

Patients with severe obesity and obstructive sleep apnea (OSA) have been shown to have abnormalities in respiratory muscle function and respiratory control. The present study was done to evaluate diaphragmatic function and the diaphragm fiber-length-compensating reflex in morbidly obese patients with OSA (1). Twelve normal subjects and 13 morbidly obese patients with OSA were studied in recumbent and upright positions. In the normal subjects, the diaphragm fiber-length-compensating reflex operated normally causing the diaphragm's inspiratory EMG to increase when the diaphragm's fibers shortened with assumption of the upright position. However, 8 of the 13 obese patients with OSA showed a decrease rather than an increase in the inspiratory diaphragmatic EMG on assuming the upright posture. Further data indicate greater diaphragmatic efficiency in the upright than in the supine position in a majority of the obese patients, a reversal of the normal response. Two possible explanations of these observations are: an abnormality of central respiratory control in obese patients with OSA and overstretching of the diaphragm in the recumbent obese patient. The observation of reduced maximal transdiaphragmatic pressures in the recumbent position in some of the obese patients with OSA supports the second explanation. Diaphragmatic overstretching may be an important mechanism in the development of hypoventilation in the morbidly obese.

Adult↗
PubMed1989

[Cardiovascular response to cerebral circulatory regulation during shifts in head position].

Cardiovascular response and its effect on cerebral regulation was examined in groups of young and old people by putting pressure on the cerebral circulatory system through rapid changes in head position. A transient increase in blood pressure was observed in both the young and old people's groups when the head was tilted up. In the old group, there was less change in both systolic blood pressure and diastolic blood pressure. A transient reduction in blood pressure was observed in both groups when the head was tilted down. However, there was less change in diastolic blood pressure in the old group. The number of heart beats before a maximum change in blood pressure was 5 to 9 beats when the head was tilted up, and there was no significant difference between the two groups. The corresponding figure when the head was tilted down was 17.1 +/- 3.51 beats in the young group, and 27.1 +/- 11.5 beats in the old group, significantly higher among the old group. All were early responses observed within 1-2 minutes. Looking at the change of pulse after the head was tilted up or down among the young group, the number of heart beats increased to reach a peak when the head was tilted up, and when the head was tilted down the number of heart beats fell to its lowest level. The affect of these two cardiovascular responses tended to compensate for cerebral perfusion pressure, which indicates the possible existence of a cerebral perfusion pressure regulatory mechanism, assisted by a carotid sinus reflex. A reduction of this function was suggested in the old group.

Adult↗
PubMedDate not supplied

[Development of righting reflexes and their influence on the development of static functions in children with infantile cerebral palsy].

In a group of 55 children with signs of central nervous system lesions the development of righting reflexes and static functions was observed during the first 3 years of life. A delay and disturbances in the development of righting reflexes and static functions was observed with differences between the individual groups of infantile cerebral palsy.

Age Factors↗
PubMed1981

[Interactions of general body-posture, oral and facial region. II. Polyelectromyographic investigations (author's transl)].

Based on previous observations we used surface poly-electromyography (EMG) to trace influences of eye and tongue movements on skeletal muscles. While we could not show ocular effects using this method, we could demonstrate clearcut influences of lingual lateral movements on the sternocleidomastoid (SCM) muscles. Voluntary lateral movements of the tongue inside the mouth were accompanied by an increase of the amplitude of the EMG of the contralateral SCM muscle, while lateral movements of the tongue outside the mouth produced an increase of the amplitude of the ispilateral SCM muscle. Frequency characteristics of the EMG remained unchanged. There were no such alterations with passive tongue movements. These seemingly postural lingual reflexes are discussed in the light of Bosma's concept of maintenance of pharyngeal airways.

Adolescent↗
PubMed1995

Activation of the Bezold-Jarisch reflex in the sitting position for shoulder arthroscopy using interscalene block.

A retrospective analysis of 116 patients who underwent shoulder arthroscopy in the sitting position with interscalene block (ISB) revealed 20 patients who experienced potentially dangerous vasovagal events characterized by sudden severe hypotension and bradycardia (Group 1). The event occurred 61 +/- 18 min after the block placement. Ninety-six patients (Group 2) did not experience a vasovagal event. Of the patients in Group 2, 18 received beta-adrenergic blockers for increasing heart rate and/or arterial blood pressure (Group 2B) while 78 did not (Group 2A). The number receiving beta-adrenergic blockers was significantly greater than in Group 1 (18/96 vs 0/20, P < 0.05). There were no significant demographic or baseline hemodynamic differences between groups, but the beta-adrenergic blocker and vagal groups showed significantly greater intraoperative peak heart rates (P < 0.05). All patients received epinephrine in their local anesthetic for ISB, incision sites, and articular irrigating solution. Total and weight-corrected epinephrine doses differed significantly between groups (lowest in Group 2A, P < 0.01). Activation of the Bezold-Jarisch reflex, induced by increased circulating epinephrine levels and the sitting position, is the postulated mechanism.

Adult↗
PubMed1997

Aviation spatial orientation in relationship to head position, altitude interpretation, and control.

INTRODUCTION: Recently, a visually driven neck reflex was identified as causing head tilt toward the horizon during VMC flight. If this is the case, then pilots orient about a fixed rather than moving horizon, implying current attitude instruments inaccurately present spatial information. The purpose of this study was to determine if the opto-kinetic cervical neck reflex has an effect dependent on passive (autopilot) or active control of the aircraft. Further, findings could help determine if the opto-kinetic cervical reflex is characteristic of other flight crewmembers. METHODS: There were 16 military pilots who flew two 13-min VMC low-level routes in a large dome flight simulator. Head position in relation to aircraft bank angle was recorded by a head tracker device. During one low-level route, the pilot had a supervisory role as the autopilot flew the aircraft (passive). The other route was flow manually by the pilot (active). RESULTS: Pilots consistently tilted the head to maintain alignment with the horizon. Similar head tilt angles were found in both the active and passive flight phases. However, head tilt had a faster onset rate in the passive condition. CONCLUSION: Results indicate the opto-kinetic cervical reflex affects pilots while actively flying or in a supervisory role as the autopilot flies. The consistent head tilt angles in both conditions should be considered in attitude indicator, HUD, and HMD designs. Further, results seem to indicate that non-pilot flight crewmembers are affected by the opto-kinetic cervical reflex which should be considered in spatial disorientation and airsickness discussions.

Aerospace Medicine↗
PubMed1999

What functions do reflexes serve during human locomotion?

Studies on the reflex modulation of vertebrate locomotion have been conducted in many different laboratories and with many different preparations: for example, lamprey swimming, bird flight, quadrupedal walking in cats and bipedal walking in humans. Emerging concepts are that reflexes are task-, phase- and context-dependent. To function usefully in a behaviour such as locomotion wherein initial conditions change from step to step, reflexes would have to show modulation. Papers are reviewed in which the study of different reflexes have been conducted during different behaviours, with an emphasis on experiments in humans. A framework is developed in which the modulation and flexibility of reflexes are demonstrated. Alterations in cutaneous, and muscle (stretch and load receptor) reflexes between sitting, standing and walking are discussed. Studies in which both electrical, mechanical and 'natural' receptor activation have been conducted during walking are reviewed. Reflexes are shown to have important regulatory functions during human locomotion. A framework for discussion of reflex function throughout the step cycle is developed. The function of a given reflex pathway changes dynamically throughout the locomotor cycle. While all reflexes act in concert to a certain extent, generally cutaneous reflexes act to alter swing limb trajectory to avoid stumbling and falling. Stretch reflexes act to stabilize limb trajectory and assist force production during stance. Load receptor reflexes are shown to have an effect on both stance phase body weight support and step cycle timing. After neurotrauma or in disease, reflexes no longer function as during normal locomotion, but still have the potential to be clinically exploited in gait modification regimens.

Animals↗
PubMed1984

Responses to head tilt in cat central vestibular neurons. I. Direction of maximum sensitivity.

Responses to head tilt were recorded from vestibular neurons in and around the lateral vestibular nucleus (LVN) of the decerebrate cat. Each animal had all six semicircular canals rendered nonfunctional by a plugging procedure. Each cell was studied by slowly tilting the cat, using one or both of two paradigms. In the first method, sinusoidal tilts (0.05 or 0.1 Hz) were used to produce bidirectional stimuli in up to 12 pairs of directions, including left/right (roll tilt) and fore/aft (pitch). The second method imposed a constant 10 degree tilt; the direction of the tilt was rotated around the animal by an appropriate combination of roll and pitch motions. Neurons responded by maximally increasing their discharge frequency in a particular direction of head tilt from the horizontal. Each cell's response could be described by a vector in the animal's horizontal plane whose orientation is given by the direction of the most effective stimulus and whose length represents the neuron's maximal sensitivity to tilt. The two methods of stimulation yielded equivalent response vectors. Response vectors were obtained for 100 neurons. The distribution of vector directions for these vestibular neurons was not uniform; there was a conspicuous absence of neurons with fore/aft-directed vectors. The sensitivity of these cells (length of the response vector) ranged from 10 to 230 impulses X s-1 X g-1 (median 50). Neurons whose vectors lay in the ipsilateral half-plane (which would be excited by ear-down tilt) tended to be less sensitive than those with contralateral vectors. Neurons excited by ear-up tilt tended to be located ventrally in the LVN, while those excited by ear-down tilt were more evenly distributed. There was no other obvious correlation of vector orientation with the anatomical locus of the cell in the LVN. The directional selectivity of the responses of these neurons to head tilts are similar to those previously reported tin utricular afferents. The broad distribution of response vector orientations provides an appropriate substrate for vestibulospinal reflexes to a wide variety of head tilts.

Afferent Pathways↗
PubMed1991

Neurally mediated syncope detected by carotid sinus massage and head-up tilt test in sick sinus syndrome.

It is generally accepted that a positive response to carotid sinus massage (CSM) or head-up tilt (HUT) in patients affected by syncope suggests a reflex cause of the syncope. To study the role of the autonomic nervous system in causing syncope in the sick sinus syndrome (SSS), CSM and HUT were performed in 35 consecutive patients (20 men, mean age 70 +/- 9 years) with syncope and SSS. Results were compared with those in 35 patients affected by syncope that, despite careful cardiovascular and neurologic examination, were of uncertain origin (21 men; mean age 68 +/- 9 years) and with those of 35 subjects without syncope (20 men; mean age 69 +/- 10). All patients underwent CSM in the supine and standing positions for 10 seconds and HUT to 60 degrees for 60 minutes. In the patients with SSS, the full reproduction of spontaneous symptoms by CSM occurred in 21 (60%) and by HUT, in 19 (54%). At least 1 test was positive in 28 patients (80%): cardioinhibitory or mixed responses in 69%, vasodepressor responses in 11%. The percentages of positive tests in the patients with syncope of uncertain origin were similar to or slightly less than those of patients with SSS (CSM 63%, HUT 26%, overall 74%) with cardioinhibitory or mixed responses in 54% and vasodepressor in 20% (p less than 0.05). In control subjects, syncope was induced by CSM in 1 (3%) and by HUT in 2 (6%); overall positivity was 9%. In conclusion, in most patients affected by syncope and SSS, an abnormal neural reflex probably plays a major role in causing syncope.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1987

Cardiovascular response to orthostatic tilt in patients with severe congestive heart failure.

Baroreflex mediated haemodynamic responses and aortic pulsatile stretch were studied in patients with congestive heart failure due to ischaemia. Seven patients with severe congestive heart failure (baseline angiographic ejection fraction 21(3)% (mean(SEM); left ventricular end diastolic volume and pressure 351(43) ml and 22(3) mmHg respectively) were compared with seven control subjects whose angiographic ejection fraction was 74(3)%. Passive 45 degrees upright tilt was used to unload baroreceptors. Aortic pulsatile stretch (pulsatile distension as percentage of diastolic diameter) was calculated from echocardiographic measurements of aortic diameters. Upright tilt caused a significant decrease in cardiac filling pressures in patients with congestive heart failure, as in control subjects. During tilt control subjects had substantially increased systemic vascular resistance and heart rate and decreased stroke volume, but arterial pressure, cardiac index, and aortic pulsatile stretch were maintained constant. Patients with congestive heart failure developed peripheral vasodilatation, had no increase in heart rate, and failed to maintain arterial mean and systolic pressures in the tilted position. They had, however, maintained a constant pulse pressure and increased cardiac index, stroke volume, and aortic pulsatile stretch. The response to upright tilt in patients with congestive heart failure may be explained by faulty sympathetic reflexes, causing vasodilatation and hypotension rather than vasoconstriction, and a rise in stroke volume due to the decrease in afterload.

Aorta↗
PubMed1991

Afferent signals from the extraocular muscles of the pigeon modify the electromyogram of these muscles during the vestibulo-ocular reflex.

There is no general agreement on whether afferent signals from the extraocular muscles play any part in oculomotor control. However, we have previously shown that they modify the responses of cells in the oculomotor control system during the vestibulo-ocular reflex (VOR). If, as we suspect, these signals have an important role in the control of the VOR from moment-to-moment, we should be able to demonstrate similar, functionally significant, modifications at the output of the reflex. We have recorded the electromyographic activity of several extraocular muscles of the right eye during the VOR and while imposing movements on the left eye. We describe how the activity of the muscles, reflected in the electromyogram, is modified in specific ways depending on the parameters of the imposed eye movements. The effects of the extraocular afferent signals on the eye-muscle responses to vestibular drive during the slow phase of the VOR appear to be corrective. Thus the present results provide strong evidence that afferent signals from the extraocular muscles are concerned in the control of the reflex from moment-to-moment, and suggest that the wider question of their role in oculomotor control merits further consideration.

Afferent Pathways↗