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At least 1,531 records · Page 85Linked to original sources
PubMed1977

Effects of postural changes of the upper limb on reflex transmission in the lower limb. Cervicolumbar reflex interactions in man.

The influence of passive changes in upper limb position on the excitability of three myotatic arc reflexes (soleus, quadriceps, and biceps femoris) of the lower limb has been explored on 42 volunteers. The results indicate that the excitability of the three myotatic arcs can be influenced at a distance by postural modifications of the upper limb. When the ipsilateral upper limb is forwards or the contralateral backwards, a facilitation of both soleus and quadriceps tendon reflexes is observed while the biceps femoris reflexes are reduced. This pattern of facilitation and inhibition is reversed when the ipsilateral upper limb is backwards or the contralateral forwards. The facilitations as well as inhibitions of proximal myotatic arc reflexes are quantitatively more marked than that of the soleus reflex. Facilitation and inhibition are not linearly related to the angle of the arm with the trunk. Effects begin at a considerable angle, become maximal at 45 degrees, and progressively disappear for greater values. It is suggested that the distinct pattern of facilitation and inhibition which is exerted in reciprocal fashion on extensor and flexor motor nuclei might depend on the long propriospinal neurones connecting cervical and lumbar enlargements.

Achilles Tendon↗
PubMed1989

Central and peripheral effects of the dihydropyridine calcium channel activator BAY K 8644 in the rat.

Following intraperitoneal (i.p.) administration BAY K 8644 (0.5-4 mg/kg) induced an increase in blood pressure associated with bradycardia, increased tail-flick latency in response to radiant heat, decreased locomotion, induced muscle contraction, postural changes and also reduced reflex activity. Only the postural changes and reduced locomotion were seen after intracerebroventricular administration (5-20 micrograms/kg), suggesting that the other effects are mediated peripherally. All the above effects were antagonised by the calcium channel blocker nifedipine. BAY K 8644 (4 mg/kg i.p.) also significantly increased homovanillic acid and 3,4-dihydroxyphenylacetic acid concentrations in the cortex and striatum, an effect which could also be reversed by nifedipine. Apart from inducing hypotension and tachycardia, nifedipine alone had no effect on any of the above parameters. The analgesic-like activity of BAY K 8644 observed in the tail-flick test appears to be related to its vasoconstrictor effects as the peripherally acting vasodilator phenylephrine had similar analgesic activity. These results show that both central and peripheral dihydropyridine-sensitive calcium channels mediate the effects of BAY K 8644. Although a physiological role for the dihydropyridine-sensitive voltage-operated calcium channel in the CNS remains to be demonstrated, activation of these channels can clearly have functional effects.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1994

Physiological tremor and control of limb position in 1 and 0 G.

Muscle and skeletal mechanoreceptors play an important role for the regulation of muscular tone and the genesis of normal Physiological Tremor (PT). For example if a big limb as the arm or leg is kept against the gravity vector, the la afferent spindle discharges continuously control the load bearing flexor in a negative feedback manner in order to compensate the gravity vector and to the stabilize arm position. This servo-like action, denoted as 'stretch reflex', not only increases static postural stability (tonic stretch reflex) but also counteracts against external disturbances by dynamically increasing the muscle tone. Muscle spindles are very sophisticated sensory organs. They have an own innervation and the endings of the nuclear bag fibres are highly sensitive for small microstretches. EMG and microneurografic studies showed their importance in the mechanism of the 8-12 Hz component for PT. In a 0 G a limb becomes position controlled. In contrast to 1g, where control of limb position is a subordinated function of force compensation in the load bearing muscle, an antagonistic control scheme is necessary in 0 G to compensate the arm against positional drifts. As a consequence there is a shift from load dependent (muscular) to position dependent (skeletal) mechanoreceptors that become involved in the neural control process. As the control process is reflected in the tremor pattern, we investigated arm tremor in a constant limb position in 1 and 0 G.

Arm↗
PubMed1980

Evidence that the human jaw stretch reflex increases the resistance of the mandible to small displacements.

1. Small 'step' or sinusoidal displacements were imposed on the mandible while human subjects maintained an average biting force of 10 N. Phase-related changes in the force resisting sinusoidal displacement were used to determine the mechanical stiffness of the human mandibular system as a function of the frequency of stretching. 2. Jaw-muscle electromyographic (e.m.g.) responses to 'step' stretches were of 8 msec latency and generated a very substantial force response. Jaw-muscle e.m.g. responses having longer latency were not observed. 3. The mechanical stiffness of the human mandible was relatively constant as a function of the frequency of stretching, having a typical magnitude of about 15 N/mm (+/- 200 micrometers stretch) or 10 N/mm (+/- 1500 micrometers stretch) at mean biting forces of 10 N. The force resisting displacement was phase-advanced at all frequencies. 4. Modulation of jaw muscle electrical activity evoked by sinusoidal stretches increased in amplitude as a function of increasing stretch frequency. E.m.g. modulation was 60--100 degrees advanced at frequencies of 1--10 Hz, but the phase decreased at higher frequencies, becoming negative (lagging stretch) at frequencies of 30 Hz and above. These characteristics are consistent with the idea that the jaw stretch reflex is dependent on jaw muscle spindle afferent fibres exciting jaw-closing motoneurones by relatively direct (but not necessarily monosynaptic) connexions. 5. The relationship between jaw-muscle activity and voluntary fluctuations of isometric biting force suggests that human jaw muscles can be modelled as a second-order linear 'filter'. The corner frequency for human jaw muscle is about 3 Hz; thus it would appear to be considerably slower than jaw muscle of monkeys. 6. The reflex stiffness of the human mandible, estimated quantitatively on the assumption that human jaw muscle stiffness is similar to the intrinsic stiffness of the gastrocnemius of the cat, ranges between 5 and 9 N/mm at frequencies between 1 and 8 Hz. Since this reflex stiffness is about the same as muscle stiffness in this frequency range, we conclude that the stretch reflex of the human mandible contributes functionally to its postural stability. 7. Reflex stiffness appears to be greater in the monkey mandible relative to muscle stiffness than in the human mandible. The difference is argued to be a manifestation of the difference in jaw muscle contraction speed between the two species. 8. The fact that the mandibular stretch reflex appears to be stronger than the stretch reflex of the limbs of intact animals and humans is discussed in terms of the special anatomical and functional features of the mandible.

Adult↗
PubMed1995

'Vestibular compensation': neural plasticity and its relations to functional recovery after labyrinthine lesions in frogs and other vertebrates.

Removal of the labyrinthine organs on one side is followed by a number of severe postural and dynamic reflex deficits. Some of these deficits, in particular the posture of head and body, are normalized again over a period that varies strongly between species. Other, more persistent motor deficits are substituted, e.g. by the saccadic system. This partial normalization of the function is accompanied by changes in response properties of the central vestibular neurons on the operated side. Available evidence suggests the occurrence of reactive synaptogenesis in cat and frog. In the latter species the synaptic efficacy of commissural vestibular connections increases and the metabolic activity of central vestibular neurons on the operated side recovers post-operatively. The onset of both changes, however, is delayed by about 30 days, which is too late to be causally related with the initial, rapid period of postural recovery in frog and cat. In frogs additional, early (7-15 days p.o.) and late (45-60 p.o.) synaptic changes were detected in the branchial spinal cord. These multiple changes survive the isolation of the spinal cord and must be propriospinal in origin. Selective lesions of individual vestibular nerve branches indicate that inactivation of utricular inputs is a sufficient and necessary condition to provoke postural deficits and early spinal changes similar to those after hemilabyrinthectomy. Therefore, a close correlation between spinal plasticity and postural recovery is indicated. In essence, the elimination of vestibular afferent inputs results in a series of behavioral distortions that are partially normalized by a multitude of synaptic mechanisms at distributed anatomical sites over different periods of time.

Animals↗
PubMed2000

Reflex sympathetic dystrophy: misdiagnosis in patients with dysfunctional postures of the upper extremity.

The purpose of this case-control study was to assess the frequency of the inappropriate diagnosis of reflex sympathetic dystrophy (RSD) in patients who presented with dysfunctional postures of the upper extremity (n = 43). This group of patients with a dysfunctional posture was compared with a randomly selected control group of patients who presented with pain but no dysfunctional posture (n = 88). The patients underwent radiographic evaluation after review of previous medical records and history and physical examination. Patients with dysfunctional postures had a significantly higher frequency (63%) of a previous inappropriate diagnosis of RSD compared with the control group (6%). None of the patients in either group had objective findings consistent with a diagnosis of RSD. Patients presenting with dysfunctional postures of the upper extremity may be misdiagnosed as having RSD and rarely meet the criteria for this diagnosis.

Adolescent↗
PubMed1983

Inhibition of vestibular and neck reflexes in forelimb extensor muscles during the episodes of postural atonia induced by an anticholinesterase in decerebrate cat.

In precollicular decerebrate cats, the multiunit EMG activity of forelimb extensor muscles (e.g. the triceps brachii) was recorded during sinusoidal stimulation of labyrinth and neck receptors at the frequencies of 0.026-0.15 Hz, +/- 10 degrees and the resulting responses were tested during tonic activation of a cholinergic mechanism. In agreement with previous findings, the first harmonic component of the EMG responses to roll tilt of the animal leading to selective stimulation of labyrinth receptors was characterized by an increased activity during side-down tilt and a decreased activity during side-up tilt (labyrinth responses); on the other hand just the opposite changes were elicited for the same directions of neck rotation (neck responses). For the parameters of stimulation reported above, the responses were always related to position and not to velocity of displacement. Intravenous injection of an anticholinesterase (eserine sulphate, 0.10-0.15 mg/kg) which produced a state of postural atonia, associated with bursts of rapid eye movements (REM), similar to that occurring spontaneously in unrestrained cats during desynchronized sleep or REM sleep, also decreased the tonic activity of the triceps brachii and abolished the EMG responses of this muscle to sinusoidal stimulation of labyrinth and neck receptors. This suppression persisted throughout the episode of postural atonia associated with REM bursts. The abolition of the labyrinth and neck reflexes acting on forelimb muscles was not only dependent on the dose of anticholinesterase, but also on the state of the animal. In fact, somatosensory or acoustic stimuli applied during the REM episodes abolished the rhythmic oculomotor activity and determined the prompt recovery of both the decerebrate rigidity and the EMG responses of the triceps brachii to labyrinth and neck stimulation. The postural atonia as well as the tonic depression of the vestibular and neck reflexes acting on forelimb extensor muscles can in part at least be attributed to cholinergic activation of medullary reticulospinal neurons exerting a postsynaptic inhibitory influence on extensor motoneurons. However, since these inhibitory reticulospinal neurons collaborate with excitatory vestibulospinal neurons to the motoneuronal responses during stimulation of labyrinth and neck receptors, we cannot exclude that the suppression of the vestibular and neck reflexes may also depend on occlusion of the unit responses at reticular level.

Animals↗
PubMed1999

[Characteristics of computerized tomography of the brain in congenital hemiparesis].

Congenital hemiparesis is defined as an unilateral disorder of movement and posture, with clinical signs of spasticity with flexor hypertonicity, increased tendon reflexes and characteristic posturing. We have examined a group of 26 children with congenital hemiparesis (14 boys and 12 girls) with mean age of 3.5 years (range 6 months to 9 years). 24 had been born at term (% weeks gestation) and 2 were preterm (% completed weeks gestation). From the neuroimaging point of view, congenital hemiparesis form a rather heterogeneous group. CT scans revealed: porencephalic cyst (6), unilateral ventricular enlargement (2), cortical atrophy with unilateral ventricular enlargement (1), hypodense zones resulting from previous hemathermous (4), normal CT scans (6), and 7 cases have not had CT scans for technical reasons (war conditions). Congenital hemiparesis mainly affects term children with prenatal origin in majority of cases. Vascular occlusions (in utero stroke) originating from various pathophysiological factors, maternal or fetal, may result in congenital hemiparesis. Normal CT findings should be revised by using MRI, which provides direct evidence of white matter lesions.

Brain↗
PubMed2002

The effect of perturbation acceleration and advance warning on the neck postural responses of seated subjects.

The muscle and kinematic responses of subjects exposed to postural perturbations have been shown to vary with platform acceleration when this acceleration was covaried with platform velocity or displacement. The purpose of the current study was to isolate platform acceleration and examine its effect on the neck muscle response and head kinematics of seated subjects exposed to anterior perturbations. Thirty-six subjects (20 females, 16 males) underwent two blocks of 36 perturbations. Three different perturbations with peak accelerations of 7.7, 14.7, and 21.7 m/s(2) up to a common velocity of 0.5 m/s were used. In one block, subjects received an audible warning corresponding to the platform acceleration magnitude, and in the other block, no advance warning was given. Onset and amplitude of the sternocleidomastoid and cervical paraspinal muscle responses were measured using surface electromyography. Kinematic measures included linear and angular accelerations and displacements of the head. The results showed no differences in either the preperturbation posture or the muscle or kinematic responses between the warned and unwarned trials. Significant differences were observed in the onset and amplitude of the muscle and kinematic variables with perturbation acceleration, although these response differences were not linearly graded with perturbation acceleration. Gradation of muscle activation times has not been previously observed in postural perturbation studies, and their gradation with platform acceleration in the current study suggested that platform acceleration was a strong regulator of the reflex muscle response in postural perturbations.

Acceleration↗
PubMed1994

Sustained paradoxical vasodilation during orthostasis in heart failure: a factor in the edema pathogenesis?

Baroreceptor-induced peripheral reflex vasoconstriction during upright posture is an important edema-prevention mechanism in humans. Congestive heart failure (CHF) has been associated with blunted baroreceptor control of regional blood flow during short-term head-up tilt. The effect of prolonged unloading of baroreceptors on subcutaneous blood flow of the calf was investigated in 12 healthy subjects and in 13 patients with severe idiopathic dilated cardiomyopathy (New York Heart Association functional class III or IV). The subjects were studied both supine and sitting for 3-h periods. When sitting, subcutaneous vascular resistance decreased -26 +/- 19% in CHF patients and increased 90 +/- 69% in control subjects (P < 0.0001). The corresponding subcutaneous blood flow increased 43 +/- 29% in patients with CHF compared with the decrease of -42 +/- 17% in control subjects (P < 0.0001). I conclude that patients with CHF secondary to idiopathic dilated cardiomyopathy have an abnormal baroreceptor-mediated peripheral vasodilation during orthostatic stress that is sustained for hours. This extended paradoxical vasodilation may participate as an additional pathophysiological mechanism contributing to lower extremity edema in patients with CHF.

Adult↗
PubMed1988

An evaluation of the hemiplegic subject based on the Bobath approach. Part II: The evaluation protocol.

A protocol of evaluation of the hemiplegic patient based on the Bobath approach to treatment is presented. Six parameters are evaluated: sensorium, muscle tone, reflex activity, active movement, postural reactions and pain. The first and last of these are included because of their possible effects on the motor recovery process of the hemiplegic patient. The other four are directly borrowed from the Bobath modality of treatment. For each of these parameters, the procedures are given for its evaluation along with its respective rating scales. These scales are of an ordinal nature ranging from 0 to 3. It is suggested that this new evaluation protocol is fully compatible with the therapeutic modality developed by Bobath and as well is adequate to quantify patient progress in the principle aspects treated by this well used rehabilitation approach.

Disability Evaluation↗
PubMed1989

Methodological considerations contributing to variability of the quadriceps H-reflex.

The clinical usefulness of the quadriceps H-reflex is limited because of the difficulty of elicitation and its inherent variability in amplitude. In the present study we attempted to identify the influence of methodological variables (head position and remote muscle contractions) on the amplitude of the H-reflex evoked in vastus medialis, vastus lateralis and rectus femoris from the right leg of 13 healthy adult subjects. Square wave stimuli (1-ms duration) were delivered percutaneously to the femoral nerve. The 50% maximal amplitude H-reflexes were evoked while the subject reclined with head facing to the right, left, up and down or while the subject performed Jendrassik's maneuver. The results show a significant increase in the reflex amplitude when the subject's head was turned to the right; there was either a mild increase or no change in amplitude of the response when the subjects faced to the left, up and down. The evoked potential tended to decrease when the subjects closed their eyes; however, the tendency to increase with neck position was not changed. Remote muscle contractions enhanced the amplitude of the response. These results present further evidence of the characteristics of the quadriceps H-reflex and identify postural influences as one controllable source of variability in the L3-L4 root electrodiagnostic test.

Adult↗
PubMed1997

Reflex control of autonomic function induced by posture change during the menstrual cycle.

This study was designed to determine whether autonomic regulation induced by posture changes varies during the menstrual cycle. Heart rate variability (HRV) was analyzed in women with normal menstrual cycles (n = 10, age range 20-37 years) during 3 min periods of controlled frequency breathing (15 breaths/min) in supine followed by sitting positions. In a supine or sitting position, high frequency (HF) components of HRV, which reflects only parasympathetic activity, were significantly high in the follicular phase compared with those in the menstrual phase, suggesting that parasympathetic nerve activity increases in this phase. Following the change of position to sitting from supine, the HF component decreased significantly in the menstrual, ovulatory and luteal phases, but not the follicular or premenstrual phase. After changing the position to sitting, the low to high frequency component ratio, which reflects the balance of autonomic nerve activities, was increased significantly in the menstrual, luteal and premenstrual phases, indicating that sympathetic nerve activities in these phases became predominant by the sitting position. These results suggest that parasympathetic nerve activity is predominant in the follicular phase, resulting in an impairment of baroreflex caused by posture changes. Moreover, baroreflex control of the sympathetic component, not the parasympathetic component, increases in the premenstrual phase, while the reflex response of the sympathetic component is less in the ovulatory phase compared with the menstrual or luteal phase. We concluded that baroreflex regulation of autonomic functions induced by changing positions is modified during the menstrual cycle. A difference of a balance of ovarian hormones may be responsible for these changes of autonomic functions during the menstrual cycle.

Adult↗
PubMed1989

Injections of a beta-adrenergic antagonist in pontine reticular structures modify the gain of vestibulospinal reflexes in decerebrate cats.

1. The norepinephrine (NE)-containing locus coeruleus (LC) neurons control posture as well as the gain of the vestibulospinal reflexes either through direct coeruleospinal (CS) projections or by inhibiting the dorsal pontine reticular formation (pRF) and the related medullary inhibitory reticulospinal (RS) system. The question whether these inhibitory influences on the pRF are mediated through beta-adrenoceptors was investigated by injecting in precollicular decerebrate cats small doses of the non-selective beta-adrenergic antagonist propranolol in different pontine tegmental structures. 2. Injection of propranolol (usually 0.25 microliters at the concentration of 4.5 micrograms/microliters of saline) in dorsal pontine structures, which decreased the tonic contraction of limb extensors ipsilateral to the side of the injection, greatly increased the amplitude of the multiunit EMG responses of the ipsilateral triceps brachii to roll tilt of the animal at 0.15 Hz, +/- 10 degrees. Correspondingly, the response gain of the forelimb extensor to labyrinth stimulation increased. Moreover, a slight decrease in phase lead of the responses was observed. These responses were always characterized by an increased EMG activity during ipsilateral tilt and a decreased activity during contralateral tilt, as shown in the control records (alpha-responses). The same injection also produced in some instances an increase of the extensor tonus of the contralateral limbs, associated with an increased EMG activity of the contralateral triceps brachii; on the other hand, the amplitude of modulation and thus the response gain of this muscle to the same parameters of labyrinth stimulation decreased, while the response pattern reversed (beta-responses), thus being opposite to that displayed by the triceps brachii ipsilateral to the side of the injection. 3. The changes in posture and reflexes described above appeared 10-20 min after unilateral injection of propranolol in the pRF, reached in highest values in about 60-100 min and persisted for more that three hours before returning to the control level. These effects were not due to irritative phenomena following injection of the fluid, since neither changes in posture nor in the response gain of the triceps brachii to labyrinth stimulation were observed after injection of an equal volume of saline in the pRF of that side. Moreover, the magnitude of the effects increased to some extent in relation to the dose of the beta-adrenergic blocker. 4. Histological controls indicated that the structure responsible for these postural and reflex changes was located in the dorsal pontine tegmental region immediately ventral to the LC and included the peri-LC alpha and the surrounding dorsal pRF.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1980

Blind evaluation of body reflexes and motor skills in learning disability.

Motor dysfunctions have been associated with learning disabilities in casual observation and systematic study. However, most prior work has concentrated solely on high-level skills and has been subject to observer bias. In this study, boys with learning disability were blindly compared with paired controls on measures of postural and equilibrium reflexes as well as skills. Learning-disabled children as a group showed significant deficits on all measures; a few, however, were totally without deficit. The implications of these findings for controversies about the role of motor dysfunction in learning disabilities are examined.

Child↗
PubMedDate not supplied

Labyrinthine influences on locus coeruleus neurons.

The locus coeruleus (LC) complex, located in the dorsolateral pontine tegmentum, is composed principally of noradrenergic neurons, which project to broad regions of the CNS, including the spinal cord. Experiments were performed in precollicular decerebrate cats to ascertain whether units histologically identified within the LC complex, and having the physiological characteristics of noradrenergic neurons, would respond to sinusoidal stimulation of labyrinth receptors. Among 141 LC complex neurons, 16 of which could be activated antidromically by stimulation of the spinal cord at T12-L1, 80 (i.e. 56.7%) responded to roll tilt of the animal at 0.15 Hz, +/- 10 degrees. The responses were particularly related to the extreme animal displacements, thus being attributed to stimulation of macular utricular receptors. The proportion of responsive units, and also the average gain of the responses, were higher in the LCd and the subcoerular (subLC) area than in the LCa. Moreover in the same structures the majority of units showed a beta-pattern of response (excitation during side-up tilt), which contrasted with the predominant alpha-pattern (excitation during side-down tilt) displayed by the previously recorded vestibulospinal neurons projecting to the same segments of the spinal cord. The role that the noradrenergic coeruleospinal neurons exert in the dynamic control of posture during the vestibulospinal reflexes is discussed.

Animals↗