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At least 235 records · Page 13Linked to original sources
PubMed1993

Gating of reflexes in ankle muscles during human stance and gait.

Holding the body's centre of gravity steady represents the crucial variable for the stabilization of posture in upright stance in man. Results from two experimental approaches suggest that force-dependent receptors are required, in addition to the well-known systems involved in sway stabilization, for equilibrium control. One approach concerns bilateral leg muscle activation during stance. Unilateral or bilateral leg displacements were induced while subjects stood on a treadmill with split belts. A unilateral displacement induced a bilateral EMG response. During bilateral displacements the EMG activity was linearly summed or subtracted, depending on whether the legs were displaced in the same or opposite directions. Both legs acted in a cooperative manner: each limb affected the strength of muscle activation and the time-space behaviour of the other. This interlimb coordination is suggested to be mediated by spinal interneuronal circuits, which are themselves under supraspinal (e.g., cerebellar) control. The other approach concerns the modulation of postural reflexes under stimulated "microgravity" ir. water immersion. An approximately linear relationship was found between contact forces and impulse-directed EMG response amplitudes in the leg muscles. Out of water loading of the subjects resulted in no further increase of the response amplitude. It was concluded that the function of proprioceptive reflexes involved in the stabilization of posture depends on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of body's centre of mass with respect to the feet. The interaction of the afferent input from these receptors with the other systems involved in postural control is not yet fully understood.

Ankle↗
PubMed1996

Head and body positions affect thermoregulatory tonus in deltoid muscles.

Electromyograms (EMGs) were recorded from both deltoid muscles (DMs) when subjects were sitting, standing, and bending the head laterally at different cold sensations to clarify the role of head and body positions in the thermoregulatory tonus. At room temperature (22 degrees C), neither EMG related to thermoregulatory muscle tonus (TMT) nor were changes in EMG intensity observed during changes in posture. At a cold temperature (5 degrees C), when the subjects felt slightly cold or cold, the averaged surface EMG intensity of TMT was approximately 2-3 microV during sitting with the head held upright. The EMG of TMT was 7.23 +/- 2.99 microV in subjects sitting with the head upright when feeling cold and extremely cold and increased to 14.75 +/- 5.15 microV (P < 0.01) when the subjects stood at ease and to 19.96 +/- 11.01 microV (P < 0.01) when the subjects stood on tiptoes. Lateral head bending in subjects standing at ease and feeling extremely cold increased the EMG 40-60% (P < 0.01) in the contralateral DM without any significant effect on the ipsilateral DM. The results suggest that in humans TMT is influenced by tonic postural reflexes.

Adult↗
PubMed1979

The polystyrene vacuum wheelchair cushion.

A polystyrene bead vacuum wheelchair cushion has been tried with several patients with abnormal postural reflex activity. Excess spasticity can be reduced by this means and sitting comfort enhanced.

Humans↗
PubMed1980

Studies of parkinsonian movement: 2. Initiation of fast voluntary eye movement during postural disturbance.

Delay in initiation of rapid voluntary eye movements (saccades) in bradykinetic parkinsonian patients and normal subjects was recorded with and without postural disturbances (rotation of the body and head). Parkinsonian patients as a group exhibited longer delays in the initiation of saccades. The delay increased during postural disturbance in both the patients and the normal subjects. The study failed to substantiate the hypothesis that postural reflexes interfere with the initiation of voluntary movement in Parkinsonism.

Adult↗
PubMed1986

Responses of interneurons in the cat cervical cord to vestibular tilt stimulation.

The responses of interneurons in the cervical spinal cord of the decerebrate cat to whole-body tilt were studied with a goal of identifying spinal elements in the production of forelimb vestibular postural reflexes. Interneurons both in the cervical enlargement and at higher levels, from which propriospinal neurons have been identified, were examined, both in animals with intact labyrinths and in animals with nonfunctional semicircular canals (canal plugged). Most cervical interneurons responding to tilt respond best to rotations in vertical planes aligned within 30 degrees of the roll plane. Two to three times as many neurons are excited by side-up roll tilt as are excited by side-down roll. In cats with intact labyrinths, most responses have dynamics proportional either to (and in phase with) the position of the animal or to a sum of position and tilt velocity. This is consistent with input from both otolith organs and semicircular canals. In animals without functioning canals, the "velocity" response is absent. In a few cells (8 out of 76), a more complex response, characterized by an increasing gain and progressive phase lag, was observed. These response dynamics characterize the forelimb reflex in canal-plugged cats and have been previously observed in vestibular neurons in such preparations.

Animals↗
PubMed1987

Pontine reticular origin of cholinergic excitatory afferents to the locus coeruleus controlling the gain of vestibulospinal and cervicospinal reflexes in decerebrate cats.

1. Previous experiments had shown that the medullary inhibitory reticulospinal (mRS) neurons act 180 degrees out-of-phase with respect to the excitatory vestibulospinal (VS) neurons during the vestibular and the neck reflexes involving the limb extensor motoneurons. This finding suggested that the higher the firing rate of the medullary inhibitory RS neurons in the animal at rest, the greater the disinhibition which affects the limb extensor motoneurons during side-down roll tilt of the animal or side-up neck rotation, thus leading to an increased gain of response of limb extensors to sinusoidal stimulation of labyrinth and neck receptors. The gain of these postural reflexes would then represent a sensitive test to evaluate the background discharge of the inhibitory reticulospinal system of the medulla. 2. The discharge of the inhibitory mRS neurons is under the tonic excitatory control of cholinergic pontine reticular formation (pRF) neurons which are also self-excitatory, while these cholinergic pontine neurons are in turn inhibited by the norepinephrine (NE)-containing locus coeruleus (LC) neurons, which are also self-inhibitory due to mechanisms of recurrent and/or lateral inhibition. The present experiments were performed to find out whether cholinergic and cholinoceptive pontine reticular neurons, which are under the inhibitory control of the LC neurons, also send axons to the LC on which they may exert an excitatory influence. This excitatory effect would then counteract the self-inhibitory influence mediated by the NE, which acts on the alpha 2-adrenoceptors distributed on the somatodendritic membrane of the LC neurons. 3. In precollicular decerebrate cats, local injection into the dorsal aspect of the pontine tegmentum of 0.25 microliter of a solution of the muscarinic blocker atropine sulphate at the concentration of 6 micrograms/microliter of sterile saline did neither modify the postural activity in the ipsilateral limbs nor the response gain of the ipsilateral forelimb extensor triceps brachii to sinusoidal stimulation of labyrinth receptors (roll tilt of the animal at 0.15 Hz, +/- 10 degrees). These negative results were attributed to the fact that in these preparations the activity of the cholinergic and cholinoceptive pRF neurons and the related inhibitory mRS neurons is very low, due to the tonic discharge of the NE-containing LC neurons, which exert a prominent inhibitory influence on the underlying reticular structures.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Role of serotonin for scoliotic deformity in pinealectomized chicken.

STUDY DESIGN: The effect of intraperitoneal injection of 5-hydroxytryptophan (5-HTP) versus control in pinealectomized chickens. OBJECTIVE: To find if the serotonin may have some role in the cause of treatment of idiopathic scoliosis. SUMMARY OF BACKGROUND DATA: One of the causes of idiopathic scoliosis is thought to be the disruption of postural reflex. Serotonin has been proposed to have a crucial role in maintaining normal postural muscle tone or postural equilibrium. METHOD: Forty pinealectomized chickens served as controls, and an additional 40 pinealectomized chickens received daily intraperitoneal injections of 5-hydroxy-tryptophan, a precursor of serotonin, which can pass through the blood-brain barrier. Spine radiographs were examined to measure the scoliotic deformity. RESULTS: Scoliosis developed in all 40 pinealectomized chickens (control), whereas only 28 chickens in the 5-hydroxytryptophan-treated group (6 in severe, 22 in mild) had scoliosis developed. The remaining 12 chickens grew up with normal spines. Most chickens with mild scoliosis did not have curve progression but continued to have wedged vertebrae. CONCLUSION: Serotonin deficit secondary to a defect of melatonin may have disturbed postural muscle tone or postural equilibrium resulting in scoliosis in pinealectomized chicken. Prevention from the development of scoliosis or its progression in chickens treated with 5-hydroxytryptophan suggests that serotonin may have potential therapeutic value.

5-Hydroxytryptophan↗
PubMed1992

Regulation of bipedal stance: dependency on "load" receptors.

According to recent observations, influence of body load has to be taken into account for the neuronal control of upright stance in addition to the systems known to be involved in this regulation (e.g. afferent input from vestibular canals, visual and muscle stretch receptors). The modulation of compensatory leg muscle electromyographic (EMG) responses observed during horizontal body posture indicates the existence of a receptor system which responds to loading of the body against the supporting platform. This receptor should be located within the extensor muscles because a compensatory EMG response and a loading effect on this response was only present following translational, but not rotational impulses. As the EMG responses were identical to those obtained during upright stance, it is argued that these load receptors activate postural reflexes. According to recent observations in the spinal cat, this afferent input probably arises from Golgi tendon organs and represents a newly discovered function of these receptors in the regulation of stance and gait.

Biomechanical Phenomena↗
PubMed1989

Autologous adrenal medullary transplant in progressive supranuclear palsy.

We transplanted autologous adrenal medullary cells to the caudate nucleus in 3 patients with progressive supranuclear palsy, using the method Madrazo has employed for neural transplantation in Parkinson's disease. Major and minor complications occurred post-operatively from which the patients recovered. One patient had a marked improvement in his postural stability and a decreased incidence of falling. This change was evident at 1 month after surgery and has remained for the 6 months of follow-up. Postural reflexes were not altered in the other 2 patients. There was no change in extraocular movements, speech, or the rigid-bradykinetic features of parkinsonism in any patient. Adrenal medullary transplantation has only limited efficacy in progressive supranuclear palsy.

Adrenal Medulla↗
PubMed2006

[Prematurity as a motor development risk factor].

UNLABELLED: The objective of this study was to show how the number of weeks of gestation affects babies' motor development. Prenatal brain damage is the most common cause of baby's neurological development deviation. This deviation can both be simple and complex. The objective was also to compare motor development of prematurely born babies with asphyxia or pathologic brain substrate. PATIENTS AND METHODS: Study included fifty two risk babies with symptoms, divided into three groups. First group were babies born prematurely, second were babies born prematurely with asphyxia and third were babies born prematurely with pathologic brain substrate. Vojta method diagnostics has shown that all studied babies have had deviation in postural reflexes development. After being treated using Vojta method, it was monitored at which age which groups of babies formed motor patterns. Results have shown that the group of babies born prematurely with pathologic brain substrate needed the longest period to form specific motor patterns.

Asphyxia Neonatorum↗
PubMed1992

Response of pontomedullary reticulospinal neurons to vestibular stimuli in vertical planes. Role in vertical vestibulospinal reflexes of the decerebrate cat.

1. To investigate the neural substrate of vestibulospinal reflexes in decerebrate cats, we studied the responses of pontomedullary reticulospinal neurons to natural stimulation of the labyrinth in vertical planes. Our principal aim was to determine whether reticulospinal neurons that terminate in, or are likely to give off collaterals to, the upper cervical segments had properties similar to those of the vestibulocollic reflex (VCR). 2. Antidromic stimulation was used to determine whether the neurons projected to the neck, lower cervical, thoracic, or lumbar levels. Dynamics of the responses of spontaneously firing neurons were studied with sinusoidal stimuli delivered at 0.05-1 Hz and aligned to the plane of body rotation, that produced maximal modulation of the neuron (response vector orientation). Each neuron was assigned a vestibular input classification of otolith, vertical canal, otolith + canal, or spatial-temporal convergence (STC). 3. We found, in agreement with previous studies, that the largest fraction of pontomedullary reticulospinal neurons projected to the lumbar cord, and that only a small number ended in the neck segments. Neurons projecting to all levels of the spinal cord had similar responses to labyrinth stimulation. 4. Reticulospinal neurons that received only vertical canal inputs were rare (1 of 67 units). Most reticulospinal neurons (48%) received predominant otolith inputs, 18% received otolith + canal input, and only 9% had STC behavior. These data are in sharp contrast to the results of our previous studies of vestibulospinal neurons. A considerable portion of vestibulospinal neurons receives vertical canal input (38%), fewer receive predominantly otolith input (22%), whereas the proportion that have otolith + canal input or STC behavior is similar to our present reticulospinal data. 5. The response vector orientations of our reticulospinal neurons, particularly those with canal inputs (canal, otolith + canal, STC) were predominantly in the roll quadrants. There was no evidence of convergence of inputs from like canals across the midline (e.g., right anterior + left anterior). 6. Two characteristics of the VCR, STC behavior and bilateral input from symmetric vertical canals (in some muscles), cannot be accounted for by the reticulospinal neurons that we studied. Because these characteristics are also not seen in vestibulocollic neurons, they are likely to be the result of the appropriate convergence of vestibular signals in the spinal cord. 7. Pontomedullary reticulospinal neurons seem particularly well suited to play a role in gravity-dependent postural reflexes of neck and limbs.

Acoustic Stimulation↗
PubMed1968

Onset of and recovery from diving bradycardia in ducks.

1. No evidence was found of a ;postural reflex' in ducks. Neither the position of the head nor the water temperature affected the cardiac response to diving.2. In ducks with access to air through a tracheal cannula, submersion did not invariably cause apnoea until the water level reached the glottis. Heart rate was closely related to respiratory frequency, and bradycardia did not occur during submersion unless there was a reduction in respiratory frequency or a cessation of ventilation altogether.3. When apnoea and bradycardia did occur during submersion, the first inspiration upon surfacing was 2-3 times larger than normal and was accompanied by an instantaneous rise in heart rate.4. Atropinization or cold block of the vagus abolished diving bradycardia. Only one vagal trunk was involved in cardiac chronotropic control at any one time. This vagal trunk also appeared to be more important in control of respiratory frequency.5. beta-adrenergic receptor blockade did not affect either diving bradycardia or post-dive tachycardia.6. The results show that the cardiac chronotropic response both during and after submergence is controlled solely by changes in parasympathetic vagal activity.

Anesthesia, Conduction↗
PubMed1976

Myelotomy for control of mass spasms in paraplegia.

A new myelotomy knife is described and a procedure, designed to sever certain reflex connections while preserving as many corticospinal connections as possible, is presented. Through intermittent dorsal midline incisions the gray matter lateral to the central canal is severed bilaterally under the microscope from L-1 to S-1. This procedure relieved mass spasms and hyperactive reflexes in 14 paraplegic or tetraplegic patients, but preserved postural reflexes and whatever voluntary motor power the patients had prior to myelotomy. Before myelotomy all patients were bedridden. Afterward nine patients were able to use a wheel chair and five were able to walk with the use of parallel bars or crutches.

Adult↗
PubMed1984

Visual localization with eye movements: a review.

This paper reviews and discusses the most popular theories which have been proposed to account for the stability of the visual environment during eye movements. The subject is discussed chiefly from the stand-point of phylogeny rather than its contemporary treatment which attempts to explain neural mechanism by analogy with robotic systems or models. Certain conclusions are formed, and it is postulated that the constancy of egocentric directions following an eye movement is affected by the same mechanism that serves to retain the positional constancy of objects during the operation of the primitive postural reflex.

Afterimage↗