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PubMed1988

Partial and complete deafferentation of cat hindlimb: the contribution of behavioral substitution to recovery of motor function.

After partial (spared-root) or complete hindlimb deafferentation, locomotion and accurate limb placement during locomotion recover considerably. In the present study movement was studied during and after recovery to determine whether altered motor patterns could substitute for normal ones in the recovery of motor behavior. In acute L6 spared-root preparations somatosensory postural reflexes are impaired, accurate limb placement deficient and joint angle measurements show altered kinematic motor patterns during locomotion. As somatosensory postural reflexes and accurate limb placement recover, so do the motor patterns. After complete deafferentation motor patterns are more disturbed. Somatosensory postural reflexes remain absent but as descending reflexes recover, so does accurate limb placement during locomotion. In deafferented hindlimbs, in contrast to spared-root preparations motor patterns observed chronically (after recovery of accurate placement) are persistently abnormal indicating that novel motor patterns can replace normal ones in the recovery of goal-directed behavior. The results suggest that behavioral substitution can contribute to recovery of useful movement.

Animals↗
PubMed2002

Ankle reflex stiffness during unperceived perturbation of standing in elderly subjects.

Postural reflex activity during unperceived perturbation of standing was investigated in 38 elderly subjects (70-96 years old) and 10 younger adults (19-48 years old), and it was related in the elderly group to a history of unexplained falling in the 12 months prior to testing. Ankle torque (T) and ankle angle (A) were recorded during unperceived forward pulls to obtain the ankle stiffness (DeltaT/DeltaA), providing a measure of postural reflex activity at the ankle. Elderly nonfallers and younger adults had similar ranges of normalized ankle reflex stiffness. High ankle stiffness was significantly more common in elderly multiple fallers than in elderly nonfallers (p =.018). Furthermore, a majority of unstable elderly subjects who had reported a single unexplained fall also had unusually high ankle stiffness (p =.004). Multiple fallers and unstable subjects tended to overshoot backward on pull release in comparison with nonfallers (p =.003), which is suggestive of an overactive reflex response that might contribute to postural instability.

Accidental Falls↗
PubMed1994

Impairment of the postural venoarteriolar reflex in aged individuals.

The venoarteriolar vasoconstriction reflex plays a major role in the prevention of leg oedema in the upright position in man. We studied the venoarteriolar vasoconstriction reflex with laser Doppler flowmetry in young (21 subjects, age 17-27) and very old (20 subjects, age 75-100) healthy volunteers. In the group of young volunteers, after lowering of the lower extremity 50 cm below the heart level, cutaneous blood flux decreased to 16.6% of the baseline, whereas in the group of old persons the venoarteriolar reflex was impaired and the flux decreased only to 29.2%. The difference between the two groups was statistically significant (p < 0.001). These results may explain the increased prevalence of postural oedema in old people.

Adolescent↗
PubMed2005

Reflex control of the spine and posture: a review of the literature from a chiropractic perspective.

OBJECTIVE: This review details the anatomy and interactions of the postural and somatosensory reflexes. We attempt to identify the important role the nervous system plays in maintaining reflex control of the spine and posture. We also review, illustrate, and discuss how the human vertebral column develops, functions, and adapts to Earth's gravity in an upright position. We identify functional characteristics of the postural reflexes by reporting previous observations of subjects during periods of microgravity or weightlessness. BACKGROUND: Historically, chiropractic has centered around the concept that the nervous system controls and regulates all other bodily systems; and that disruption to normal nervous system function can contribute to a wide variety of common ailments. Surprisingly, the chiropractic literature has paid relatively little attention to the importance of neurological regulation of static upright human posture. With so much information available on how posture may affect health and function, we felt it important to review the neuroanatomical structures and pathways responsible for maintaining the spine and posture. Maintenance of static upright posture is regulated by the nervous system through the various postural reflexes. Hence, from a chiropractic standpoint, it is clinically beneficial to understand how the individual postural reflexes work, as it may explain some of the clinical presentations seen in chiropractic practice. METHOD: We performed a manual search for available relevant textbooks, and a computer search of the MEDLINE, MANTIS, and Index to Chiropractic Literature databases from 1970 to present, using the following key words and phrases: "posture," "ocular," "vestibular," "cervical facet joint," "afferent," "vestibulocollic," "cervicocollic," "postural reflexes," "spaceflight," "microgravity," "weightlessness," "gravity," "posture," and "postural." Studies were selected if they specifically tested any or all of the postural reflexes either in Earth's gravity or in microgravitational environments. Studies testing the function of each postural component, as well as those discussing postural reflex interactions, were also included in this review. DISCUSSION: It is quite apparent from the indexed literature we searched that posture is largely maintained by reflexive, involuntary control. While reflexive components for postural control are found in skin and joint receptors, somatic graviceptors, and baroreceptors throughout the body, much of the reflexive postural control mechanisms are housed, or occur, within the head and neck region primarily. We suggest that the postural reflexes may function in a hierarchical fashion. This hierarchy may well be based on the gravity-dependent or gravity-independent nature of each postural reflex. Some or all of these postural reflexes may contribute to the development of a postural body scheme, a conceptual internal representation of the external environment under normal gravity. This model may be the framework through which the postural reflexes anticipate and adapt to new gravitational environments. CONCLUSION: Visual and vestibular input, as well as joint and soft tissue mechanoreceptors, are major players in the regulation of static upright posture. Each of these input sources detects and responds to specific types of postural stimulus and perturbations, and each region has specific pathways by which it communicates with other postural reflexes, as well as higher central nervous system structures. This review of the postural reflex structures and mechanisms adds to the growing body of posture rehabilitation literature relating specifically to chiropractic treatment. Chiropractic interest in these reflexes may enhance the ability of chiropractic physicians to treat and correct global spine and posture disorders. With the knowledge and understanding of these postural reflexes, chiropractors can evaluate spinal configurations not only from a segmental perspective, but can also determine how spinal dysfunction may be the ultimate consequence of maintaining an upright posture in the presence of other postural deficits. These perspectives need to be explored in more detail.

Journal Article↗
PubMed1997

Effects of 20 days horizontal bed rest on maintaining upright standing posture in young persons.

The effects of 20 days horizontal bed rest (BR) on postural reflex were studied by measuring fluctuation of center of gravity in the body during two legs or one leg upright standing in 10 young volunteers. The fluctuation was decided as total moving distance of the center recorded during 60sec standing on a force plate. The stability was measured by the moved area. After BR, the moving distance increased during two legs standing with open eyes (p<0.05), but statistically unchanged with closed eyes. The moving area decreased during right one-leg standing with closed eyes (p<0.05), but unchanged during left one-leg standing. Despite with open eyes the increased distance suggested that postural reflexes to maintain upright position were probably decreased by increased unsuitable feedback informations from the visual receptor deconditioning during BR. The decreased area during right one-leg standing with closed eyes also suggested that the declined standing posture reflex was probably related to more rapidly lowered functions for maintaining standing position in the dominating leg than in the other.

Adult↗
PubMed1987

Postural cardiovascular reflexes: comparison of responses of forearm and calf resistance vessels.

Simultaneous measurements were made of changes in vascular resistance in the forearm and calf in response to moving from supine to sitting or to head-down tilt. The subjects were healthy male volunteers, 21-63 yr. Blood flows were measured by venous occlusion plethysmography using mercury-in-Silastic strain-gauges. The gauges were maintained at the same level relative to the heart during the postural changes. Arterial blood pressure was measured by auscultation; heart rate was counted from the plethysmograms. Changing from supine to sitting caused a decrease in forearm blood flow from 4.13 +/- 0.14 to 2.16 +/- 0.19 ml.100 ml-1.min-1. Corresponding calf flows were 4.21 +/- 0.32 and 4.40 +/- 0.59 ml.100 ml-1.min-1. There was no change in mean arterial blood pressure, and heart rate increased by 8.0 +/- 1.5 beats/min. Arrest of the circulation of both legs with occlusion cuffs on the thighs before sitting, to prevent pooling of blood in them, reduced the degree of forearm vasoconstriction. Neck suction (40 Torr) during sitting, to oppose the decrease in transmural pressure at the carotid sinuses, inhibited the vasoconstriction. During a 30 degrees head-down tilt, there was a dilatation of forearm but not of calf resistance vessels. A Valsalva maneuver caused a similar constriction of both vascular beds. Thus, when changes in vascular resistance in forearm and calf are compared, the major reflex adjustments to changes in posture take place in the forearm.

Adult↗
PubMed1979

Vagal and sinoaortic reflexes in postural control of circulation and renin release.

Anesthetized cats were subjected to two 10-min trials of head-up tilting spaced 60 min apart. Bilateral cervical vagotomy, performed after the first tilting episode, did not affect the hemodynamic response to the change in posture, but significantyly and markedly reduced the increase in renin release from the innervated kidney. After sinoaortic denervation a marked and sustained arterial hypotension occurred during tilting, and the postural increase in renin release, though still limited to the innervated kidney, was even greater. When pressure homeostasis to tilting was disturbed, the renin release response was seen to be independent of the vagi, as it occurred after combined vagotomy and sinoaortic denervation. Maintenance of arterial pressure during tilting is mainly due to sinoaortic reflexes, whereas vagal reflexes are mostly responsible for the postural increase in renin release. The vagally independent release of renin observed when the cardiovascular response to tilting is impaired, is probably due to a direct action of arterial hypotension on intrarenal receptors, an action occurring only in innervated kidneys.

Animals↗
PubMed1997

Saccular influence on the otolith-spinal reflex and posture during sudden falls of the cat.

HYPOTHESIS: The saccule provides important input for the otolith spinal reflex during sudden falls in the cat. BACKGROUND: Previous studies on cats have identified two distinct components of muscle activity in response to sudden falls: an early otolith-dependent component (OSR) and a later nonlabyrinthine component associated with landing. The presence of an otolith-dependent reflex suggests a discrete role of the otolith organs in the control of posture and locomotion. METHODS: The influence of saccular input on the OSR during sudden falls was studied by simultaneous video and electromyographic (EMG) recordings obtained from saccular-deficient deaf white cats and white cats with normal hearing. RESULTS: A total of 628 sudden falls from five cats (two normal, one unilaterally deaf and two bilaterally deaf) were studied. Normal cats had a total of 337 drops, 276 of which (82%) were acceptable; a unilaterally deaf cat had a total of 79 drops, 56 of which (71%) were acceptable; deaf cats had a total of 212 drops, 177 of which (83%) were acceptable. The earliest of five observed behavioral events was that of forelimb extension which had a mean latency of 98 +/- 32 msec in normal cats and 139 +/- 28 msec in deaf cats (p < 0.0001). The mean latency of early EMG activity in normal cats was 19 +/- 7 msec and in deaf cats was 30 +/- 13 msec (p < 0.0001). The unilaterally deaf cat exhibited behavior and early EMG responses that were similar to those of normal cats. Deaf cats displayed poor body control during landings that improved with experience. CONCLUSIONS: These data demonstrate that the saccule provides important input for the otolith spinal reflex in the cat, and cats that lack both saccules have discernible behavioral and EMG differences in response to sudden falls, when compared with normal cats.

Animals↗
PubMed1986

Early outcome prediction in severe head injury: comparison between children and adults.

The prognostic value in 49 children and 56 adults of the following parameters recorded on admission was analyzed: oculocephalic and light reflexes, posturing, Glasgow Coma Scale (GCS), the need for ventilatory support, and the presence of associated injuries. All patients had been in coma for at least 6 h. The presence of intracranial hematoma and the duration of coma were recorded and the relative risk of poor outcome calculated. There was poor outcome in 51% of the children and 61% of the adults. Oculocephalic and light reflexes, posturing, GCS, need for ventilatory support, and duration of coma were significantly related to the outcome in children. Only oculocephalic and light reflexes, and posturing were significantly related to the outcome in adults. Some parameters appeared to have different prognostic value in children and in adults: the simultaneous evaluation of oculocephalic reflex and need for ventilation was the best prognostic guide in children, the light reflex was the best prognostic indicator in adults.

Adolescent↗