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PubMed1976

The control of breathing in birds with particular reference to the initiation and maintenance of diving apnea.

Avian respiratory pacemaker activity is dependent on some form of peripheral input but it may be inhibited by both central and peripheral stimulation. At present the results of central nervous stimulation are difficult to interpret but, aside from cortical influences, diving apnea appears to be maintained, in the face of increasing chemoreceptor input, by noxious stimulation of the upper respiratory tract and depression of the output of medullary respiratory neurons by advancing hypercapnia. If this is so, an obvious problem for future research is what initiates the prompt onset of hyperpnea when the animal surfaces and breathes. It is known that post-dive hyperpnea is little affected by either carotid body or pulmonary denervation, so peripheral chemoreceptors are unlikely to play a major role in this response.

Action Potentials↗
PubMed1994

The repeatability of posturographic measurements and the effects of sleep deprivation.

The repeatability of posturographic measurements and the effects of sleep deprivation on them were investigated in 23 volunteers over a period of four months. Postural stability was studied by evaluating body sway velocity and the maximal and average vibration-induced shifts of the centre of pressure in the anterio-posterior and lateral directions. The posturographic test was performed with and without exposure of the calf muscles to vibration. Subjects were tested both with their eyes open and closed, and the measurements were performed weekly during the first month and once every month thereafter. The interindividual results differed more than the intraindividual ones, indicating that posturographic measurements are most suitable for functional monitoring in one person's tests. The dispersion of the results did not diminish with time, nor did the body sway decrease. The findings suggest that no learning takes place in nontrained persons. In the second part of the research, measurements were performed twice after the subjects had been awake the previous night or 24 hours. Postural stability did not deteriorate in this situation.

Adult↗
PubMed1993

Vestibular and proprioceptive modulation of postural synergies in normal subjects.

One way of investigating different muscle synergies underlying human balance control is to assume that only 1 or 2 centrally preprogrammed synergies are available to reestablish upright stance when it is perturbed. According to this hypothesis, the many, apparently different, synergies elicited by rotation or translation of a support-surface on which test subjects stand, in fact, result from a modulation of muscle responses induced by different amplitudes of afferent inputs. To test this hypothesis, we probed the balance control of 16 normal subjects with 5 combinations of rotation and translation of the support surface. Each combination yielded a constant angle (3 or 4 degrees) and angular velocity (18 and 36 degrees/s, respectively) over the first 120 ms of ankle dorsiflexion but resulted in differing velocities of upper leg, trunk, and head movements. These first 120 ms of link movements and the resulting muscle responses were analysed for amplitude and timing modulation using 3 techniques. First, velocities of initial link movements and areas of muscle EMG activity were examined separately for the minimum number of descriptors, which would optimally describe the linear variation of the interlink amplitude synergy with respect to the amount of support-surface rotation or translation employed to perturb balance. Initial trunk angular velocity, which was highly correlated with head linear acceleration (r = 0.9), provided the first best descriptor of initial link movements. Ankle angular velocity provided the second descriptor because it was not correlated with trunk angular velocity. The amplitude modulation synergy of EMG responses could be characterised by the modulation of tibialis anterior and paraspinal muscles between 160 and 240 ms and by that of soleus between 80 and 120 ms after stimulus onset. The linear combination of these best descriptors of link movements and that for EMG response amplitudes changed continuously in an identical manner with changes in the stimulus combination. Second, multivariate linear correlations between the amplitudes of initial link velocities and muscle EMG response areas best describing the response amplitude synergy were examined. Several significant correlations (r > 0.6) were obtained between leg and trunk muscle activity 120 ms after stimulus onset and trunk, or upper leg angular velocity, or head linear velocity, prior to 120 ms. Finally, crosscorrelations between muscle responses were examined for consistent interlink timing synergies between muscle responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1998

Identification, localization, and modulation of neural networks for walking in the mudpuppy (Necturus maculatus) spinal cord.

We tested the hypothesis that the neural networks for walking in the mudpuppy can be divided into a flexor and an extensor center, each of which contains collections of interneurons localized in the vicinity of their motoneuron pools. Combining a battery of techniques, we identified and localized the elbow flexor center and its motoneuron pool in the C2 segment and the elbow extensor center and its motoneuron pool in the C3 segment. Rhythmic flexion or extension of the limb in isolation could be induced by continuous trains of current pulses of the C2 or C3 segments, respectively. Independent activation could also occur after application of glutamate receptor agonist NMDA. Part of segment C2 in isolation generated rhythmic elbow flexor bursts, whereas part of segment C3 in isolation generated rhythmic elbow extensor bursts. An isolated region spanning the C3 roots generated both flexor and extensor bursts. The step cycle was modulated in a phase-dependent manner by stimulation of the dorsal roots, the ventral roots, or either of the two centers. The effects of ventral root stimulation were removed by deafferentation to block reafferent input attributable to muscle contraction induced by the stimulation. We conclude that the neural networks for walking contain at least a flexor and an extensor generator that are localized in close apposition to the motoneuron pools, that the two centers can work independently despite the fact that there are reciprocal inhibitory interconnections between them, and that sensory input interacts with the spinal neural networks to reset the ongoing walking rhythm in a phase-dependent manner.

Animals↗
PubMed2001

Postural reflexes evoked by tapping forehead and chest.

We investigated whether a tap with a reflex hammer to the forehead can elicit responses in the leg muscles and whether vestibular stimulation is the crucial prerequisite for eliciting these responses. We also measured the postural changes caused by the tap and by the compensatory, presumably reflex-like reactions of the subject. Tap-evoked activity of leg muscles was easily elicited during upright stance in normal subjects and was also seen in two subjects without vestibular function. The pattern of muscle activation clearly showed a counteraction to the tap-evoked perturbation of stance. Taps applied to the chest elicited similar reflexes. Since these two conditions imply a different activation of the vestibular apparatus, the vestibular input alone cannot account for the observed leg muscle reflexes. We suggest that multisensory reflex pathways that integrate vestibular and proprioceptive inputs account for these reflexes.

Adult↗
PubMed1994

Proprioception enhancement for anterior cruciate ligament deficiency. A prospective randomised trial of two physiotherapy regimes.

We performed a prospective, double-blind, randomised, clinical trial to investigate the efficacy of two regimes of rehabilitation for knees with anterior cruciate ligament deficiency (ACLD). Fifty ACLD patients were randomly allocated to one of two treatment groups: a programme of muscle strengthening (T) or a programme designed to enhance proprioception and improve hamstring contraction reflexes (P). An indirect measure of proprioception, the reflex hamstring contraction latency (RHCL), and a functional scoring system were used to record the status of the knee before and after the 12-week course of physiotherapy. Sagittal knee laxity was also measured. There was improvement in mean RHCL and in the mean functional score in both groups after treatment. The improvement in group P was significantly greater than that in group T. There was no significant change in joint laxity after treatment in either group. In both groups there was a positive correlation between improvement in RHCL and functional gain.

Adolescent↗
PubMed2004

The immediate effects of tension of counterforce forearm brace on neuromuscular performance of wrist extensor muscles in subjects with lateral humeral epicondylosis.

STUDY DESIGN: Within-subject repeated-measures study. OBJECTIVES: To examine the immediate effects of counterforce forearm brace on isokinetic strenght stretch reflex, passive stretching pain threshold of the wrist extensors, and proprioception of the wrist in subjects with lateral humeral epicondylosis for different strap tensions of a forearm brace. BACKGROUND: Counterforce forearm bracing has been used for treating lateral humeral epicondylosis, but the effect of brace tension has not been well reported. METHODS AND MEASURES: Fifteen subjects diagnosed with lateral humeral epicondylosis on their dominant arm were tested under 4 randomized conditions: (1) no brace, (2) brace with minimal tension, (3) brace with 25-N tension, and (4) brace with 50-N tension. The tests included isokinetic wrist extensors strength, passive stretching force in wrist flexion to elicit pain in the wrist extensors, wrist proprioception, and stretch reflex latency of the extensor carpi ulnari. A repeated-measures MANOVA was used to analyze the data and significant results were further analyzed with post hoc linear contrasts (alpha = .05). RESULTS: Among the 4 conditions, significant differences were found in wrist proprioception P = .032) and pain threshold to passive stretching of the wrist extensors (P = .05), but were not found in wrist extension isokinetic strength and stretch reflex latency of the extensor carpi ulnaris. CONCLUSION: A forearm counterforce brace, as applied in this study, affects wrist joint proprioception and increases the pain threshold to passive stretching of the wrist extensors in subjects with lateral humeral epicondylosis, but it has no effect on wrist extensor strength and stretch reflex latency of the extensor carpi ulnaris.

Adult↗
PubMed2002

The pathophysiology of spasticity.

Spasticity is only one of several components of the upper motor neurone (UMN) syndrome, known collectively as the 'positive' phenomena, that are characterized by muscle overactivity. Other components include tendon hyper-reflexia, clonus, the clasp-knife phenomenon, flexor and extensor spasms, a Babinski sign, and spastic dystonia. Spasticity is a form of hypertonia due to hyperexcitable tonic stretch reflexes. It is distinguished from rigidity by its dependence upon the speed of the muscle stretch and by the presence of other positive UMN signs. Hyperactive spinal reflexes mediate most of these positive phenomena, while others are due to disordered control of voluntary movement or abnormal efferent drive. An UMN lesion disturbs the balance of supraspinal inhibitory and excitatory inputs, producing a state of net disinhibition of the spinal reflexes. These include proprioceptive (stretch) and nociceptive (flexor withdrawal and extensor) reflexes. The clinical syndrome resulting from an UMN lesion depends more upon its location and extent, and the time since it occurred, than on the pathology of the lesion. However, the change in spinal reflex excitability cannot simply be due to an imbalance in supraspinal control. The delayed onset after the lesion and the frequent reduction in reflex excitability over time, suggests plasticity in the central nervous system. Knowledge of the electrophysiology and neurochemistry of spinal reflexes, together with the action of antispasticity drugs, helps us to understand the pathophysiology of spasticity.

Humans↗
PubMed1997

Central modifications of reflex parameters may underlie the fastest arm movements.

Descending and reflex pathways usually converge on common interneurons and motoneurons. This implies that active movements may result from changes in reflex parameters produced by control signals conveyed by descending systems. Specifically, according to the lambda-model, a fast change in limb position is produced by a rapid change in the threshold of the stretch reflex. Consequently, external perturbations may be ineffective in eliciting additional reflex modifications of electromyographic (EMG) patterns unless the perturbations are relatively strong. In this way, the model accounts for the relatively weak effects of perturbations on the initial agonist EMG burst (Ag1) usually observed in fast movements. On the other hand, the same model permits robust reflex modifications of the timing and shape of the Ag1 in response to strong perturbations even in the fastest movements. To test the model, we verified the suggestion that the onset time of the Ag1, even in the fastest movements, depends on proprioceptive feedback in a manner consistent with a stretch reflex. In control trials, subjects (n = 6) made fast unopposed elbow flexion movements of approximately 60 degrees (peak velocity 500-700 degrees/s) in response to an auditory signal. In random test trials, a brief (50 ms) torque of 8-15 Nm either assisting or opposing the movement was applied 50 ms after this signal. Subjects had no visual feedback and were instructed not to correct arm deflections in case of perturbations. In all subjects, the onset time of the Ag1 depended on the direction of perturbation: it was 25-60 ms less in opposing compared with assisting load conditions. Assisting torques caused, at a short latency of 37 ms, an additional antagonist EMG burst preceding the Ag1. The direction-dependent effects of the perturbation persisted when cutaneous feedback was suppressed. It was concluded that the direction-dependent changes in the onset time and duration of the Ag1 as well as the antagonist activation preceding the Ag1 resulted from stretch reflex activity elicited by the perturbations rather than from a change in the control strategy or cutaneous reflexes. The results support the hypothesis on the hierarchical scheme of sensorimotor integration in which EMG patterns and movement emerge from the modification of the thresholds and other parameters of proprioceptive reflexes by control systems.

Adult↗
PubMed1979

The absence of proprioceptive nerve endings in the human periodontal ligament: the role of periodontal mechanoreceptors in the reflex control of mastication.

A review of the literature was conducted to determine the presence or absence of proprioceptive nerve endings in the human periodontal ligament. A histologic review of the periodontal ligament innervation concluded that nerve endings found were those mediating pain, pressure, or touch and that there is no histologic evidence of any "classic" proprioceptive nerve ending in the periodontal ligament. A summary is given concerning the precise role of nerve endings in the periodontal membrane, their afferent pathways, and the role of masticatory muscle proprioception, jaw reflexes, and the temporomandibular joint in the coordinated control of mastication and mandibular proprioception.

Afferent Pathways↗
PubMed1977

Reflex and reticular modulation of first-order proprioceptive neurons of the mesencephalic trigeminal nucleus.

Several investigations have shown that the vagus nerve and the reticular formation can affect the reflex responses of the masticatory muscles. The present research has been devoted to analyze the mechanism of such modulations of the masseteric reflex in the lamb. Extracellular records of the electrical activity of the mesencephalic trigeminal nucleus (MTN) was carried out in immobilized lambs by means of tungsten microelectrodes. Units were found which responded to lowering the jaw and to stretching the masseter muscle: they were identified as the first-order neurons of the masticatory proprioception on the basis of their electrophysiological properties. Single-shock or repetitive electrical stimulations of the cervical vagus nerve and of the bulbo-pontine reticular formation could affect the unitary discharge of the MTN: different patterns of activation and inhibition of the MTN units were seen; however, the activation was the most prominent effect. The responses did not depend upon the circulatory effects of the vagal stimulation. Thus the conclusion can be reached that the vagus and the reticular substance can modulate the masseteric reflex at level of the perikarya of the afferent pathway. Such a statement is supported also by the presence of synaptic boutons on the soma of the MTN neurons.

Action Potentials↗
PubMed1990

Functions of a proprioceptive sense organ in freely moving insects: characteristics of reflexes elicited by stimulation of the locust metathoracic femoral chordotonal organ.

(1) The metathoracic femoral chordotonal organ is an identified joint angle receptor of the locust hindleg. In order to assess and quantify the functions of this sense organ in the control of posture, mechanical stimuli were applied to the main ligament of the receptor in freely standing locusts. These stimuli produced an afferent discharge that mimicked a sudden small (10-15 degree) change in the angle of the femoro-tibial joint of the hindleg. The reflex effects that resulted from afferent stimulation were monitored myographically in the tibial extensor and flexor muscles. The angle of the femoro-tibial joint at the onset of sensory stimulation was also recorded by still photography. (2) As previously reported, stimulation of the chordotonal organ in freely standing animals produced resistance reflexes in tibial muscles that opposed the apparent joint movement. However, we also found that, at certain joint angles, a different mode of reflex response was elicited in which motoneurons to the tibial flexor muscle fired in response to apparent movements in any direction. (3) In this study, characteristics of resistance reflexes in the tibial extensor muscle were analyzed quantitatively, as that muscle is innervated by only one slow excitatory motoneuron. The gain of the resistance reflex (ratio of the firing frequency during afferent stimulation versus the rate of activity prior to the stimulus) was quite high in all preparations, and represent a greater than two-fold increase in motoneuron frequency (mean 2.11 +/- 0.54 S.D.). The reflex gain was also highest at the lowest initial rates of motoneuron activity (circa 5 Hz) and declined for higher firing frequencies (maximum 35 Hz).(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗