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PubMed2004

Trigeminocardiac reflex. A clinical phenomenon or a new physiological entity?

The trigemino-cardiac reflex (TCR) is defined as the sudden onset of parasympathetic dysrhythmia, sympathetic hypotension, apnea or gastric hypermotility during stimulation of any of the sensory branches of the trigeminal nerve. The sensory nerve endings of the trigeminal nerve send neuronal signals via the Gasserian ganglion to the sensory nucleus of the trigeminal nerve, forming the afferent pathway of the reflex arc. This afferent pathway continues along the short internuncial nerve fibers in the reticular formatio to connect with the efferent pathway in the motor nucleus of the vagus nerve. Clinically, the trigemino-cardiac reflex has been reported to occur during craniofacial surgery, balloon-compression rhizolysis of the trigeminal ganglion, and tumor resection in the cerebellopontine angle. Apart from the few clinical reports, the physiological function of this brainstem-reflex has not yet been fully explored. From experimental findings, it may be suggested that the trigemino-cardiac reflex represents an expression of a central neurogenic reflex leading to rapid cerebrovascular vasodilatation generated from excitation of oxygen-sensitive neurons in the rostral ventrolateral medulla oblongata. By this physiological response, the adjustments of the systemic and cerebral circulations are initiated to divert blood to the brain or to increase blood flow within it. As it is generally accepted that the diving reflex and ischemic tolerance appear to involve at least partially similar physiological mechanisms, the existence of such endogenous neuroprotective strategies may extend the actually known clinical appearance of the TCR and include the prevention of other potentially brain injury states as well. This may be in line with the suggestion that the TCR is a physiological, but not a pathophysiological entity.

Afferent Pathways↗
PubMed1997

Influence of long-latency reflex modulation on the performance of quick adjustment movements.

The effect of long-latency reflex modulation on the performance of a quick adjustment movement following a muscle stretch was studied in 26 healthy male subjects. When the subjects felt a sudden angle displacement in the direction of a wrist extension they were required to make an adjustment movement by moving a handlebar, held in the hand, to align with a target position as quickly and as accurately as possible. The index of performance (adjustment time) was the time taken to move the handle to the target position from stretch onset. A DC torque motor was used to evoke electromyographic (EMG) reflex responses on a wrist flexor. Averaging of the rectified EMG, recorded from surface electrodes placed over the flexor, showed short- and long-latency reflexes (M1 and M2 components). For all subjects, the amplitudes of the reflex components decreased during the adjustment movement because the target position for this study was fixed to the extension side of the wrist joint. The decrease in the M2 component, which is considered to be a transcortical reflex, was significantly larger than the decrease in the M1 component, which is spinal reflex. The main finding was of a positive correlation between the length of adjustment time and the degree of reduction of M1 and M2 with the adjustment movement (r = 0.602 for M1, P < 0.01; r = 0.850 for M2, P < 0.001). Moreover, there were correlations between the consistency of the voluntary response onset and the degree of M2 decrease (r = 0.577, P < 0.01), and between the consistency of the voluntary response onset and the length of the adjustment time (r = 0.603, P < 0.01). Therefore, we have concluded that the subjects who were able to perform adjustment movements within a short time could modulate the long-latency reflex of the muscle involved in such movements in order to make the function of their voluntary muscle activity more effective, and thus were able to respond appropriately.

Adult↗
PubMed2006

Sonographic investigation of the rectoanal inhibitory reflex: a qualitative pilot study in healthy females.

PURPOSE: The rectoanal inhibitory reflex has been studied using various methods, e.g., anometry and electromyography. The aim of this study was to apply ultrasound for direct visualization of the rectoanal inhibitory reflex. METHOD: The rectoanal inhibitory reflex was induced in ten healthy females (age range, 21-55 years) by injection of small amounts of water (7, 12, and 20 ml), into the rectum. The intra-anal pressure was measured with a microtransducer and the rectoanal inhibitory reflex was visualized with real-time transvaginal or transperineal sonography. RESULTS: The rectoanal inhibitory reflex consisted of a reduction in the intra-anal pressure and relaxation of the internal anal sphincter, manifested as an increase in the inner diameter of the internal anal sphincter from the mean of 11 to 16 mm (P<0.001). Simultaneously, a wave of rectal contents entered the anal canal. The distance from the most distal border of the rectal contents to the anal verge decreased from a mean of 33 to 20 mm (P<0.001). The rectoanal inhibitory reflex ended with a retrograde transport returning anal contents into the rectum. During the retrograde transport a contraction in the internal anal sphincter was observed. CONCLUSIONS: The rectoanal inhibitory reflex can readily be visualized with ultrasound as a wave of rectal contents entering the anal canal. The transport into the anal canal was not of voluntary origin and could be either noticed or not noticed by the subjects. The observed retrograde transportation in the anal canal was not noted by the subjects; it is related to a contraction in the internal anal sphincter and visualized for the first time using ultrasound.

Adult↗
PubMed1984

Macular reflexes in optic atrophy.

We investigated the annular reflex of the macula and the foveal reflex in 14 eyes with various degrees of optic atrophy by means of red-free fundus photographs. The patients ranged in age from 13 to 34 years (mean age, 25.9 years). We compared our observations with data obtained from 51 age-matched normal eyes. Optic atrophy was found to be associated with changes in the reflexes of the macular area. Alterations occurred in all eight eyes that had visual acuities of 20/50 or worse. Changes in the annular reflex of the macula were more significant in younger patients (less than or equal to 25 years of age) than in older patients. In the younger group, the annular reflex was blunt, distorted, and fragmented, and showed an irregular extension toward the foveal area, whereas in the old group it showed less specific attenuation. Fading of the foveal reflex was observed in both groups. Changes in the retinal reflexes of these patients result from alterations in the ganglion cell and nerve fiber layer and should be included among the signs of optic atrophy. They can help determine the extent of optic atrophy and can be useful clinical clues in children whose optic disks are difficult to examine. They should not be mistaken for signs of associated primary retinal disorders.

Adolescent↗
PubMed1993

Glossopharyngeal-hypoglossal nerve reflex of the frog in metamorphosis.

In adult frogs, a reflex discharge is elicited from the hypoglossal nerve by mechanical and chemical stimuli to the centre of the tongue surface and electrical stimuli to the glossopharyngeal nerve innervating tongue. However, there has been no report concerning the embryological stage at which this reflex develops. The metamorphosis of a frog is divided into three parts, premetamorphic, metamorphic and climax stage. In the climax stage, the forelimbs are lengthened and the tail gradually shortened. The glossopharyngeal-hypoglossal nerve reflex arose in the early climax stage, during which the tongue appeared on the floor of the mouth. At this stage, the conduction velocities of the first compound action potential of the glossopharyngeal and hypoglossal nerves were about 8.7 and 9.3 m/s, respectively. The latency of the reflex was long, especially the central latency. The response of the glossopharyngeal nerve and the reflex discharge from the hypoglossal nerve upon mechanical stimulation of the tongue were smaller in the tadpole than in the adult frog. As metamorphosis proceeded, the conduction velocity of these nerves increased; the latency shortened, especially the central latency; the reflex response to mechanical stimulus increased. These results suggest that, although the glossopharyngeal-hypoglossal nerve reflex is developed in the early climax stage, it is completed only in the adult frog. Therefore, adult frogs living mainly on land may reject and swallow prey by this reflective tongue movement.

Action Potentials↗
PubMed1994

The effects of inhibitory controls triggered by heterotopic noxious stimuli on a jaw reflex evoked by perioral stimuli in man.

Electromyographic recordings (EMGs) were made from the active masseter muscle of the inhibitory reflex evoked by application of electrical stimuli to the skin of the upper lip in 11 human subjects. In control sequences, the reflex had a mean latency and duration of 41 +/- 1.7 and 44 +/- 2.6 ms, respectively. The magnitude of the reflex (measured by integration of the EMG) was significantly reduced by the application of cold (3 degrees C) or hot (47-48 degrees C) but not warm (38-46 degrees C) water to a hand or foot. The strongest stimuli (3 or 48 degrees C) produced mean reductions of the reflex magnitude in the range of 62-85%. These effects occurred regardless of whether the background activity in the masseter was raised or lowered during the application of the thermal stimuli. Thus, activity in nociceptive nerves from widespread areas of the body can modulate jaw reflexes in man by exerting an influence on the reflex pathway at a point before the motor neurones. This may involve the system of 'diffuse noxious inhibitory controls', which have been shown to depress limb flexion reflexes and neuronal activity in the spinal dorsal horn and trigeminal nuclear complex.

Cold Temperature↗
PubMed1996

Neural mechanisms and axon reflexes in asthma. Where are we?

For many years, asthma has been classified as a "neural" disease, with an imbalance between constrictor and dilator nerves being responsible for the symptomatology. Although, nowadays, asthma is recognized as an inflammatory disorder of the airways, neural mechanisms remain very important; axon reflexes, in particular, have received a lot of attention in recent years. In this commentary, an overview is given on the innervation of the airways and its relevance in asthma, and potential new insights in airways innervation are discussed. In a second part, the role of axon reflexes is highlighted. Although neuropeptides such as substance P and neurokinin A are present in human airways, where they produce many of the features characteristic of asthma, and although there is an elevation of their content in induced sputum from asthmatics, there is still no clear direct evidence for the existence of operational axon reflexes in human airways. Most of the research focused on this subject is performed in guinea pigs, where such an axon reflex clearly operates in the airways. In these animals, different receptors have been identified on C-fiber endings, which, upon stimulation, cause inhibition of neuropeptide release. Some of these receptors have also been identified on human airway nerves. Therefore, it has been suggested that modulation of axon reflexes could be of potential benefit in asthma treatment. Indeed, some drugs (e.g. sodium cromoglycate, nedocromil sodium, and ketotifen), which have been demonstrated to partially inhibit neuropeptide release in guinea pig airways, have anti-inflammatory effects on neuropeptide release in guinea pig airways, do not seem to have any anti-inflammatory effects in human asthma. Other drugs, however, such as beta2-mimetics, which have a much more pronounced inhibitory effect in asthma. In conclusion, although there is a lot of indirect evidence for the existence of axon reflex mechanisms in human airways, most of the data now available are derived from animal studies. The key question of whether axon reflexes are operational in human airways remains unanswered. Hopefully, the near future will bring a solution to this enigma with the introduction of very potent tachykinin antagonists for the treatment of human asthma.

Animals↗
PubMed1976

On spinal noradrenaline receptor supersensitivity: correlation between nerve terminal densities and flexor reflexes various times after intracisternal 6-hydroxydopamine.

The noradrenaline (NA)-dependent hindlimb flexor reflex that can be elicited by pinching the foot of acutely spinalized rats given nialamide-DOPA or clonidine was evaluated different time intervals (14 days-6 months) after intracisternal injections of 6-OH-dopamine (6-OH-DA) and correlated to the degree of bulbospinal catecholamine (CA) denervation as seen by Falck-Hillarp fluorescence histochemistry. Six and 14 days after 6-OH-DA, when almost all NA nerve terminals of the spinal cord had degenerated, the NA receptors where supersensitive to stimulation with clonidine as evidenced by an increased flexor reflex. This supersensitivity gradually disappeared as new nerve terminals were formed in the grey matter of the spinal cord during the following 3-6 months. The supersensitivity phenomenon 14 days after 6-OH-DA could also be demonstrated by L-DOPA given to animals pretreated with 100 mg/kg nialamide. Using this relatively low dose of nialamide, almost no reflex response was seen in the control group. Using a higher degree of monoaminoxidase inhibition (nialamide 200 mg/kg) also non-supersensitive, NA receptors became maximally stimulated. Therefore, 6-OH-DA treated rats now showed a weaker reflex than controls, the reflex response being directly correlated to the number of nerve terminals present that could form NA from the precursor. Using 5,6-dihydroxytryptamine, which selectively destroys 5-hydroxytryptamine (5-HT) nerves, it was shown that the flexor reflex changes were specifically related to the NA nerves and unchanged by the simultaneous presence or absence of 5-HT nerve terminals. This was further supported by the finding of a correlation between amount of nerve terminals and flexor reflex responses in individual animals, especially at longer survival times both in the clonidine and the nialamide-DOPA experiments.

Animals↗
PubMed1981

Suppressive influences from periaqueductal gray and nucleus raphe magnus on respiration and related reflex activities and on solitary tract neurons, and effect of naloxone.

Possible opiate-related descending influences from the periaqueductal gray matter (PAG) and nucleus raphe magnus (NRM) were tested on the activity of neural systems involved in respiration and related reflex functions in cats. Stimulation of PAG and NRM could powerfully suppress the simple buccopharyngeal reflexes of jaw-opening and tongue-protrusion and the more complex reflexes of coughing and swallowing; respiration in contrast appeared to be only weakly influenced. The reflexly induced responses of 57 single reflex interneurons recorded in the solitary tract nucleus (NST) could also be markedly suppressed by PAG and NRM conditioning stimulation. In contrast, the rhythmic activity of 30 respiratory neurons in NST was not abolished by PAG and NRM stimuli but most did show a decrease in the peak firing frequency of each rhythmic burst. The suppressive effect of PAG and NRM stimulation on the reflexes and NST reflex interneurons could be reduced by the intravenous administration of naloxone. These studies indicate that neuronal functions associated with respiration and respiratory-related activities can be suppressed by descending influences from PAG and NRM that are in part opiate-related. The observations add to the accumulating evidence that the raphe system is implicated in functions other than pain and its control, and they may also be relevant to clinical observations of opiate-induced effects on respiration and the cough reflex.

Animals↗
PubMed1989

Gain and spatial characteristics of human lip-muscle reflexes.

Mechanically evoked early and late excitatory reflexes (E1 and E2) and suppression responses (S) were studied in human lip muscle. Acceleration pulses were applied at 30-150 m/s2 independently to the upper and lower lips during lip rounding and lower-lip depression postures, and to both lips during a lip-press posture. E1 responses were prevalent during lip rounding and press gestures and S responses during lip depression. Reflex magnitudes were well correlated with stimulus acceleration for the 3 response components, with E1 responses showing the strongest association. The slopes of linear equations relating reflex and stimulus magnitudes, i.e. reflex gains, for E1 and E2 responses were highly variable across subjects. This variability was partially related to subject gender, females showing larger reflex gains. Two novel findings on the spatial aspects of lip-muscle reflexes are that: (1) S responses in lower-lip muscle are more prevalent to upper-lip versus lower-lip stimulation, and (2) E1 and E2 gains in lower-lip muscle are larger for stimulation of the lower lip compared to stimulation of the upper lip. Further testing suggested that this latter pattern differs with form of stimulation, with a laterally directed sliding stimulus on the upper lip producing predominant effects in both the upper- and lower-lip muscle, and an indenting stimulus producing the largest reflexes in muscle of the stimulated lip.

Adult↗
PubMed1992

Visceral and postural reflexes evoked by genital stimulation in urethane-anesthetized female rats.

The present study describes several muscular reflexes produced by genital stimulation, the nerves that subserve them, and the visceral and postural effects induced by these reflexes. Electrical stimulation of the iliococcygeus (ic) and pubococcygeus (pc) (striated) muscles produced movement of the vaginal orifice and wall, membranous urethra, tail and pelvis. Electrical stimulation of the psoas major (pm) or iliacus (i) (striated) muscles produced movements of the lumbar vertebrae and extension of the ipsilateral hindlimb. Sensory mechanostimulation elicited responses of these muscles as follows: stimulation of the perineal skin, clitoral sheath or distal vagina produced reflex contraction of the ic and pc muscles. Stimulation of the cervix produced reflex contraction of the pm and i muscles and also blocked the above reflex contraction of the ic and pc muscles. Both the cervical stimulation-induced blockage of the ic and pc reflex response, and the cervical stimulation-induced activation of pm and i muscles was prevented by bilateral transection of the viscerocutaneous branch of the pelvic nerve. Based on the above observations, it is proposed that stimulation of the vaginal surface of the cervix resulting from penile intromission and/or seminal plug deposition during mating behavior in the rat may reflexively active pm and i, thereby contributing to the hindleg postural rigidity and lordotic dorsiflexion that are characteristic of the normal mating posture in female rats.

Abdominal Muscles↗
PubMed1993

Effects of tonic vibration reflex on motor unit recruitment in human wrist extensor muscles.

Tonic vibration reflex was used to investigate the effects of muscle spindle Ia afferent activation on motor unit (MU) recruitment in human wrist extensor muscles. The MU force recruitment threshold recorded in the extensor carpi radialis muscles were quantitatively compared under two experimental situations: (1) during tonic isometric reflex contractions induced by mechanical tendon vibration and during voluntary contractions performed at the same velocity; (2) during two voluntary imposed ramp contractions (0.25 N.s-1) performed the one immediately before, and the other immediately after a tonic vibration reflex. In the first situation, it was observed that the Ia afferents activated by tendon vibration exerted a strong homonymous facilitatory action on their bearing muscles (extensor carpi radialis longus and brevis), while their heteronymous action on the synergistic muscle (extensor carpi ulnaris) was very weak. The MU recruitment thresholds in the extensor carpi radialis muscles were therefore significantly lower during the tonic reflex contraction than during the voluntary contraction. In the second situation, the tonic vibration reflex induced a facilitatory after-effect which decreased the MU recruitment thresholds during the subsequent voluntary imposed ramp contraction. It is suggested that this post-vibratory effect may have been due either to a postsynaptic potentiation of the motoneurones or to a reflex sensitization of the muscle spindles increasing their response to voluntary isometric contraction and consequently, increasing their facilitatory reflex action on the motoneurone pool.

Adult↗
PubMed1996

Soleus H-reflex depression induced by ballistic voluntary arm movement in human.

A biomechanical and neurophysiological analysis of anticipatory postural adjustments associated with the early phase of a voluntary arm movement was carried out in normal human subjects. Arm elevation, performed at maximal velocity, was studied with unilateral arm movement in freely and counterbalanced (suspended in a safety harness) standing humans. The ground reaction force of both legs, tangential acceleration of the shank and electromyographic activity (EMG) of the anterior deltoid (AD), biceps femoris (BF) and soleus (Sol) muscles were recorded. Sol H-reflexes of both legs were also elicited. To examine how the Ia inhibitory and presynaptic inhibitory pathways are related to anticipatory postural adjustments, additional Sol H-reflexes were elicited using the classical conditioning-test technique (time interval 2 and 15 ms, respectively). In this study, we systematically described biomechanical and EMG phenomena that precede and follow the onset of voluntary arm movements. Prior to and during the arm movement (i.e. AD activation), a sequence of EMG modifications occurred in ipsilateral BF and Sol muscles. Those modifications preceding BF activation included silent phases in Sol EMG and depression of Sol H-reflexes. By comparing EMG modifications with depressions of the Sol H-reflex, we conclude that Ia and presynaptic inhibitory pathways do not play a specific role in those Sol H-reflex depressions. Moreover, because Sol H-reflex depression occurs in both freely standing and counterbalanced postures, anticipatory postural adjustment appear to be preprogrammed in the central nervous systems unrelated to peripheral neural mechanisms. Since changes of EMG activities of ipsilateral BF and Sol appeared simultaneously and Sol H-reflex depressions were dependent on EMG activities of ipsilateral BF, control commands to anticipatory postural adjustment would excite BF and inhibit Sol.

Adult↗
PubMed1977

The effect of the narcotic antagonists naloxone, naltrexone and nalorphine on spinal cord C-fiber reflexes evoked by electrical stimulation or radiant heat.

C-fiber reflexes were recorded from an S1 ventral root in the acute decerebrate low spinal cat following stimulation of the ipsilateral superficial peroneal nerve or application of radiant heat to the metacarpel footpad. Naloxone when administered i.v. increased the electrically evoked C-fiber reflex to 158% (+/- 23.8% S.E.M.) of control 10 min after administration; whereas, naltrexone, 0.0025 mg/kg, increased the C-fiber reflex to 206 +/- 26.1% (S.E.M.) of control. Naloxone in a dose of 0.050 mg/kg increased the radiant heat evoked ventral root reflext to 161 +/- 19.5% of control. Nalorphine, 1 mg/kg, facilitated the electrically evoked C-fiber reflex to 282 +/- 75% of control. These findings that naloxone and naltrexone facilitated these reflexes in doses too small to have non-specific excitatory effects and that nalorphine facilitated the C-fiber reflex at a dose level that is depressant to the flexor reflex in the chronic spinal dog are consistent with a hypothesis that these effects are due to antagonism of a naturally occurring opiate-like inhibitory substance.

Action Potentials↗
PubMed1990

The effect of ketanserin on cardiovascular reflexes in conscious normotensive and spontaneously hypertensive rats.

The effect of ketanserin (3 mg/kg i.v.) on the baroreceptor heart rate reflex and the Bezold-Jarisch reflex was examined in conscious Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). In the control situation (before ketanserin treatment), reflex bradycardia in response to phenylephrine (baroreflex) and phenyldiguanide (Bezold-Jarisch reflex) were impaired in SHR as compared with WKY, while reflex tachycardia in response to nitroprusside was similar in the two groups. However, after ketanserin administration in SHR, there was a reversal of the baroreflex-mediated tachycardia in response to nitroprusside into a bradycardic response. The nitroprusside-induced bradycardia was not caused by the release of 5-HT stimulating chemosensitive vagal afferents since the 5-HT3 receptor antagonist MDL 72222 did not block this response. In the same SHR, the Bezold-Jarisch reflex evoked by phenyldiguanide and the phenylephrine-induced bradycardia were potentiated by ketanserin. All the above effects of ketanserin were less evident in the WKY. Ketanserin did not alter vagal efferent function in anaesthetized SHR since it did not affect bradycardia induced by electrical stimulation of the vagus nerve. Therefore, it is suggested that ketanserin has sensitised cardiac vagal afferent mechanisms in SHR, which led to a normalization of reflex bradycardic function to a level normally observed in conscious normotensive WKY (i.e. prior to ketanserin treatment).

Animals↗
PubMed1994

Inhibition of a somatic nociceptive reflex by gastric distention in humans.

BACKGROUND/AIMS: The spinal nociceptive RIII reflex, an exteroceptive cutaneous-muscular flexion reflex, is powerfully and specifically inhibited by painful heterotopic somatic stimuli. The aim of the present study was to evaluate the effects of nonpainful and painful visceral stimuli on this reflex. METHODS: In nine healthy volunteers, the effects of five levels of gastric distention were tested on the RIII reflex, recorded from the biceps femoris, and elicited by electrical stimulation of the ipsilateral sural nerve. Distentions were performed by means of a balloon that was placed in the proximal part of the stomach and connected to an electronic barostat. The sensations evoked by gastric distention were scored using a graded (0-6) questionnaire. RESULTS: The 200- and 400-mL distention levels elicited no significant modifications of the RIII reflex; the 600-, 800-, and 1000-mL levels inhibited the RIII reflex by 25%, 35%, and 55%, respectively. The magnitude of this inhibition correlated significantly (P < 0.0001) with both the level of distention and the intensity of visceral perception. CONCLUSIONS: Gastric distention produces volume-dependent inhibition of the somatic RIII reflex in humans. This model may provide an interesting tool for objective and quantitative evaluation of normal and disturbed visceral sensations in humans.

Adult↗
PubMed1983

Differences in responsiveness to testosterone of penile reflexes and copulatory behavior of male rats.

The display of penile reflexes and copulatory behavior appears to reflect the activity of two different underlying neuronal system, both of which are modulated by systemic testosterone (T) concentration. To indirectly compare the two systems, the responsiveness to T of penile reflexes and copulatory behavior was examined. In the first experiment castrated spinal male rats were given penile reflex tests while receiving replacement T through Silastic capsule implants filled with T (50 mm T). After capsule removal the number of penile erections and flips declined within 24 hr and gradually decreased for 12 days. Subjects were then reimplanted with new 50-mm T capsules. The number of penile flips and erections increased within 6 and 12 hr. respectively. This is a much more rapid response rate to T than has been established for copulatory behavior. In the second experiment castrated spinal male rats were tested for penile reflexes with a 50-mm T capsule, which was then replaced with a 10-, 5-, or 2-mm T or an empty capsule. The number of penile reflexes declined in a dose-response fashion. In the third experiment, castrated sexually experienced male rats were tested for copulatory behavior with two 25-mm T capsules which were then replaced with a 10 or 2-mm T or an empty capsule. Only males with empty capsules had decrements in copulatory behavior, revealing that a low level of T can maintain virtually normal sexual behavior despite a marked decline in penile reflex activity. The neuronal system underlying penile reflexes (spinal neurons) is apparently much more responsive to changes in T concentrations than the neuronal system underlying motivational and appetitive aspects of copulatory behavior (brain neurons).

Animals↗
PubMed1989

Regulation of wrist stiffness by the stretch reflex.

In restoring the angular position after a displacement, the role of the muscle stretch reflex was investigated by comparing the restored angular torques and angular positions in the wrist under ischaemic and non-ischaemic conditions in normal human subjects. The wrist compliance (COM), defined as the dynamic relation between the angular position and the angular torque of the joint, was calculated to quantify the changes in the restoration of a displacement after abolishing the stretch reflex by ischaemia. The elasticity from the COM-function was found to be single most important factor controlled by the stretch reflex. The elasticity that equals the static stiffness of the system increased by more than 100%, from 0.21 Nm degree-1 with abolished reflex to 0.45 Nm degree-1 with intact reflex. Our results have shown that the stretch reflex assists in the rapid return of the limb to its original position after a mechanical displacement. When the reflex was blocked by ischaemia, the perturbation displaced the limb further away from the initial position.

Adult↗