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Results for “Reflex, Monosynaptic”

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At least 577 records · Page 32Linked to original sources

PubMed2006

Middle-finger reflex.

A new reflex is described: middle-finger extensor reflex elicited by percussion of tendon insertion of musculus extensor digitorum communis in forearm. Following percussion using a reflex hammer, two EMG responses from the belly of the muscle were recorded: a short latency monosynaptic reflex with a latency of 31.4 +/- 1.5 ms (M1), and a long-latency middle-finger reflex with a mean latency of 64.8 +/- 6.31 ms (M2), the former being a monosynaptic extensor reflex, and the latter belonging to a spino-cortico-spinal reflex circuitry. It was suggested that the middle-finger extensor reflex elicited by radial nerve afferents and efferents (C7-C8) would be of clinical and theoretical importance.

Afferent Pathways↗

PubMed1988

[Pharmacological comparison of the CNS effects of propentofylline and caffeine].

The CNS effects of propentofylline and caffeine, methylxanthine derivatives, were compared. In mice, caffeine antagonized diazepam-induced muscle relaxation and the inhibitory effect of diazepam against pentylenetetrazole-induced convulsions, but propentofylline did not. In spinal cats, the dorsal root reflex potentials were inhibited by caffeine but not affected by propentofylline, and the monosynaptic reflex potentials were increased by propentofylline but not influenced by caffeine. The results indicate that propentofylline differs from caffeine in that it neither antagonizes diazepam nor affects the GABA system.

Animals↗

PubMed1984

Opioid antagonists and spinal reflexes in the anaesthetized cat.

In barbiturate-anaesthetized cats, intravenous naloxone (0.025-0.10 mg/kg) increased the amplitude of monosynaptic reflexes produced by electrical stimulation of the nerves to the biceps-semitendinosus and gastrocnemius muscles and the complex reflexes to electrical stimulation of myelinated afferents of the sural and tibial nerves and reflexes to electrical stimulation of unmyelinated primary afferents of the tibial nerve. Increases in reflexes were also produced by the (-)- but not the (+)-isomer of the opiate antagonist N- furylmethylnormetazocine (both isomers being given in the dose range 0.03-0.20 mg/kg). The doses of naloxone increasing reflexes to C primary afferents had no effect on the responses of some dorsal horn neurones with cutaneous receptive fields to the same stimuli. The results suggest that, in anaesthetized cats, inhibition involving opioid peptides at some stage is present on many motoneurones. This inhibition may have relevance to animal behaviour after injury.

Animals↗

PubMed1997

Influence of short-term ischemia on segmental spinal cord reflex functions in cats.

In the lumbar spinal cord in cats, microcirculatory (laser Doppler flowmetry) and segmental neurophysiological parameters [monosynaptic reflexes of a flexor and extensor, polysynaptic reflexes from a cutaneous nerve, and the cord dorsum potential (CDP)] were determined in context with ischemias of 1-10 min. Ischemias were achieved by aortic snare occlusion of the descending aorta and were pooled into deep and moderate ones (0-20% and 20-50% residual spinal cord blood flow). Three phases of reaction to ischemia were defined: a period of decreasing responses, a period of delay until recovery, and a recovery period from beginning to completeness of recovery. Although the period of decreasing responses was relatively constant, the delay until recovery could be correlated with duration and depth of ischemia. The recovery period depended mainly on the duration of ischemia. For 2-6-min ischemias, the correlation between depth and duration of ischemia to the delay until recovery or to the recovery period tended to be linear. The period of decreasing responses, the delay until recovery, and the recovery period of mono- and polysynaptic reflexes behaved in a comparable way and demonstrated similar susceptibility to ischemia. The CDP turned out to be the most stable response, indicating a higher resistance of the first-order interneurons to ischemia than of motor neurons.

Animals↗

PubMed1976

[Reflex responses during the early period of recovery of motor function in a transplanted limb].

In immobilized anesthetized rats, monosynaptic reflex responses before and after (3 months) the autoreplantation of the left hind limb were studied. The early period after replantation was characterized by the lowering of excitability, the increase of latency, the decrease of differences between reflex responses to nerves stimulation. Differences existed between responses to stimulation of flexors and extensors but only with a major time summation which suggested that they were due to dendrite processes in chromatotized motoneurons.

Animals↗

PubMed2003

Facilitation of the jaw reflexes by stimulation of the red nucleus in the rat.

The effects of the red nucleus (RN) stimulation on the jaw-opening reflex (JOR) and the masseteric monosynaptic reflex (MMR) were studied in anesthetized rats. The JOR was evoked by electrical stimulation of the inferior alveolar nerve. The MMR was evoked by electrical stimulation of the mesencephalic trigeminal nucleus. The JOR and the MMR were recorded as electromyographic responses of the anterior belly of the digastric and the masseter muscles, respectively. The conditioning electrical stimulation of the RN facilitated both the JOR and the MMR bilaterally. The facilitatory effect on the JOR was much larger than that on the MMR. Additionally, microinjection of monosodium glutamate into the RN also elicited facilitation of the JOR and the MMR. The results suggest the RN plays an important role in reflex control of jaw movements.

Animals↗

PubMed1990

Effects of muscle history on the stretch reflex in cat and man.

1. This is a report of experiments on cat and man which demonstrate effects of a muscle's previous history of contraction and length changes on the size of the stretch reflex. 2. In adult human subjects the size of the tendon jerk was measured in ankle extensor muscles by tapping the Achilles tendon. Muscle conditioning consisted of a maximum voluntary contraction with the foot dorsiflexed or plantarflexed by 30 deg from the test position, after which the subject was asked to relax while the foot was held still for several seconds before being returned to the test position and a tendon tap given. After a contraction of the lengthened muscle the tendon jerk was smaller than after a contraction of the shortened muscle. 3. The experiment was then repeated, but instead of a tendon jerk an H (Hoffmann) reflex was elicited by transcutaneous electrical stimulation of the tibial nerve in the popliteal fossa. The reflex after a conditioning contraction of the lengthened muscle was larger than after a contraction of the shortened muscle. In other words muscle conditioning produced opposite effects on the tendon jerk and H reflex. 4. These findings were confirmed in cats anaesthetized with chloralose. After a conditioning contraction of triceps surae at a length 5 mm longer than the test length (hold-long) a quick tendon stretch produced a smaller reflex response than following a conditioning contraction with the muscle 5 mm shorter than the test length (hold-short). The reverse trend was seen with a reflex elicited by direct electrical stimulation of the muscle nerve, which stimulates the H reflex. 5. One consequence of a conditioning contraction is that it leads to an alteration of the level of resting discharge of muscle spindles. We propose that the larger tendon jerk after a contraction of the shortened muscle is the result of changes in stretch sensitivity of muscle spindles. The reverse effect on the H reflex we attribute to a rise in the level of resting discharge of muscle spindles, which, we propose, leads to reflex inhibition of motoneurones. 6. We support this conclusion with evidence from an experiment in which the size of the conditioning step was systematically altered. Even quite small hold-short conditioning steps led to depression of the H reflex in man and the monosynaptic reflex in cats. Recordings from single afferents showed that such small steps were also accompanied by a detectable rise in spindle resting discharge.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1983

Stimulation techniques and response characteristics of the M and F waves and H reflex in dogs.

The voltage and duration of electrical rectangular pulsed stimuli needed to produce an F wave and a monosynaptic reflex (H wave) and the characteristics of these responses were recorded in clinically normal dogs. Optimal stimulus to produce H waves was 0.1 to 0.2 ms and less than 80 volts. F waves were variable in appearance and were most evident following 0.5 ms and 125 to 150 volt stimulation. F waves had shorter latency than comparable H waves.

Animals↗

PubMed1978

Segmental reflexes mediated by joint afferent neurons in cat knee.

1. Reflex effects mediated by knee joint afferent neurons were tested using the electrically evoked monosynaptic reflex in motoneurons innervating muscles which act about the knee. 2. Joint afferents were excited using small extension movements of the knee, stimuli which have been shown to be effective in activating a large fraction of the myelinated fibers in joint nerves. Because of the variability of reflex responses observed by others under similar experimental conditions, experimental control and data collection were done automatically under computer control. Large numbers of trials were presented in random sequence, and the resulting data were sorted and averaged. 3. Positive feedback was observed in both knee extensor (vasti) and knee flexor (posterior biceps-semitendinosus (PB-ST)) motoneuron populations. Vasti motoneurons were excited, and PB-ST motoneurons were inhibited by knee extensions when the posterior articular nerve (PAN) was intact; these effects were lost or substantially reduced when the PAN was cut. 4. Using knee extension stimuli, no reliable reflex effects were observed which could be attributed to afferents in medial articular nerve.

Animals↗

PubMed1987

Involvement of noradrenergic systems in the effects of conditioning stimulation of the lower brain stem on the lumbar spinal reflex in rats.

The effects of conditioning stimulation at various positions in the pons and the medulla on the lumbar spinal monosynaptic reflex (MSR) were examined in rats. The conditioning stimulation facilitated the MSR. Facilitation with long latency was completely blocked by phenoxybenzamine, chlorpromazine or haloperidol. Phenoxybenzamine and chlorpromazine inhibited the MSR. Haloperidol, on the other hand, augmented the MSR, and this effect became more potent after the brain stem had been transected at the upper part of the medulla oblongata. These results suggest that pontine noradreneric systems have a facilitatory influence on the MSR via alpha-adrenoceptors, and that alpha-blockers exert an inhibitory effect on the MSR by blocking these receptors.

Adrenergic alpha-Antagonists↗

PubMed2005

Comparison of the effects on spinal reflexes of acetylsalicylate and metamizol in spinalized and normal rats.

The effects of nonsteroidal antiinflammatory drugs, acetylsalicylate and metamizol, on spinal monosynaptic reflexes were investigated in spinalized and normal rats. Adult rats (n=36) weighing 150-200 g were anesthetized with ketamine and artificially ventilated. Half of rats were spinalized at C1 level. A laminectomy was performed in the lumbosacral region. Following electrical stimulation of the sciatic nerve by single pulses, reflex potentials were recorded from the ipsilateral L5 ventral root. Acetylsalicylate was administered orally (100 mg/kg for both spinalized and normal rats). Metamizol was administered intramuscularly (15 mg/kg for both spinalized and normal rats). These drug administrations significantly decreased the amplitude of reflex response in all groups (p < 0.05). These data verify that observed inhibition by acetylsalicylicate and metamizol may be at the level of spinal cord. Also we suggested that the cyclooxygenase products of arachidonic acid may play an important role in regulating the reflex potential.

Animals↗

PubMed1977

[Effect of ammonium acetate on depolarization processes in the central terminals of primary afferents].

Experiments on cats determined that ammonium acetate injected intravenously (2-4 mM/kg) supressed the processes of primary afferent depolarization (PAD) which are thought to be responsible for the presynaptic inhibition of spinal reflexes. The supression was transient and proceeded in paralle to depression of postsynaptic inhibition of monosynaptic reflexes. Ammonium acetate slightly decreased the amplitude of the negative postsynaptic potentials recorded form the dorsal surface of lumbar cord in response to stimulation of hind limb afferent nerves and increased polysynaptic reflex discharges in appropriate ventral roots. These findings make it unlikely that the ammonium depression of PAD is a result of impairment of interneuronal activity. A suggestion is made that ammonium depression of PAD results from diminition of the EMF for synaptic currents producing PAD.

Acetates↗

PubMed1973

Modulation of postural reflexes by voluntary movement. I. Modulation of the active limb.

Experiments were performed involving isometric activation/relaxation of the agonist-antagonist muscle groups about the ankle joint. It is shown that phasic changes of foot torque in the dorsal direction are associated with a transient inhibition of the soleus H-reflex which is independent of anterior tibial contraction. During phasic changes in foot torque in the plantar direction, facilitation, as opposed to disinhibition of the soleus H-reflex, is graded by soleus contraction. These results support the hypothesis that the sensitivity of the monosynaptic reflex arc is one of the controlled variables of the motor system. The stretch reflex of a shortening muscle is generally facilitated, while that of a lengthening muscle is inhibited. These hypotheses are in keeping with our present knowledge of the linkage between skeletomotor and fusimotor neurones for the organization of voluntary movements.

Ankle Joint↗

PubMed1987

Reflex excitability of human soleus motoneurones during voluntary shortening or lengthening contractions.

1. We investigated the possibility that increase or decrease in the monosynaptic reflex excitability of the soleus muscle in man might play a role in matching the muscle mechanical output to the voluntary command aimed at performing isotonic contractions or relaxations, at various velocities. 2. Rectified and integrated electromyographic activity (e.m.g.) and the H reflex of soleus were measured during plantar flexions against a constant load (shortening contractions) or dorsal flexions resisting the load (lengthening contraction), performed without activation of pretibial muscles. 3. At the same ankle joint angle, integrated e.m.g. was larger during shortening contractions than during lengthening contractions. During shortening contractions, integrated e.m.g. increased as a function of the velocity of plantar flexion. During lengthening contractions, integrated e.m.g. decreased as a function of dorsal flexion and angular velocity and nearly disappeared in the last part of the most rapid lengthening contractions. 4. During shortening contractions, the H reflex increased beyond the extent expected for the level of e.m.g. activity; during lengthening contractions, reduction of the H reflex below control values at rest occurred in spite of background e.m.g. activity. 5. When the level of e.m.g. activity was kept constant, the above changes in H reflex were larger in both directions as a function of the velocity of the movement. 6. Passive rotation in the dorsal direction contributed to the inhibition observed during lengthening contractions. 7. It is suggested that these changes in the excitability of the H reflex, probably presynaptic in origin, serve the purpose of appropriately modulating the rate and extent of motoneurone recruitment during shortening and lengthening contractions. This allows the foot to follow a constant-velocity path in spite of the perturbing effects of the spindle afferent inputs and of the muscle characteristics described by the force--length and force--velocity diagrams.

Action Potentials↗

PubMed1988

Low dose epidural morphine does not affect non-nociceptive spinal reflexes in patients with postoperative pain.

In order to determine the selectivity of the antinociceptive effect of epidural morphine, the electrophysiological features of a monosynaptic reflex were investigated before and after epidural morphine (2-3 mg) required for pain relief, in 4 patients suffering from postoperative pain. The reflex tested was the H reflex from the soleus muscle. Not only the classical Hmax/Mmax ratio, but also the threshold and the slope of the rising phase of the recruitment curve of H and M responses were analyzed. It was found that epidural morphine did not change significantly any of these parameters, at least during the 60 min post-injection period. By contrast, as usually observed clinically, epidural morphine produced an onset of pain relief by the 25th-30th min following injection. These data support the hypothesis that epidural morphine produced a 'selective spinal analgesia in man.'

Anesthesia, Epidural↗

PubMed1995

Effects of hindlimb cutaneous afferent inputs on spinal reflex recording from tail muscle motoneurons in the spinalized cat.

In 4 spinalized cats, the effects of afferent inputs from hindlimb cutaneous nerves (sural cutaneous nerve: Sur) on mono-and poly-synaptic reflex recorded from tail muscle motoneurons were studied before and after spinal lesioning at S2-3 level. Monosynaptic reflex was enhanced by ipsilateral Sur stimulation at short conditioning-test stimulus interval and this effect was not observed after spinal lesion of ipsilateral side of spinal cord. Polysynaptic reflex was inhibited by stimulation of Sur in both sides and this inhibitory effect was depressed by contralateral spinal lesioning.

Afferent Pathways↗

PubMed1993

Opioid action on spinal cord reflexes due to dorsolateral pontine tegmentum stimulation.

Electrical stimulation of the dorsolateral pontine tegmentum (DLPT) produces phasic facilitatory and inhibitory actions on the lumbar spinal monosynaptic reflexes (MSRs) of both flexor and extensor muscle nerves in the decerebrate cat. Naloxone, an opioid receptor antagonist, given intravenously or intraspinally enhanced the DLPT-induced potentiation of MSRs in most of the reflexes studied. However, systemic naloxone had no significant effect on the unconditioned MSR of the spinal cord. Intraspinal microinjections of naloxone significantly attenuated the DLPT-induced inhibition of MSRs of both flexors and extensors, similar to the action of systemic injection of naloxone, indicating a direct opioid action at the spinal ventral horn level upon DLPT stimulation. Results of the present experiment further support the anatomical finding that there are pontospinal enkephalinergic pathways in the cat, and indicate that these descending pathways modulate spinal motor outflow.

Animals↗

PubMed1981

The human jaw jerk: electrophysiologic methods to measure the latency, normal values, and changes in multiple sclerosis.

The reflex contraction of the masseter muscles to the stretch imposed by a tap on the chin is a monosynaptic reflex. This reflex contraction of the master muscles was present in all control subjects but commonly absent in definite multiple sclerosis (MS) patients. In a few MS patients the latency was prolonged. Abnormalities in the jaw jerk, however, were less frequent than with the blink reflex responses to supraorbital nerve stimulation or light stimulation. Nonetheless, there were patients in whom the blink reflexes were normal but the jaw jerk responses was abnormal. The last observation suggests that the jaw jerk may be occasionally helpful in the detection of brainstem lesions in MS.

Adolescent↗