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A reflex contraction of the human orbicularis oculi muscles can be evoked by stimulation of either the supraorbital region ("blink reflex") or the cornea ("corneal reflex"). We found that the latency of the corneal reflex was longer, and the duration was longer than the R2 component of the blink reflex. The absolute refractory period of the R2 component of the blink reflex was longer after supraorbital than after corneal conditioning stimulation. When the R2 component of the blink reflex was habituated by repetitive stimuli, stimulation of the cornea still evoked a reflex, but supraorbital stimulation produced only a depressed R2 response. These findings suggest that the two reflexes do not have identical neural connections.
The maintenance of arterial pressure at levels adequate to perfuse the tissues is a basic requirement for the constancy of the internal environment and survival. The objective of the present review was to provide information about the basic reflex mechanisms that are responsible for the moment-to-moment regulation of the cardiovascular system. We demonstrate that this control is largely provided by the action of arterial and non-arterial reflexes that detect and correct changes in arterial pressure (baroreflex), blood volume or chemical composition (mechano- and chemosensitive cardiopulmonary reflexes), and changes in blood-gas composition (chemoreceptor reflex). The importance of the integration of these cardiovascular reflexes is well understood and it is clear that processing mainly occurs in the nucleus tractus solitarii, although the mechanism is poorly understood. There are several indications that the interactions of baroreflex, chemoreflex and Bezold-Jarisch reflex inputs, and the central nervous system control the activity of autonomic preganglionic neurons through parallel afferent and efferent pathways to achieve cardiovascular homeostasis. It is surprising that so little appears in the literature about the integration of these neural reflexes in cardiovascular function. Thus, our purpose was to review the interplay between peripheral neural reflex mechanisms of arterial blood pressure and blood volume regulation in physiological and pathophysiological states. Special emphasis is placed on the experimental model of arterial hypertension induced by N-nitro-L-arginine methyl ester (L-NAME) in which the interplay of these three reflexes is demonstrable.
Electromyographic activity of dorsal neck muscles elicited by sinusoidal rotations of the body and head was studied in decerebrate cats over a wide range of rotational frequencies and amplitudes. Rotation of the body with the head held fixed in space elicited a cervicocollic reflex (CCR) in the biventer cervicis, complexus, obliquus capitis inferior, rectus capitis major, and splenius muscles. As stimulus amplitude increased, CCR amplitude increased first rapidly and then more slowly, displaying two linear incremental sensitivity ranges. In contrast, the vestibulocollic reflex (VCR) elicited by whole body rotation had a minimum stimulus threshold below which no response was observed, whereas the vestibuloocular reflex (VOR) saturated at intermediate stimulus intensities. When stimulus frequency was varied, the CCR exhibited second-order dynamic behavior. At frequencies below 0.5 Hz, muscle EMG activation was in phase with peak platform angular deviation in the direction that stretched the muscle, and the gain measured as the percent modulation of EMG activity per degree of rotation remained constant. As frequency increased to 3-4 Hz, response phase advanced by 120 deg or more and gain increased with a slope approaching 40 dB/decade. The data were well-fitted by second-order transfer functions containing two zeros. Both the dynamic behavior of the CCR and its high sensitivity to small stimuli resemble the properties of muscle spindle primary afferents, suggesting that the latter may provide the major input responsible for the CCR. Dynamic properties and gains of the CCR and VCR were quite similar at frequencies between 0.2 and 3-4 Hz. Transfer functions of both reflexes contained two zeros whose time constants were correlated in a population of 11 cats, suggesting that reflex dynamics may be matched to the mechanical properties of each animal's head-neck system. Interaction of the CCR and VCR was studied under two conditions. When the head was driven by a servomotor while the body remained stationary, EMG activation by the two reflexes added linearly to produce a large response. When the body was rotated with the head allowed to counterrotate about the C1-C2 joint, the two reflexes combined linearly in an antagonistic fashion: the CCR acted to oppose head rotations produced by the VCR, thus preventing the ratio of head counterrotation to body rotation from exceeding 0.5. The data indicate that the CCR and VCR behave approximately linearly, both individually and in combination. Acting together, the two reflexes assist each other in preventing oscillation of the head on a stationary body.(ABSTRACT TRUNCATED AT 400 WORDS)
It has been shown previously that the amplitude of the acoustic startle reflex is enhanced, and the amplitude of the light reflex reduced, when subjects anticipate an aversive event, compared to periods when subjects are resting ('fear-potentiated startle reflex' and 'fear-inhibited light reflex'). We examined whether the anxiolytic diazepam would reverse the effects of threat on the startle and pupillary reflexes. Twelve male volunteers participated in three weekly sessions in which they received oral treatment with placebo, diazepam 5 mg and diazepam 10 mg, according to a balanced crossover double-blind design. One hour after ingestion of the treatments, miotic responses to light pulses and electromyographic responses of the orbicularis oculi muscle to sound pulses were elicited during alternating periods in which the threat of an electric shock (electrodes attached to the subject's wrist) was present (THREAT) and absent (SAFE). The THREAT condition was associated with a significant increase in the amplitude of the electromyographic (EMG) response, a significant reduction of the miotic response amplitude, and an increase in self-rated anxiety. Diazepam attenuated all these effects of THREAT. Diazepam did not affect the amplitude of the miotic response under the SAFE condition, but did suppress the EMG response under this condition. These results confirm the validity of the fear-potentiated startle reflex and fear-inhibited light reflex as laboratory models of human anxiety, and reveal some differences between the effects of diazepam on the two reflexes.
The embryonic development of reflex forelimb movements produced by cutaneous stimulation of the forepaw was examined in five inbred strains of the house mouse, Mus musculus. A quantitative electron microscopic study of synapse formation between the neurons that comprise the spinal cutaneous reflex arc was also carried out on specimens from three of the strains subjected to reflex testing. This investigation provides evidence that there is significant genetically-associated variability in the developmental timing of synapse formation within this disynaptic pathway and in the reflex behavior which it mediates. Specifically, it was found that C57BL/6J embryos had greater numbers of synaptic junctions in the reflex pathway at embryonic days 14-16, and they also showed reflex movements earlier than LP/J embryos. C57BL/6J embryos also showed a more rapid increase in the number of boutons during this embryonic period. CBA/CaJ embryos displayed a temporal pattern of development that differed from both C57BL/6J and LP/J. At E15, CBA/CaJ embryos were more similar to LP/J with regard to both reflex activity and synapse number, but by E16, CBA/CaJ values for both of these measures were more similar to C57BL/6J. On the basis of the data detailed in the text, we suggest that the strains differ in the following manner: C57BL/6J embryos develop boutons rapidly but appear to be relatively inefficient in the actual formation of synaptic junctions; CBA/CaJ embryos develop boutons at a slower rate than C57BL/6J but form synaptic junctions more efficiently; LP/J embryos develop boutons slowly and are also relatively inefficient in forming synaptic junctions. The genetic implications of--and some developmental processes which might be responsible for--the observed strain differences in the timing of synaptic development are discussed in the text. There was no detectable genetic variability of the basic sequence in which the neurons of the cutaneous reflex arc develop their synaptic connections. For all three strains examined, the data indicated that synaptic closure occurred in a retrograde sequence with respect to the direction that neurotransmission normally flows between the neurons of this pathway. This finding agrees with results obtained by other investigators from a number of diverse vertebrate species, and such a widespread lack of variability implies that a retrograde sequencing of synapse formation is involved in the development of specific neuronal connectivities.
In the acute phase of cardiac ischemia there is an imbalance of the autonomic outflow with a depression of the baroreceptor reflex. Carotid chemoreceptor stimulation evokes an increase on arterial blood pressure and bradycardia in the anesthetized and paralyzed animal. The activation of cardiac chemosensitive fibers elicit the Bezold-Jarisch reflex comprising a decrease of arterial blood pressure and bradycardia. In the present study, we studied the modifications of the carotid chemoreceptor reflex and the Bezold-Jarisch reflex elicited during the acute phase of myocardial infarction (MI) in the anesthetized and paralyzed rabbit. Rabbits were anesthetized with pentobarbitone, paralyzed and artificially ventilated. The carotid sinus region was exposed and a cannula was inserted retrogradely through the external carotid artery into the carotid bifurcation; the carotid body was stimulated by a lobeline injection. A catheter was advanced, via the right carotid artery, to the origin of the aorta and the Bezold-Jarisch reflex was evoked by an injection of ATP. The baroreflex was provoked by an increase in after-load or by clamping the common carotid artery. Heart ischemia was provoked by ligation of the descending coronary artery. Arterial blood pressure, carotid artery pressure, heart rate and electrocardiogram were monitored. Stimulation of cardiovascular and cardiac receptors was performed before and after coronary ligation. Results show an overall increase in the cardiovascular reflex responses elicited by stimulation of chemically activated receptors and an overall decrease of the baroreceptor responses after MI. In conclusion, these data show the existence of an enhancement of the reflex cardiovascular responses to carotid chemoreceptor and cardiac chemosensitive receptors stimulation and confirmed the depression of baroreceptor reflexes following heart ischemia that could account for the imbalance of the autonomic output observed in the acute phase of myocardial infarction.
An animal model using the spinal rat was characterized. Electrical stimulation of the dorsal nerve of the penis elicited reflex tonic erections of the penile body and reflex bulbospongiosus muscle activity, flips and ejaculations. The tonic erections of the penile body are independent from contractions of the bulbospongiosus muscle and appear to be the result of a neurovascular process. Our observations suggest that reflex bulbospongiosus muscle activity, flips and ejaculations are a single complex reflex response, which we define as reflex ejaculatory response. Two parameters predicted the occurrence and type of reflex response. The visualization of bulbospongiosus muscle activity during surgical isolation of the dorsal nerve of the penis was sufficient to anticipate the elicitability of reflex ejaculatory responses. The latter, together with a systemic systolic pressure > or = 73 mmHg., warranted the elicitability of reflex tonic erections. The similarities found in the physiology of rat tonic penile body erections and of human erections make this model promising for further elucidation of sexual function. Moreover, the present model may prove useful for the investigation of neurogenic erectile dysfunction, and of neurogenic ejaculatory disorders.
BACKGROUND AND PURPOSE: Although both starting position and stretching velocity play an important role in reflex response, their interaction with stretch reflexes has not been thoroughly investigated. This study examined the interaction effect of starting position and stretching velocity on the reflex threshold angle (RTA) of the stretch reflex in the soleus muscle of normal and spastic subjects. METHODS: The spastic group included 11 ankles from 7 subjects with a history of upper motor neuron lesions. Their ages ranged from 22 to 40 years. Another 10 healthy subjects served as the control group. RTAs of the stretch reflex in the soleus muscle were measured for a matrix of starting positions and stretching velocities. The matrix design enabled the use of a 2-way analysis model to investigate the effect of starting position and stretching velocity on the RTA. RESULTS: No interaction effect was found in either the phasic stretch reflex (PSR) or the tonic stretch reflex (TSR) in the spastic group, or in the PSR in the normal group. The RTA of the PSR in both spastic and normal groups was significantly affected by starting position but not by stretching velocity. In contrast, the RTA of the TSR in the spastic group was affected by both starting position and stretching velocity. Stretching velocity and starting position played independent roles in determining the RTA of both the PSR and the TSR of the spastic group and in the PSR of the normal group. CONCLUSIONS: The lack of interaction between length-sensitive and velocity-sensitive muscle spindles in both normal and spastic subjects supports the hypothesis that they independently modulate the stretch reflex. Results for the RTA of the TSR demonstrated that spasticity results in disinhibition of motoneuron excitability with different thresholds.
In 80 controls latencies of flexor carpi radialis (FCR) and in 94 controls latencies of soleus H-reflexes correlated well with length of the extremity, body height and age. Multiple regression equations using latency as a variable dependent on age and body height can be best used in practice when both reflexes are employed for demonstration of proximal pathology. The majority (69%) of 93 patients with various polyneuropathies showed abnormalities in both reflexes illustrating that proximal nerve segments are frequently involved. Four per cent had abnormal FCR H-reflexes with normal soleus H-reflexes whereas the reverse was found in 19% of the patients. Abnormal FCR H-reflexes occurred with normal motor and sensory conduction velocities in the peripheral part of the median nerve in 14%, whereas the reverse was seen in 12%, indicating that FCR H-reflex examination is a valuable supplement to conventional conduction studies for detection of electrophysiologically existing pathology.
INTRODUCTION: To determine the percentage of appearance of the H reflex and long latency reflexes (LLRs) in the thenar and hypothenar muscles of normal subjects to a fixed threshold mixed nerve electrical stimulus and variable degrees of muscle contraction. METHODS: Fifteen subjects aged 21 to 32 years of age without any prior history of central or peripheral neurological diseases volunteered for the study. The stimulation was a constant currrent given at the wrist with the cathode positioned proximally; started at 1 mA and it was gradually increased mA by mA until the M response appeared with the subject relaxed. The intensity of the stimulation was thereafter kept constant. The contraction was an abducting movement of the thumb in the case of the thenar muscle and abduction of the digiti minimi in the case of the hypothenar muscle and was sustained throughout the study. The reflexes were elicited with a repetition rate of 3 Hz, the stimulus was a square pulse of 0.5 ms. We used a low frequency pass filter of 10 Hz and a high frequency pass filter of 10 kHz. The sweep speed was set a 10 ms per division. The responses were averaged 200 times and then smoothed. RESULTS: The mean intensity of the stimulus that evoked the H response, for all subjects, was 7.5 2.8 mA. The mean latency of the H reflex elicited with stimulation of the median nerve was 26 ms 2.03 ms (std. error 0.28, maximum 28.2, minimum 22.0). The mean latency of the H reflex elicited with stimulation of the ulnar nerve was 25.1 ms 1.64 ms (std. error 0.230, maximum 28, minimum 22.3). The difference between the percentage of responses attained under a relaxed condition and with any kind of muscle contraction was highly significant statistically using the Chi square method (p < 0.001). When we compared the percentage of the H responses obtained with slight, moderate, strong contraction, and contraction against resistance, between them, we did no find a significant difference. The LLRs appeared only in the trials with strong contraction. CONCLUSIONS: The H reflexes and the LLRs of the thenar and hypothenar muscle were not obtained with threshold stimulation when these muscles were relaxed. With any degree of muscle contraction the H reflex in these muscles could be obtained in 94 percent of the trials. Maximal contraction and contraction against resistance were the best conditions to elicit long latency responses.
CONTEXT: Previous research indicates that osteopathic manipulative treatment based on counterstrain produces a decrease in the stretch reflex of the calf muscles in subjects with Achilles tendinitis. OBJECTIVES: To study the effects of counterstrain on stretch reflex activity and clinical outcomes in subjects with plantar fasciitis. METHODS: In a single-blind, randomized controlled trial of crossover design, the effects of counterstrain were compared with those of placebo in adult subjects (N=20) with plantar fasciitis. The subjects were led to believe that both the counterstrain and placebo were therapeutic modalities whose effects were being compared. Ten subjects (50%) were assigned to receive 3 weeks of counterstrain treatment during phase 1 of the trial, while the other 10 subjects were given placebo capsules. After a 2- to 4-week washout period, phase 2 of the trial began with the interventions reversed. Clinical outcomes were assessed with daily questionnaires. Stretch reflex and H-reflex (Hoffmann reflex) in the calf muscles were assessed twice during each laboratory visit, before and after treatment in the counterstrain phase. RESULTS: No significant changes in the electrically recorded reflexes of the calf muscles were observed in response to treatment. However, changes in the mechanical characteristics of the twitches resulting from the electrical responses were observed. Peak force and time to reach peak force both increased (P< or =.05) in the posttreatment measurements, with the increase being significantly more pronounced in the counterstrain phase (P< .05). A comparison of pretreatment and posttreatment symptom severity demonstrated significant relief of symptoms that was most pronounced immediately following treatment and lasted for 48 hours. CONCLUSIONS: Clinical improvement occurs in subjects with plantar fasciitis in response to counterstrain treatment. The clinical response is accompanied by mechanical, but not electrical, changes in the reflex responses of the calf muscles. The causative relation between the mechanical changes and the clinical responses remains to be explored.
In contrast to limb muscles, little is known about the role of the asymmetric tonic neck reflex (ATNR) on jaw-elevator muscles. The effect of rotation of the head on the H-reflex in the anterior part of the temporal muscle after masseteric nerve stimulation was evaluated. Eight healthy volunteers (7 males and 1 female, age range 18 to 27 years, mean age 22 years) participated. The masseteric M-response and the masseteric and temporal H-reflexes were elicited by stimulating the masseteric nerve using a monopolar needle technique. The electromyographic activity of the muscles was recorded by surface electrodes. The ATNR was modified by changing position of the head: 30 degrees rotation towards the stimulated side (+N), 30 degrees rotation towards the non-stimulated side (-N) and 0 degree central position (C). The heteronymous temporal H-reflex was elicited at a stimulus intensity of 120% maximal M-response at a frequency of 1 Hz, in random series of 5 to 20 sweeps, up to 30-50 sweeps for each position. On-line averaging was performed. A significant reduction of the H-reflex amplitude was observed in the -N position (p-0.02 paired "t"-test, p = 0.015 Wilcoxon signed rank test), while a significant increase was present in the +N position (p = 0.007 PTT and WSR). Also multivariate analysis yielded a significant influence of head rotation on H-reflex amplitude (p = 0.0032). It can be concluded that the ATNR has a significant influence on the H-reflex of the human temporal muscle.
Human withdrawal-reflex receptive fields were assessed in 10 healthy subjects during standing with even support on both legs. Two electrical-stimulus intensities (1.2 and 2.2 times the pain threshold, PTh) were used. The painful stimuli were delivered in random order to 12 positions distributed over the foot sole. Tibialis anterior (TA), soleus (SO), vastus lateralis (VL), semitendinosus (ST), and iliopsoas (IL) reflexes were recorded. Further, the vertical force was recorded and the center or pressure (CoP) was assessed in the frontal and sagittal planes on both legs. Reflexes were observed at both intensities with the strongest reflexes at the high intensity. Around the ankle joint, SO reflexes dominated, which is in contrast to previous observations for subjects sitting. An unloading of the limb was found on the stimulated leg associated with a simultaneous loading of the contralateral leg. The shift in load was most pronounced for stimulation of the heel. The flexors ST and IL also had strong reflexes with reflex patterns correlated to the pattern of unloading. The shift in vertical force was accomplished by a move of the CoP in the anterior direction on the stimulated limb (contraction of SO), which simultaneously caused a small movement of the CoP in the lateral direction. In the present standing conditions, the ankle extensor played a dominant role in the withdrawal pattern in contrast to previous studies during sitting, relaxed conditions.
Reflex heart block was studied in 20 dogs anesthetized with sodium pentobarbital and in 5 trained unanesthetized dogs. Three different vagal reflexes were produced: the Marey response during hypertension caused by administering methoxamine, a cardiogenic hypertensive chemoreflex activated by injection of serotonin into the left atrium and the Hering-Breuer reflex observed during normal respiration of unanesthetized dogs. In every dog during any of the three reflexes heart block was consistently observed after the normal slowing response of the sinus node had been selectively eliminated by the direct perfusion of 10 microgram of atropine into the sinus node artery. This was a uniform response despite its being variously produced by a pressor reflex, a chemoreflex or an extracardiac bronchopulmonary reflex. Transient heart block is therefore to be anticipated during reflexes with vagal efferent components if for any reason the sinus node is incapable of slowing suitably. The possible clinical relevance of these experimental observations is discussed.
A new reflex which I call the 'ano-urethral reflex' is described and its clinical significance discussed. It was studied in 16 volunteers with normal vesical and rectal functions. A concentric needle electrode was introduced into the external and sphincter (stimulating), and another one into the external urethral sphincter (recording). The reflex response was recorded by EMG apparatus. The external urethral sphincter basal activity was increased with stimulation of the external anal sphincter. This reflex response was absent when the external and sphincter was anesthetised. The average latency of the reflex was 129.5 ms. Reflex urethral sphincter contraction at defecation guards against involuntary micturition which may result from rectal distension and levator contraction. The anourethral reflex can be a valuable diagnostic tool in routine investigations of patients with urological and proctological complaints.