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Sensory and motor innervation of the proboscis by branches of the maxillary and labial nerves of the worker honey bee has been investigated in specimens stained vitally by methylene blue or viewed by scanning electron microscopy. A chordotonal organ consisting of a single scolopidium is present in the maxillary palp. Flexion of the maxillary palp occurs only passively, induced by the flexion of the galea. This chordotonal organ may function as a proprioceptor for the movement of the galea. Another chordotonal organ exists in the prementum of the labium. It contains, on the average, 12 sensory cells and presumably responds to the bending of the labial palp. A nerve-net of bipolar cells arises from the sensory branches of the maxillary nerve. Free nerve endings derived from the periphery of this nerve-net expand broadly on the intersegmental membranes connected to the stipes. The right and left nerves to the dilator muscles of the salivarium exchange branches, resulting in the reciprocal innervation of each muscle.

Eyelid movements are mediated mainly by the orbicularis oculi and the levator palpebrae superioris muscles. In blinking they show a strictly reciprocal innervation. Blepharospasm manifests as involuntary eyelid closure, however, there are also a number other diseases resulting in the inability to open the eyelid. We analysed clinical and electromyographical findings in 81 patients with disturbances of eyelid opening. Among these were 63 with tonic or clonic dystonic activity only in the orbicular part of orbicularis oculi muscle, 43 with additional dystonic activity in the palpebral part of orbicularis oculi muscle = idiopathic blepharospasm. Ten showed isolated activity in the palpebral part of orbicularis oculi muscle = palpebral variant of blepharospasm. Four exhibited synchronous activity in the orbicularis oculi and the levator palpebrae superioris muscles = disturbance of the antagonistic inhibition. Another four had no activity in the levator palpebrae superioris muscle while activity in the palpebral part of orbicularis oculi muscle was normal = apraxia of eyelid opening. A distinction is relevant for the therapeutic modality and the exact spot as which to inject botulinum toxin. In apraxia of eyelid opening after manual opening the eyelid remains open up to the next contraction of the orbicularis oculi muscle (Zwickau's eye sign).

summary One of the relaxation techniques that have been used by physical therapists when treating patients with temporomandibular disorders, is the agonist contract–antagonist relax technique (AC). When the AC technique is applied, a submaximal resistance to the jaw opening movement is necessary to cause relaxation of the masticatory muscles. No information about the effect of this technique on masticatory or cervical muscles has been found in the literature. Thus, the aim of this study was to evaluate the electromyographic activity of the masseter and anterior temporalis and the upper trapezius and splenius capitis during resisted jaw opening movement. A convenience sample of 30 students was used. Electromyography activity of the superficial masseter, anterior temporalis, upper trapezius and splenius capitis was registered before, during and after the application of this resistive movement to jaw opening. A two-way anova with repeated measures analysis was used to analyse data. The level of significance was at α = 0·05. The EMG activity of both the masticatory muscles and the cervical muscles increased during and after the application of resisted jaw opening (P

The connections of a potential auditory circuit were determined in the medulla of the toadfish (Opsanus tau). Fluorescent dextran amines placed in the medial torus semicircularis (mTS) retrogradely filled cells primarily in the dorsal region of the descending octaval nuclei (DON) with contralateral predominance. Fluorescent dextran amines placed in the DON revealed commissural fibers that cross the midline with the internal arcuate tract. The interconnections are consistent with a dorsal-ventral organization of the DON: reciprocal innervation is present for the left and right dorsal zones of the DON and for the left and right ventral zones of the DON. Based on projections to the medial (auditory) TS and the reciprocal connections, the dorsal region of the DON appears to be the major auditory processing site in the medulla and also may be a site for directional, binaural comparisons. The ventral region of the DON may be a site for bilateral vestibular processing. Double-labelling experiments revealed that some of the descending octaval cells projecting to the contralateral DON also project to the mTS. Based on the auditory pathway indicated by this study, future neurophysiological investigations of sensitivity to directional sound stimuli should begin in the dorsal DON of the toadfish.

Neurons may serve different functions over the course of an organism’s life. Recent evidence suggests that cortical subplate neurons including those that reside in the white matter may perform longitudinal multi-tasking at different stages of development. These cells play a key role in early cortical development in coordinating thalamocortical reciprocal innervation. At later stages of development, they become integrated within the cortical microcircuitry. This type of longitudinal multi-tasking can enhance the capacity for information processing by populations of cells serving different functions over the lifespan. Subplate cells are initially derived when cells from the ventricular zone underlying the cortex migrate to the cortical preplate that is subsequently split by the differentiating neurons of the cortical plate with some neurons locating in the marginal zone and others settling below in the subplate (SP). While the cortical plate neurons form most of the cortical layers (layers 2-6), the marginal zone neurons form layer 1 and the SP neurons become interstitial cells of the white matter as well as forming a compact sublayer along the bottom of layer 6. After serving as transient innervation targets for thalamocortical axons, most of these cells die and layer 4 neurons become innervated by thalamic axons. However, 10-20% survives, remaining into adulthood along the bottom of layer 6 and as a scattered population of interstitial neurons in the white matter. Surviving subplate cells’ axons project throughout the overlying laminae, reaching layer 1 and issuing axon collaterals within white matter and in lower layer 6. This suggests that they participate in local synaptic networks, as well. Moreover, they receive excitatory and inhibitory synaptic inputs, potentially monitoring outputs from axon collaterals of cortical efferents, from cortical afferents and/or from each other. We explore our understanding of the functional connectivity of these cells at different stages of development.

We investigated the immediate and long-term changes in static eye alignment with acute superior oblique palsy (SOP) in the monkey. When the paretic eye was patched immediately after the lesion for 6–9 days, vertical alignment slowly improved. When the patch was removed and binocular viewing was allowed, alignment slowly worsened. In contrast when a monkey was not patched immediately after the lesion vertical alignment did not improve. We also show that a model of the eye plant can reproduce the observed acute deficit induced by SOP, but only by abandoning Robinson's symmetric simplification of the reciprocal innervation relationship within pairs of agonist–antagonist muscles. The model also demonstrated that physiologic variability in orbital geometry can have a large impact on SOP deficits.

Since muscle coactivation increases the stiffness and stability of a joint, greater coactivation is likely during faster than slower movements. Very few studies, though, have been conducted to verify this hypothesis. Moreover, a large number of studies have examined coactivation of muscles surrounding the knee joint whereas there are few reports on the elbow joint. The aim of this study was therefore to compare the antagonist activation of the elbow flexors and extensors during isokinetic concentric exercises and to investigate the influence of angular velocity on their activation. Twelve men participated in the study. The surface electromyographic signals (sEMG) were recorded from the biceps brachii (BB) and triceps brachii (TB) muscles during three maximal voluntary isometric contractions (MVC) of elbow flexors and extensors and a set of three maximal elbow flexions and extensions each at 15 degrees, 30 degrees , 60 degrees, 120 degrees, 180 degrees, and 240 degrees.s(-1). Normalized root mean square (RMS) of sEMG was calculated during the isokinetic phase of movement as an index of sEMG amplitude. During elbow flexion, the antagonist activation of BB averaged 16.2% lower than TB, and this difference was statistically significant at all angular velocities. The normalized RMS values ranged from 26.0% +/- 19.0 at MVC to 37.8% +/- 13.9 at 240 degrees.s(-1) for antagonist TB activation, and from 5.7% +/- 5.2 at MVC to 18.9% +/- 8.6 at 240 degrees.s(-1) for antagonist BB activation. No influence of angular velocity on agonist and antagonist activity was found. Moreover, flexion and extension torques were both strongly affected by the amount of antagonist activation. The functional specialization of the two muscle groups could be responsible for the different levels of antagonist activation. The frequent use of BB, which is not assisted by gravity during daily activities, could lead to reduced coactivation due to a better functioning of the control system based upon reciprocal innervation. These findings may have significant implications in the design of rehabilitation programs directed to the elbow joint.

1. Simultaneous intracellular recordings were made from longitudinal muscle (LM) and circular muscle (CM) cells of guinea-pig distal colon during the peristaltic reflex. 2. Spontaneous rhythmical depolarizations with superimposed action potentials (mean amplitude: 19 +/- 2 mV) were regularly recorded from the LM (mean interval: 7 +/- 1 s). In contrast, in the CM layer, spontaneous action potentials occurred with an irregular frequency. Although spontaneous action potentials in LM were rarely correlated in time with those in CM, spontaneous inhibitory junction potentials (sIJPs) were found to occur synchronously in both muscles (5 out of 27 animals; 19 %). 3. Graded inflation of an intra-luminal balloon or mucosal stimulation oral to the recording electrodes elicited gradeable compound IJPs synchronously in both LM (mean amplitude: 6 +/- 1 mV) and CM (mean amplitude: 9 +/- 1 mV) (descending inhibitory reflex). Evoked IJPs were often followed by action potentials in both muscle layers. 4. Mucosal stimuli applied anal to the recording electrodes elicited compound excitatory junction potentials (EJPs) synchronously in both muscles layers that were often associated with the generation of action potentials. In the LM, evoked EJP amplitudes ranged from 3 mV (subthreshold) to 31 mV (including the action potential) and in the CM from 4 mV (subthreshold) to 44 mV (including the action potential). 5. Apamin (500 nM) reduced the evoked IJP in the CM by 55 % (from 11 +/- 2 to 5 +/- 1 mV), but caused no significant reduction in the LM layer (from 8 +/- 1 to 6 +/- 1 mV). Apamin-resistant IJPs in both muscle layers were likely to be due to nitric oxide, since they were abolished by L-NA (100 microM). 6. Atropine (1 microM) abolished the ascending excitatory reflex in both muscles. 7. Injection of neurobiotin into the LM and CM confirmed that simultaneous intracellular recordings were made from different muscle layers. 8. In conclusion, during the peristaltic reflex, the LM and CM layers receive synchronous inhibitory neuromuscular inputs during descending inhibition and synchronous excitatory neuromuscular inputs during ascending excitation. No evidence was found to support reciprocal innervation.

Electromyographic (EMG) activity of orbicularis oculi and levator palpebrae muscles was recorded to study the origin of involuntary eyelid closure in 33 patients. The evoked blink reflex in all patients and in 23 controls was also studied. To examine the excitability of facial motoneurons and bulbar interneurons in individual patients and to compare the results with EMG findings, R1 and R2 recovery indices were calculated in all subjects, as the average of recovery values at 0.5, 0.3, and 0.21 second interstimulus intervals. Based on EMG patterns, the patients were divided into three subclasses: EMG subclass 1, 10 patients with involuntary discharges solely in orbicularis oculi muscle; EMG subclass 2, 20 patients with involuntary discharges in orbicularis oculi and either involuntary levator palpebrae inhibition or a disturbed reciprocal innervation between orbicularis oculi and levator palpebrae; EMG subclass 3, three patients who did not have blepharospasm, but had involuntary levator palpebrae inhibition in association with a basal ganglia disease. The total patient group showed an enhanced recovery of both R1 and R2 components compared with controls. Although 30 out of 33 patients had blepharospasm (EMG subclasses 1 and 2), R1 recovery index was normal in 64% and R2 recovery index was normal in 54%. Patients with an abnormal R2 recovery index had an abnormal R1 recovery index significantly more often. All patients from EMG subclass 1 had an abnormal R2 recovery index, whereas all patients from EMG subclass 3 had normal recovery indices for both R1 and R2 responses. Seventy five per cent of the patients from EMG subclass 2 had normal recovery indices. The results provide further evidence that physiologically blepharospasm is not a homogeneous disease entity, and indicate that different pathophysiological mechanisms at the suprasegmental, or segmental level, or both are involved.

Differences in electromyographic (EMG) activity between brief isometric maximum voluntary contractions under conditions of (1) agonist contraction and (2) agonist-antagonist co-contractions were assessed for elbow flexors (biceps brachii) and elbow extensors (triceps, long head). Expressing maximum EMG co-contraction activity as a ratio of agonist maximum EMG activity of the same muscle yielded EMG ratios consistently below 1.0 ( mean= 0.48for flexion and0.76for extension ). Flexor EMG ratios did not co-vary with elbow position but extensor EMG ratios approached 1.0 or sometimes greater at shorter muscle lengths (elbow extension). Findings were in general accord with Sherrington's original proposal of ‘double reciprocal innervation’. Neural circuitry designed to limit full muscle activation during co-contractions may serve to protect the joint against excessive tangential or compressive forces.

Since Sherrington's convincing demonstration of the reciprocal innervation of opposing muscles, it has generally been thought that antagonist muscles are inactive during most voluntary movements. However, more recent evidence suggests that excitation of Renshaw cells may facilitate antagonist coactivation whereas excitation of Ia inhibitory neurons can induce reciprocal inhibition. A body of evidence has accumulated to indicate some of the circumstances which particularly favour the co-contraction of antagonist muscles. Isometric prehension, either in the precision grip or the power grip, can be shown to be one of the most important examples of antagonist coactivation. Studies of the discharge of single Purkinje cells of the intermediate cerebellar cortex in awake monkeys during performance of a maintained grip revealed that the majority of these neurons are deactivated during antagonist co-contraction. In contrast, other, unidentified neurons of the cerebellar cortex were as a group activated during grasping. It is suggested that the Purkinje cells act to inhibit antagonist muscles during reciprocal inhibition but are themselves inhibited during antagonist coactivation. These results support a suggestion made by Tilney and Pike in 1925 that the cerebellum plays an important role in switching between the coactivation and reciprocal inhibition of antagonist muscles.

A clear pattern of reciprocal innervation was found among the orbicularis oculi and the frontalis muscles in man during voluntary contractions. In contrast, facial afferent input was shown to be devoid of reciprocal action on these muscles. The results indicate a lack of γ control in facial muscles.

A case of unilateral retraction of the eyeball in downward gaze as well as downshoot with the retraction when an outward horizontal movement of the contralateral eye was attempted has been introduced. The case has an exotropia with inability to adduct involved eye. The face turned to the left to minimize diplopia in the primary position. During the retraction, the lid widened slightly. An analyses by electrooculography and electromyography suggested that there was an abnormal neural connection between the vertical recti of the involved eye and the contralateral lateral rectus muscle. Co-contraction of vertical recti and loss of the reciprocal innervation were seen at the involved eye. Surgical treatment for exotropia, and total transplantation of vertical recti to the insertion of the involved medial rectus resulted in a slight reduction of the exotropia with the face straight, but not in the retraction as well as adduction and elevation of the involved eye. Based on the results, a central mechanism to produce above abnormality was described.

In cats anesthetized with alpha-chloralose and urethane, the medulla oblongata was explored with electrical and/or chemical stimulation for vasopressor actions. Chemical stimulation included semimicroinjection of sodium glutamate or microinjection of dl-homocysteic acid (DLH). The dorsal (DM), particularly its dorsomedial (DMM) portion, and the ventrolateral (VLM) regions were found to be most sensitive to both electrical and chemical stimulation. In between these two regions there was an area in the ventral portion of the gigantocellular and the parvocellular reticular nuclei that was sensitive to electrical and somewhat sensitive also to chemical stimulation. The responses to chemical stimulation indicate the existence of perikarya in these three areas for vasopressor actions. The most active response of VLM followed microinjection of DLH into the region of nu. paragigantocellularis lateralis (PGL) and subretrofacial nu. These responses were about 30% greater than those from DM where the most active area was found in the DMM region including the nu. and tractus solitarius. When an extensive area of VLM was lesioned bilaterally with kainic acid (KA, 1 μg/100 nl), the resting systemic arterial blood pressure (SAP) fell 42% and the pressor response on DM stimulation fell by more than 80%. In contrast, after similar KA bilateral destruction of DM the resting SAP fell 38% and the pressor responses from VLM decreased 67%. When only a limited area in the PGL/subretrofacial nu. of the rostral VLM (3–4 pressor sites, 1 mm apart) on one side was lesioned, the resting SAP remained unaltered while the pressor response on the ipsilateral DMM decreased 76%. On the other hand, when a similar smaller KA lesion (3–4 sites) was made in the DMM, although the resting SAP did not change, the pressor response on stimulation of the ipsilateral rostral VLM decreased 28%. Further lesioning of the contralateral DMM then decreased the rostral VLM pressor response 62% without much alternation in the resting SAP. Results of the present experiments are in accordance with our previous results that neuronal perikarya for vasopressor action exist not only in VLM but also in DM (18,34) with the function of VLM slightly predominant over DM. It seems highly possible that reciprocal innervation exists between DM and VLM, at least between DMM and the PGL/subretrofacial nu. region.

A young female outpatient experienced painful tonic contractions in the right triceps surae muscles as a result of a partial damage of the right peroneal nerve. Electrophysiological recordings of the soleus muscle showed a tonic EMG activity and an hyperexcitability of the monosynaptic H reflex (Hmax/Mmax ratio: 90%). Application of transcutaneous electrical nerve stimulation (TENS, 1–2 min) on the peroneal nerve trunk at the head of the fibula resulted both in a pain relief and in the disappearance of the tonic activity in the muscles supplied by the antagonist nerve. Simultaneously, the Hmax/Mmax ratio decreased to normal values (49%). This was followed by an after-effect lasting more than 30 min. The potential role of an impairment of reciprocal inhibition in the originating mechanism of these troubles is discussed.

The flexors and extensors of the hind limb of the cat were simultaneously activated by stretch of a homolateral flexor muscle or by a nocuous stimulus to the homolateral paw under the conditions of the present experiments, in which the muscles under investigation were maximally retracted after detachment of the tendons from their insertions. The simultaneous activation of flexors and extensors was observed in acute and chronic spinal preparations, and sometimes in decerebrate animals. However, when in such preparations the extensor muscle was made to contract by loading its tendon, stretch of the antagonistic flexor muscles and pinching of the toes of the homolateral leg usually resulted in extensor inhibition and flexor excitation, in agreement with the classical tenet of reciprocal innervation. The reflex figure seems to be to an important extent the result of the inflow of afferent impulses.

Rapid eye movements were dynamically measured, recorded and analyzed following electrical stimulation of the cerebellum vermis subcortex and the third and sixth oculomotor nuclei in the midbrain in an alert spinal cat preparation. The stimulus consisted of suprathreshold and subthreshold 1.5 V, 0.03 mA pulse trains, whose physiological characteristics could be best defined in terms of their “envelopes.” The “warmup”, increased latency, higher and more variable threshold and other aspects of the response to cerebellar stimulation are in contrast to the more constant shorter latency, and lower threshold of the response to brain stem stimulation. Quantitative control-system analysis yielded gain and phase plots derived from Fourier transform of step input-output experiments. Transfer functions representing simple linear control models for cerebellum-to-eye movement and brain-stem-to-eye movement were obtained. These consisted of 1st-, 2nd- or 3rd-order lag elements with time constants ranging from 30 to 60 milliseconds and as well minimum-phase elements corresponding to latencies ranging from 10 to 30 milliseconds. Cerebellum-to-brain-stem transfer functions were obtained by deconvolution—actually division in the frequency domain (subtraction in the logarithmic Bode diagrams)—and quantitative comparison was made between cerebellar effects and brain-stem stimulation. Attempts were made to produce artificial reciprocal innervation in brain-stem stimulation experiments to compare with the natural reciprocal innervation (and conjugate eye movements) obtained with cerebellar stimulation. Of special interest were the experiments showing that cerebellar stimulation (at subthreshold values for direct production of eye movements) influenced responses to brain-stem stimulation. The increased gain and higher-frequency responses obtained provide direct evidence for the role of the cerebellum as an adaptive gain controller, and for its possible function as a “calibrator organ” for eye movements.

Introduction On the basis of analogy with other autonomically innervated muscles, the ciliary body should have a sympathetic as well as a parasympathetic nerve supply. Although there is wide acceptance of such a dual innervation, the distribution of the nerve elements in the ciliary muscle is controversial. Much clinical and experimental investigation has been performed in an attempt to resolve this controversy. Henke, 1 in 1860, postulated that the circular and longitudinal fibers of the ciliary muscle had opposing actions in accommodation, a hypothesis that Warlomont 2 agreed with on the basis of his anatomic studies on human and animal eyes. In 1891, Morat and Doyon, 3 working with animal eyes (dog, cat, and rabbit) suggested that the sympathetic system was related to distance accommodation by inhibiting the ciliary muscle, while the parasympathetic system was active in near accommodation. The concept of reciprocal innervation was again proposed by Henderson, 4

When one voluntarily flexes the arm at the elbow, two things occur : first, there is sent to the biceps muscle an excitatory impulse from the motor cortex; second, there is sent simultaneously to the triceps muscle an inhibitory impulse. This association of an excitatory stimulus to a muscle or group of muscles with a simultaneous inhibitory stimulus to the antagonistic muscle or group was first discovered by Sherrington in 1893. 1 He found that in the case of the flexors and extensors of the limbs excitation of one group was always accompanied by relaxation of the other, and the occurence of this phenomenon was sufficiently widespread to warrant the annunciation of a law, which he called the law of reciprocal innervation. This states that during active contraction of a muscle there occurs a simultaneous relaxation in its antagonist. "As contraction progresses in a muscle, for example an extensor, contractile

Posture, locomotion and evoked activity was investigated clinically and electromyographically in cats with intradurally (6 cats) or extradurally (7 cats) deafferented hind legs. Within 3–4 weeks after the deafferentation an overaction of extensor muscles developed characterized by an extension posture of the deafferented extremity when the cats were sitting, standing, walking or jumping. Reciprocal innervation was disturbed during stepping. Only intradurally operated cats showed rigidity as evidenced by increased resistance to passive flexion of the limb and persistent electrical activity in the extensor muscles when investigated in a standardized position (sling). The hind limb of extradurally operated cats hung loosely without resistance to passive flexion and without spontaneous electrical activity. Crossed extensor reflexes were elicited in intradurally deafferented cats only. Damage to the spinal cord by the intradural operation was evidenced by a disturbance in bladder function as well as by the anatomic findings on the operated side: tissue defects, signs of degeneration in the lateral funiculi and a decrease in interneurones. Similarly as in an asphyxiated cord (Gelfan and Tarlow 1959) the rigidity in intradurally operated cats might be due to hypersensitivity of partially denervated motoneurones. A slight reduction of synaptic connections to motoneurones is likely to occur in extradurally deafferented cords as well. This might explain that also in these cats the deafferented hind leg was often in the posture of extension.

The object of the present communication is to report to the Society further on the occurrence in so-called “voluntary” muscles of inhibition as well as of contraction , as result of excitation of the cortex cerebri . We have obtained by excitation of the cerebral cortex some remarkable instances of what one of us has described under the name of “ reciprocal inervation ,” that is, a species of co-ordinate innervation in which the relaxation of one set of a co-ordinated complexes of muscle-groups occurs as accompaniment of the active contraction of another set.

In a form er number of these ‘Proceedings’ attention was drawn to a particular form of correlation existing between the activity of antagonistic muscles. In it, one muscle of an antagonistic couple is, it was shown, relaxed in accompaniment with active contraction of its mechanical opponent. The instance then cited was afforded by certain of the extrinsic muscles of the eyeball, but I had previously noted indications of a like arrangement in studying the reflex actions affecting the muscles at the ankle-joint of the frog,4 and it seemed probable that the kind of co-operative co-ordination demonstrated for the ocular muscles might be of extended application and occurrent in various motile regions of the body.

As clues to the functional disintegration of the central nervous system in hemorrhagic shock, the ipsilateral quadriceps femoris stretch reflex and the crossed extension reflex were selected for study. Experimental models were 12 intact and 4 decerebrate dogs (by the Sherrington method) and 22 decerebrate cats (10 by the Sherrington method and 12 by the Pollock-Davis method). The stretch reflex was examined in all animals, and the crossed extension reflex was studied in 4 decerebrate dogs and 18 decerebrate cats (8 Sherrington and 10 Pollock-Davis) before, during, and after 2 hours of hemorrhagic hypotension at 30 mm. Hg. The stretch reflex persisted usually for many minutes at the blood pressure of 30 mm. Hg. It recovered after reinfusion of the shed blood unless the animal remained hypotensive. Transient augmentation of the crossed extension reflex occurred occasionally just before depression of this reflex. The crossed extension reflex was deprived of its prolonged tonic contraction by further bleeding. Thereafter, the decerebrate animal's crossed extension reflex was flaccid, resembling that of the spinal animal. Animals are not invariably obedient to Sherrington's principle of double reciprocal innervation in the state of acute hemorrhagic shock. In no case did the crossed extension reflex persist after the stretch reflex was abolished by hemorrhagic shock. After reinfusion of the shed blood, the crossed extension reflex recovered in only 3 (very imperfectly in 2 cats and nearly perfectly in 1 cat) out of 17 animals (2 dogs and 15 cats). It is concluded that the functional integrity of multisynaptic reflex (represented by the crossed extension reflex) is readily impaired by hemorrhagic shock and is hard to restore, while that of the monosynaptic reflex (represented by the stretch reflex) is rather insusceptible to hemorrhagic shock and is easy to restore.

Extracellular microelectrede studies were made on 47 units of the abducens nucleus in rabbits. In normal head position, the abducens units showed great differences in their discharged impulses only when the external rectus muscle was more strongly stimulated. Others showed a discharge of up to 60/sec, even when the eye was in normal position. Accordingly the muscles moving the eye were under continuous tonic innervation. Maximal frequencies observed were over 300/sec. There were further characteristic features in vestibular nystagmus: In contradistinction to the neurones of the reticular formation, the discharge frequency was regular. During the slow ipsilateral phase there was a crescendo-like increase in frequency. The ensuing, almost linear, contraction of the muscle was accompanied by a linear increase in discharge frequency of the motoneurone during isotonic contraction. Additionally, an afterrecruitment of new units could be observed in which the sequence of activated neurones was strictly maintained. During the slow contralateral phase of nystagmus, the neurones which did not discharge spontaneously remained silent; the others showed a decrescendo-like discharge pattern. In other words, there was not a complete relaxation of the muscle. During the rapid ipsilateral phase both types of neurones were activated, but, in contrast to the slow phase, the maximal frequency was found at the beginning. The corresponding movement of the bulb in the opposite direction, however, was linked with a cessation of neuronal discharges. The reciprocal innervation of eye muscles was apparent even at microphysiological level. The discharge frequency was also tested during deviations from the normal position, i. e. with the head turned to each side, forwards, and backwards. Increase and decrease in the discharge frequency occured during antagonistic movements. In abnormal positions the rotation activity also was tested. Under such conditions, the tonic and phasic predilection types observed here were not definitely fixed but could be changed from one frequence pattern to the other variations of its central or peripheral drives.

The following two reactions, observable in the extensor muscle of the knee, appear not without importance for the reflex co-ordination of antagonistic movements at that joint. They are reactions favourably studied in decerebrate rigidity. The cat is the animal in which, under that condition, my results have been chiefly obtained. The reactions can be observed as follows:—In the decerebrate animal a preparation of the extensor of the knee is so made that by detachment of other muscles, or severance of other nerves, the vasto-crureus muscle, with its nerve-branch from the anterior crural trunk, remains the sole nerve-muscle component intact in the whole limb. The vasto-crureus is one of those muscles which, after decerebration, exhibits the marked tonus characteristic of decerebrate rigidity. This tonus of the vasto-crureus then maintains the knee in an attitude of partial or complete extension. The flexor muscles of the knee, together with all the other muscles acting on that joint, have been paralysed by section of their nerves.

The reflex in the hind limbs of the spinal Xenopus, in response to a single break induction shock applied to the web of one foot, has been recorded by two string galvanometers recording simultaneously on one photographic plate. The reflex consists of homonymous flexion and heteronymous extension. The electrical responses consist of polyphasic or oscillatory variations, of which there are two types: I uncomplicated, due to a single activation of the muscle through its motor nerve; and II complicated, due to successive activations through the nerve and showing evidence of interference. Evidence is not found in this reflex of reciprocal innervation. Both extensor and flexor muscles yield electrical responses in both limbs. In the same-side limb reflex activity starts in the knee-flexor muscle —gracilis—but the extensor muscle—cruralis—becomes active less than a thousandth of a second later. The gastrocnemius follows the thigh muscles after an interval corresponding to the delay of a set of synapses in the spinal centre plus an interval due to its longer nerve path. In the limb opposite to the stimulated foot activity appears simultaneously in the extensor and flexor of the knee, and this follows the onset of activity in the same-side limb by an interval—the cross-over time—corresponding to the delay of a set of synapses. The outflow of excitation to the gastrocnemius acting heteronymously is simultaneous with that to the thigh muscles, so that the crossed gastrocnemius follows the crossed cruralis and gracilis by only a short interval due to its longer nerve path. The outflow of excitation to the tibialis anticus, homonymous, and heteronymous is simultaneous with that to the thigh muscles. The delay of a synapse-set at 14°C. is about 6 σ (thousandths of a second). It is suggested that this is not the delay at a single synapse. Analysis of the reflex delays of the thigh muscles shows that one synapse-set is involved in the intracentral conduction of the homonymous reflex, and two synapse-sets are involved in the heteronymous reflex. While it is the general rule that the effective excitation for the crossed reflex passes through the centre by a path containing two synapse-sets, the presence of a preliminary deflection indicates that a slight excitation is transmitted by a shorter path from one side to the other. Certain variations from the usual time relations are found to occur.

I. In previous notes on this subject the examples of reciprocal innervation taken from the limb muscles have usually been from muscles acting at the knee. An advantage offered there is that the vasti and crureus , extensors of the knee, act directly on that one joint alone. A muscle acting on two joints is often an extensor of one of the joints and a flexor of the others. When such a muscle is thrown into contraction by reflex action, there may be a dilemma as to whether it is as an extensor or as a flextor, that it is acting, and the answer will depend partly on the kind is gastrocnemius ; it extends the ankle and flexes the knee. It is, therefore, of interest to examine how this muscle behaves when its antagonist, tibialis anticus , a flexor of the ankle, is thrown into contraction by reflex action. Stimulation of any among various points of skin, or of the proximal end of various afferent nerves of the leg, excites reflex contraction of tibialis anticus. A nerve often used for the purpose in my observation has been the cutaneous branch of the peroneal nerve about a centimetre above the ankle (cat). In the reflex which then occurs in the limb, the following points can be made out. The ankle is flexed, and with the flexion of ankle occurs also flexion at knee and hip. If the anterior crural, obturator, hamstring, and popliteal nerve trunks, the insertions of iliopsoas, and psoas parvus, and the origin of pectineus muscles be severed, active flexion of knee and hip are excluded from the reflex. The active flexion at ankle still persists. On inspecting the tendons of the pretibial flexors of the ankle, that of tibialis anticus is seen to be drawn upward at each reflex, and with it also those of extensor longus digitorum and peroneus longus, but in my experience these latter are retracted less. If, in addition to the nerves and muscles mentioned above as severed, but the branch from the popliteal nerve to the gastrocnemius be spared, and that muscle be exposed to inspection, usually no change in that muscle appears.

1. Synaptic responses of alpha extensor motoneurones to stimulation of cutaneous nerves of the hind limb were recorded from the lumbosacral region in decerebrate and decerebrate-spinal unanaesthetized cats. Responses to ipsi- and contralateral stimulation are compared. 2. Usually a single volley in an ipsilateral cutaneous nerve led to an inhibitory post-synaptic potential while one in a contralateral cutaneous nerve led to an excitatory post-synaptic potential or to discharge of the cell, thus demonstrating the classical reciprocal innervation pattern. In some cells either ipsilateral or crossed spinal action was of opposite sign to normal. 3. Tests using graded stimulation showed the range of myelinated afferents associated with crossed spinal actions to be narrower than that for ipsilateral actions; for the sural nerve the ranges are 1-6 μ and 1-9 μ respectively. A substantial proportion of the coarser myelinated afferents do not make connexion with alpha motoneurones on either side of the cord; in the sural nerve this proportion includes the range 10-17 μ. 4. Central transmission times for ipsilateral and crossed-spinal actions were estimated after making systematic allowance for conduction time to the cord in the associated cutaneous afferents. Mean values for inhibitory pathways from ipsilateral cutaneous nerves were about 2 msec, while those for crossed spinal facilitatory pathways were notably greater, 3-5 msec. 5. Crossed spinal actions were more profoundly depressed by anaesthesia than were corresponding ipsilateral actions. 6. Interpretation of the results was aided by a separate study of the input to the spinal cord; stimulus strength is related to the diameters of the cutaneous fibres excited and to peripheral conduction time in those fibres.

Dystonic movements and postures were analysed with surface electromyography in idiopathic dystonia musculorum deformans. Involuntary muscular contraction occurring in the recumbent posture, on standing, and responses to passive stretch and isometric voluntary contraction were observed in neck, trunk and extremity muscles and the results are summarized as follows: 1. (1) Tonic non-reciprocal, involuntary activity appeared in agonists and antagonists. This dystonia was directly stimulated by postural effort, such as attempted sitting or standing, or by attempted voluntary movement. 2. (2) Regular or irregular grouping of action potentials appeared in the EMG in most cases in which synchronous activity among different muscles is characteristic. 3. (3) Simple voluntary contraction developed smoothly in spite of the dystonic disorder. Weakness and disorders of reciprocal innervation were observed in some muscles. 4. (4) Regular grouping of action potentials at around 10 c/sec appeared frequently on voluntary contraction. 5. (5) Passive stretch of dystonic muscles, at stages of the disease preceding absolute fixity of posture, seldom provoked or increased tonic contraction reflexly. The response to stretch was indirect, either as a paradoxical reaction of Westphal (contraction of antagonist muscles), or as a delayed enhancement of dystonia. The pattern of response to stretch was related to the duration of dystonia in the muscles concerned, being more labile when the development of dystonia had been recent. These findings are discussed in relation to athetosis, symptomatic dystonia and dystonia in flexion.

Discharges of single neurons in the nuclei of the cat's laryngeal nerves were recorded extracellularly with microelectrodes during electrical stimulation of the laryngeal nerves, which were severed close to the larynx. Stimulation of the superior laryngeal nerve evoked discharges of neurons During stimulation of the laryngeal branch of the recurrent nerve in the nucleus tractus solitarii responses with a mean latency of 12.72 msec were registrated. Single potentials evoked by recurrent nerve stimulation in both vagal nuclei could be completely inhibited by preceding stimuli of the superior laryngeal nerve but not vice versa. Inspiration-coupled “spontaneous” activity in the nucleus tractus solitarii was inhibited during and after stimulation (up to 200 msec) of the superior laryngeal nerve only. During this inhibition the inspiration's depth and frequency decreased. The results demonstrate some properties of the central connection of the vagal nuclei.

Under conditions of routine experiment stimulation of the central cut end of the intercostal nerve evoked reflex discharges simultaneously in several intercostal nerves of the same and contralateral side of the thorax. No reciprocity in these reflexes was noted. In the present experiments it was shown (that in unanesthetised spinal cats the reflex discharges in the intercostal nerves were facilitated by the mechanical stimulation of the ipsilateral parietal pleura and were inhibited by the same kind of stimulation of the contralateral pleura. Thus, the existence of the reciprocal segmental reflexes between the left and the right sides of the thorax was established for the first time.

Reciprocal innervation of antagonistic eye muscles has been more or less generally accepted since the time of the experiments of Sherrington.1 Recently, however, some controversy has arisen, due chiefly to the experiments of Tilney and Pike2 and of Lorente de No.3 These investigators have concluded that the law of reciprocal innervation is not valid in the case of antagonistic eye muscles. It therefore seemed to us desirable to further investigate this problem. The animals we used in our experiments were dogfish (Mustelus californicus and Triakis semifasciatis). In order to demonstrate the phenomenon of reciprocal innervation we have employed a slightly different method from any used heretofore. Instead of stimulating the cerebral hemisphere or rotating an animal around one of its principal body axes to evoke eye movements, we employed the method used by Maxwell.4 Briefly, this method consists in exposing a semicircular canal and subsequently applying a mechanical stimulus to its ampulla.Labyrinthine exci...

In a previous communication upon this subject, I gave the results obtained in an experimental examination of the antagonistic correlation which at least potentially exists in the muscular action of the opening of the palpebral aperture. The orbicularis palpebrarum and the levator palpebrœ superioris to a certain extent an antagonistic couple. During the course of last year I took opportunity to examine the co-ordination of the same antagonistic muscles in the movement, not of the opening of the palpebral fissure, but of its closure.

Reference is made to the life of Bielschowsky and his influence on the clinical assessment of strabismus. His approach to the study of ocular movement was founded on the work of Hering whom he referred to as “the master of physiology of space sense and movements of the eyes” and Sherrington who formulated the law of reciprocal innervation.

1. Field and intracellular potentials were recorded in the abducens and oculomotor nuclei of the frog following stimulation of the anterior branch of the ipsi- and contralateral vestibular nerves. 2. Intracellular recordings from ocular motoneurons demonstrated that in frogs, as in higher vertebrates, there exists a reciprocal labyrinthine innervation of ocular motoneurons. For example, abducens motoneurons received inhibition and excitation from the ipsi- and contralateral VIIIth nerves, respectively. 3. Vestibular impulses arrived in the motor nuclei ca. 1.7 msec after VIIIth nerve stimulation, and the earliest EPSPs and IPSPs were produced in motoneurons ca. 2.5 msec after stimulation. These data suggest a disynaptic linkage between the VIIIth nerve and the ocular motor nuclei. 4. Removal of the cerebellum had no influence on the vestibular-evoked PSPs recorded in motoneurons. This finding suggested that the PSPs were produced through pathways running via the vestibular nuclei and the MLF to motoneurons.

We report high resolution oculographic recordings on a patient with convergent-retraction nystagmus (Parinaud's Sign). Recordings show opposed adducting saccades which are slightly asynchronous (8 ms), in contrast to the conjugate horizontal saccades which are exactly synchronous (0.3 ms). Normal saccadic velocity of these opposed adductions necessarily implies reciprocal innervation of horizontal and vertical agonist-antagonist pairs. Lateral view cine films show absence of retraction, apparently as a consequence of normal orbital mechanics. We suggest that normal mechanisms for dynamic overshoot saccades are involved in the production of these abnormal opposed adducting saccades.

1. The electrical activity of single trochlear motoneurons (TMns) and axons of second order vestibular neurons presumably terminating on these motoneurons were studied during natural stimulation of semicircular canals and otolith organs in cats anesthetized with Ketamine. 2. Null point analysis showed that TMns received an excitatory canal input from the contralateral posterior canal, and labyrinthine lesion experiments suggested that the functionally synergistic, ipsilateral anterior canal provides an inhibitory input. A small number of motoneurons showed orthogonal canal convergence. 3. In addition to the canal projections most TMns received an otolithic input. Firing rate was proportional to lateral head tilt and was of the β type. Most units also responded to pitch with an increase and decrease in firing rate on nose-up and nose-down positioning, respectively. Lesion experiments indicated that the otolith responses are the results of reciprocal innervation of TMns by contralateral (excitatory) and ipsilateral (inhibitory) otolith projections. 4. During sinusoidal rotation in yaw (canal only stimulation) the mean phase lag re acceleration of the response of TMns increased from 60 ° at 0.025 Hz to 126 ° at 1.0 Hz. In roll (canal plus otolith stimulation) the phase lag of TMn responses measured 180 ° and 130 ° at 0.025 and 1.0 Hz, respectively. Phase-lags measured in Vi and Vc axons were less by ca. 15 °. 5. The otolith contribution to TMn responses in roll was calculated by vectorial subtraction of the yaw from the roll responses: A phase lag of 10 (0.025 Hz) to 90 ° (0.5 Hz) re. displacement was noted and gain was constant over the same range. Similar lag dynamics were revealed in TMns when studied during ramp displacement of the head. 6. The possible functional role of central canal-otolith convergence and the differences between the responses of primary vestibular afferents and secondary vestibular neurons and TMns will be discussed.

To evaluate the pathologic state accurately and objectively, fifteen patients with spastic diplegia were examined with surface electromyography (EMG) of the rectus femoris, medial hamstring, anterior tibial and gastrocnemius muscles. Seven showed disturbed reciprocal innervation (disturbed group) and 8 showed reciprocal innervation (non disturbed group). The disturbance of reciprocal innervation on EMG showed a positive correlation with delay in onset of crawling by 10 months (p less than 0.05), a low level of motor development (p less than 0.005) and more abnormal CT findings. Four patients in the disturbed group showed various abnormalities in X-rays of the hips. Surface EMG findings of crawling muscle may be useful for understanding the pathologic state of crawling in spastic diplegia.

The electrical activity and the circumstances of contraction of the internal and external intercostal muscles were studied during quiet breathing in non-anesthetized rabbits resting in the sternal semirecumbent position. The activity was recorded via clip electrodes implanted in both muscles in a series of interspaces. The greater part of the expiratory phase was characterized by slight activity in both the internal and external intercostals, preceded and followed by brief periods of inactivity. Inspiration was accompanied by continuous activity in both sets of muscles until the last 20–40 ms of that phase. It was found that both internal and external intercostals were active during inspiration, that their activity was at its greatest during this phase, and that this activity was characterized by a progressive increase in external intercostal activity. There was no evidence of reciprocal innervation of intercostal muscles in this study.

Introduction The reciprocal innervation of the smooth vesical detrusor and striated muscles of the pelvic floor has been well documented by cystometry, electromyography, a combination of the two, and various anesthetic procedures. Thus a good working hypothesis has been provided for physiological and pathological micturition.1-5According to common neurological nomenclature, therefore, only proprioceptive reflex activity has been studied. In contrast, the reflex activity which correlates stimuli of the bladder mucosa and responses of the detrusor and pelvic floor musculature has not been explored. Three factors motivated the present study. 1. A continuing interest in the bulbocavernosus reflex,6which is diagnostically important in differentiating somatomotor lesions above and below the conus; this reflex becomes significant in the proper classification and treatment of patients with traumatic cord bladder because the conus contains the spinal visceromotor reflex centers of the bladder. Experience with sacral neurotomy on patients with spinal cord injury

In cats whose spinal cords had been asphyxiated for various periods of time, van Harreveld and Marmont1 found that after recovery the hind legs could show an exaggerated extensor tone which usually stayed until death (in some experiments 3 weeks in total). Considering that after this time the acute effect of asphyxia will have disappeared, it was concluded that the high extensor tone is caused by a more or less selective damage of an inhibiting system present in the cord which normally keeps the tone in check.A further study of these phenomena was made. A period of asphyxia for 30 minutes was usually followed within a few hours by the development of high extensor tone without abolishment of the flexor reflex. However, the effect of pinching the foot was not the same in all animals; sometimes it caused a regular flexor reflex with flexion in ankle and knee; in other experiments it caused, after the flexion, an extension of the leg, and in a few cases this stimulus caused instead of flexion an increase of t...