Volley Of Impulses Research Articles

Electromyographic evidence for a digastric reflex evoked by perioral stimuli in humans

summary Electromyographic recordings (EMGs) were made using skin surface electrodes placed over the anterior digastric muscle in seven subjects. In every case, short bursts of electrical stimuli to the upper lip produced a response in the EMG that had a minimum latency of 62.0 ± 10.8 ms (mean ± SD). By contrast, no responses were seen when single pulse stimuli were applied. In 6/7 subjects, the minimum stimulation intensity that produced the reflex was described as being sharp or painful. In three additional experiments, single motor units were recorded within the digastric muscle using needle electrodes. In two of these experiments, there was evidence of reflex activity 60–110 ms after the application of painful electrical stimuli to the lip. These findings confirm that perioral stimuli can evoke a digastric reflex in humans and suggest that this reflex requires the summation that results from successive volleys of impulses in a large number of nociceptive afferent neurones.

Electromyographic evidence for a digastric reflex evoked by perioral stimuli in humans.

Electromyographic recordings (EMGs) were made using skin surface electrodes placed over the anterior digastric muscle in seven subjects. In every case, short bursts of electrical stimuli to the upper lip produced a response in the EMG that had a minimum latency of 62.0 +/- 10.8 ms (mean +/- SD). By contrast, no responses were seen when single pulse stimuli were applied. In 6/7 subjects, the minimum stimulation intensity that produced the reflex was described as being sharp or painful. In three additional experiments, single motor units were recorded within the digastric muscle using needle electrodes. In two of these experiments, there was evidence of reflex activity 60-110 ms after the application of painful electrical stimuli to the lip. These findings confirm that perioral stimuli can evoke a digastric reflex in humans and suggest that this reflex requires the summation that results from successive volleys of impulses in a large number of nociceptive afferent neurones.

A Preferential Inhibition of Impulses in C-fibers of the Rabbit Vagus Nerve by Veratridine, an Activator of Sodium Channels

In seeking a means to reverse local anesthetic block of peripheral nerve, we examined the actions of veratridine (VTD), an agent known to antagonize competitively the binding of local anesthetics to Na channels. The actions of VTD, a steroidal alkaloid "activator" of voltage-gated Na channels, were studied in the rabbit vagus nerve by two methods. In one, the effects of VTD on compound action potentials (APc) propagating through a "veratrinized" segment (11-mm) of nerve were measured by extracellular recording. Single volleys of impulses were unaffected by VTD, but trains of impulses, triggered by repetitive stimulation, were selectively diminished. This "use-dependent" reduction was greatest for the C-fiber component of the APc, less for B-fibers, and inconsequential for A-fibers. Use-dependent inhibition was enhanced by higher stimulation frequency and by increased VTD concentration, and reversed rapidly when stimulation ceased. If the nerve sheath remained intact, the rate of VTD action was far less than in desheathed nerves, but the effects were the same. In the other experimental system, membrane potentials were measured in the veratrinized region of the nerve by a sucrose-gap method. Repetitive stimulation, particularly of C-fibers, produced a cumulative VTD-induced depolarization (VID) that was sustained over several seconds and during which the C-fiber APc was selectively reduced. We propose that this local, use-dependent VID provides the means to inhibit impulses propagating through the veratrinized region. The preferential effect of VTD on C-fibers suggests its possibilities as a relatively selective agent for block of impulse trains in nociceptive afferents.

Interaction among different sensory units within a single fungiform papilla in the frog tongue.

The possible interaction among different sensory units in the frog tongue was studied using several single papillae dually innervated by the medial and lateral branches of the glossopharyngeal (IXth) nerve. The afferent activity in one branch exposed to NaCl stimulation of the papilla revealed marked inhibition after antidromic electrical stimulation (100 Hz, 30 s, and 3 V) of the other branch. The degree of inhibition depended on the number of sensory responses observed in the electrically stimulated branch as well as the nature of the stimulated sensory units. Statistical analysis suggested that antidromic activation of gustatory units conducting the responses to NaCl and quinine and slowly adapting mechanosensitive units produced a large antidromic inhibition amounting to 19-25%, but that of gustatory units conducting the responses to acetic acid and rapidly adapting mechanosensitive units gave rise to only a slight inhibition. To examine the differential effects of these sensory units in antidromic inhibition, antidromic impulses were evoked by chemical stimulation of the adjacent papilla neuronally connected with the dually innervated papilla under study. Antidromic volleys of impulses elicited by NaCl or quinine stimulation produced a large inhibition of the afferent activity in the other branch, as induced by NaCl stimulation of the dually innervated papilla. Plausible mechanisms of synaptic interaction in peripheral gustatory systems are considered.

Lumbosacral evoked potentials (LSEPs) and cortical somatosensory evoked potentials (SEPs) in patients with lesions of the conus medullaris and cauda equina

Evoked potentials from unilateral stimulation of the posterior tibial nerve at the knee were recorded over the spinous processes S1, L4, L2, T12 and from the ‘lower extremity’ portion of the sensory cortex (Cz) in 29 patients who exhibited clinical and electromyographic signs of conus medullaris or cauda equina lesions. Simultaneous recording of the lumbosacral evoked potentials (LSEPs) and cortical somatosensory evoked potentials (SEPs) permitted evaluation of the relative effectiveness of the peripheral stimulus in eliciting responses in the lumbosacral segments of the spinal cord and in the cortex of the brain. In patients with cauda equina lesion, each major component of LSEP can be absent or the peak can have a reduced amplitude and a prolonged latency. The degree of impairment of the LSEP runs in parallel to the degree of severeness of the cauda equina lesion. The recording of LSEP responses with surface electrodes represents a reliable test for the detection of mild cauda equina abnormalities, but the surface recording technique is not sensitive enough to differentiate between severe incomplete and severe complete cauda equina lesions. On the other hand, concurrent recording of responses evoked at lumbosacral and cortical levels by the same stimuli did detect instances in which the first-order afferents were capable of delivering an adequate volley of impulses to evoke a sizeable cortical response without evidence of an associated postsynaptic response in the spinal cord. Such findings are good evidence of a problem localized in the gray matter of the spinal cord. Patients with traumatic spinal cord injury localized at cervical or thoracic vertebral levels may also have an unrecognized lesion of the cauda equina which can cause symptoms that are viewed as ‘unusual’ until the association with a cauda equina lesion is recognized.

Functional properties of the cerebellorubral synapses in the cat

Facilitation of cerebellorubral transmission was illustrated in nembutalized cats on paired stimulation of the cerebellar nucleus interpositus by an example of monosynaptic EPSPs of the rubrospinal neurons. It was found that the facilitation stated is not determined by the change in the presynaptic volley of impulses. There is reason to believe that the facilitation is determined by specific features of functioning of the cerebellar synapses on the red nucleus neurons.

Selective depressant action of antidromic impulses on gustatory nerve signals.

The depressant action of antidromic volleys of impulses on gustatory nerve signals from the tongues of bullfrogs was studied. Electrical stimulation of the glossopharyngeal nerve at a rate of 100 Hz for 10 s and at supramaximal intensity slightly depressed the integrated glossopharyngeal nerve responses to quinine and to mechanical taps to the tongue. The same antidromic stimuli resulted in a 30-40% reduction in the responses to salt, acid, water, and warmed saline, but depressed greater than 80% of the afferent impulses firing spontaneously. The magnitude of responses to quinine and NaCl and the number of spontaneous discharges decreased gradually with an increase in either the frequency or the duration of antidromic stimuli. Similar results were obtained with intensities above the threshold for exciting gustatory and slowly adapting mechanosensitive fibers. The time required to recover from termination of the antidromic stimuli to two-thirds of the maximal amount of depression ranged between 6 and 7 min, with no significant differences among the depressions. The possible mechanisms involved in the antidromic depression of gustatory nerve signals are discussed.

Mechanical changes in the amphibian spinal cord produced by afferent volleys of nerve impulses

A volley of impulses entering the toad spinal cord via large myelinated fibers in the lumbar dorsal roots was shown to evoke a contraction of the cord, which lasted for about 100 ms or more. A volley entering the cord antidromically via the ventral roots produced only a small, brief contraction. When two electric shocks were delivered to the same dorsal roots at a short interval, the contraction associated with the second shock was small; a period of about 1 s was required for a full recovery. When two shocks were applied separately to two neighboring dorsal roots, the contraction associated with the second shock was partially or totally occluded. Electric polarization of the dorsal root fibers produced mechanical changes in the cord. The effects of magnesium salt, GABA, glutamate and several other neuropharmacological agents on the contractile process were investigated. The experimental findings suggest that the contractile process is related to the phenomenon of primary afferent depolarization.

Swelling of frog dorsal root ganglion and spinal cord produced by afferent volley of impulses

Electrical stimulation of the frog sciatic nerve was found to produce rapid, transient swelling of the 8th and 9th dorsal root ganglia followed by prolonged swelling of the spinal cord. Swelling of the ganglion is analogous to the rapid mechanical change observed in invertebrate axons during excitation. The mechanical change observed in the spinal cord is probably related to prolonged depolarization of the primary afferent fibers near their terminals.

Lateral inhibition shapes the oscillatory responses of the horseshoe crab's compound eye

The synchronized response of the compound eye of the horseshoe crab to uniform illumination arises from the integration of excitation with the strong lateral inhibition present in many specimens. At the higher levels of excitation, the steady production of nerve impulses by individual eccentric cells is often replaced by periodically recurring volleys of impulses. This behavior is shown here to be the result of the temporal behavior of the post-synaptic potentials responsible for lateral inhibition. For a broad class of inhibitory potentials, a simple condition is established which separates potentials which permit volleys at high excitation levels from those which support only the steady production of impulses throughout the physiological range of excitations.

Role of the giant cerebral ganglion neuron in control of defensive behavior ofHelix lucorum

Neurons participating in contraction of the ommatophore retractor ofHelix lucorum were studied by morphological and electrophysiological methods. Staining by the cobalt filling method revealed a giant cerebral ganglion neuron which sends a fiber into the motor branch of the ipsilateral optic nerve. Both spontaneous and evoked contraction of the retractor was shown to be preceded by a volley of action potentials in the giant neuron. The high-frequency volley of impulses evoked by intracellular stimulation of this neuron leads to contraction of the ipsilateral ommatophore retractor; the intensity of this contraction depends on the discharge frequency. The composition of the sensory inputs of the neuron is discussed. A conclusion is drawn on the motor function of this cerebral ganglion neuron in the escape reflex ofH. lucorum.

Changes in primary afferent depolarization of sensory neurones during peripheral nerve regeneration in the cat.

1. Micro-electrode recordings were made from normal and regenerating sural nerve fibres in cats. Increases in the excitability of the central terminals of these fibres after conditioning stimulation of other sural nerve fibres were taken as evidence for primary afferent depolarization. 2. At all recovery times studied the excitability changes seen were significantly less than those seen in control animals. Two factors contributed to the changes in primary afferent depolarization. First, the proportion of fibres that showed no evidence of primary afferent depolarization increased significantly. This proportion became smaller as recovery progressed. Secondly, where primary afferent depolarization was present, the magnitudes of the effects were slightly but significantly decreased compared with control values. 3. Excitability changes of the central terminals of sural nerve fibres were also measured after conditioning stimulation of the ipsilateral, unlesioned accessory sural nerve. One month after sural nerve transection there was a significant increase in the proportion of fibres showing no evidence of excitability changes following accessory sural nerve conditioning stimulation compared with control animals. Thus, the loss of primary afferent depolarization of regenerating sural nerve fibres was neither simply a consequence of desynchronization of the volley of impulses entering the spinal cord after conditioning stimulation of other regenerating sural fibres, nor due to fewer fibres being activated during conditioning stimulation of the lesioned nerves. 4. A possible explanation of these results is that after peripheral nerve crush or transection the central terminals of the damaged fibres retract or atrophy. Then as regeneration of the nerve proceeds, the central terminals of the fibres re-form.

An hypothesis on information, memory and perception

It is generally held that a sensory receptor serves, in some way to “map” an external event (such as a light or sound signal) onto some internal or neural event (such as a volley of impulses moving along an axon toward the brain). Or schematically external event→neural event It is postulated in this paper that it is not the external event, but rather uncertainty about the nature of the external event, which produces the neural activity. In place of the traditional map it is hypothesized that we should substitute rate of change of uncertainty about an external event→neural event It follows from this revised mapping process that one perceives only those external events about which he was initially uncertain. One cannot perceive something about which he is perfectly certain. It is seen that various observed sensory phenomena, such as the process of adaptation and the fading of a fixed retinal image, issue directly from this new hypothesis.

Correlation analysis of delta activity generated in cerebral hypoxia

1. 1. Differences in spatial and temporal characteristics between polymorphous delta activity (PDA) and “standard slow complexes” (SSCs) resulting from grave cerebral hypoxia have been demonstrated by means of digital correlation analysis and on line recording of correlograms. 2. 2. PDA observed in the human EEG and the ECoG of dogs is characterized by the absence of periodic organization (high extinction indices of auto- and crosscorrelation functions) and absence of spatial synchronization when recorded from widely separated areas of the hemispheres (low correlation coefficients, significant and variable time shifts), with bilateral symmetry of slow waves being preserved. 3. 3. Delta waves recorded from nucleus amygdalae, nucleus caudatus, thalamus, hypothalamus and midbrain in the dog differ from cortical PDA by a more synchronous and rhythmically arranged process. 4. 4. During the establishment of SSC activity correlograms show a synchronous process common to all cortical and subcortical areas characterized by very high values of correlation coefficients. 5. 5. It is suggested that the unorganized slow wave PDA process could arise under conditions of hypoxic dysfunction of distant cortico-cortical relationships, accompanied by weak subcortical pacemaker influences. The process reflects local coexcitation of relatively limited cortical areas. The particular statistical characteristics of SSCs generated during further increase in oxygen deficit can be accounted for by simultaneous generation of responses in some subcortical areas to single volleys of impulses from a hypothetical pacemaker, accompanied by a passive wave propagation towards a cortex completely depressed by hypoxia.

Central Mechanisms of Swallowing

Department of Physiology, Fujita-Gakuen University School of Medicine, Toyoake, 470-11Neural organization leading to elicitation and achievement of swallowing is of reflex in its fundamental character. Afferent impulses from the oral, pharyngeal and laryngeal mucosa readily trigger the center of the reflex, the medullary swallowing center, into action. The center is endowed with characteristic property of intergration that controls rigidly the order, duration, intensity and type of behaviour of the participating motoneurons, and hence of the muscles of swallowing. Furthermore, the activity level of the center for repetitive excitation is subserved by an intricate coordination between neurons situated in the anterolateral areas of the frontal cerebral cortex and those in the pontine reticular formations delimitted dorsolaterally to the superior olivary nucleus in both sides.The integrating property of the medullary swallowing center, however, seems immature at the stage of birth, and likely to develop through the period of 2 to 3 months postnatally. During this period of immaturity, the achievement of swallowing would depend variously upon the afferent impulses that are initiated secondarily by the act of swallowing.When swallowing occurs, the neurons of respiratory organization behave consistently as if they were the neurons that participate to swallowing, by revealing momentary activation or arrest in the discharge of impulses. Conversely, when asphyxia occurs, the medullary motoneurons that participate to swallowing become active to discharge volleys of impulses in phase with inspiration or expiration. Reflex swallowing is more readily produced during inspiration than during expiration. Rhythmic activities of motoneurons of mastication are also modified by swallowing. These swallow-combined modifications of respiration and mastication are well preserved after motoparalysis, and hence would suggest mutual and inter-central relations between neural organizations of swallowing and the two others.Based on these facts, some comments have been made on the possible mechanism of dysfunction of swallowing and on future problems involed.

Transfer of the hippocampal output by the anterior thalamic nuclei

This study was performed in the cat with the aim of clarifying the transfer properties of the thalamic nuclei anterior ventralis and anterior medialis with respect to volleys of impulses elicited by delivering trains of electrical stimuli of different frequency and intensity to the contralateral hippocampus. The results show that the responses of the nucleus anterior ventralis are only intensity-dependent whereas those of the nucleus anterior medialis depend on both stimulus intensity and frequency. The nucleus anterior ventralis performs an operation of input-output transfer within one of the loops of the Papez circuit. The nucleus anterior medialis is under the influence of both the hippocampus and a thalamoneocortical feedback activated by the output of the nucleus itself. This nucleus, therefore, operates as a gate controlling the integration of archicortical and neocortical activities.

On the functional significance of the circuit of papez

Summary This study was performed with the aim of clarifying the functional properties of the circuit of Papez as a feedback loop regulating hippocampal activity. The circulation in the loop of volleys of impulses elicited by delivering to the hippocampus trains of low-frequency electrical stimuli was studied in the cat by recording unit activity at mammillary, thalamic, cingulate and hippocampal levels. The results show the properties of two feedback loops, one related to the nucleus anterior ventralis and the other to the nucleus anterior medialis. The output of the nucleus anterior ventralis is dependent on the hippocampal output, whereas the output of the nucleus anterior medialis is affected by both hippocampal and extralimbic thalamo-neocortical influences. The intermodulation of septal and feedback volleys at the level of the hippocampal region appears, in physiological conditions, to underlie the regulation of hippocampal bioelectrical activity in general and of theta rhythm in particular. A revelant effect of the output of the anterior thalamic nuclei consists in the depression of unit activity of the gyrus cinguli and area retrosplenialis.

The distribution of cutaneous receptors in the rabbit's hind limb and differential electrical stimulation of their axons.

1. The receptive field properties and conduction velocities of single dorsal root axons, activated from the sural and cutaneous branches of the posterior tibial (medial plantar) nerves, were examined in anaesthetized rabbits.2. The sural nerve sample included all types of units previously recorded from the saphenous nerve (Brown & Iggo, 1967). In particular it was shown that electrical stimulation of the sural nerve at strengths up to 1.3T produced a volley of impulses in a pure population of slowly adapting units (Type I units).3. The medial plantar sample showed an absence of Type I slowly adapting units and Type T hair follicle units. Corresponding to this there were no touch corpuscles or tylotrich hairs in the skin of the hind foot and the fastest medial plantar axons conducted at 60-70 m/sec as opposed to 80-85 m/sec for the sural nerve. Stimulation of the medial plantar nerve at stimulus strengths close to threshold produced a volley of impulses in a nearly pure population of Type G hair follicle units.

Potentials of spinal motoneurons in cats with experimental tetanus

Potentials of motoneurons of the lower segments of the spinal cord were recorded with the aid of intracellular microelectrodes in experiments on cats with induced tetanus produced by injection of tetanus toxin (1500–2000 mouse LD50) into the extensor muscles of the left shin. Neither afferent volleys of impulses in cutaneous and muscle nerves, nor antidromic volleys in the corresponding ventral roots, produced IPSPs in motoneurons of the extremity into which toxin was injected. The form both of antidromic peak potentials and of monosynaptic EPSPs in motoneurons in which IPSPs were blocked by tetanus toxin did not differ from the form of corresponding potentials of motoneurons in normal cats. The values of threshold depolarization for peak discharges during synaptic and direct stimulation were equal in tetanus and control motoneurons. Resistance and time constant values of the membrane in "tetanus" motoneurons did not differ from the corresponding values for "control" motoneurons.

Inhibitory interaction between motoneurons of adjacent segments in the frog spinal cord

Inhibition of motoneurons through impulses in recurrent axon collaterals of neighboring motoneurons in the spinal cord of Xenopus laevis was investigated. The method of monosynaptic testing was employed. A slow dorsal root potential (A-DRP) was elicited by the same antidromic volley of impulses that caused recurrent inhibition of monosynaptic reflex responses. The presence of depolarization of dorsal root fibers indicates the operation of a presynaptic inhibitory mechanism. The time course of the inhibitory effect produced by a recurrent volley on the excitability of neighboring motoneurons closely resembled the time course of the A-DRP elicited by the same recurrent volley. The inhibitory effect of an antidromic stimulus depended on the pathway through which the motoneurons under investigation were excited. If recurrent inhibition was postsynaptic, the inhibitory effect would have been independent of the testing pathway. The results presented indicate that recurrent inhibition in the frog is a presynaptic process. The mechanism by means of which recurrent inhibition is effected in the frog, therefore differs from the postsynaptic Renshaw mechanism involved in recurrent inhibition of spinal motoneurons in mammals.