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At least 91 records · Page 5Linked to original sources
PubMed1988

Conduction of neural impulses in human mechanoreceptive cutaneous afferents.

1. It was the aim of the present study to isolate and identify the components underlying the human sensory compound action potential and to study their axonal conduction velocities and refractory periods. For this purpose the technique of percutaneous microneurography was combined with intradermal electrical stimulation of nerve fibre terminals. Sixty-four median and ulnar nerve afferents innervating the glabrous skin of the digits were isolated and type identified. 2. The range of axonal conduction velocities was wide (20-60 m/s), but similar for each afferent category (20-60 m/s). Most afferents conducted slower than expected from the intrafascicularly recorded compound potential (50-60 m/s) and their conduction velocities generally decreased from the base to the tip of the digits. 3. The duration of the absolute axonal refractory periods of all types of afferents ranged from 0.7 to 3.5 ms. The duration of the total refractory periods ranged from 3 to 9 ms. Both absolute and total axonal refractory periods were inversely correlated (r = -0.70 and r = -0.67) with their axonal conduction velocities. 4. The size of individual action potentials was significantly correlated with axonal conduction velocities, although the correlation coefficient was relatively low (r = 0.43), even after correction for variability due to electrode resistance (partial correlation r = 0.44). 5. The results showed that different types of cutaneous afferents cannot be separated on the basis of their axonal conduction properties. The data demonstrate features of neural impulse conduction along the entire axonal tree and which are inaccessible to routine electrodiagnostic procedures. The present approach provides a sensitive means for assessing, in health and disease, nerve conduction in terminal axons.

Action Potentials↗
PubMed1984

A "convertible pore" model of neural membrane conductance.

Instead of the single-channel pore proposed earlier [Wooldridge, D. E. (1984) Proc. Natl. Acad. Sci. USA 81, 5609-5612] for the transit of conductance ions through the neural membrane, a pore with a second channel for "influence ions" of calcium or magnesium is considered in this paper. By entering trapping centers at the closed inner ends of the new channels, the influence ions are postulated to alter the rates of chemical reactions that change the configurational state of the gates guarding the inner ends of the nearby conductance channels. This makes the permeability of the conductance channels strongly dependent on voltage. Using a four-state reaction scheme for both the sodium and potassium pore systems, a computer model of the membrane conductance is constructed. When suitable values are assigned to its parameters, the model closely reproduces the results of the Hodgkin-Huxley voltage-clamp and action potential experiments.

Action Potentials↗
PubMedDate not supplied

Intraoperative measurements of auditory-evoked potentials in three patients with acoustic neuroma.

Auditory brainstem responses (ABRs), electrocochleograms and the evoked potentials from the internal auditory canal were recorded simultaneously in 3 acoustic neuroma (AN) patients. The neural conduction in the internal auditory canal was examined by recording the compound action potentials of the cochlear nerve. In an AN patient with wave I only in the ABR, the neural conduction of the excitement in the cochlear nerve was blocked within the internal auditory canal. In 2 AN patients with elongated interpeak latency differences between waves I and V in ABRs, the neural conduction velocity of the cochlear nerve was lower than that of normal subjects. These results provide neurophysiological evidence that low neural conduction velocity in the cochlear nerve results in the abnormal ABR.

Adult↗
PubMed2000

Vibration-induced multifocal neuropathy in forestry workers: electrophysiological findings in relation to vibration exposure and finger circulation.

OBJECTIVES: To investigate neural conduction in the upper limbs of symptomatic forestry workers with and without exposure to hand-transmitted vibration. A further aim was to assess the possible relationships between vibration exposure, nerve conduction and finger circulation in the forestry workers who used chain saws. METHODS: A detailed neurophysiological investigation was performed on the upper extremities of 20 chain saw workers, 20 forestry operators with heavy manual work but without vibration exposure, and 20 healthy male controls. All subjects were screened to exclude polyneuropathy. Measurements of sensory and motor nerve conduction (velocity and amplitude) were obtained bilaterally from the median, ulnar and radial nerves. To assess peripheral vascular function, the forestry workers underwent a cold test with plethysmographic measurement of finger systolic blood pressure (FSBP). In the chain saw operators, vibration exposure was evaluated according to the International Standard ISO 5349. Indices of daily vibration exposure and lifetime cumulative vibration dose were estimated for each chain saw operator. RESULTS: Sensory nerve conduction in several segments of the median and radial nerves was significantly reduced in the chain saw operators compared with that in the workers doing heavy manual work and the controls. The neurophysiological pattern more frequently observed in the chain saw operators was a multifocal nerve conduction impairment to several neural segments with predominant involvement of sensory rather than motor fibres. Sensory nerve conduction velocities in the hands of the chain saw operators were inversely related to both daily and lifetime cumulative vibration exposures. In the vibration-exposed forestry workers, neither were sensori-motor complaints associated with vascular symptoms (finger whiteness) nor were electrophysiological data related to cold-induced changes in FSBP. CONCLUSIONS: Exposure to hand-transmitted vibration, in addition to ergonomic stress factors, can contribute to peripheral nerve disorders occurring in forestry workers who operate chain saws. The findings of this study suggest the existence of an exposure-effect relationship for vibration-induced neuropathy. Different underlying mechanisms are likely to be involved in the pathogenesis of the neurological and vascular components of the hand-arm vibration syndrome.

Adult↗
PubMed1986

Compression of rat spinal cord in vitro: effects of ethanol on recovery of axonal conduction.

The effect of ethanol on recovery of neural conduction after spinal cord compression was evaluated in an isolated rat spinal cord preparation. Controlled compression of 50 to 75 percent of the cord cross-section was delivered using a piezoelectric translator. Postcompression compound action potential (CAP) amplitude, latency, and refractory periods were measured relative to pre-compression values. Recovery of CAP's was compared for spinal cords exposed to ethanol in vitro (100 mg/dl bath concentration, started one hour prior to compression) versus those maintained in normal artificial CSF. The in vitro effects of ethanol were evaluated on spinal cords from rats maintained on a normal diet and from those repeatedly intoxicated with ethanol for 15 days prior to the acute experiment. Compression of the cord resulted in an immediate 68% decrease in CAP peak amplitude and an increase in latency (171%) and refractory period (256%). In normal bathing medium, CAP amplitude recovered to 83% of pre-compression values 180 minutes after compression. The addition of ethanol to the artificial CSF did not directly affect CAP parameters, but combined with compression, CAP amplitude recovered to only 42% of pre-compression values 180 minutes after impact (p less than .01). Recovery was less affected by acute ethanol exposure in cords from ethanol pretreated animals. CAP amplitude recovered to 83% of pre-compression levels and was not different from compression-only recovery (p less than 0.10). The data suggest that direct effects of ethanol on axonal membranes may affect the sensitivity of axons to mechanical trauma or their capacity to recover normal function. Since spinal cords from repeatedly exposed animals are less sensitive to the acute effects of ethanol, ethanol may be acting to "fluidize" the axonal membrane.

Alcoholic Intoxication↗
PubMed1989

Brainstem auditory evoked responses in chronic renal failure and the effect of hemodialysis.

Brainstem auditory evoked responses (BAER) were recorded in patients with chronic renal failure before commencement of chronic dialysis treatment, and in patients with end-stage renal failure on chronic hemodialysis for several years. Both groups of patients had delayed latencies of the third and fifth waves. The patients on hemodialysis revealed delayed latency of interpeak I-V as well. There was no correlation between wave latency, serum urea, creatinine, PTH or duration of chronic hemodialysis treatment. A hemodialysis session led to a slight shortening of the third wave. This study suggests that neural conduction along the brainstem in patients with chronic renal failure is delayed even before hemodialysis is started. Although 1 dialysis session may have some beneficial effect, long-term hemodialysis treatment does not seem to shorten the delay in neural conduction observed in patients with chronic renal failure.

Adolescent↗
PubMed1996

Auditory evoked potentials in multiple sclerosis: correlation with magnetic resonance imaging.

The present study addresses issues regarding the location of neural sources (i.e. generators) of human auditory evoked potentials (AEPs), and the pattern of neural conduction in the auditory pathway. AEPs were recorded from fifteen patients with multiple sclerosis (MS) and compared to normals. The recordings included auditory brainstem responses (ABRs), mid-latency responses (MLRs), and long-latency responses (LLRs). AEP latency abnormalities were related to the locus of demyelinating lesions, as determined by magnetic resonance imaging (MRI) scans. The data demonstrated several anatomical patterns relating abnormal ABR wave intervals and abnormal MRI signals. From these patterns specific loci for ABR neural sources in the brainstem might be postulated. In addition, the earlier the ABR waves, the more unilateral the abnormalities appeared, suggesting bilateral sources for later waves. The MLRs were highly correlated with ABR wave V and were associated with greater abnormality in MRI signals in midbrain and forebrain regions. In general, patients with abnormal LLRs also had widespread AEP and MRI abnormalities, supporting a multiple source approach for the N1 wave of the LLRs. The observation that LLRs were only abnormal in the presence of bilateral ABR abnormalities suggests a cross wiring which would serve as a compensatory mechanism for unilateral disturbances. The AEP data showed dissociation between early and late wave abnormalities, thus supporting parallel channels for neural conduction in the central auditory system. Such a model calls for some degree of independence of AEP generators along the auditory pathway.

Adult↗
PubMed1983

Nervous impulse propagation along peripheral and central fibres in patients with chronic renal failure.

In thirty-one patients with chronic renal failure we measured the conduction velocities in the proximal regions of median and peroneal nerves and concurrently evaluated the propagation properties of an afferent input along the related central (spinal and supraspinal) sensory pathways. In 26 of these patients the sensorimotor velocities of median, peroneal and sural nerves were also calculated. Lower limb peripheral conduction was more frequently abnormal than that of upper limb, the distal segment being involved to a greater degree. Since central propagation was more impaired during lower (11 out of 27 cases) than during upper limb (1 out of 27 patients) stimulation and the intracranial propagation time was rarely prolonged, a predominantly spinal defective impulse conduction was hypothesized. Neurophysiological data seem to confirm that early stages of defective neural conduction in CRF are in agreement with the model of central-peripheral distal axonopathy. However, an abnormal impulse propagation was also rarely found in proximal districts of peripheral fibres as well as along the intracranial sensory pathways. Correlations were found between some of the impulse propagation properties and the duration of CRF or dialysis. Serum parathyroid hormone, creatinine and BUN levels were correlated with some peripheral and central conduction indexes.

Adolescent↗
PubMed1987

Compression induced damage on in-situ severed and intact nerves.

The effect of rapid as well as sustained compressive forces applied to the surface of intact and severed peroneal nerves of rabbits was studied. Considerable effort was taken to ensure a quantitative and consistent experimental paradigm. Stimuli were delivered to the sciatic nerve, and the compound action potential was recorded in the peroneal nerve, with compressive forces applied more proximally on the peroneal nerve. It was found that the conduction of action potentials on the larger nerve fibers was more sensitive to compressive force than that of the smaller nerve fibers, although all nerve fibers stopped conducting when sufficient compression was applied to the nerve. The effect on the conduction of action potentials on the nerve fibers appeared to be determined both by Laplace's law (as previously reported by others) and the viscoelastic properties of the entire nerve. Relatively low compressive forces (20 gm applied over approximately 7 sq mm) were found to decrease the neutral conduction of the larger nerve fibers for at least two hours, whereas stagnation of blood circulation was not found to affect measurably the neural conduction of all the nerve fibers for up to two hours.

Action Potentials↗
PubMed2000

[Electrophysiological study of the lateral dorsal cutaneous nerve: technical applicability and normal values].

The distal nerve conduction study of the long nerve in the leg is more efficient to work with so that it can establish the early diagnosis of the majority of polyneuropathies. The main purpose of this study is the technical applicability of the orthodromic neural conduction examination of the dorsal cutaneous branch of the sural nerve (lateral dorsal cutaneous nerve) on healthy people, and define the normal values used as references to compare with the proximal segment. Forty five persons mean age 41.56 years old (range 19-75) were examined, and the sensory nerve action potentials were registered from ninety feet. The active recording superficial electrode was placed below and behind the lateral malleolus and the stimulating electrode was placed 10 cm distal to the recording superficial electrode at the dorsal lateral aspect of the feet. The mean value for the lateral dorsal cutaneous nerve conduction velocity was 47.35 +/- 4.8 m/s and for amplitudes 4.19 +/- 1.9 microV. The sensory conduction velocity in the distal segment was 14% lower than the proximal one. The sensory nerve action potential amplitude of the distal segment was 73% lower than the proximal one. The lower normal limit recommended for conduction velocity of this nerve plus correction for skin temperature of 34 degrees C is 38 m/s. Some differences in amplitude and conduction velocity among group ages are to be considered.

Adult↗
PubMed1995

[A chronic spinal cord compression model in a rat with a 354A tumor].

A posterior spinal cord compression model was produced in a rat with a 354 A tumor. Here we report the compression process using MRI (at 2.11 tesla), the progression of paralysis in the posterior limbs, the pathological changes in the neural tissues, and the spinal evoked potentials (SpEPs). A relatively flat spinal cord compression model was established by the interposition of free fatty tissue between the tumor and dura mater. The anteroposterior diameter of the compressed cord (AP), the width of the compressed cord (W), the cross-sectional areas of the spine (A), the mean of the anteroposterior diameters of the cord at the levels of the adjacent cephalic and caudal vertebral bodies (AP), and the mean of the cross-sectional areas of the cord at the levels of the adjacent cephalic and caudal vertebral bodies (A) were measured on axial views from MRI. Paralysis of the posterior limbs occurred in this model when A/A became less than 60%, AP/AP became less than 35% and AP/W became less than 20%. Pathological changes became apparent in the neural tissues when A/A became less than 50-60%, AP/AP became less than 25-30% and AP/W became less than 15%. Polyphasic wave-forms were noted when A/A became less than 60%, AP/AP became less than 35% and AP/W became less than 20%. When the A/A became less than 40%, the histopathological changes became marked. SpEPs could no longer be detected at this degree of compression, indicating that all neural conduction had been blocked.

Animals↗
PubMed2001

Direct tramadol application on sciatic nerve inhibits spinal somatosensory evoked potentials in rats.

We sought to determine the possible neural conduction blockade of tramadol and whether there is evidence of localized neural toxicity with spinal somatosensory evoked potential (SSEP) measurements. Male Wistar rats were used. SSEP, elicited by supramaximally stimulating the hind paw and recorded from the thoracolumbar and the first and second lumbar interspinous ligaments, was monitored. SSEPs were obtained before drug application as the pretreatment baseline and measured every 15 min after treatment for 2 h and at 60-min intervals thereafter until SSEP returned to baseline or for another 4 h. Two small strips of Gelfoam (0.6 x 1.0 cm(2)) soaked with the drug were placed under and over the left sciatic nerve for a 30-min period. Gelfoam was prepared with tramadol hydrochloride (Tramal; the US trade name is Ultram) 5, 2.5, and 1.25 mg, diluted if needed with saline to a total volume of 100 microL (5%, 2.5%, and 1.25%, respectively). The control data were obtained from the right side limb with normal saline by following the same method. Spinal SSEPs were measured after 48 h to detect the late neural damage. The results showed that direct tramadol application on sciatic nerves dose-dependently reduced both the amplitude and conduction velocity of SSEPs when compared with the pretreatment baseline. All SSEPs returned to pretreatment baseline, and no significant changes of SSEP between bilateral limbs were noted at the 48-h measurements. No evidence of irreversible conduction blockade indicative of local neural toxicity was seen. Pretreatment with naloxone 1 mg/kg failed to block the changes of SSEP produced by 2.5% tramadol 100 microL. We conclude that tramadol exerts a local anesthetic-type effect on peripheral nerves.

Analgesics, Opioid↗
PubMed1977

Scleroedema (Buschke). A case report.

A case of scleroedema is reported in a 28-year-old man with severe neuromuscular involvement. Failure in neural conduction as well as muscular degeneration and necrosis were seen. Histopathological study showed resorption and formation of scar tissue probably secondary to ischaemia. In addition there was increase in neutral, sulphated and non-sulphated mucosubstances in the dermal and endomysial connective tissue.

Adult↗