Stimulus-response functions of slowly adapting mechanoreceptors in the human glabrous skin area.
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1. Single unit impluses were recorded from the ulnar and median nerves of awake human subjects with tungsten electrodes inserted percutaneously in the upper arm. 2. One hundred and one slowly adapting receptors with receptive fields in the glabrous skin area were studied. The units were classified as type SA-I and type SA-II largely on the basis of their responses to lateral stretching of the skin. Eighty-eight receptors did not respond to this type of stimulus (type SA-I), whereas thirteen receptors readily responded to stretching (type SA-II), AND OFTEN EXHIBITED DIRECTIONAL SENSITIVITY. 3. The SA-I receptors showed no spontaneous discharge, and the discharge pattern was mostly rather irregular, whereas most of the SA-II receptors had a spontaneous discharge, and a very regular discharge pattern. 4. The conduction velocities of the afferent were all in a A alpha range. The mean value for the SA-I receptors was 58-7 plus or minus 2-3m/sec, and for the SA-II receptors 45.3 plus or minus 3.6 m/sec. 5. The neural response to stimuli of varying skin indentation amplitudes was analyzed. The threshold for a dynamic response ranged for the SA-I receptors from 0.15 to 1.35 mm and for the SA-II receptors from 0.25 to 0.95 mm. The threshold for a static discharge ranged for the SA-I receptors from 0.25 to more than 2.0 mm and for the SA-II receptors from 0.55 to 1.65 mm. 6. The stimulus-response functions were analysed for 25 SA-I receptors and 2 SA-II receptors. A hyperbolic log tangent function was the best description when the neural response was defined as the total number of impluses evoked by a stimulus of 1 sec duration. When only the static part of this type of plot was analyzed, a power function was a very good description for many units, but other functions (linear, logarithmic exponential, log tanh) were equally good or better for many units. This was also the dase when the mean impulse frequency of the sustained discharge was defined as a measure of the neural response. These two latter types of plots were clearly negatively accelerating, the exponent of the power function being 0.66 (mean). (+info)
Functional changes of the primary somatosensory cortex in patients with unilateral cerebellar lesions.
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Although cerebellar lesions do not cause evident sensory deficits, it has been suggested recently that the cerebellum might play a role in sensory acquisition and discrimination. To determine whether the cerebellum influences the early phases of cortical somatosensory processing, we recorded cortical somatosensory evoked potentials after median nerve stimulation in five patients with unilateral cerebellar damage. We also performed a dipolar source analysis of traces by means of brain electrical source analysis. In all patients, the amplitude of the frontal N24 and parietal P24 components, as well as the strength of the corresponding dipolar sources, were significantly smaller after stimulation of the symptomatic side. These neurophysiological findings indicate that the primary somatosensory cortical processing is altered after contralateral cerebellar damage. They represent the first indication of a possible substrate for the reduction in cerebral blood flow observed in the parietal cortex after cerebellar lesion. Furthermore, the present data allow characterization of the functional influence of the cerebellar input to the primary somatosensory cortex as specifically acting over the inhibitory components of somatosensory processing. (+info)
Effects of temperature on the excitability properties of human motor axons.
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The effects of temperature on parameters of motor nerve excitability were investigated in 10 healthy human subjects. The median nerve was stimulated at the wrist and compound muscle action potentials were recorded from the abductor pollicis brevis. Multiple excitability measures were recorded: stimulus-response curves, the strength-duration time constant (tauSD), threshold electrotonus, a current-threshold relationship and the recovery of excitability following supramaximal activation. Recordings were made at wrist temperatures of 35, 32 and 29 degrees C by immersing the arm proximal to the wrist in a water-bath. Cooling increased the relative refractory period by 7.8% per degree C (P < 0.0001), slowed the accommodation to depolarizing currents by 4.0% per degree C (P < 0.0001) and increased tauSD by 2.6% per degree C (P < 0.01), but most other excitability parameters were not affected significantly. The effects of temperature on threshold electrotonus were investigated further in separate studies on two subjects over the range 28-36 degrees C and found to be complex. Whereas the rate of accommodation to depolarizing current was closely related to instantaneous temperature, the threshold increase induced by hyperpolarizing current was most sensitive to changes in temperature, probably because warming the nerve causes a transient hyperpolarization by accelerating the electrogenic sodium pump. Consequently, it may be preferable to make allowances for differences in skin temperature when testing patients for abnormal excitability parameters, rather than to change the temperature to a standard value. For most excitability parameters, however, temperature control is not as important as it is for conduction velocity measurements. (+info)
Management of thoracic outlet syndrome.
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This overall management program for thoracic outlet compression syndrome is based upon experience with 153 extremities in 149 patients and the results of others. The following conclusions are documented and discussed. 1) Diagnosis is based chiefly upon history; physical signs are inconstant and often absent. 2) Major vascular problems are unusual; angiography is not always necessary. 3) Electromyography is not always critical but does aid in diagnosis of carpal tunnel syndrome. 4) Non-operative treatment relieves most patients; operative decompression is indicated for a minority. 5) Transxillary first rib resection, with removal of cervical rib is the best operation. 6) Carpal tunnel decompression should be done concomitantly when needed. 7) Operation is relatively safe. (+info)
Contribution of perfusion pressure to vascular resistance response during head-up tilt.
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We measured brachial and femoral artery flow velocity in eight subjects and peroneal and median muscle sympathetic nerve activity (MSNA) in five subjects during tilt testing to 40 degrees. Tilt caused similar increases in MSNA in the peroneal and median nerves. Tilt caused a fall in femoral artery flow velocity, whereas no changes in flow velocity were seen in the brachial artery. Moreover, with tilt, the increase in the vascular resistance employed (blood pressure/flow velocity) was greater and more sustained in the leg than in the arm. The ratio of the percent increase in vascular resistance in leg to arm was 2.5:1. We suggest that the greater vascular resistance effects in the leg were due to an interaction between sympathetic nerve activity and the myogenic response. (+info)
Complex intracellular messenger pathways regulate one type of neuronal alpha-bungarotoxin-resistant nicotinic acetylcholine receptors expressed in insect neurosecretory cells (dorsal unpaired median neurons).
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Although molecular biology provides new insights into the subunit compositions and the stoichiometries of insect neuronal nicotinic acetylcholine receptors (nAChRs), our knowledge about the phosphorylation/dephosphorylation mechanisms of native neuronal nAChRs is limited. The regulation of alpha-bungarotoxin-resistant nAChRs was studied on dissociated adult dorsal unpaired median neurons isolated from the terminal abdominal ganglion of the cockroach Periplaneta americana, using whole-cell, patch-clamp technique. Under 0.5 microM alpha-bungarotoxin treatment, pressure ejection application of nicotine or acetylcholine onto the cell body induced an inward current exhibiting a biphasic current-voltage relationship. We found that two distinct components underlying the biphasic curve differed in their ionic permeability and pharmacology (one being sensitive to d-tubocurarine, and the other affected only by mecamylamine and alpha-conotoxin ImI). This indicated that two types of alpha-bungarotoxin-resistant nAChRs (named nAChR1 and nAChR2) mediated the nicotinic response. These two components were also differentially sensitive to rundown and intracellular messengers. Intracellular application of 0.1 mM cAMP only increased the current amplitude mediated by nAChR1. Using forskolin (1 microM), W7 and H89, we demonstrated that adenylyl cyclase, sensitive to calcium/calmodulin complex, regulated nAChR1 via a cAMP/cAMP-dependent protein kinase cascade. By contrast, internal cAMP concentration higher than 0.1 mM reduced the current amplitude. This effect, mimicked by high external concentration of forskolin (100 microM) and IBMX, was reversed by okadaic acid, suggesting the implication of a protein phosphatase. Using KN-62, we demonstrated that calmodulin-Kinase II also modulated directly and indirectly nAChR1, via an inhibition of the phosphatase activity. Finally, we reported that phosphorylation/dephosphorylation of nAChR1 strongly affected the action of the widely used neonicotinoid insecticide imidacloprid. (+info)
An alternative method for restoring opposition after median nerve injury: an anatomical feasibility study for the use of neurotisation.
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Opposition, one of the most important functions of the hand, is lost or impaired after median nerve injury. Complete recovery does not always occur after treatment, and various techniques of opponensplasty are used for restoring opposition. This study was performed in order to develop an alternative method for selective restoration of thenar muscle function. Ten arms from 5 cadavers were used. The median nerve with its thenar motor branch (Tb) and the anterior interosseous nerve with its motor branch to pronator quadratus (PQb) were prepared in the distal forearm. The mean widths and the number of myelinated fibres of these nerves were: PQb 1.3+/-0.10 mm, Tb 1.4+/-0.12 mm and PQb 912+/-88 mm, Tb 1020+/-93 mm. The minimum necessary distance from the distal flexor crease of the wrist for neurotisation of the Tb by the PQb was 60+/-5.41 mm. It was concluded that PQb-Tb neurotisation would be possible anatomically. The advantages are that motor function is reestablished with a motor nerve, the diameters and the number of myelinated fibres of both nerves are similar, the loss of function after denervation of the pronator quadratus is slight and opponensplasty still remains as a final option. (+info)
Carpal tunnel syndrome: modern diagnostic and management techniques.
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Carpal tunnel syndrome is a common disorder characterised by the classical symptoms of numbness and paraesthesiae along the distribution of the median nerve. Thenar muscle weakness is a late manifestation of advanced disease. Tinel's and Phalen's signs are helpful in suggesting the diagnosis. The symptoms and signs arise from entrapment of the median nerve. Electrophysiological tests are helpful in confirming the diagnosis and magnetic resonance imaging may be used in the diagnosis of atypical cases. Ergonomic manoeuvers and steroid injections may alleviate symptoms in mild cases. Surgery is reserved for severe cases and those who do not respond to conservative therapy. Open carpal tunnel release is the classical surgery with usually excellent results. Endoscopic carpal tunnel release surgery was introduced to decrease the morbidity of open surgery. This latter technique also has its complications and is still being refined. (+info)