PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Nerve Fibers, Myelinated”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1977

[Quantitative studies on the regeneration of myelinated nerve fibers. III. Variations in the number and size of regenerated fibers after localized freezing].

The number and size of myelinated nerve fibers have been determined at standard levels in the nerve to medial head of right and left gastroenemius muscles of 45 rats in which the left sciatic nerve had suffered an localized freezing. The nerves have been observed from 10 to 720 days after the operation. In the contralateral nerve, the number of myelinated fibers decreased in average to 18.8%, the mean diameter to 11,2%. Male rats appeared to be more sensitive than female to the effects of the operation. In the regenerating nerve, the number of myelinated fibers returned to normal during 4th week and later increased up to a mean of 124%. Their distribution became bimodal after the 60th day. Both histograms could be superposed by the 330th day and the mean diameter came back to normal soon afterwards.

Animals↗
PubMed1977

[Variation in the number and size of myelinated nerve fibers regenerated after repeated localized freezing of the sciatic nerve of rats].

The number and size of myelinated fibres have been determined in the nerve to medial head of the gastrocnemius muscle of Rats in which the sciatic nerve had been frozen locally 1 to 5 times at monthly intervals. The contralateral nerve was used as a control. When the measurements were made one month after the last freezing, the number of fibres increased progressively until the 3rd freezing, reaching about 220% of the normal value. No higher values were observed after 4 or 5 freezings. The mean diameter of fibres decreased with the number of operations. When the measurements were made 3, 6, 12 or 18 months after the 3rd freezing, the number of fibres decreased by about 30% between the 1st and the 3rd month and then stabilized. The mean diameter of fibres increased progressively. However, at the 18th month, the size of the myelinated fibres had not reached the normal value.

Animals↗
PubMed1978

Myelinated nerve fiber supply and muscle spindles in the respiratory muscles of cat: quantitative study.

The present study was undertaken to provide quantitative data on the myelinated fibers of the phrenic and intercostal nerves and the number of spindles in the main respiratory muscles of the cat. The myelinated component of the phrenic and intercostal nerves was studied in the cat. Histograms of sequency distributions as a function of nerve fiber diameter were established for normal nerves. Certain nerves were then examined 35 to 40 days after excision of the dorsal spinal ganglia. The muscle spindles of the corresponding muscles were counted and localized, and, on the basis of several morphological criteria, were classified with those usually described in the interosseous muscles. The study of the nerves, as that of the spindles, demonstrates clear differences of proprioceptive innervation among the respirator muscles. The lateral part of the diaphragm and the Triangularis sterni have practically no spindles. The external muscles of the first thoracic spaces are very rich in spindles. Respiratory muscles can be ranged in an almost continuous manner between these two extremes.

Animals↗
PubMedDate not supplied

[Grid for the simultaneous calculation and determination of the dimensions of myelinated nerve fibers].

To make convenient a simultaneous calculation and measurement of myelinic nerve fibers a network with the known length of the square's side is proposed. The use of such a network in studying the myeloarchitectonics of the nerves helps economize the time needed for this purpose. The network is simple to manufacture and can be prepared at any photolaboratory. The possibility of using it also for other purposes is indicated.

Animals↗
PubMed1977

Density of sodium channels in mammalian myelinated nerve fibers and nature of the axonal membrane under the myelin sheath.

The density of sodium channels in mammalian myelinated fibers has been estimated from measurements of the binding of [3H]saxitoxin to rabbit sciatic nerve. Binding both to intact and to homogenized nerve consists of a linear, nonspecific, component and a saturable component that represents binding to the sodium channel. The maximum saturable binding capacity in intact nerve is 19.9 +/- 1.9 fmol-mg wet-1; the equilibrium dissociation constant, Kt, is 3.4 +/- 2.0 nM. Homogenization makes little difference, the maximum binding capacity being 19.9 +/- 1.5 fmol-mg wet-1 with Kt = 1.3 +/- 0.7 nM. These values correspond to a density of about 700,000 sodium channels per node--i.e., about 12,000 per mum2 of nodal membrane. From the difference between the values of maximum saturable binding capacity in intact and homogenized preparation, given the statistical uncertainty of their estimate, it seems that the internodal membrane can have no more than about 25 channels per mum2. The significance of these findings for saltatory conduction and in demyelinating disease is discussed.

Animals↗
PubMed1979

Diffusion of ions in myelinated nerve fibers.

The diffusion of ions towards or away from the inner side of the nodal membrane in preparations, the cut ends of which are placed in various media, was investigated. The ion concentration changes were calculated by numerical solution of the unidimensional electrodiffusion equation under a variety of media compositions, axoplasmic diffusion coefficients, and internal anionic compositions. The potassium and cesium ion diffusion along the axon towards the node was determined experimentally by two different electrophysiological methods. On the basis of comparison between the experimental data and the computational predictions the axoplasmic potassium ion diffusion coefficient was determined to be almost equal to that in free aqueous solution, while that of cesium ion was close to one half of that in aqueous solution. Utilizing the values of diffusion parameters thus determined, we solved the electrodiffusion equation for a number of common experimental procedures. We found that in short fibers, cut 0.1-0.2 cm at each side of the node, the concentration approached values close to the new steady-state values within 5-30 min. In long fibers (over 1 cm long) steady-state concentrations were obtained only after a few hours. Under some conditions the internal concentrations transiently overshot the steady-state values. The diffusion potentials generated in the system were also evaluated. The ion concentration changes and generation of diffusion potential cannot be prevented by using side pools with cation content identical to that of the axoplasm.

Animals↗
PubMed1979

Unusual particle trajectories and structural arrangements in myelinated nerve fibers.

Others have reported that axonally transported particles, which usually travel in a direction roughly parallel to the axis of the nerve fiber, may suddenly shift sideways as though changing tracks. Examples of this rare type of movement are shown for particles undergoing transport in myelinated axons of Xenopus laevis. An examination of the structure of axons from Xenopus showed that some microtubules, neurofilaments, and elements of endoplasmic reticulum may also exhibit marked deviations from the axial direction. It is concluded that it is not necessary to propose any mechanism for changing tracks in order to explain the particle motion.

Animals↗
PubMed1977

Complex oligodendroglial invaginations within myelinated nerve fibers of the central nervous system during axonal degeneration.

Ultrastructural studies of spinal cord in rats subjected to hyperbaric oxygen exposure and experimental spinal cord trauma have resulted in frequent degeneration of axons. In both experimental situations central nervous system myelinated fibers containing complex cytoplasmic interdigitations of electron lucent, normal appearing cytoplasm, and dense cytoplasm, interpreted as degenerative, were observed. In some of the complex profiles the electron lucent cytoplasm could be traced back to the inner mesaxon, where its relation to the latter indicated a glial origin. Cytochemical evaluation of acid phosphatase activity in the complex cytoplasmic interdigitations revealed that both components contain significant lysosomal activity. The complex structures are interpreted as being sequestrations of degenerating axoplasm by distal adaxonal oligodendroglial processes, possibly representing an unusual form of heterophagocytosis.

Acid Phosphatase↗