scholarly journals Actin Filament Turnover Drives Leading Edge Growth during Myelin Sheath Formation in the Central Nervous System

2015 ◽  
Vol 34 (2) ◽  
pp. 139-151 ◽  
Author(s):  
Schanila Nawaz ◽  
Paula Sánchez ◽  
Sebastian Schmitt ◽  
Nicolas Snaidero ◽  
Mišo Mitkovski ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Actin Filament ◽  
Myelin Sheath ◽  
Leading Edge ◽  
Sheath Formation ◽  
The Central Nervous System

Fyn tyrosine kinase participates in the compact myelin sheath formation in the central nervous system

2000 ◽  
Vol 37 (1) ◽  
pp. 21-31 ◽  
Author(s):  
Chika Seiwa ◽  
Ichiro Sugiyama ◽  
Takeshi Yagi ◽  
Taisen Iguchi ◽  
Hiroaki Asou
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Tyrosine Kinase ◽  
Myelin Sheath ◽  
Sheath Formation ◽  
The Central Nervous System ◽  
Fyn Tyrosine Kinase

scholarly journals Individual neuronal subtypes control initial myelin sheath growth and stabilization

2020 ◽  
Vol 15 (1) ◽  
Author(s):  
Heather N. Nelson ◽  
Anthony J. Treichel ◽  
Erin N. Eggum ◽  
Madeline R. Martell ◽  
Amanda J. Kaiser ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Central Nervous System ◽  
Nervous System ◽  
Myelin Sheath ◽  
Time Lapse ◽  
Marked Individual ◽  
Larval Zebrafish ◽  
Sheath Formation ◽  
Time Lapse Imaging

Abstract Background In the developing central nervous system, pre-myelinating oligodendrocytes sample candidate nerve axons by extending and retracting process extensions. Some contacts stabilize, leading to the initiation of axon wrapping, nascent myelin sheath formation, concentric wrapping and sheath elongation, and sheath stabilization or pruning by oligodendrocytes. Although axonal signals influence the overall process of myelination, the precise oligodendrocyte behaviors that require signaling from axons are not completely understood. In this study, we investigated whether oligodendrocyte behaviors during the early events of myelination are mediated by an oligodendrocyte-intrinsic myelination program or are over-ridden by axonal factors. Methods To address this, we utilized in vivo time-lapse imaging in embryonic and larval zebrafish spinal cord during the initial hours and days of axon wrapping and myelination. Transgenic reporter lines marked individual axon subtypes or oligodendrocyte membranes. Results In the larval zebrafish spinal cord, individual axon subtypes supported distinct nascent sheath growth rates and stabilization frequencies. Oligodendrocytes ensheathed individual axon subtypes at different rates during a two-day period after initial axon wrapping. When descending reticulospinal axons were ablated, local spinal axons supported a constant ensheathment rate despite the increased ratio of oligodendrocytes to target axons. Conclusion We conclude that properties of individual axon subtypes instruct oligodendrocyte behaviors during initial stages of myelination by differentially controlling nascent sheath growth and stabilization.

scholarly journals A STRUCTURAL ANALYSIS OF THE MYELIN SHEATH IN THE CENTRAL NERVOUS SYSTEM

1967 ◽  
Vol 34 (2) ◽  
pp. 555-567 ◽  
Author(s):  
Asao Hirano ◽  
Herbert M. Dembitzer
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Electron Microscope ◽  
Myelin Sheath ◽  
Cerebral White Matter ◽  
Experimental Conditions ◽  
Myelin Sheaths ◽  
Basic Theme ◽  
Cell Processes ◽  
The Central Nervous System

The cerebral white matter of rats subjected to a variety of noxious experimental conditions was examined in the electron microscope. Several unusual configurations of the myelin sheath are identified in addition to the usual configuration. These variations include the presence of (a) formed organelles within the inner and outer loops, (b) isolated islands of cytoplasm in unfused portions of the major dense lines, (c) apparently unconnected cell processes between the sheath and the axon, and (d) concentric, double myelin sheaths. A generalized model of the myelin sheath based on a hypothetical unrolling of the sheath is described. It consists of a shovel-shaped myelin sheet surrounded by a continuous thickened rim of cytoplasm. Most of the unusual myelin configurations are explained as simple variations on this basic theme. With the help of this model, an explanation of the formation of the myelin sheath is offered. This explanation involves the concept that myelin formation can occur at all cytoplasmic areas adjacent to the myelin proper and that adjacent myelin lamellae can move in relation to each other.

scholarly journals The giant myelinated nerve fibres of the prawn

1942 ◽  
Vol 231 (582) ◽  
pp. 293-311 ◽  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Myelin Sheath ◽  
Single Cells ◽  
Myelinated Fibre ◽  
Complete Fusion ◽  
Giant Fibre ◽  
The Central Nervous System ◽  
Giant Fibres ◽  
Myelinated Fibres

Evidence is given that the median and lateral longitudinal giant myelinated fibres in the central nervous system of the prawn Leander serratus are syncitial structures, each formed by the fusion of the processes of many segmental nerve cells. Septa are found at intervals in the axoplasm of the median fibres, but they never completely transect it. They are probably relics of a condition similar to that in the earthworm where the giant fibre running the length of the cord is formed of a chain of segmental syncitial axons each divided from its neighbour by a complete septum which presumably functions as a synapse. The motor giant fibres, which are segmental and pass out of the central nervous system to the muscles, are the processes of single cells: the axoplasms of the two fibres of the pair in each segment undergo complete fusion with each other and then redivision before leaving the central nervous system. These motor giant fibres are non-myelinated within the central nervous system, although as great in diameter as other heavily myelinated fibres. They are myelinated outside the central nervous system. In the prawn therefore myelin sheath thickness is not an invariable function of axon diameter. The lateral giant-fibre synapses show complete axoplasmic discontinuity and their structure does not support Johnson’s creation of a new category of synaptic relations. Two types of synapses between fibres are described. In the first, found in the lateral giant-fibre chain, two myelinated fibres lie closely side by side for a considerable distance, but their neuroplasms are separated by a myelin layer except over an extent of less than 10 μ . In the second type, found at the point of contact of both the median and lateral fibres with the motor fibres, a myelinated fibre has synaptic connexions with a large non-myelinated fibre through many fine axonic processes which pass out through a small gap in the myelin sheath.

scholarly journals The Structure and Conduction Velocity of the Medullated Nerve Fibres of Prawns

1941 ◽  
Vol 18 (1) ◽  
pp. 50-54 ◽  
Author(s):  
W. HOLMES ◽  
R. J. PUMPHREY ◽  
J. Z. YOUNG
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Conduction Velocity ◽  
Myelin Sheath ◽  
Axon Diameter ◽  
Relative Thickness ◽  
Nodes Of Ranvier ◽  
Nerve Fibres ◽  
The Central Nervous System ◽  
Myelinated Fibres

1. The structure of the myelinated fibres of prawns is described, and the homologies of the nucleated sheath which lies between the axon and the fatty layer discussed. 2. The relative thickness of the myelin sheath increases with decrease in total diameter of the fibre along a curve similar in shape to that found in vertebrates and earthworms. 3. Nodes of Ranvier are found in the sheaths of most fibres of a diameter greater than about 13µ 4. The nodes are similar to those in vertebrate nerves in that the myelin sheath is interrupted at the node. 5. The conduction velocity of fibres in the central nervous system of axon diameter 26µ and total diameter 35µ is between 18 and 23 m. per sec., a rate faster than is found in the "unmyelinated" fibres of similar size in other crustacea.

scholarly journals Central and Peripheral Neuromuscular Adaptations to Ageing

2020 ◽  
Vol 9 (3) ◽  
pp. 741 ◽  
Author(s):  
Riccardo Borzuola ◽  
Arrigo Giombini ◽  
Guglielmo Torre ◽  
Stefano Campi ◽  
Erika Albo ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Functional Decline ◽  
Leading Edge ◽  
Diagnostic Procedures ◽  
Voluntary Activation ◽  
Muscle Quality ◽  
Compensatory Mechanism ◽  
Age Related ◽  
The Central Nervous System

Ageing is accompanied by a severe muscle function decline presumably caused by structural and functional adaptations at the central and peripheral level. Although researchers have reported an extensive analysis of the alterations involving muscle intrinsic properties, only a limited number of studies have recognised the importance of the central nervous system, and its reorganisation, on neuromuscular decline. Neural changes, such as degeneration of the human cortex and function of spinal circuitry, as well as the remodelling of the neuromuscular junction and motor units, appear to play a fundamental role in muscle quality decay and culminate with considerable impairments in voluntary activation and motor performance. Modern diagnostic techniques have provided indisputable evidence of a structural and morphological rearrangement of the central nervous system during ageing. Nevertheless, there is no clear insight on how such structural reorganisation contributes to the age-related functional decline and whether it is a result of a neural malfunction or serves as a compensatory mechanism to preserve motor control and performance in the elderly population. Combining leading-edge techniques such as high-density surface electromyography (EMG) and improved diagnostic procedures such as functional magnetic resonance imaging (fMRI) or high-resolution electroencephalography (EEG) could be essential to address the unresolved controversies and achieve an extensive understanding of the relationship between neural adaptations and muscle decline.

scholarly journals Individual neuronal subtypes control initial myelin sheath growth and stabilization

2019 ◽  
Author(s):  
Heather N. Nelson ◽  
Anthony J. Treichel ◽  
Erin N. Eggum ◽  
Madeline R. Martell ◽  
Amanda J. Kaiser ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Central Nervous System ◽  
Nervous System ◽  
Myelin Sheath ◽  
Time Lapse ◽  
Marked Individual ◽  
Larval Zebrafish ◽  
Sheath Formation ◽  
Time Lapse Imaging

AbstractBackgroundIn the developing central nervous system, pre-myelinating oligodendrocytes sample candidate nerve axons by extending and retracting process extensions. Some contacts stabilize, leading to the initiation of axon wrapping, nascent myelin sheath formation, concentric wrapping and sheath elongation, and sheath stabilization or pruning by oligodendrocytes. Although axonal signals influence the overall process of myelination, the precise oligodendrocyte behaviors that require signaling from axons are not completely understood. In this study, we investigated whether oligodendrocyte behaviors during the early events of myelination are mediated by an oligodendrocyte-intrinsic myelination program or are over-ridden by axonal factors.MethodsTo address this, we utilized in vivo time-lapse imaging in embryonic and larval zebrafish spinal cord during the initial hours and days of axon wrapping and myelination. Transgenic reporter lines marked individual axon subtypes or oligodendrocyte membranes.ResultsIn the larval zebrafish spinal cord, individual axon subtypes supported distinct nascent sheath growth rates and stabilization frequencies. Oligodendrocytes ensheathed individual axon subtypes at different rates during a two-day period after initial axon wrapping. When descending reticulospinal axons were ablated, local spinal axons supported a constant ensheathment rate despite the increased ratio of oligodendrocytes to target axons.ConclusionWe conclude that properties of individual axon subtypes instruct oligodendrocyte behaviors during initial stages of myelination by differentially controlling nascent sheath growth and stabilization.

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