Computer Model for Action Potential Propagation Through Branch Point in Myelinated Nerves

2001 ◽  
Vol 85 (1) ◽  
pp. 197-210 ◽  
Author(s):  
Lei Zhou ◽  
Shing Yan Chiu
Keyword(s):  
Action Potential ◽  
Branch Point ◽  
Myelin Sheath ◽  
Nerve Fibers ◽  
Myelinated Nerve ◽  
Axonal Membrane ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Action Potential Propagation ◽  
Periaxonal Space

A mathematical model is developed for simulation of action potential propagation through a single branch point of a myelinated nerve fiber with a parent branch bifurcating into two identical daughter branches. This model is based on a previously published multi-layer compartmental model for single unbranched myelinated nerve fibers. Essential modifications were made to couple both daughter branches to the parent branch. There are two major features in this model. First, the model could incorporate detailed geometrical parameters for the myelin sheath and the axon, accomplished by dividing both structures into many segments. Second, each segment has two layers, the myelin sheath and the axonal membrane, allowing voltages of intra-axonal space and periaxonal space to be calculated separately. In this model, K ion concentration in the periaxonal space is dynamically linked to the activity of axonal fast K channels underneath the myelin in the paranodal region. Our model demonstrates that the branch point acts like a low-pass filter, blocking high-frequency transmission from the parent to the daughter branches. Theoretical analysis showed that the cutoff frequency for transmission through the branch point is determined by temperature, local K ion accumulation, width of the periaxonal space, and internodal lengths at the vicinity of the branch point. Our result is consistent with empirical findings of irregular spacing of nodes of Ranvier at axon abors, suggesting that branch points of myelinated axons play important roles in signal integration in an axonal tree.

Activity-Dependent Modulation of Axonal Excitability in Unmyelinated Peripheral Rat Nerve Fibers by the 5-HT(3) Serotonin Receptor

2006 ◽  
Vol 96 (6) ◽  
pp. 2963-2971 ◽  
Author(s):  
Philip M. Lang ◽  
Gila Moalem-Taylor ◽  
David J. Tracey ◽  
Hugh Bostock ◽  
Peter Grafe
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Action Potentials ◽  
Serotonin Receptor ◽  
Nerve Fibers ◽  
Nerve Trunk ◽  
Axonal Membrane ◽  
Membrane Hyperpolarization ◽  
Axonal Excitability ◽  
Activity Dependent

Activity-dependent fluctuations in axonal excitability and changes in interspike intervals modify the conduction of trains of action potentials in unmyelinated peripheral nerve fibers. During inflammation of a nerve trunk, long stretches of axons are exposed to inflammatory mediators such as 5-hydroxytryptamine [5-HT]. In the present study, we have tested the effects of m-chlorophenylbiguanide (mCPBG), an agonist at the 5-HT(3) serotonin receptor, on activity- and potential-dependent variations in membrane threshold and conduction velocity of unmyelinated C-fiber axons of isolated rat sural nerve segments. The increase in axonal excitability during application of mCPBG was much stronger at higher frequencies of action potentials and/or during axonal membrane hyperpolarization. The effects on the postspike recovery cycle also depended on the rate of stimulation. At an action potential frequency of 1 Hz or in hyperpolarized axons, mCPBG produced a loss of superexcitability. In contrast, at 0.33 Hz, a small increase in the postspike subexcitability was observed. Similar effects on excitability changes were found when latency instead of threshold was recorded, but only at higher action potential frequencies: at 1.8 Hz, mCPBG increased conduction velocity and reduced postspike supernormality. The latter effect would increase the interspike interval if pairs of action potentials were conducted along several cm in an inflamed nerve trunk. These data indicate that activation of axonal 5-HT(3) receptors not only enhances membrane excitability but also modulates action potential trains in unmyelinated, including nociceptive, nerve fibers at high impulse rates.

scholarly journals A Lead Field Two-Domain Model for Longitudinal Neural Tracts—Analytical Framework and Implications for Signal Bandwidth

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
G. Fischer ◽  
M. Kofler ◽  
M. Handler ◽  
D. Baumgarten
Keyword(s):  
Action Potential ◽  
Evoked Potentials ◽  
Body Surface ◽  
Peak Frequency ◽  
Theoretical Framework ◽  
Neural Pathways ◽  
Pass Filter ◽  
Field Function ◽  
Low Pass Filter ◽  
Lead Field

Somatosensory evoked potentials are a well-established tool for assessing volley conduction in afferent neural pathways. However, from a clinical perspective, recording of spinal signals is still a demanding task due to the low amplitudes compared to relevant noise sources. Computer modeling is a powerful tool for gaining insight into signal genesis and, thus, for promoting future innovations in signal extraction. However, due to the complex structure of neural pathways, modeling is computationally demanding. We present a theoretical framework which allows computing the electric potential generated by a single axon in a body surface lead by the convolution of the neural lead field function with a propagating action potential term. The signal generated by a large cohort of axons was obtained by convoluting a single axonal signal with the statistical distribution of temporal dispersion of individual axonal signals. For establishing the framework, analysis was based on an analytical model. Our approach was further adopted for a numerical computation of body surface neuropotentials employing the lead field theory. Double convolution allowed straightforward analysis in the frequency domain. The highest frequency components occurred at the cellular membrane. A bandpass type spectral shape and a peak frequency of 1800 Hz was observed. The volume conductor transmitting the signal to the recording lead acted as an additional bandpass reducing the axonal peak frequency from 200 Hz to 500 Hz. The superposition of temporally dispersed axonal signals acted as an additional low-pass filter further reducing the compound action potential peak frequency from 90 Hz to 170 Hz. Our results suggest that the bandwidth of spinal evoked potentials might be narrower than the bandwidth requested by current clinical guidelines. The present findings will allow the optimization of noise suppression. Furthermore, our theoretical framework allows the adaptation in numerical methods and application in anatomically realistic geometries in future studies.

scholarly journals The Myelin Sheath Maintains the Spatiotemporal Fidelity of Action Potentials by Eliminating the Effect of Quantum Tunneling of Potassium Ions through the Closed Channels of the Neuronal Membrane

2019 ◽  
Vol 1 (2) ◽  
pp. 287-294 ◽  
Author(s):  
Abdallah Barjas Qaswal
Keyword(s):  
Potassium Channels ◽  
Action Potential ◽  
Myelin Sheath ◽  
Quantum Tunneling ◽  
Action Potentials ◽  
Quantum Physics ◽  
Demyelinating Diseases ◽  
Neuronal Membrane ◽  
Potassium Ions ◽  
Axonal Membrane

The myelin sheath facilitates action potential conduction along the axons, however, the mechanism by which myelin maintains the spatiotemporal fidelity and limits the hyperexcitability among myelinated neurons requires further investigation. Therefore, in this study, the model of quantum tunneling of potassium ions through the closed channels is used to explore this function of myelin. According to the present calculations, when an unmyelinated neuron fires, there is a probability of 9.15 × 10 − 4 that it will induce an action potential in other unmyelinated neurons, and this probability varies according to the type of channels involved, the channels density in the axonal membrane, and the surface area available for tunneling. The myelin sheath forms a thick barrier that covers the potassium channels and prevents ions from tunneling through them to induce action potential. Hence, it confines the action potentials spatiotemporally and limits the hyperexcitability. On the other hand, lack of myelin, as in unmyelinated neurons or demyelinating diseases, exposes potassium channels to tunneling by potassium ions and induces the action potential. This approach gives different perspectives to look at the interaction between neurons and explains how quantum physics might play a role in the actions occurring in the nervous system.

scholarly journals ISOLATION OF THE PERIAXONAL SPACE OF THE CENTRAL MYELINATED NERVE FIBER WITH REGARD TO THE DIFFUSION OF PEROXIDASE

1969 ◽  
Vol 17 (8) ◽  
pp. 512-516 ◽  
Author(s):  
ASAO HIRANO ◽  
NORWIN H. BECKER ◽  
H. M. ZIMMERMAN
Keyword(s):  
Horseradish Peroxidase ◽  
Nerve Fiber ◽  
Myelin Sheath ◽  
Node Of Ranvier ◽  
Myelinated Nerve Fiber ◽  
Outer Loop ◽  
Myelinated Nerve ◽  
Lateral Loop ◽  
Periaxonal Space

Horseradish peroxidase was implanted into rat forebrains and the distribution with respect to the periaxonal space was examined. The peroxidase filled the extracellular spaces. Usually, however, the flow stopped at the junction of the outer loop and the outermost lamella of the myelin sheath and at the outermost lateral loop at the node of Ranvier. Therefore, in most cases, the periaxonal space was devoid of peroxidase. Occasionally, however, peroxidase in small amounts evidently penetrated the junctions and could sometimes be clearly demonstrated within the periaxonal space.

Development of 4-AP and TEA sensitivities in mammalian myelinated nerve fibers

1988 ◽  
Vol 60 (6) ◽  
pp. 2168-2179 ◽  
Author(s):  
D. L. Eng ◽  
T. R. Gordon ◽  
J. D. Kocsis ◽  
S. G. Waxman
Keyword(s):  
Sciatic Nerve ◽  
Action Potential ◽  
Compound Action Potential ◽  
Nerve Fibers ◽  
Repetitive Firing ◽  
Base Line ◽  
Channel Blockers ◽  
Myelinated Nerve ◽  
Sucrose Gap ◽  
Compound Action

1. The sensitivities of mammalian myelinated axons to potassium channel blockers was studied over the course of development using in vitro sucrose gap and intra-axonal recording techniques. 2. Application of 4-aminopyridine (4-AP; 1.0 mM) to young nerves led to a delay in return to base line of the sciatic nerve compound action potential and to a postspike positivity (indicative of hyperpolarization) lasting for tens of milliseconds. These effects were very much attenuated during the course of maturation. 3. Tetraethylammonium chloride (TEA; 10 mM) application alone had little effect on the waveform of the compound action potential at any age. However, the 4-AP-induced postspike positivity was blocked by TEA, Ba/+, and Cs+. This block was observed in Ca2+-free electrolyte solutions containing EGTA (1.0 mM). 4. Immature sciatic nerves (approximately 3 wk postnatal) were incubated in a potassium-free electrolyte solution containing 120 mM CsCl for up to 1 h in an attempt to replace internal potassium with cesium. When the nerves were tested in the sucrose gap chamber using solutions containing 3.0 mM CsCl substituted for KCl, the compound action potential was broadened and a prolonged depolarization appeared, but there was no postspike positivity; the CsCl effect was similar to the combined effects of 4-AP and TEA. 5. Intra-axonal recordings were obtained to study the effects of 4-AP and TEA on individual axons. In the presence of 4-AP a single stimulus led to a burst of action potentials followed by a pronounced afterhyperpolarization (AHP) in sensory fibers. The AHP was blocked by TEA. In motor fibers 4-AP application resulted in action potential broadening with no AHP. 6. Repetitive stimulation (200-500 Hz; 100 ms) was followed by a pronounced AHP in both sensory and motor fibers at all ages studied. This activity-elicited AHP was sensitive to TEA at all ages. 7. The results indicate that 4-AP and TEA sensitivity change over the course of development in rat sciatic nerve. The effects of 4-AP are much more pronounced in immature nerves than in mature nerves, suggesting that 4-AP-sensitive channels become masked as they are covered by myelin during maturation. However, the TEA-sensitive channels, demonstrable after repetitive firing, remain accessible to TEA after myelination. These channels therefore may have a nodal representation.

scholarly journals Action Potential Propagation and Synchronisation in Myelinated Axons

2019 ◽  
Author(s):  
Helmut Schmidt ◽  
Thomas R. Knösche
Keyword(s):  
White Matter ◽  
Action Potential ◽  
Myelin Sheath ◽  
Action Potentials ◽  
Structural Parameters ◽  
Node Of Ranvier ◽  
Model Parameters ◽  
Mathematical Framework ◽  
Whole Brain ◽  
Action Potential Propagation

AbstractWith the advent of advanced MRI techniques it has become possible to study axonal white matter non-invasively and in great detail. Measuring the various parameters of the long-range connections of the brain opens up the possibility to build and refine detailed models of large-scale neuronal activity. One particular challenge is to find a mathematical description of action potential propagation that is sufficiently simple, yet still biologically plausible to model signal transmission across entire axonal fibre bundles. We develop a mathematical framework in which we replace the Hodgkin-Huxley dynamics by a spike-diffuse-spike model with passive sub-threshold dynamics and explicit, threshold-activated ion channel currents. This allows us to study in detail the influence of the various model parameters on the action potential velocity and on the entrainment of action potentials between ephaptically coupled fibres without having to recur to numerical simulations. Specifically, we recover known results regarding the influence of axon diameter, node of Ranvier length and internode length on the velocity of action potentials. Additionally, we find that the velocity depends more strongly on the thickness of the myelin sheath than was suggested by previous theoretical studies. We further explain the slowing down and synchronisation of action potentials in ephaptically coupled fibres by their dynamic interaction. In summary, this study presents a solution to incorporate detailed axonal parameters into a whole-brain modelling framework.Author summaryWith more and more data becoming available on white-matter tracts, the need arises to develop modelling frameworks that incorporate these data at the whole-brain level. This requires the development of efficient mathematical schemes to study parameter dependencies that can then be matched with data, in particular the speed of action potentials that cause delays between brain regions. Here, we develop a method that describes the formation of action potentials by threshold activated currents, often referred to as spike-diffuse-spike modelling. A particular focus of our study is the dependence of the speed of action potentials on structural parameters. We find that the diameter of axons and the thickness of the myelin sheath have a strong influence on the speed, whereas the length of myelinated segments and node of Ranvier length have a lesser effect. In addition to examining single axons, we demonstrate that action potentials between nearby axons can synchronise and slow down their propagation speed.

scholarly journals The mechanosensitive ion channel TRAAK is localized to the mammalian node of Ranvier

2019 ◽  
Author(s):  
Stephen G. Brohawn ◽  
Weiwei Wang ◽  
Jürgen R. Schwarz ◽  
Annie Handler ◽  
Ernest B. Campbell ◽  
...  
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Polyclonal Antibodies ◽  
Node Of Ranvier ◽  
Nerve Fibers ◽  
Resting Membrane Potential ◽  
Myelinated Nerve ◽  
Myelinated Nerve Fibers ◽  
Behavioral Studies ◽  
Mechanosensitive Ion Channel

ABSTRACTTRAAK is a membrane tension-activated K+ channel that has been associated through behavioral studies to mechanical nociception. We used specific monoclonal antibodies in mice to show that TRAAK is localized exclusively to nodes of Ranvier, the action potential propagating elements of myelinated nerve fibers. Approximately 80 percent of myelinated nerve fibers throughout the central and peripheral nervous system contain TRAAK in an all-nodes or no-nodes per axon fashion. TRAAK is not observed at the axon initial segment where action potentials are first generated. We used polyclonal antibodies, the TRAAK inhibitor RU2 and node clamp amplifiers to demonstrate the presence and functional properties of TRAAK in rat nerve fibers. TRAAK contributes to the ‘leak’ K+ current in mammalian nerve fiber conduction by hyperpolarizing the resting membrane potential, thereby increasing Na+ channel availability for action potential propagation. Mechanical gating in TRAAK might serve a neuroprotective role by counteracting mechanically-induced ectopic action potentials. Alternatively, TRAAK may open in response to mechanical forces in the nodal membrane associated with depolarization during saltatory conduction and thereby contribute to repolarization of the node for subsequent spikes.

scholarly journals Enhanced neural tracking of the fundamental frequency of the voice

2020 ◽  
Author(s):  
Jana Van Canneyt ◽  
Jan Wouters ◽  
Tom Francart
Keyword(s):  
Fundamental Frequency ◽  
Auditory Nerve ◽  
Neural Response ◽  
Nerve Fibers ◽  
Center Frequency ◽  
Neural Processing ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Low Pass ◽  
The Voice

AbstractObjective‘F0 tracking’ is a novel method that investigates the neural processing of the fundamental frequency of the voice (f0) in continuous speech. Through linear modelling, a feature that reflects the stimulus f0 is predicted from the EEG data. Then, the neural response strength is evaluated through the correlation between the predicted and actual f0 feature. The aim of this study was to improve upon this ‘f0 tracking’ method by optimizing the f0 feature.ApproachSpecifically, we aimed to design a feature that approximates the expected EEG responses to the f0. We hypothesized that this would improve neural tracking results, because the more similar the feature and the neural response are, the easier it will be to reconstruct the one from the other. Two techniques were explored: a phenomenological model to simulate neural processing in the auditory periphery and a low-pass filter to approximate the effect of more central processing on the f0 response. Since these optimizations target different aspects of the auditory system, they were also applied in a cumulative fashion.ResultsResults obtained from EEG evoked by a Flemish story in 34 subjects indicated that both the use of the auditory model and the addition of the low-pass filter significantly improved the correlations between the actual and reconstructed feature. The combination of both strategies almost doubled the mean correlation over subjects, from 0.78 to 0.13. Moreover, canonical correlation analysis with the modelled feature revealed two distinct processes contributing to the f0 response: one driven by the compound activity of auditory nerve fibers with center frequency up to 8 kHz and one driven predominantly by the auditory nerve fibers with center frequency below 1 kHz.SignificanceThe optimized f0 features developed in this study enhance the analysis of f0-tracking responses and facilitate future research and applications.

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