Node of Ranvier length as a potential regulator of myelinated axon conduction speed
- University College London, United Kingdom
- Iwate Medical University, Japan
Figures
Figure 1 with 1 supplement
Heterogeneity of Ranvier node lengths in the optic nerve and cerebral cortex.
(A) Confocal image of a single optic nerve node of Ranvier showing the node labelled with antibody to NaV1.6 (green) and paranodes labelled for Caspr (red). (B) Intensity profile of Caspr staining …
Figure 1—figure supplement 1
Heterogeneity of Ranvier node lengths in the optic nerve.
Top: EM picture of node of Ranvier in the adult optic nerve, showing surrounding oligodendrocytes (paranodal loops false-coloured green), an astrocyte (pink) and the node length. In practice node …
Figure 2
Node of Ranvier lengths are correlated along an axon.
(A) Composite confocal image of a single axon in the corpus callosum iontophoretically labelled with tetramethylrhodamine dextran (red). Three consecutive nodes of Ranvier are highlighted and shown …
Figure 3
Predicted effect on conduction speed of different node lengths.
(A–F) Calculated conduction speed as a function of node length for axons in (A) the optic nerve and (B–F) the cortical grey matter. For panels A–F, simulations were carried out assuming either that …
Tables
Table 1
Electrical and geometrical parameters of the models.
Parameter | Symbol | Value | Units |
|---|---|---|---|
Nodal Na+ conductance* | gNa | 3000 | mS/cm2 |
Nodal K+ conductance* | gKs | 80 | mS/cm2 |
Nodal persistent Na+ conductance* | gNap | 5 | mS/cm2 |
Leakage conductance Node* Internode | gL
|
80 0.1 |
mS/cm2 mS/cm2 |
Myelin membrane conductance | gmy | 1.0 | mS/cm2 |
Axon membrane capacitance† Node Internode |
cax
|
0.9 0.9 |
μF/cm2 μF/cm2 |
Myelin membrane capacitance†,‡ | cmy | 0.9 | μF/cm2 |
Axoplasmic resistivity | ρax | 70 | Ω.cm |
Periaxonal resistivity | ρp | 70 | Ω.cm |
Resting potential | Er | −82 | mV |
Leakage potential | ELk | −83.38 | mV |
Na+ reversal potential | ENa | 50 | mV |
K+ reversal potential | EK | −84 | mV |
Node diameter Optic nerve Cortex |
|
0.73 0.64 |
μm μm |
Node length Optic nerve Cortex |
|
1.02 1.50 |
μm μm |
Paranode length Optic nerve Cortex |
|
2.11 1.90 |
μm μm |
Paranodal effective periaxonal space Optic nerve Cortex |
|
0.0077 0.0123 |
nm nm |
Internodal axon diameter Optic nerve Cortex |
|
0.82 0.73 |
μm μm |
Internodal periaxonal space |
| 15 | nm |
G ratio Optic nerve Cortex |
|
0.78 0.81 |
|
Number of myelin wraps Optic nerve Cortex |
|
7 5 |
|
Internode length Optic nerve Cortex |
|
139.26 81.7 |
μm μm |
-
*Values for standard node length: 1.02 µm in optic nerve, 1.50 µm in cortex; these are constant for simulations with fixed nodal conductance density, but scaled inversely with node length for simulations where number of nodal channels is kept constant.
-
†Membrane capacitance values are from Gentet et al. (2000).
-
‡Figures are per myelin membrane. There are two membranes per myelin lamella.
