Simulation of nerve fiber based on anti-resonant reflecting optical waveguide

Abstract

Light and optical techniques are widely used for the diagnosis and treatment of neurological diseases as advanced methods. Understanding the optical properties of nervous tissue and nerve cells is vital. Using light sources in these methods raises significant challenges, such as finding the place of light transmission in nerve fibers that could be an appropriate substrate for neural signaling. The myelinated axons are a promising candidate for transmitting neural signals and light due to their waveguide structures. On the other hand, with the emergence of diseases such as multiple sclerosis and disorders within the production and transmission of nerve signals, because of the demyelination, understanding the properties of the myelinated axon as a waveguide is obtaining additional necessity. The present study aims to show that the myelinated axon’s refractive index (RI) profile plays an essential role in transmitting the beams in it. According to the nerve fiber, RI profile and its similarity to depressed core fiber with lower RI of the core compared to the cladding, the behaviors of the nerve fiber based on anti-resonant reflecting optical waveguide structure are investigated by taking into account the realistic optical imperfections. Light launching to the myelin sheath and axon is shown by introducing the axon and myelin sheath as a waveguide in the presence of both axon and myelin with bends, myelin sheath variation, and node of Ranvier.

Optical polarization evolution and transmission in multi-Ranvier-node axonal myelin-sheath waveguides

“…There are a number of features that can be added to our myelinated axon model to better describe the biological reality 11,13,36 , as has been examined in previous studies thus far to measure transmission through short segments of the myelin sheath. Polarization evolution in the myelin sheath can be assessed across realistic ranges of biological parameters -notably axon radius, g-ratio, and biophoton wavelength -and in the presence of realistic optical imperfections such as bends in the axon, varying myelin thickness, irregular cross-section shapes and areas, paranodal regions and the positive radial birefringence of the myelin sheath 66,67 .…”

“…Their treatment to estimate transmission across inter-neuron distances demonstrated that biophoton transmission along myelinated axons is possible within realistic expectations of these optical imperfections. This has sparked various theoretical studies 13,[36][37][38][39][40][41] , and the possibility of myelin sheath waveguides has been well-supported through subsequent simulations. Another biophoton-motivated simulation study 13 considered (optical spectral range) mode propagation in the context of a myelinated axon model containing the detailed multi-lamellar structure of the myelin sheath.…”

“…It has also been recognized that the cross-section of myelinated nerve fiber can be considered a depressed-core fiber due to its refractive index profile. Myelinated nerve fiber can be treated as an anti-resonant reflecting optical waveguide 36 (a model developed for depressed-core fibers 42 ) wherein myelin, as the high-index cladding, will confine and transmit incident light well even in the presence of optical imperfections.…”