Myelin Sheath as a Dielectric Waveguide for Signal Propagation in the Mid‐Infrared to Terahertz Spectral Range

Abstract

The myelin sheath enables dramatic speed enhancement for signal propagation in nerves. In this work, myelinated nerve structure is experimentally and theoretically studied using synchrotron-radiation-based Fourier-transform infrared microspectroscopy. It is found that, with a certain mid-infrared to terahertz spectral range, the myelin sheath possesses a ≈2-fold higher refraction index compared to the outer medium or the inner axon, suggesting that myelin can serve as an infrared dielectric waveguide. By calculating the correlation between the material characteristics of myelin and the radical energy distribution in myelinated nerves, it is demonstrated that the sheath, with a normal thickness (≈2 µm) and dielectric constant in nature, can confine the infrared field energy within the sheath and enable the propagation of an infrared signal at the millimeter scale without dramatic energy loss. The energy of signal propagation is supplied and amplified when crossing the nodes of Ranvier via periodic relay. These findings provide the first model for explaining the mechanism of infrared and terahertz neurotransmission through myelinated nerves, which may promote the development of biological-tissue label-free detection, biomaterial-based sensors, neural information, and noninvasive brain-machine interfaces.

On the delay in propagation of action potentials

“…This results in an attenuated field strength when the pulsed signal arrives at the next signal source (20,17,19,21). This model explains well the highly overlapped successive action potentials as shown in Figure 1.…”

Cell vibron polariton resonantly self-confined in the myelin sheath of nerve

“…Based on the characteristics of the myelin sheath, together with the ultra-weak emission of biophotons 24,28,[33][34] , we built a full quantum mechanics (QM) model involving the photon-vibron coupling for exploring its effects in the myelin sheath. Considering that the myelin thickness was much less than its perimeter and length [15][16] and the confinement of specific-frequency light in a cylinder majorly depended on the cylindrical thickness (but not on its diameter) 30 , we employed a thin-film model ( Fig. 1 middle lower) for myelin sheath to present physics more clearly.…”

“…Subsequently, based on classical electromagnetic fields, a hypothesis of micron-scalar waveguide was proposed stating that IR light can travel in the myelin sheaths of nerves, serving as signals between neurons in addition to the well-established electrochemical signals [28][29] . Very recently, Liu and his coworkers proposed that energy of the IR-light signal propagating in myelin sheaths was supplied and amplified when crossing the nodes of Ranvier via periodic relay 30 . It is well known that waveguide performance clearly depends on the refractive difference of the core and cladding materials, while the refractivity is closely related to the excitation frequencies of materials.…”

Detection of living cervical cancer cells by transient terahertz spectroscopy

“…Because of this characteristic, THz technology can obtain the characteristic absorption peaks of cells and biological macromolecules, also known as “characteristic absorption spectrum.” Due to the low‐photon energy (4.1 meV@1 THz), the THz waves do not cause directly ionization of the sample and have a unique advantage to be used to detect living cell samples. [ 5–8 ] The characteristics of THz, such as transitivity, wideband, coherence, low energy, hydroscopicity and characteristic absorption spectrum, provide a new research method for us to reveal the rules of action between biological macromolecules and cells in the microscopic field.…”