1.School of Information and Communication Engineering, North University of China, Taiyuan 030051, China 2.School of Chemical Engineering and Technology, North University of China, Taiyuan 030051, China
Fund Project:Project supported by the National Defense Science and Technology Innovation Special Zone of China (Grant No. 02-ZT-008)
Received Date:05 March 2021
Accepted Date:22 March 2021
Available Online:07 June 2021
Published Online:05 August 2021
Abstract:Neurons collect information from different parts of the biological body, generate signals and control their functions and activities. There are electromagnetic communication channels between neurons apart from the action potentials. Microtubules are the largest cytoskeletal filaments in neurons, with a diameter of about 25 nm. Microtubule is composed of alpha- and beta-tubulin subunits assembled into hollow cylindrical polymers supporting dynamical growth, and facilitate transport of proteins. In axons, dendrites, growth cones, and migratory neurons, microtubules are generally tightly organized in array and uniformly oriented. Because of the polarity and charge distribution of tubulins, the vibrations of microtubules generate electromagnetic fields. In this paper, electromagnetic fields induced by different vibrational modes of microtubules are studied. The vibrational mode of tubulins calculated using the normal mode analysis shows that there are abundant vibrational modes in the terahertz range. The electric fields of different vibration modes show distinct distribution features. The induced electromagnetic fields of microtubules can be stronger than thermal noise because of reduced permittivity of intracellular fluid for higher frequencies in a nanometric confined region. Since water exhibits layered structuring near all surfaces independent of their hydrophilicity, the permittivity of water surrounding tubulins between microtubules is expected to decrease significantly because of surface-induced alignment of water molecular dipoles. While the permittivity of surrounding medium decreases to 5, the electromagnetic potential energy between two 100-nm-long microtubules can be stronger than the thermal energy within a 30-nm-long distance. As high frequency vibrations are generally localized in the microtubule, terahertz electromagnetic interactions can be present between tubulins and short microtubules. Because the separation between microtubule arrays in neurons is in a range from 20 nm to 100 nm, electromagnetic interactions between microtubules can dominate the thermal motions, and affect the biological functions. Simulation results show that the electromagnetic potential energy increases over one order of magnitude when the vibration amplitude is changed from 0.1 nm to 0.4 nm. The results indicate that the electromagnetic interaction between microtubules is important for a better understanding of neural functions and communication. Terahertz stimulations can be used to detect and modulate the neural signals. The microtubule vibration generated magnetic field can be applied to disease diagnosis and brain-machine interface. Keywords:neuron/ microtubule/ electromagnetic fields/ dielectric constant
图 4 不同长度微管屈曲振动势能的传播特性 (A = 0.1 nm, ${\varepsilon }_{\rm{r}}=80)$ Figure4. Vibrating potential transferring performance in different length of microtubule at A = 0.1 nm, ${\varepsilon }_{\rm{r}}=80$.
3.微管振动产生电磁场23.1.溶液介电常数 -->
3.1.溶液介电常数
溶液的介电常数随频率和空间尺度的变化而变化. 如图5所示, 水溶液介电常数随频率变化, 在低频时(< 10 GHz), 水的介电常数实部接近静态时的值(${\varepsilon }_{\rm{r}}=80)$, 在高频(> 100 GHz)时${ \varepsilon }_{\rm{r}}$下降到10, 在THz频段接近5. 同时, 神经细胞中微管间的纳米尺度空间限制, 也将减小溶液的介电常数. 因此, 相比静电场作用, 100 GHz —10 THz电磁场在纳米范围内的溶液中作用距离更远. 图 5 水溶液介电系数的频率响应 Figure5. Permittivity of intracellular fluid of neuron as a function of frequency.