有髓鞘神经纤维冲动传导的计算机模拟

在分析电压箝位法大量实验结果的基础上,Hodgkin 和 Huxley 提出了乌贼大神经可兴奋膜的数学模型。此后,很多工作表明这个模型能够模拟无髓鞘神经的兴奋与传导。在这个模型的基础上,Fitzhugh 结合有髓鞘神经纤维的电缆特性,首先利用计算机描述了有髓鞘神经的跳跃传导现象。后来,Goldman 和 Albus 用 Frankenha-user 和 Huxley 提出的朗氏节膜方程,重新计算了有髓鞘神经纤维上的传导现象,表明传导速度与纤维直径成正比。关于温度、溶液中 Na 离子浓度、髓鞘厚度等对兴奋传     

相连四组神经的传入对在体肠系膜下神经节细胞兴奋的作用

运用在体细胞内电位记录法,观察了与肠系膜下神经节（IMG）相连的四组神经对IMG神经元自发电位活动的影响,结果显示扩和结肠或膀胱时,IMG细胞自发电位活动增加;切断或阻滞任一组神经均使IMG细胞电位活动受抑。其中结肠神经和腹下神经分别传导源自结肠尾段和膀胱等盆腔脏器的外周性兴奋,节间神经同时传导源自脊髓的中枢性和结肠的外周笥兴奋,肠系膜下神经节细胞的兴奋不仅源自脊髓,而且来源于结肠和膀胱。定量研究表明后者比前者对神经节细胞兴奋的影响更大。     

先天性巨结肠Bcl-2的表达及意义

1886年丹麦医生Hirschsprung首先描述了先天性巨结肠症,故又称为Hirschsprung's Disease(HD)。HD发病率居先天性畸形的第二位,平均每5000个成活新生儿中发生1例,其病理学基础是病变肠段结肠壁神经节细胞缺如。但HD的病因较为复杂,迄今仍有争议。Bcl-2蛋白是凋亡抑制基因Bcl-2的表达产物,具有遏止细胞凋亡的作用。在正常神经系统发育过程中,Bcl-2蛋白在外周神经系统中长期表达,提示Bcl-2蛋白对外周神经系统神经元的存活起了重要的作用,尤其是外周神经受到伤害时,Bcl-2蛋白有助于外周神经的修复。目前,Bcl-2蛋白对神经     

大白鼠交感节前神经再生的研究Ⅰ.生化、组化与功能观察

用液氮骤冻造成大白鼠交感节前神经变性后,通过神经末梢乙酰胆碱含量、胆碱酯酶活性测定以及电刺激交感干时外周反应等研究其再生规律。结果表明冻伤后3周内再生过程进展迅速,神经结构与功能均有相当程度的恢复;3周后再生过程转慢,直至一年时各指标仍远未达到正常。这证明交感节前神经的再生过程不同于中枢及其它外周神经而独具特征。     

腹部迷走神经在血压调节中的作用

迷走神经是一种混合性神经,传入纤维占绝大多数。腹部迷走神经对血压的调节是通过中枢和外周两方面的作用来完成的。腹部迷走神经的传入冲动可以经本身的传入纤维到达延脑的孤束核及其邻近的网状结构而影响血压。兴奋腹部迷走神经外周端可以引起腹腔器官组织释放儿茶酚胺、组织胺等体液因素而作用于外周血管。这些都不是胆硷能纤维的作用。兴奋腹部迷走神经所引起的冲动还可以某种联系方式经内脏大神经的传入纤维到达孤束核。但是二者之间是如何联系和接通的,尚待进一步研究。     

成年哺乳动物神经发生的关键调控环节:GABA的作用由兴奋到抑制的转变

近年,调控成年哺乳动物神经干细胞增殖、迁移、分化和成熟的信号分子逐渐被揭示,其中γ-氨基丁酸(gamma-aminobutyric acid,GABA)由兴奋到抑制的转变是神经发生的一个关键环节.与传统的GABA抑制作用不同,在未成熟神经细胞中,GABA以一种自分泌或旁分泌的方式释放并作用于GABAa受体,表现出明显的兴奋作用,这种兴奋对成年动物神经发生起重要调节作用,随着神经元的成熟,GABA的兴奋作用逐渐被抑制作用取代,此后,GABA完成从调节神经发生到传递抑制性神经冲动的转变.GABA调节神经发生的确切机制尚有待进一步研究.     

感觉神经元中的神经肽及其有关的外周功能

速激肽(P 物质,神经激肽 A,神经肽 K)和降钙紊基因相关肽共存于感觉神经元中,其神经末梢中枢端止于脊髓背角,外周端止于内脏器官和皮肤粘膜等组织。刺激感觉神经,这两类神经肽即可从末梢端释放。速激肽和降钙素基因相关肽在感觉神经外周端的释放引起一系列的局部反应,如:毛细血管通透性增加、小动脉血管扩张、正性心率和正性肌力作用、非血管平滑肌张力的改变以及囱主神经节上的慢兴奋突触后电位。     

“神经系统”前数课的教学法

第一课神经系统的意义;关于其构造的概念本课从关于神经系统的意义的谈话开始.令学生以动物行为为例,描述当时感觉、神经、脑等器官的作用.回忆在课题“哺乳动物的神经系统”中研究过的例子(七年级),在这里,学生曾经初步地获得了刺激与兴奋的观念.     

多巴胺及多巴胺转运蛋白与帕金森病

一、多巴胺(DA)的合成、 释放与失活 DA是中枢神经系统的儿茶酚胺类神经递质,在植物神经系统某些神经节也起着神经递质的作用。在外周和中枢神经系统,DA是去甲肾上腺素和肾上腺素的前体。已知的DA功能与中枢神经系统有关,曾认为,多巴胺能神经传递仅存在于中枢神经系统。而对它的外周作用却了解较少。事实上,许多外周组织对外源性DA也有反应,但在这些组织没有发现多巴胺能神经分布,说明没有多巴胺能神经支配的外周组织也可能存在多巴胺受体。     

关于耦合神经元活动时的能量原理

最近美国耶鲁大学的神经科学家们用实验数据表明,哺乳动物大脑皮层中神经信号的传递是一个代价昂贵的能量支出过程,而神经信号的编码是与能量代谢紧密地耦合在一起的,但是到目前为止还无法定量给出神经元活动时的能量函数。在这篇文章中,能量原理被用于神经活动和神经信息处理机制的研究,在电生理实验数据的基础上,建立神经元活动的用能量函数表示的运动方程。结果表明用能量函数表达耦合神经元的阈下电活动和动作电位,数值计算结果与用Hodgkin-Huxley方程所描述的动作电位一致。从而有可能依据能量原理从脑信息处理的角度揭示和理解大脑神经网络系统的信息表现规律。     

On shunting inhibition

The interaction between excitation and inhibition is analyzed for nerve cylinders when reversal potentials for synaptic action are included. Both impulsive and sustained conductance changes are employed to model synaptic action.Exact results, in terms of Green's functions are obtained for the solutions of the cable equation with reversal potentials when there are impulsive conductance changes. The amplification factor for an inhibitory input due to a prior excitatory input is found exactly. In the case of an infinite cylinder, the dependence of this factor on the spatial separation of the excitatory and inhibitory synapses is one plus a Gaussian density function. Similar results aply when excitation follows inhibition. There is shunting inhibition even for impulsive conductance changes in the cable, but it is very different from that for sustained conductance changes. The interaction of excitation and inhibition is also studied in the full cable equation with reversal potentials and sustained conductance changes. An exact result is obtained for the potential in response to simultaneous excitation and inhibition at the same space point in an infinite cable. The effects of timing and spatial separation of inputs is analyzed in a finite nerve cylinder by numerically integrating the cable equation by the Crank-Nicolson method. Shunting inhibition is found to be most effective, for the chosen parameter values, when inhibition quickly foolows excitation. The EPSP amplitude at the soma is found to be roughly proportional to the distance from the soma to the site of inhibition when the excitation is at the center of the nerve cylinder.Dedicated to Jane Pauley     

Conducting pathways of the superior cervical sympathetic ganglion of the cat

Individual nerves of the superior cervical sympathetic ganglion were stimulated in acute experiments on cats, and action potentials (AP) were recorded from other nerves of the ganglion in order to clarify whether or not there is transmission of excitation through the ganglion from one nerve to another and to establish whether this transmission is continuous or synaptic. The method of intracellular recording from neurons of the ganglion was also used. It is established that stimulation of the cervical sympathetic nerve evokes AP in all of the peripheral nerves of the ganglion, a circumstance that is the result of synaptic transmission of excitation. There is no transmission of excitation in the reverse direction or between any of the 12 peripheral nerves of the ganglion (including the four branches of the internal carotid nerve). Orthodromic excitation is recorded intracellularly from neurons of the ganglion during stimulation of the cervical sympathetic nerve, and antidromic excitation is recorded during stimulation of a peripheral nerve (the internal carotid nerve). It follows that the pathways through the ganglion which conduct excitation from the cervical sympathetic nerve into all of the remaining nerves of the ganglion are synaptic. Analysis of EPSP latent periods indicated that preganglionic fibers that differ sharply with respect to threshold and conduction rate (groups S₂ and S₄) converge on one and the same neurons of the ganglion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 2, pp. 216–224, March–April, 1970.     

A model of the peripheral auditory system

Summary Recent electrophysiological data obtained from auditory nerve fibers of cats have made possible the formulation of a model of the peripheral auditory system that relates the all-or-none activity of these fibers to acoustic stimulation. The components of the model are intended to represent the major functional components of the peripheral system. These components are: (i) a linear mechanical system intended to represent the outer, middle, and mechanical parts of the inner ear; (ii) a transducer intended to represent the action of the sensory cells; and (iii) a model neuron whose properties are intended to represent the nerve excitation process. A general-purpose digital computer has been used to determine the response of the model to a variety of acoustic stimuli. These results have been compared with data obtained from auditory nerve fibers.This work was supported in part by the Joint Services Electronics Program (Contract DA 36-039-AMC-03200(E); and in part by the National Science Foundation (Grant GP-2495), the National Institutes of Health (Grant MH-04737-05), the National Aeronautics and Space Administration (Grant NsG-496); and by Research Grant NB-01344, National Institute of Neurological Diseases and Blindness of the National Institutes of Health, Public Health Service.     

Does direction of induced electric field or current provide a test of mechanism involved in nerve regeneration?

We suggest an experimental comparison of two directions for applying the time-varying magnetic fields which have been found to speed spontaneous regeneration of injured peripheral nerves and in attempts to repair spinal cord injuries. Time-varying magnetic fields induce currents in a plane perpendicular to the magnetic field direction. The lower conductivity of the spinal cord's sheath (dura matter) or of the myelin sheath of peripheral nerves would seem to confine the induced electric fields and currents to the spinal cord or nerve itself. The proposed comparison could allow choosing between two possible modes of action of the fields: (1) Magnetically-induced electric fields or currents may be encouraging ion flow or otherwise helping enzyme, channel or other interactions at the cell membrane, as is thought to be the case in field stimulation of healing in bone. This mechanism should be independent of field direction. (2) Work in developing organisms and with fields applied to nerve cells in vitro has shown that neurite growth is guided parallel to both endogenous and external electric fields. This mechanism would be effective when induced electric fields are parallel, but not when they are perpendicular to the nerve. Any experimental test should seek to produce as close as possible to the same induced current intensity with both field directions. Possible confounding factors, as well as breakdowns in the assumptions of the simple model presented here, would have to be considered. This proposal was motivated by a recent report in which the authors listed a changed field direction as one of several possible reasons for an unsuccessful experiment.     

Influence of 50 Hz-1 mT magnetic field on human median nerve

In this study, human median nerve was exposed to power frequency magnetic fields in order to provide clarification for possibly changeable nerve conduction mechanism. The nerve was exposed to 50 Hz magnetic field by utilizing a special Helmholtz applicator. The experiments were carried out with six healthy human-volunteers. Median motor distal amplitude/proximal amplitude ratios were recorded from adult human median nerve pre-exposure, during, and post-exposure to a 50 Hz, 1 mT magnetic field. The result of 18 measurements shows that median motor distal amplitude/proximal amplitude ratio significantly decreases in pre-exposure state as compare to post exposure of which. The results of this study may be useful for some nerve rehabilitation, excitation, and stimulation in more effective/safe physical therapy. Additionally, 50 Hz, 1 mT sinusoidal magnetic field should not be recognizing as safe for conduction mechanism on a nerve. These mechanisms would be cleared by new advanced engineering models in other future works.     

Kelvin-Helmholtz instability for a bounded plasma flow in a longitudinal magnetic field

Kelvin-Helmholtz MHD instability in a plane three-layer plasma is investigated. A general dispersion relation for the case of arbitrarily orientated magnetic fields and flow velocities in the layers is derived, and its solutions for a bounded plasma flow in a longitudinal magnetic field are studied numerically. Analysis of Kelvin-Helmholtz instability for different ion acoustic velocities shows that perturbations with wavelengths on the order of or longer than the flow thickness can grow in an arbitrary direction even at a zero temperature. Oscillations excited at small angles with respect to the magnetic field exist in a limited range of wavenumbers even without allowance for the finite width of the transition region between the flow and the ambient plasma. It is shown that, in a low-temperature plasma, solutions resulting in kink-like deformations of the plasma flow grow at a higher rate than those resulting in quasi-symmetric (sausage-like) deformations. The transverse structure of oscillatory-damped eigenmodes in a low-temperature plasma is analyzed. The results obtained are used to explain mechanisms for the excitation of ultra-low-frequency long-wavelength oscillations propagating along the magnetic field in the plasma sheet boundary layer of the Earth’s magnetotail penetrated by fast plasma flows.     

太赫兹刺激听神经的测试平台搭建

目的 近年来，用于脑功能调控的神经调控技术蓬勃发展，很多方法已在临床上被推广应用，主要包括电极深部脑刺激、经颅磁刺激、光遗传技术、超声深脑刺激等。但是这些调控技术存在刺激靶点改变灵活性差、空间分辨率不足、需要注射病毒转染等问题。与这些技术相比，太赫兹波调控则能以较高的时空分辨率、无需引入外源基因的方式对神经活动进行干预。激光神经刺激是一种具有较明确靶向性的刺激方法，可以通过调整不同激光参数（激光波长、脉冲能量等）控制引起神经兴奋或者抑制。但是由于该研究方向的实验手段和实验平台的缺乏，相关研究开展较少。方法 针对这个问题，从听觉神经入手，在分子、细胞和在体不同层面为相关领域的研究搭建了不同的测试平台。结果 实验结果表明，这些系统在时间和空间上具有良好的耦合性和靶向性，测得的信号受噪音干扰小。结论 这些系统可以有效测试神经系统对太赫兹刺激的响应并精确控制刺激时间和位置。     

Electromuscular incapacitation results from stimulation of spinal reflexes

Electronic stun devices (ESD) often used in law enforcement, military action or self defense can induce total body uncoordinated muscular activity, also known as electromuscular incapacitation (EMI). During EMI the subject is unable to perform purposeful or coordinated movements. The mechanism of EMI induction has not been reported, but has been generally thought to be direct muscle and nerve excitation from the fields generated by ESDs. To determine the neuromuscular mechanisms linking ESD to induction of EMI, we investigated EMI responses using an anesthetized pig model. We found that EMI responses to ESD application can best be simulated by simultaneous stimulation of motor and sensory peripheral nerves. We also found that application of local anesthetics limited the response of ESD to local muscle stimulation and abolished the total body EMI response. Stimulation of the pure sensory peripheral nerves or nerves that are primarily motor nerves induced muscle responses that are consistent with well defined spinal reflexes. These findings suggest that the mechanism of ESD‐induced EMI is mediated by excitation of multiple simultaneous spinal reflexes. Although direct motor‐neuron stimulation in the region of ESD contact may significantly add to motor reactions from ESD stimulation, multiple spinal reflexes appear to be a major, and probably the dominant mechanism in observed motor response. Bioelectromagnetics 30:411–421, 2009. © 2009 Wiley‐Liss, Inc.     

Analytical theory for extracellular electrical stimulation of nerve with focal electrodes. I. Passive unmyelinated axon.

The cable model of a passive, unmyelinated fiber in an applied extracellular field is derived. The solution is valid for an arbitrary, time-varying, applied field, which may be determined analytically or numerically. Simple analytical computations are presented. They explain a variety of known phenomena and predict some previously undescribed properties of extracellular electrical stimulation. The polarization of a fiber in an applied field behaves like the output of a spatial high-pass and temporal low-pass filter of the stimulus. High-frequency stimulation results in a more spatially restricted region of fiber excitation, effectively reducing current spread relative to that produced by low-frequency stimulation. Chronaxie measured extracellularly is a function of electrode position relative to the stimulated fiber, and its value may differ substantially from that obtained intracellularly. Frequency dependence of psychophysical threshold obtained by electrical stimulation of the macaque cochlea closely follows the frequency dependence of single-fiber passive response.