(三)平滑肌活动的控制和调节

和平滑肌本身的特性具有多样性一样,它们活动所受的调控也是多种多样的,不象骨骼肌那样单纯。大多数平滑肌接受神经支配,包括来自自主神经系统的外来神经支配,其中除小动脉一般只接受交感系统一种外来神经支配外,其他器官的平滑肌通常接受交感和副交感两种神经支配。平滑肌组织、特别是消化管平滑肌肌层中还有内在神经丛存在,后者接受外来神经的影响,但其中还发现有局部传入性神经元,可以引起各种反射。平滑肌的神经-肌接头有些类似骨骼肌,但不具有后者那样特殊结构形式。支配平滑肌的外来神经纤维在进入靶组织时多次分支,分支上每隔一定距离出现一个膨大,呈念珠状,称为曲张体,其中含有分泌囊泡,它们在神经冲动到达时可以释放其中递质或其他神经活性物质;每个曲张体和靶细胞的距离亦不固定,平均约为80~100nm,这说明由神经末梢释放出来的递质分子要扩散较远距离才能达到靶细胞,而靶细胞和神经末梢的关系也不可能是固定的;凡是递质分子可以到达而又具有该递质受体的平滑肌细胞,都可能接受外来神经的影响。 平滑肌细胞约保持-55~-60mV的静息电位,产生机制和骨骼肌类似。单位平滑肌细胞有产生动作电位的能力,而且通过细胞间通道可使相邻细胞也产生动作电位。 [b]参考资料[/b] · 乔健天,关于兴奋膜的一些基本概念和新进展.生理科学进展1980;11:193~200 · 董政,朱培闳.肌醇磷脂信使系统调控骨骼肌兴奋收缩耦联.生理科学进展1994;25:121~125 · BerneRM,Levy MN.Physiology 3rd ed,CV Mosby C[XB]o[/XB],S[XB]t[/XB] Louis,1993 · WrightFM.The intestinal Na/glucose cotransporter .Ann Rev Physiol 1993;55:575~589 · ThorensR.Facilitated glucose transporters in epithelial cells.Ann Rev Physiol1993;55:591~608 · Simon.MI,Strathman MP,Gautam N.Diversity of G-protein in signaltransduction .Science 1991;252:802 · FantlWJ,Johnson DE,Williams LT.Signaling by receptor tyrosine kinases.Ann RevBiochem 1993;62:453~481 · StraderC,Fang TM,Dixon RAT.Structure and function of G-protein-coupled receptors.AnnRev Biochem 1994;63:101~132 · ClaphamD,Found M,Rochester MN.Direct G-protein activation of ion channel?Ann RevNeurosci 1994;17:441~464 · HodgkinAL.The ionic basis of nervous conduction.Science 1964;145:1148~1153 · BezanillaF,Steffani E.Voltage-dependent gating of ionic channels .Ann Rev Biophy andBiomol Structure 1994;23:819~846 · NeherE.Ion channels for communication between and within cells.Neuron 1992;8:605~612 · SakmannB.Elementary steps in synaptic transmission revealed by currents through singleion channels .Neuron 1992;8:613~629 · FrenchAS.Mechanotransduction.Ann Rev Physiol 1992;54:135~152 · ShengM,Greenberg MF.The regulation and function of c-fos and other immediate earlygenes in the nervous system .Neuron 1990;4:477~485 · FrancisArmstrong C,Jorgensen AO.Structure and development of E-C coupling units inskeletal muscle .Ann Rev Physiol 1994;56:509~534 · MottaPM.Ultrastructure of Smooth Muscle .Kluwer Academic Publishers.Lancaster,England,1990 · GalziJL,Revah F,Bessis A,Changeux JP.Functional architecture of the nicotinicacetylcholine receptor:from electric organ to brain .Ann Rev Pharmacol1991;31:37~72 · CatterallWA.Structure and function of voltage-gated ion channels.TINS 1993;16:500 · Huxley HE.The mechanism of muscle contraction .Science 1969;164:1355~1366