人体内某反射弧如图一所示，电流计的两个电极位于神经纤维膜的外侧：当给予A点不同强度刺激后，A点在不同时刻膜电位的变化情况如图二所示：图三则示意给予A点刺激后，在某一时刻不同位点膜电位的情况。请据图分析作答：
(1)图一中，虚线部分示意的结构为_____，C处一般是神经元的_____部分的细胞膜，该膜上发生的信号转换为_____。若先刺激①神经元，电流表指针偏转_____次，再刺激
②神经元，电流表指针偏转_____次，由此说明兴奋在两个神经元之间的传递是_____的。
(2)由图二分析可知，若D点受到的刺激为阈下刺激，与阈上刺激相比，Na+内流量_____，_____(能，不能)介导细胞产生动作电位。(3)轴突膜处于HI段状态时，_____离子通道大量开放，与图二中_____段膜电位状态相同。
正确答案及解析
正确答案
解析
(1)突触；细胞体或树突；化学信号→电信号；两；一；单向(2)少；不能
(3)钠：DE
(1)分析图一可知，传人神经上有神经节，细胞A为感受器，细胞B为效应器。根据突触的示意图判断有两个突触，图中虚线部分为神经元之问的结构——突触；C处为突触后膜，一般是后一个神经元的树突膜或胞体膜，突触后膜上发生的信号变化为化学信号变为电信号；信号只能由突触前膜传递到后膜、在①给予一一适当的刺激会引发局部电流，使电流表右接触点先变为外负内正，电流表偏转；当局部电流流过后，右接触点恢复为外正内负．左接触点变为外负内正，电流表再次偏转，共偏转两次。再刺激②处神经元，由于兴奋在神经元之间的传递是单向的，兴奋只能到达左端电极，不能到达右端电极，因此电流表偏转一次。
(2)分析图二可知，图中D点若所受刺激为阈下刺激，与图上刺激相比，电位差较小，说明Na+内流量减少．不能介导细胞产生动作电位。
(3)轴突膜处于HI段状态时，神经纤维处于兴奋状态，钠离子通道打开造成Na+内流，产生动作电位，图二中DE段为动作电位．因此与图二中DE段膜电位状态相同。
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