题目

   Have you got any wonderful plans for your coming winter vacation? Here are some wonderful films for you to kill time. Away We Go With a baby on his way, a young couple,  Burt and Verona, look at their lives and are puzzled about what they really want. So they hit theroad and seek a place to call home. On their journey, they visit ahandful of characters and learned a lot. It’s about takingthe scenic route in life, preparing for the hope and excitement and fear ofnew beginnings, while never forgetting to look out of the window.Orphan  Esther, a bright and well-behaved child,however,9．如图是神经-肌肉接头，其结构和功能与突触类似．当兴奋传导至突触小体时，突触间隙中的Ca2+通过突触前膜上的Ca2+通道内流，导致突触小泡与突触前膜融合，释放神经递质．血钙正常值约为9-11mg/100mL血浆．低于7mg/100mL血浆时属低血钙，低血钙即细胞外钙浓度降低，对钠内流的抑制屏障作用减弱，使神经细胞兴奋性增高．请回答下列问题：（1）传出神经末梢及其支配的肌肉在反射弧中称为效应器．科学家研究发现，刺激大脑皮层的中央前回，也会引起肌肉的收缩，此时接受刺激的是反射弧中的神经中枢．（2）乙酰胆碱属于一种兴奋性神经递质，当乙酰胆碱与肌细胞膜上相应受体结合后，引起肌肉收缩．α-银环蛇毒能与乙酰胆碱受体结合，α-银环蛇毒中毒时，肌肉表现是松弛（或不能收缩、或舒张）．（3）由题中信息可知，肌肉收缩需要钙离子，但是血钙过高却会引起肌无力，原因是血钙过高降低了神经细胞兴奋性．（4）动态皱纹又称动力性皱纹，它是由于面部表情肌长期收缩牵拉皮肤而形成的．“肉毒毒素美容”已经成为时下普遍接受的面部除皱方式．肉毒毒素是肉毒杆菌分泌的一种神经毒素，能特异地与突触前膜上Ca2+通道结合．结合图解分析“肉毒毒素美容”的原理：肉毒毒素阻止Ca2+内流，影响突触前膜释放乙酰胆碱，导致面部表情肌松弛．