问题 问答题 简答题

试述骨骼肌纤维的收缩原理。

答案

参考答案:

当运动神经上的冲动(动作电位)到达神经末梢时,通过神经一肌肉接头处的兴奋传递,使细胞膜产生兴奋。之后,肌质网向肌浆中释放钙离子,使肌浆中的钙离子瞬间升高。钙离子浓度升高后,肌钙蛋白C与钙离子结合,引起肌钙蛋白的分子结构改变,进而导致原肌球蛋白的分子结构改变,肌动蛋白分子上的活性位点暴露,粗肌丝上的横桥即与之结合。横桥与肌纤蛋白结合后会产生两种作用:①激活了横桥上的ATP酶,使ArIP迅速分解并产生能量供横桥摆动所用;②激发横桥的摆动,拉动细肌丝向A带中滑动。然后,横桥自动与肌动蛋白上的活性位点分离,并与新的活性位点结合,横桥再次摆动,拖动细肌丝又向A带中央前进一步。如此,横桥头部前后往复的运动,一步一步地在细肌丝上行走,拖动细肌丝向A带中央滑行。肌肉收缩时形成的横桥数目越多,肌肉的收缩力量也就越大。当肌浆中的钙离子的浓度升高时,肌浆网膜上的钙泵被激活。在钙泵的作用下,肌质网把钙离子泵入肌质网中,使肌浆中钙离子浓度降低,钙离子与肌钙蛋白C分离,肌钙蛋白和原肌球蛋白恢复原先的构型,原肌球蛋白再次掩盖肌动蛋白上的活性位点,阻止横桥与肌纤蛋白的相互作用,细肌丝回至收缩前的位置,肌肉舒

单项选择题 A1型题
单项选择题

Questions 56-60 are based on the following passage.
The Frugal Gourmet Cooks American
by Jeff Smith
Our real American foods have come from our soil and have been used by many groups—those who already lived here and those who have come here to live. The Native Americans already had developed an interesting cuisine using the abundant foods that were so prevalent.
The influence that the English had upon our national eating habits is easy to see. They were a tough lot, those English, and they ate in a tough manner. They wiped their mouths on the tablecloth, if there happened to be one, and they ate until you would expect them to burst. European travelers to this country in those days were most often shocked by American eating habits, which included too much fat and too much salt and too much liquor. Not much has changed! And, the Revolutionists refused to use the fork since it marked them as Europeans. The fork was not absolutely common on the American dinner table until about the time of the Civil War, the 1860s. Those English were a tough lot.
Other immigrant groups added their own touches to the preparation of our New World food products. The groups that came still have a special sense of self-identity through their ancestral heritage, but they see themselves as Americans. This special self-identity through your ancestors who came from other lands was supposed to disappear in this country. The term melting pot was first used in reference to America in the late 1700s, so this belief that we would all become the same has been with us for a long time. Thank goodness it has never worked. The various immigrant groups continue to add flavor to the pot, all right, but you can pick out the individual flavors easily.
The largest ancestry group in America is the English. There are more people in America who claim to have come from English blood than there are in England. But is their food English Thanks be to God, it is not! It is American. The second largest group is the Germans, then the Irish, the Afro-Americans, the French, the Italians, the Scottish, and the Polish. The Mexican and American Indian groups are all smaller than any of the above, though they were the original cooks in this country.

Which of the following statements is NOT true

A.English people had bad table manners.

B.American food was exclusively unique in its flavors and varieties.

C.American diet contained a lot of fat, salt and liquor.

D.Europeans were not at all accustomed to the American way of eating.