文档库 最新最全的文档下载
当前位置:文档库 › 兰大《大学英语四》16春平时作业1

兰大《大学英语四》16春平时作业1

兰大《大学英语四》16春平时作业1
兰大《大学英语四》16春平时作业1

《大学英语四》16春平时作业1

阅读理解完型填空

一、单选题(共 15 道试题,共 60 分。)

1. sun nois of fir-ngin m him___to th oor. . hurrying

. hurri

. hurry

. to hurry

正确答案:

2. I ______ my hom work this tim ystry vning. . wr oing

. ws to o

. m oing

. ws oing

正确答案:

3. I won't mk th _______ mistk nxt tim.

. lik

. sm

. nr

. similr

正确答案:

4.

- How ws your trip to Lonon, Jn?

- ___________

. Oh, wonrful in.

. I wnt thr lon.

. Th gui show m th wy.

. y pln n y us.

正确答案:

5.

- My I spk to r. rown?

- _________

. Ys, h is not in t th momnt.

. No, you n't.

. Ys, this is rown spking.

. Sorry, spking.

正确答案:

6.

- How oftn o you go ning?

-________

. I will go ning tomorrow.

. Ystry.

. vry othr y.

. I'v n ning for yr.

正确答案:

7.

-- i you win th 100 mtr r? -- Ys, I i.

-- Rlly? -- _________.

. ongrtultions

. st wishs

. Goo luk

. Right

正确答案:

8. Sh hs n working hr y n night uring ths yrs _______ sh oul py for th lost nkl. . in orr tht

. s long s

. th momnt

. us

正确答案:

9. ftr wlking hurrily for hlf n hour, I wnt to rink _______.

. somthing ol

. ol somthing

. somthing with ol

. somthing to ol

正确答案:

10. On ________ si of th strt thr r som trs.

. oth

. ithr

. vry

. ll

正确答案:

11.

- n I sk you fw qustions?

- _________

. Wht o you o?

. It's goo i.

. No, thnks.

. rtinly.

正确答案:

12. on't worry. Thr's still _____tim to go.

. littl

. littl

. fw

. fw

正确答案:

13. — ongrtultions! You won th first priz in toy’s sph ontst.— ________

. Ys, I t th othrs.

. No, no, I in’t o it wll.

. Thnk you.

. It’s plsur.

正确答案:

14.

-- I hv pss th mths xm!

-- _________. ongrtultions!

. Sorry

. om on

. Wll on

. luk

正确答案:

15.

--Hi, is Mry thr, pls?

--_____

. Hol on. I'll gt hr.

. No, sh isn't hr.

. Ys, sh livs hr.

. Ys, wht o you wnt?

正确答案:

《大学英语四》16春平时作业1

阅读理解完型填空

二、阅读理解(共 1 道试题,共 20 分。)

1.

Mny popl who work in Lonon prfr to liv outsi it, n to go in to thir offis or shools vry y y trin, r or us, vn though this mns thy hv to gt up rly in th morning n rh hom lt in th vning.

On vntg of living outsi Lonon is tht houss r hpr. vn smll flt in Lonon without grn osts quit lot to rnt. With th sm mony, on n gt littl hous in th ountry with grn of on's own.

Thn, in th ountry on n rlly gt wy from th nois n hurry of usy working livs. vn though on hs to gt up rlir n spn mor tim in trins or uss, on n slp ttr t night n uring wkns n on summr vnings, on n njoy th frsh, ln ir of th ountry. If on liks grns, on n spn on's fr tim igging, plnting, wtring n oing th hunr n on othr jos whih r n in grn. Thn, whn th flowrs n vgtls om up, on hs got th rwr togthr with thos who hv shr th srt of Ntur.

Som popl, howvr, tk no intrst in ountry things: for thm, hppinss lis in th town, with its inms n thtrs, utiful shops n usy strts, n-hlls n rsturnts. Suh popl woul fl tht thir lif ws not worth living if thy h to liv it outsi Lonon. n osionl wlk in on of th prks n fortnight's (two wks) visit to th s vry summr is ll th ountry thy wnt: th rst thy r quit prpr to lv to thos who r gl to gt wy from Lonon vry night. 1). Whih of th following sttmnts is NOT tru?_________

.

Popl who lov Ntur prfr to liv outsi th ity.

. Popl who work in Lonon prfr to liv in th ountry.

. Som popl njoying ity lif prfr to work n liv insi Lonon.

. Mny ntur lovrs, though working in Lonon, prfr to liv outsi th ity.

正确答案:

2). With th sm mony ________, on n uy littl hous with grn in th ountry.

.

gtting smll flt with grn

. hving smll flt with grn

.

rnting smll flt without grn

. uying smll flt without grn

正确答案:

3). Whn th grn is in lossom, it mns tht on ________ hs n rwr.

.

living in th ountry

. hving spnt tim working in th grn

. hving grn of his own

. hving n igging, plnting n wtring

正确答案:

4). Popl who think hppinss lis in th town woul fl tht _______ if thy h to liv outsi Lonon.

.

thir lif ws mninglss

. thir lif ws invlul

. thy in't srv hppy lif

. thy wr not worthy of thir hppy lif

正确答案:

5). Th unrlin phrs gt wy from in th 3r prgrph rfrs to ________.

.

l with

. o wy with

. sp from

. prvnt from

正确答案:

《大学英语四》16春平时作业1

阅读理解完型填空

三、完型填空(共 1 道试题,共 20 分。)

1.

Mr. lrk works in mil shool. H liks ring n oftn orrows som ooks from th lirry.

H kps ___31___ to th rio vry morning n ring nwspprs ftr suppr. So h knows muh n ths wll. His stunts worship(崇拜)him vry muh.

Mik, Mr. lrk's littl son, is only nin. H ___32___ liks ring ooks. n h oftn sks his fthr som qustions. Mr. lrk lwys thinks h's too ___33___ to unrstn him n hooss th sist ons to nswr. Of ours th oy is not pls with tht.

On y Mik r ___34___ out th lights n ws intrst in it. Whn his fthr tol him to o som houswork, h wnt on thinking of it. H sk him ___35___ qustions, n his fthr nswr ll. Thn his fthr si prouly, "Fthrs lwys know mor thn sons!"

Th oy thought for whil n si, "I on't think so!"

1).

.

fw

. listning

. lso

. young

. somthing

正确答案:

2).

.

fw

. listning

. lso

. young

. somthing

正确答案:

3).

.

fw

. listning . lso

. young

. somthing 正确答案:4).

.

fw

. listning . lso

. somthing . young

正确答案:5).

.

fw

. listning . lso

. young

. somthing 正确答案:

大学英语4(终极版)

Unit1 1.Taxes are a(n) which may fall on everybody. 税收是每个人都可能承担的义务。 2.We the authority's decision not to close the hospital. 我们赞成当局不关闭医院的决定。 3.The doctor's instructions must be exactly; the sick man's life depends on it. 医生的指示必须准确地完成;病人的生命取决于它 4.Do these opinion polls really what people are thinking? 这些民意测验真的反映了人们的想法吗? 5.I prefer to think of memorization as a stepping-stone to in use of words and phrases. 我更倾向于认为记忆是一个垫脚石,以(灵活)运用词语和短语 6.In her office memos she tended to devalue the work done by her staff. 在她的办公室备忘录中,她倾向于(贬低)工作人员所做的工作。 7.The history of railroad transport has partly been a history of for greater efficiency and profit. 铁路运输的历史部分是为了提高效率和利润而奋斗的历史。 8.He took on the new post without having the faintest idea of what it 他在新职位上没有知道会带来什么 9.He is one of the greatest experts in that field. 据说他是那个领域最伟大的专家之一。 10.Absolute secrecy is essential. , the fewer who are aware of the project the better. 绝对保密是必要的。因此,越少意识到这个项目的人越好。

兰州大学英语1套答案

1. Children need many things, but ___they need attention. in all for all above all after all 本题分值: 4.0 用户得分: 0.0 用户解答: in all 标准答案: above all 2. Many people believe we are heading for environmental disaster ___ we radically change way we live. but although unless lest 本题分值: 4.0 用户得分: 0.0 用户解答: but 标准答案: unless 3. He glanced over at her, ______ that though she was tiny, she seemed very well put together. noting noted to note having noted 本题分值: 4.0 用户得分: 4.0

用户解答: noting 标准答案: noting 4. Even though he has lived in China for many years, Mark still can not _______ himself to the Chinese customs. adopt adjust adapt accept 本题分值: 4.0 用户得分: 0.0 用户解答: adopt 标准答案: adapt 5. Sometimes you may even find several children share one patched paper, which has traveled from one hand to ____ driven by the curious nature. the others some others another others 本题分值: 4.0 用户得分: 0.0 用户解答: the others 标准答案: another 6. ____ hard I tried, I couldn’t catch up with him. No matter how much Although No matter how

1月自考旅游英语选读试题

全国2012年1月高等教育自学考试 旅游英语选读试题 课程代码:00837 请将答案填在答题纸相应位置上 I. Multiple choice: (1×15=15) Directions: Beneath each of the following sentences, there are four choices marked A, B,C and D. Choose the one that best completes the sentence. 1. The World Tourism Organization is ______ that represents all national and official tourist interests. A. a regional organization B. one of the organizations C. a national organization D. the only international organization 2. The inclusion of western words and phrases in language is due to ______ A. tourism development B. language development C. economic development D. environmental development 3. Which group of executives can be expected to enjoy luxurious accommodations, staying only at five-star hotels or equivalents? A. Technical and sales personnel. B. Company chairman and chief executives. C. Executive directors and training managers. D. General managers and human resource managers. 4. Some steps ______ to control the overuse of tourism resources, but more needs ______ and the sooner the better. A. take, do B. taken, done C. has taken, has done D. have been taken, to be done 5. The Grand Tour is a tour of certain cities in ______. A. Southern Europe B. Northern Europe C. Western Europe D. Eastern Europe 6. Some national tourism organizations have found it useful to make a further distinction between international travel and travel between ______. A. neighboring countries B. adjacent countries C. nearby countries D. bordering countries 7. Travel and tourism, as a ______ behavior, is very closely related to advances in the economy and culture of a society. A. social B. economic C. cultural D. socioeconomic 8. Tourism is a ______ of activities, services, and industries that derivers a travel experience. A. composition B. composite C. combination D. compound 9. Investment in tourism remains ______ it does in any other industry. A. the same risk as B. the same risks as C. as risky as D. as risk as 10. This motivation is frequently referred to as the “VFR”market. It’s the short form for “______”. A. visit friends and relatives B. visit friends and relations

大学英语4答案

1 V ocabulary 1. 1) A. entertaining B. entertainment C. entertained D. entertainer 2) A. recognizable B. recognized C. recognition 3) A. tempting B. temptation C. tempt 4) A. reasoned B. reasoning C. reasonable D. reason 5) A. analyzed B. analytical C. analyst D. analysis 6) A. valuable B. valuation C. valued/values D. values 7) A. humorist B. humor C. humorous D. humorless 8) A. understandable B. understanding C. understand D. misunderstood 2. 1) a sense of responsibility 2) a sense of safety/security 3) a sense of inferiority 4) a sense of superiority 5) a sense of rhythm 6) a sense of justice 7) a sense of shame 8) a sense of helplessness 9) a sense of direction 10) a sense of urgency 3. 1) Lively behavior is normal 2) Fast cars appeal to 3) diverse arguments 4) I asked my boss for clarification 5) sensitive to light 6) Mutual encouragement 7) made fun of him 8) persists in his opinion/viewpoint 9) to be the focus/center of attention 10) we buy our tickets in advance 4. 1)certain/sure 2) involved 3) end 4) behavior 5) disciplining 6) agreed 7) individually 8) first 9) response 10) question 11) attempt 12) voice 13) directly 14) followed 15) trouble 2 Vocabulary 1. Creating Compound Words STEP ONE: Column A Column B The compound words created through day throughout up man upbeat, uplift draw eared drawback

兰州大学英语3作业答案

1. This is not your radio, by ___. yours brother your brother's you brother's yours brother's 本题分值: 4.0 用户未作答 标准答案: your brother's 2. Two ___ three is five. plus minus mutiply devide 本题分值: 4.0 用户未作答 标准答案:plus 3. The policeman told the boys ___ football in this park. not playing not play not to play to not play 本题分值: 4.0 用户未作答 标准答案: not to play 4. What a ___ watch it is!

most beautiful more beautiful the most beautiful beautiful 本题分值: 4.0 用户未作答 标准答案: beautiful 5. ___ in thought, he almost ran into the car in front of him. losing having lost To lose Lost 本题分值: 4.0 用户未作答 标准答案: Lost 6. There was ___ in the meeting room. no one another anyone the one 本题分值: 4.0 用户未作答 标准答案: anyone 7. The kind old man wsa always ready ___ people I trouble. helped

新视野大学英语第四版课后练习答案--翻译52294

Unit1 1.这种植物只有在培育它的土壤中才能很好地成长。(other than) The plant does not grow well in soils other than the one in which it has been developed. 2.研究结果表明,无论我们白天做了什么事情,晚上都会做大约两个小时的梦(may have done) Research findings show that we spend about two hours dreaming every night, no matter what we may have done during the day. 3.有些人往往责怪别人没有尽最大努力,以此来为自己的失败辩护。(justify sth. by)Some people tend to justify their failure by blaming others for not trying their best. 4.我们忠于我们的承诺:凡是答应做的,我们都会做到。(remain true to) We remain tree to our commitment: Whatever we promised to do; we would do it. 5.连贝多芬的父亲都不相信自己儿子日后有一天可能会成为世界上最伟大的音乐家。爱迪生也同样如此,他的老师觉得他似乎过于迟钝。(discount;be true to) Even Beethoven's father discounted the possibility that his son would one day become the greatest musician in the world. The same is true of Edison, who seemed to his teacher to be quite dull. 6. 当局控告他们威胁国家安全。(accuse sb. of sth) They were accused by authorities of threatening the state security. l.出入除自己家以外的任何场所时,如果你带有宠物,一定要了解有关宠物的规定。 2一些女性完全可以不待在家里,而是去工作,挣一份不错的工资。但是为了家庭,她们放弃了工作。 3.你怎么为这样粗鲁的行为辩护你将会为此付出沉重的代价,因为他们己经以低毁名誉的罪名起诉你了。 4.批评有其重要作用;我们可能当时不喜欢它,但是它能激励我们去做更伟大的事情。 5.他毫不让步的行为遭到公众的反对,这使得他陷人了精神上崩溃、经济上破产的境地。6.即使你失败了,也不要被失败伤害,更不要被失败左右。记住:失败是学习过程中必要的一步;它不是学习的结束,而是学习的开始。 unit 2 1. 要是这部喜剧中的人物更幽默些的话,就会吸引更多的观众。(if…had+past participle,would+have+past participle) If the characters in this comedy had been more humorous, it would have attracted a larger audience. 2. 她从未对自己的能力失去信心,因此她有可能成为一名成功的演员。(it is a possibility to)She has never lost faith in her own ability, so it is a possibility for her to become a successful actress. 3. 我从未受过正式培训,我只是边干边学。(go along) I never had formal training, I just learned as I went along. 4.随着产品进入国际市场,他们的品牌知名度越来越高了。(find one’s way into) As their products find their way into the international market, their brand is gaining in popularity. 5.她可以编造一个故事,说自己被窃贼打晕,所有的钱都没了,但她怀疑自己是否能让这故事听起来可信。(make up)

自考旅游英语试题及答案解析浙江.doc

??????????????????????精品自学考料推荐?????????????????? 浙江省 2018 年 4 月高等教育自学考试 旅游英语试题 课程代码: 06010 Ⅰ.Make the best choice to complete the following sentences.(20%) 1.I had been sitting in my seat for at least two hours, waiting () . A. the train to start B. for the train starting C. for the train to start D. for the train start 2.This is the Chinese () , translated from English. A. publication B. editor C. printing D. version 3.Get up early and run every day in the travel, and you will () a lot from doing so. A. receive B. make C. benefit D. win 4.This morning our water supply was () because of the cold weather. A. let down B. cut off C. taken up D. brought away 5.How much are you going to () me for repairing this equipment in the attractions? A. charge B. money C. require D. need 6.Culturally, this park is divided into two () . A. parties B. sections C. days D. yards 7.A tiny village school is soon to () its 110th birthday. A. celebrate B. make C. liberate D. confirm 8.It is impossible to finish the task () . A. in so a short time B. in such short a time C. in such a short time D. in a so short time 9.Try to () what had happened just before the accident. A. talk B. speak C. describe D. say for 10.He is () more hard-working than any of the other boys in the class. A. by far B. by way of C. by now D. by and by 1

大学英语四

对外经济贸易大学远程教育学院 2011-2012学年第二学期 《大学英语(四)》复习大纲 一、单选题 1. at the meeting that everyone present was convinced. () A. So forcefully he spoke B. So forcefully did he speak C. So forcefully was he spoken D. So forcefully has he spoken 2. Alice usually her little brother when her parents are away from home.() A. looks on B. looks for C. looks about D. looks after 3. his things, he hurried to the station.() A. Having packed up B. Packed up C. Packing up D. Being packed up 4. Hardly the people ran toward it.() A. the plane had landed when B. had the plane landed when C. the plane had landed than D. had the plane landed than 5. It is people, not things are decisive.() A. what B. those C. that D. who 6. He was not enough to give the old woman his seat on the

大学体验英语综合4 教程习题答案

精简答案大学体验英语-综合教程4 Unit1 Passage A Read and think 3 1~5 BADDC Read and think 4 1.media 2.images 3.abusive 4.fulfilling 5.recognition 6.status 7.stresses 8.aware 9.deserve Read and complete 5 1. obligation 2. applauded 3. fulfilled 4. mirror 5. flexibility 6. devalue 7. striving 8. entailed 9. supposedly 10. Consequently Read and complete 6 1.referred to as 2.at best 3.by the same token 4.at large 5.held up...as Read and translate 8 1.随着职务的提升,他担负的责任也更大了。 With his promotion,he has taken on greater responsibilities.

2.他感到他没有必要再一次对约翰承担这样的责任了。 He felt he did not have to make such a commitment to John any more. 3.闲暇时玛丽喜欢外出购物,与她相反,露西却喜欢呆在家里看书。 Mary likes to go shopping in her spare time, as opposed to Lucy,who prefers to stay at home reading. 4.说好听一点,可以说他有抱负,用最糟糕的话来说,他是一个没有良心或没有资格的权力追求者。 At best he’s ambitious,and at worst a power-seeker without conscience or qualifications. 5.我们已经尽全力想说服他,但是却毫无进展。 We have striven to the full to convince him ,but we have made no headway. 大学体验英语-综合教程4 Unit2 Passage A Read and think 2 1~5 ACAAC Read and think 4 1.warned https://www.wendangku.net/doc/269273720.html,munication 3.dangerous 4.identities 5.cheated 6.illustrates 7.advantages 8.differently 9.appearance 10.opportunities Read and complete 5 1.awaited 2.have overtaken 3.pose 4.cues 5.has undermined 6.soptted 7.judged 8.distracted 9.offend

旅游英语考试试卷

旅游英语 一、单项选择题(在每小题列出的四个备选项中只有一个是符合题目要求的,请将其代码填写在题后的括号内。多选无分。每小题1分,共20分) 1. This book is worth _____. C A. to read it B. reading it C. reading D. to read 2. Beijing is well __________ its beautiful scenery and the Great Wall. D A. known as B. known to C. known about D. known for 3. This question is too hard, it is __________ my comprehension. B A. below B. beyond C. over D. without 4. The workers are busy __________ models for the exhibition. D A. to make B. with making C. being making D. making 5. Do you think Tommy is________the truth? C A. saying B. speaking C. telling D. talking 6. No sooner had she entered the house ________the telephone rang. B A. when B. than C. as D. while 7. .--____________? C -- We are looking for a pair of sports shoes. A. What do you do B. What do you like C. Can I help you D. Do you need help 8. It was not__ midnight that they discovered the children were not in their beds. D A. before B. at C. after D. until 9. We look forward to _____ to the opening ceremony. D A. invite B. be invited C. having been invited D. being invited 10. Excuse me, but it is time to have your temperature______. B A. taking B. taken C. took D. take 11. “__________ does Mr. Johnson go to London on business?” At least once a month.” B A. How many B. How long C. How often D. How 12. _____ is known to all, too much smoking will cause lung cancer. C A. That B. It C. As D. What 13. The new system contained a large _____ of information about an daily life. B A. deal B. amount C. number D. account 14. I don’t like to disturb you, because you’re quite tired ________ working hard today. A A. of B. on C. out D. with 15. The teacher asked his students to leave enough _____ on the page forcorrection. A

大学英语4课文原文

Para1 An artist who seeks fame is like a dogchasing his own tail who, when he captures it, does not know what else to do but to continue chasing it.The cruelty of success is that it often leads those who seek such success to participate in their own destruction. 艺术家追求成名,如同狗自逐其尾,一旦追到手,除了继续追逐不知还能做些什么。成功之残酷正在于它常常让那些追逐成功者自寻毁灭。 "Don't quit your day job!" is advice frequently given by understandably pessimistic family members and friends to a budding artist who is trying hard to succeed. The conquest of fame is difficult at best, and many end up emotionally if not financially bankrupt. Still, impure motives such as the desire for worshipping fans and praise from peers may spur the artist on. The lure of drowning in fame's imperial glory is not easily resisted. 对一名正努力追求成功并刚刚崭露头角的艺术家,其亲朋常常会建议“正经的饭碗不能丢!”他们的担心不无道理。追求出人头地,最乐观地说也困难重重,许多人到最后即使不是穷困潦倒,也是几近精神崩溃。 Fame's spotlight can be hotter than a tropical jungle-a fraud is quickly exposed, and the pressure of so much attention is too much for most to endure.It takes you out of yourself: You must be what the public thinks you are, not what you really are or could be. The performer, like the politician, must often please his or her audiences by saying things he or she does not mean or fully believe. Curiously enough, it is those who fail that reap the greatest reward: freedom! They enjoy the freedom to express themselves in unique and original ways without fear of losing the support of fans. Failed artists may find comfort in knowing that many great artists never found fame until well after they had passed away or in knowing that they did not sell out. They may justify their failure by convincing themselves their genius is too sophisticated for contemporary audiences. Unit2 He was an immensely talented man, determined to a degree unusual even in the ranks of Hollywood stars. His huge fame gave him the freedom—and, more importantly, the money—to be his own master. He already had the urge to explore and extend a talent he discovered in himself as he went along. "It can't be me. Is that possible? How extraordinary," is how he greeted the first sight of himself as the Tramp on the screen. But that shock rousedhis imagination.Chaplin didn't have his jokes written into a script in advance; he was the kind of comic who used his physical senses to invent his art as he went along. Lifeless objects especially helped Chaplin make "contact" with himself as an artist. He turned them into other kinds of objects. Thus, a broken alarm clock in the movie The Pawnbroker became a "sick" patient undergoing surgery; boots were boiled in his film The Gold Rush and their soles eaten with salt and pepper like prime cuts of fish (the nails being removed like fish bones). This physical transformation, plus the skill with which he executed it again and again, is surely the secret of Chaplin's great comedy. He also had a deep need to be loved—and a corresponding fear of being betrayed. The two were hard to combine and sometimes—as in his early marriages—the collision between them resulted in disaster. Yet even this painfully-bought self-knowledge found its way into his comic creations. The Tramp never loses his faith in the flower girl who'll be waiting to walk into the sunset with him; while the other side of Chaplin makes Monsieur Verdoux, the French wife killer, into a symbol of hatred for women.

兰州大学英语班听力答案 (1)

Every minute of every day, blood flows through every corner of your body. The flow of blood brings oxygen and other nutrients to your tissues. Then it loads up the waste products of your metabolism and carries them away. This system of nutrient exchange is what keeps your organs and tissues alive. It’s made possible only because of the steady beating of your heart—the driving force of your circulatory system. How can your heart keep beating and beating, never stopping, and rarely getting out of sync? It’s possible because of the specialized type of muscle—cardiac muscle—that makes up the heart tissue, and also because of the action of the specialized electrical pathways that run through the heart’s walls. Before I go into cardiac muscle, let’s back up a bit. You may recall from last time that the action of muscle is always to contract. Muscles can extend only passively. They extend as they relax between contractions. You’ll also recall that the human body has different types of muscles. For example, skeletal muscle controls the body movements, and cardiac muscle controls the body’s blood flow. Skeletal muscle is found throughout the body, but cardiac muscle is found only in one place—the heart. Skeletal muscles get the name from the fact that their movement is based on the contractions of muscles working against the skeleton. Skeletal muscles are attached to the bones, and they move the bones by contracting. A skeletal muscle consists of a bundle of long fibers running the length of the muscle. The bundles of fibers are arranged in a regular pattern—a repeating pattern of light and dark bands. This pattern is called striation, and skeletal muscle is also known as striated muscle. When a muscle contracts, the length of each bundle is reduced. A skeletal muscle contracts only when it’s stimulated by a motor neuron. Cardiac muscle, on the other hand, contracts rhythmically all on its own. Cardiac muscle cells can generate impulses on their own, without any input from the nervous system. They can do this because of complex chemical and electrical changes involving sodium, calcium and potassium, each of which carries an electrical charge. Like skeletal muscle, cardiac muscle is striated. However, the membranes between cardiac muscle cells contain specialized regions that provide direct contact among cells. What this means is, an electrical impulse generated in one part of the heart will spread to all the cardiac muscle cells. Thus, the whole heart will contract. Cardiac muscle cells can generate impulses without any input from the nervous system. In contrast to this, skeletal muscles don’t contract unless the nervous system tells them to. A single cardiac muscle cell will “beat” even when it’s isolated from the heart and placed in cell culture in the laboratory. If you removed a little piece of muscle from your heart and put it in a dish, you would see it continue to contract. That’s because cardiac muscle cells have something called an action potential. Electrically, they’re set up so, so that sodium and calcium—positive ions—change places with potassium—a negative ion—across the cell membrane. This happens automatically, over and over again. When sodium, calcium, and potassium ions move into or out of a cardiac cell, it causes the muscle to contract. What we think of as a heartbeat is really a serious of contractions in the cardiac muscle. When the heart’s walls contract, they force blood out of the chambers and

相关文档