Muscles and Human Body
It is in the joints of the human body that movements of the bones take place. The movement itself is caused by the pull of sheets and cords of very tough tissue called muscle. Muscle tissue has the special ability to shorten itself so that the bone on which it pulls has to move. When muscle tissue shortens, it also bunches up. Muscle tissue covers the body in sheets and bands that lie between the skin and the skeleton. The bones are the framework of the body, but the muscles fill out the body shape. Most muscles extend from one bone to another. When the muscle between the bones shortens, one bone has to move. The point where the muscle is fastened to the unmoving bone is called the origin of the muscle, whereas the point where the muscle is not fastened to the bone that is to be moved is called the insertion. Sometimes the muscle is not attached directly to the bone but to a tough, nonstretchable cord, or tendon, that is attached to the bone. Muscles do not push; they can only pull. To bend the arm at the elbow, the muscle at the front of the upper arm has to shorten and bunch up. To unbend the arm other muscles in the back of the arm have to shorten. These two sets of muscles - the front and the back - are said to act in opposition to each other. When one set is working, the other set is usually relaxed. But there are times when both of them work. Sometimes muscles are called upon to do more than simply pull in one direction. They may have to perform a turning motion. To be able to do this, the muscle must be attached to the bone at an angle. By pulling, the muscle can cause the bone to pivot. A few muscles have special functions. The diaphragm, for example, forces the lungs to take in air. This part of breathing is not primarily a bone moving operation.
上一篇: 六级阅读主旨题答题技巧及实战(5)
下一篇: 六级阅读主旨题答题技巧及实战(1)
国内英语资讯:Chinas top legislator to visit Norway, Austria, Hungary
体坛英语资讯:21-year NBA veteran Vince Carter plans to return for 22nd season
国内英语资讯:China not to compromise on major principles, capable to cope with challenges: think tanks
体坛英语资讯:Su Bingtian and Xie Zhenye team up to run mens 4x100m relay in IAAF World Relays Yokohama
国际英语资讯:Indian Prime Minister-elect Modi meets with ailing finance minister
体坛英语资讯:Table tennis test event held at 7th Military World Games venue
国内英语资讯:Ukraines president-elect, Chinese ambassador meet on cooperation
体坛英语资讯:Report: Kovac to leave Bayern
国际英语资讯:Spotlight: At least 17 dead, over 40 hospitalized in Indias spurious liquor tragedy
懒得撸铁?神奇T恤让你秒变肌肉男
Do All the Asian People Look the Same 所有亚洲人看起来都一样吗
国内英语资讯:Chinas top political advisor meets Taiwan delegation
国际英语资讯:Feature: Childhood changes dramatically between Syrian father, son
国际英语资讯:Lithuanian PM Skvernelis admits defeat, Nauseda, Simonyte head to presidential runoff
国际英语资讯:Pakistan reaches agreement with IMF for 6 bln USD package over 3 years
国际英语资讯:UN Day of Vesak opens in Vietnam
国内英语资讯:Various activities feature 1000-day countdown to Beijing 2022
2019年6月英语四级作文预测:电脑
一对母女送给我的小幸运
体坛英语资讯:Why a Man. City FA Cup win would be good news for neighbors United
国内英语资讯:Implementation plan for national ecological civilization pilot zone unveiled
国内英语资讯:Chinese opera on legendary monk to debut in New York City
国内英语资讯:China to boost community-based elderly care, childcare, household services
体坛英语资讯:Warriors triumph against Rockets for 2-0 series lead
体坛英语资讯:Atletico Madrid beat Guangzhou Evergrande 2-0 in U15 tournament
智商可预测,未来试管婴儿将可选择“最聪明的”胚胎
世界各地河流均被抗生素污染 非洲和亚洲最严重
国际英语资讯:UN monitoring team verifies Yemens Houthi withdrawal from Hodeidah ports
体坛英语资讯:Chinese forward Wu Lei commits his future to Espanyol
国际英语资讯:Sudans military council denies attempts to disperse sit-in at army headquarters