59 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.
人生经典哲言翻译
各个星座适合读哪本名著?
西班牙85岁女公爵为嫁情郎散尽家产
国际英语资讯:Perus ex-president Toledos extradition could take a year: FM
飞来奶牛砸中汽车
国内英语资讯:Report warns of prominent security risks on cloud platforms in China
《裸婚时代》刘易阳的经典语录
国际英语资讯:UN envoy decries killing of Turkish diplomat in Iraqs Erbil
体坛英语资讯:Newcomer Madagascars 2-0 win over giant Nigeria rocks AFCON
女性独自旅游去哪里最危险?南非居首,美国次之
你生命的波纹可能影响世界
国内英语资讯:Xi meets Chinese diplomatic envoys to foreign countries
Tips In America 美国的小费
能否学好数学由基因决定 与智商无关
喜欢自嘲的人更健康 事业易成功
国际英语资讯:U.S. House holds attorney general and commerce secretary in contempt of Congress
一天中什么时候跑步最舒服
日本设计师打造气球礼服
美宇航局称地球生命或源于外层空间
史上最倔强母亲 十年万里求医终得子
闪电约会闪电恋爱闪电结婚
凯特婚纱细腰照 被指有PS嫌疑
夫妻共同朋友圈可致丈夫性冷淡
2018下半年CATTI笔译二级真题(英译汉)第二篇
口译备考之会议套语学习
意考古学家:马克波罗可能是个骗子
国际英语资讯:New Greek parliament sworn in after general elections
施瓦辛格穿印字T恤 自嘲从妻子手中逃生
与同事相处融洽寿命会更长
国内英语资讯:China allocates disaster relief supplies to flood-hit Hunan
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |