陳蕙雅思教材 - 雅思閱讀精選 (Muscles and Human)

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 itselfso that the bone on which it pulls has to move.

When muscle tissueshortens, it also  bunches up.  Muscle tissue covers

the  body in sheets and bands that lie between theskin and the skeleton.

The bones are theframework of the body, but the muscles fill out the body

shape. Most musclesextend from one bone to another. When the muscle

between the bonesshortens, one bone has to move. The point where the

muscle is fastened to theunmoving  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 thebone but to a tough, nonstretchable cord, or

tendon, that is attachedto the bone. Muscles do not push; they can only

pull. To bend the arm atthe elbow, the muscle at the front of the upper

arm has to shorten andbunch up. To unbend the arm other muscles in the

back of the arm have toshorten. These two sets of muscles - the front and

the back - are said toact in opposition to each other. When one set is

working, the other set isusually relaxed. But there are times when both of

them work. Sometimesmuscles are called upon to do more than simply pull in

one direction. They mayhave to perform a turning motion. To be able to do

this, the muscle must beattached to the bone at an angle. By pulling, the

muscle can cause the boneto pivot. A few muscles have special functions.

The diaphragm, forexample, forces the lungs to take in air. This part of

breathing is notprimarily a bone  moving operation.

肌肉和人體  骨骼運動發生在人體的關節部位。這種運動是由稱為肌肉的片狀或條狀的 強韌組織拖動而引起的。

肌肉組織有一種特殊的收縮能力，可以帶動與之相連的骨骼。 肌 肉在收縮的同時，也會聚成團。 肌肉以條狀或片狀形式佈滿全身，存在於皮膚與骨架之間。

骨骼是身體的支架，而肌肉則構成了人的體形。  大多數肌肉接兩塊骨頭，但當肌肉收縮時 只有一塊骨頭運動。

肌肉與不動骨相連的一端叫肌起端，與動骨相連的一端叫附著端。 有 些肌肉不與骨骼直接相連，而是連著附在骨骼上的不能收縮的帶狀組織或腱上。  肌肉不能

推動而只能拉動骨骼。  要從肘部彎曲手臂，就要收縮上臂正面的肌肉。  要伸直手臂，背面 的肌肉就得收縮。  

這兩組肌肉，正面的和背面的，稱為相反運動肌肉。  當一組工作時，另 一組就休息。  但有時它們也一起工作。  有時我們要求肌肉不僅僅做簡單的單向拖動。

它 們需要轉動。  但只有當肌肉與骨骼形成一定角度時，它們才能轉動，從而拖動骨骼繞某個 軸旋轉。  有幾塊肌肉的作用較特殊，例如隔膜肌。  

它帶動肺部吸入空氣。  呼吸基本上不 是骨骼運動帶動的。