[英語學習PLUS] 分享1108- 運動系統

     運動系統

More than six billion humans live on earth. We look different, act differently, and think different thoughts. However, we all share the same basic structure, and our bodies all have the same kinds of systems inside. This is because we are all human.

All living things have genes, and humans all have human genes. Genes help determine how a person looks and behaves. Many traits are inherited, such as body size, eye color, and hair texture. So are chances for developing certain diseases and even personality traits. However, everyone inherits the body’s most important systems.

The human body is like a machine with many working parts. Together, these parts can do a lot of work. The parts depend on one another to support the machine. Each part has specific needs and abilities.

Scientists categorize body parts by the work they do. Just as every community has people who perform different jobs, the body has different parts that do different jobs. A community needs all its workers to do their jobs, or there will be trouble. The body needs all its parts to work well, too. If they don’t, there will be trouble, usually in the form of illness or injury.

The Skeletal System

The skeletal system is the framework for the body. It supports the body, gives it shape, and supports muscles that allow the body to move. All the bones in the body are linked by joints, and together they form the skeleton. Bones often protect vital organs. For example, the rib cage protects the heart, and the skull protects the brain. The skeletal system also provides substances that aid the immune system.

The Muscular System

The skeleton could not work without the muscular system, which performs all body movements. Some muscles attach to bones, whereas others work on their own. Muscles can contract, or get shorter, creating a pulling force. Most muscles come in pairs so that one muscle pulls your body one way and the other muscle pulls your body the other way. This allows you to move.

There are three types of muscles: skeletal, cardiac, and smooth. Skeletal muscles are used for activities such as running, lifting, and swimming, and these muscles tire easily. In contrast, cardiac muscle is found in the wall of the heart, where it contracts tirelessly to create your heartbeat. Lastly, smooth muscles perform vital functions such as swallowing.

有超過六十億人住在地球上，我們看起來不同，行為不同，想法也不同，但卻擁有相同的基本構造，而我們的體內也有相同的系統，因為我們都是人類。

所有的生物都有基因，人類也有人類的基因。基因會決定一個人看起來的樣子，以及行為舉止。許多特徵都是遺傳而來的，像是體型、眼睛顏色、頭髮粗細，得到特殊疾病的機率，以及人格特質。然而，每個人都遺傳到了身體最重要的系統。

人類的身體就像一個有很多運轉零件的機器，零件組裝在一起時，可以做很多的事，彼此相互依賴以運作機器。每一個零件也都有特定的需求和功能。

科學家將身體的部位依其功能來分類。就像每個社會的人們各司其職，身體的不同部位也擔任了各種不同工作。一個社群需要所有人做好自己的工作，否則就會出現問題，身體也需要各部位好好地運作，如果不這樣的話，那就會有問題了，而問題通常是以疾病或受傷的方式呈現。

骨骼系統

骨骼系統是身體的架構，支撐身體，賦予它形狀，此外也支撐讓身體可以運動的肌肉。身體裡所有的骨頭都由關節連接，組合在一起就形成了骨架。骨頭通常會保護重要的器官，舉例來說，肋骨保護心臟，而頭骨則保護大腦。骨骼系統也提供了免疫系統所需的物質。

肌肉系統

如果沒有負責身體運動的肌肉系統，骨骼系統是無法運作的。有些肌肉依附在骨頭上，有些則是獨立運作。肌肉能夠收縮，以產生拉力。大多數的肌肉都是成對的，這樣一來，一條肌肉往某個方向拉扯，另一條肌肉則朝反方向拉，一來一往才能產生運動。

肌肉有三種類型：骨骼肌、心肌和平滑肌。骨骼肌是用來活動的，像跑步、舉重和游泳，這些肌肉很容易疲勞。相對地，心肌出現在心壁上，孜孜不倦地收縮以產生心跳。最後，平滑肌負責執行一些重要的功能，如吞嚥等。

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