How your muscular system works - Emma Bryce

譯者: Sherl H 審譯者: Chialing Fong

Each time you take a step,

每當你跨出一步

200 muscles work in unison to lift your foot,

200 條肌肉同心協力抬起你的腳

propel it forward,

向前推進

and set it down.

並放下它

It's just one of the many thousands of tasks performed by the muscular system.

這只是肌肉系統 上千項工作裡的其中之一

This network of over 650 muscles covers the body

這個由超過 650 個肌肉 組成的網絡遍布全身

and is the reason we can blink,

讓我們能夠眨眼

smile,

微笑

run,

奔跑

jump,

跳躍

and stand upright.

和站直

It's even responsible for the heart's dependable thump.

連心臟可靠的撲通聲也是由它負責的

First, what exactly is the muscular system?

首先 肌肉系統究竟是什麼呢？

It's made up of three main muscle types:

它由三種主要的肌肉類型組成

skeletal muscle, which attaches via tendons to our bones,

骨骼肌 藉由肌腱附著在我們骨頭上

cardiac muscle, which is only found in the heart,

心肌 只能在心臟找到

and smooth muscle, which lines the blood vessels and certain organs,

以及平滑肌 作為血管和某些器官的內襯

like the intestine and uterus.

例如腸和子宮

All three types are made up of muscle cells,

這三種肌肉都由肌肉細胞

also known as fibers, bundled tightly together.

也稱作肌纖維 緊緊綁成束狀

These bundles receive signals from the nervous system

這些肌束接受神經系統傳來的訊號

that contract the fibers, which in turn generates force and motion.

收縮纖維 接著產生力量和動作

This produces almost all the movements we make.

這產生了我們絕大多數的運動

Some of the only parts of the body

唯有身體的某些部分

whose motions aren't governed by the muscular system

運動不受肌肉系統控制

are sperm cells,

像是精細胞

the hair-like cilia in our airways,

我們呼吸道中像頭髮的纖毛

and certain white blood cells.

和某些白血球

Muscle contraction can be split into three main types.

肌肉收縮的類型主要可以分成三種

前兩種縮短和延長肌纖維

The first two, shortening muscle fibers and lengthening them,

generate opposing forces.

產生相反的力量

So the biceps will shorten while the triceps will lengthen or relax,

所以當三頭肌延長 也就是放鬆時 二頭肌會縮短

pulling up the arm and making it bend at the elbow.

拉起手臂 並使它在手肘處彎曲

This allows us to, say, pick up a book,

這讓我們能夠 比方說 拿起一本書

or if the muscle relationship is reversed, put it down.

當肌肉的關係對調時 放下書

This complementary partnership exists throughout the muscular system.

這種互補的合作關係 存在於整個肌肉系統

The third type of contraction creates a stabilizing force.

第三種收縮產生穩定的力量

In these cases, the muscle fibers don't change in length,

這類情況下 肌纖維的長度不改變

but instead keep the muscles rigid.

但卻保持肌肉靜止

This allows us to grip a mug of coffee or lean against a wall.

這讓我們能夠緊握一杯咖啡 或者斜靠在牆上

It also maintains our posture by holding us upright.

這也讓我們保持直立 來維持我們的體態

Skeletal muscles form the bulk of the muscular system,

骨骼肌構成肌肉系統的大部分

make up about 30-40% of the body's weight,

組成約 30% 至 40% 的體重

and generate most of its motion.

並產生身體大部分的動作

Some muscles are familiar to us, like the pectorals and the biceps.

有些肌肉我們很熟悉 像是胸肌和二頭肌

Others may be less so, like the buccinator,

有些不那麼熟 像是頰肌

a muscle that attaches your cheek to your teeth,

這塊肌肉將你的臉頰和牙齒連接

or the body's tiniest skeletal muscle,

或是人體中最小的骨骼肌

a one-millimeter-long tissue fragment called the stapedius

一段一毫米長 稱為鐙骨肌的纖維

that's nestled deep inside the ear.

緊貼在耳朵的深處

骨骼肌無論長在哪裡 都與體神經系統連接

Wherever they occur, skeletal muscles are connected to the somatic nervous system,

which gives us almost complete control over their movements.

使我們對於它們的運動 幾乎有完全的主控權

This muscle group also contains two types of muscle fibers

這群肌肉也包含兩種肌纖維

to refine our motions even further, slow-twitch and fast-twitch.

慢縮肌和快縮肌 來進一步修飾我們的運動

Fast-twitch fibers react instantly when triggered

快縮肌被觸發時會馬上反應

but quickly use up their energy and tire out.

但很快就會用完能量並筋疲力盡

Slow-twitch fibers, on the other hand, are endurance cells.

相反地 慢縮肌是耐力細胞

They react and use energy slowly so they can work for longer periods.

無論是動作和使用能量的速度都很慢 因此可以作用更久

A sprinter will accumulate more fast-twitch muscles in her legs

短跑選手透過持續的訓練 會在腿上

through continuous practice,

累積較多快縮肌

enabling her to quickly, if briefly, pick up the pace,

讓她能夠很快地且短暫地 加快腳步的速度

whereas back muscles contain more slow-twitch muscles

而背部肌肉則含有較多慢縮肌

to maintain your posture all day.

可以維持你的姿勢一整天

Unlike the skeletal muscles, the body's cardiac and smooth muscles

不同於骨骼肌 身體的心肌和平滑肌

are managed by the autonomic nervous system

受到自主神經系統管理

beyond our direct control.

不會直接被我們控制

That makes your heart thump roughly 3 billion times

這使你的心臟在一生當中

over the course of your life,

跳動約 30 億次

which supplies the body with blood and oxygen.

將血液和氧供應全身

Autonomic control also contracts and relaxes smooth muscle

自主控制也會用一種節律的週期來

in a rhythmic cycle.

收放平滑肌

That pumps blood through the smooth internal walls of blood vessels,

這推動血液流經血管平滑的內壁

enables the intestine to constrict and push food through the digestive system,

使腸子能收縮 並推進食物經過消化系統

and allows the uterus to contract when a person is giving birth.

以及讓人在分娩時收縮子宮

As muscles work, they also use energy and produce an important byproduct, heat.

肌肉工作時會使用能量 並產生一個重要的副產物 熱

In fact, muscle provides about 85% of your warmth,

事實上 肌肉提供你約 85% 的溫暖

which the heart and blood vessels then spread evenly across the body

接著心臟和血管透過血液 將熱平均地

via the blood.

擴散到全身

Without that, we couldn't maintain the temperature necessary

若沒有這些 我們不可能維持

生存所需的溫度

for our survival.

The muscular system may be largely invisible to us,

肌肉系統或許在很大程度上 是我們看不見的

but it leaves its mark on almost everything we do,

但它幾乎在我們所做的每一件事上 留下痕跡

whether it's the blink of an eye or a race to the finish line.

不論是眨眼 或是衝向終點線的比賽