肌肉收缩机制

What makes a muscle contract?
::是什么使肌肉合同?

It starts with a signal from the nervous system. So it starts with a signal from your brain. The signal goes through your nervous system to your muscle. Your muscle contracts, and your bones move. And all this happens incredibly fast.
::它从神经系统发出的信号开始。所以它从你的大脑发出的信号开始。信号通过你的神经系统进入你的肌肉。你的肌肉萎缩,你的骨头移动。这一切发生得太快了。

Muscle Contraction
::肌肉压合

Muscle contraction occurs when muscle fibers get shorter. Literally, the muscle fibers get smaller in size. To understand how this happens, you need to know more about the structure of muscle fibers.
::肌肉收缩发生在肌肉纤维变短的时候。 从字面上看,肌肉纤维变小了。要了解这种情况是如何发生的,你需要更多了解肌肉纤维的结构。

Structure of Muscle Fibers
::肌肉纤维结构

Each muscle fiber contains hundreds of organelles called  myofibrils . Each myofibril is made up of two types of protein filaments:  actin  filaments, which are thinner, and  myosin  filaments, which are thicker. Actin filaments are anchored to structures called  Z lines  (see f igure below). The region between two Z lines is called a  sarcomere . Within a sarcomere, myosin filaments overlap the actin filaments. The myosin filaments have tiny structures called  cross bridges  that can attach to actin filaments.
::每根肌肉纤维都包含数百个叫做丝质的有机纤维。 每根丝质由两种蛋白丝组成:细细细细细细细细的丝质和厚厚厚的肌质纤维。Actin丝质固定在称为Z线的结构上(见下图 ) 。 两条Z线之间的区域被称为“刺青 ” 。 在沙黑中, 我的丝质与活性丝状的丝质重叠。 肌质丝质的细细细小结构称为“十字桥 ” , 可以连接丝质的丝质。

Sliding Filament Theory
::Sliding Filament 理论

The most widely accepted theory explaining how muscle fibers contract is called the  sliding filament theory . According to this theory, myosin filaments use energy from ATP to “walk” along the actin filaments with their cross bridges. This pulls the actin filaments closer together. The movement of the actin filaments also pulls the Z lines closer together, thus shortening the sarcomere.
::最广为接受的解释肌肉纤维如何结合的理论 — — 滑动丝丝理论。 根据这一理论,肌丝丝从ATP用能量“行走 ” 。 这把丝丝的动作拉近了。 丝线动作也拉近了Z线,从而缩短了刺线。

You can watch this occurring in a video animation at the link below. 
::您可以在以下链接的视频动画中观看。

When all of the sarcomeres in a muscle fiber shorten, the fiber contracts. A muscle fiber either contracts fully or it doesn’t contract at all. The number of fibers that contract determines the strength of the muscular force. When more fibers contract at the same time, the force is greater.
::当肌肉纤维中的所有正弦素都缩短时,纤维就会合起来。 肌肉纤维要么完全合起来,要么根本不合起来。 合同中的纤维数量决定了肌肉力量的强度。 当更多的纤维同时合起来时,强度会更大。

Actin, myosin and muscle contraction are discussed at   (9:38).
::Actin, 肌素和肌肉收缩在(9: 38)讨论。

Additional information about muscle contraction is available at   (9:22) and   (14:42).
::有关肌肉收缩的更多信息见(9:22)和(14:42)。

Muscles and Nerves
::肌肉和神经

Muscles cannot contract on their own. They need a stimulus from a nerve cell to “tell” them to contract. Let’s say you decide to raise your hand in class. Your brain sends electrical messages to nerve cells, called  motor neurons , in your arm and shoulder. The motor neurons, in turn, stimulate muscle fibers in your arm and shoulder to contract, causing your arm to rise. Involuntary contractions of cardiac and smooth muscles are also controlled by nerves.
::肌肉无法自行收缩。 它们需要神经细胞的刺激来“ 提醒”它们收缩。 比方说您决定在课堂上举手。 您的大脑向神经细胞发出电子信息,称为运动神经元,在手臂和肩膀上。 运动神经元反过来又刺激手臂和肩膀的肌肉纤维收缩,导致你的手臂上升。 心肌和光滑肌肉的非自愿收缩也由神经控制。

Summary
::摘要

播放段落
• According to the sliding filament theory, a muscle fiber contracts when myosin filaments pull actin filaments closer together and thus shorten sarcomeres within a fiber.
  ::根据滑动丝质理论, 肌肉纤维合同, 当肌质丝质拉动 行为在丝质上更紧密地拉在一起, 从而缩短 纤维内的弧菌。
播放段落
• When all the sarcomeres in a muscle fiber shorten, the fiber contracts.
  ::当肌肉纤维里所有的沙黑 都缩短的时候 纤维就合拍了

Review
::回顾

1. What is a sarcomere and Z-line?
::1. 什么是讽刺和Z线?

2. What are the two protein filaments of a myofibril?
::2. 眼膜的两种蛋白丝丝是什么?

3. Explain how muscles contract according to the sliding filament theory.
::3. 解释肌肉根据滑动丝丝理论是如何萎缩的。

4. A serious neck injury may leave a person paralyzed from the neck down. Explain why.
::4. 严重的颈部伤害可能导致一个人从颈部向下瘫痪,解释原因。

Watch the video at: 
::观看影片在:

Watch the video at:
::观看影片在: