首页
登录
职称英语
Biology Cardiac Muscle[img]2012q1/ct_etoefm_etoeflistz_0107_20121[/img] [br] Wha
Biology Cardiac Muscle[img]2012q1/ct_etoefm_etoeflistz_0107_20121[/img] [br] Wha
游客
2024-01-04
10
管理
问题
Biology Cardiac Muscle
[br] What happens when an electrical impulse generated in one part of the heart spreads to all the cardiac muscle cells?
Every minute of every day, blood flows through every corner of your body. The flow of blood brings oxygen and other nutrients to your tissues. Then it loads up the waste products of your metabolism and carries them away. This system of nutrient exchange is what keeps your organs and tissues alive. It’s made possible only because of the steady beating of your heart,he driving force of your circulatory system.
How can your heart keep beating and beating, never stopping, and rarely getting out of sync? It’s possible because of the specialized type of muscle-cardiac muscle-that makes up the heart tissue, and also because of the action of specialized electrical pathways that run through the heart’s walls.
Before I go into cardiac muscle, let’s back up a bit. You may recall from last time that the action of a muscle is always to contract. Muscles can extend only passively. They extend as they relax between contractions. You’ll also recall that the human body has different types of muscles. For example, skeletal muscle controls body movements, and cardiac muscle controls the body’s blood flow. Skeletal muscle is found throughout the body, but cardiac muscle is found only in one place--the heart.
Skeletal muscles get their name from the fact that their movement is based on the contraction of muscles working against the skeleton. Skeletal muscles are attached to the bones, and they move the bones by contracting.
A skeletal muscle consists of a bundle of long fibers running the length of the muscle. The bundles of fibers are arranged in a regular pattern-a repeating pattern of light and dark bands. This pattern is called striation, and skeletal muscle is also known as striated muscle. When a muscle contracts, the length of each bundle is reduced. A skeletal muscle contracts only when it’s stimulated by a motor neuron.
Cardiac muscle, on the other hand, contracts rhythmically all on its own. Cardiac muscle cells can generate impulses on their own, without any input from the nervous system. They can do this because of complex chemical and electrical changes involving sodium, calcium, and potassium, each of which carries an electrical charge.
Like skeletal muscle, cardiac muscle is striated. However, the membranes between cardiac muscle cells contain specialized regions that provide direct electrical contact among cells. What this means is, an electrical impulse generated in one part of the heart will spread to all the cardiac muscle cells. Thus, the whole heart will contract. Cardiac muscle cells can generate impulses without any input from the nervous system. In contrast to this, skeletal muscles don’t contract unless the nervous system tells them to.
A single cardiac muscle cell will "beat" even when it’s isolated from the heart and placed in cell culture in the laboratory. If you removed a little piece of muscle from your heart and put it in a dish,you would see it continue to contract. That’s because cardiac muscle cells have something called an action potential. Electrically, they’re set up so, so that sodium and calcium-positive ions-change places with potassium- a negative ion-across the cell membrane. This happens automatically, over and over again. When sodium, calcium, and potassium ions move into or out of a cardiac cell, it causes the muscle to contract.
What we think of as a heartbeat is really a series of contractions in the cardiac muscle. When the heart’s walls contract, they force blood out of the chambers and into the next chamber or the large blood vessels that lead to the rest of your body. Every day, your heart contracts 100,000 times or more, pumping more than 2,000 gallons of blood.
But, unlike the skeletal muscles in your body, your cardiac muscle can never stop and take a rest. If your heart stops beating, you have very little time-only a matter of minutes- for it to start up again before all your other body systems are permanently damaged or stop functioning altogether.
选项
A、The impulse spreads to the bones.
B、The cardiac muscles extend.
C、The heart beats faster.
D、The whole heart contracts.
答案
D
解析
The professor says ...an electrical impulse generated in one part of the heart will spread to all the cardiac muscle cells. Thus, the whole heart will contract. (2.2)
转载请注明原文地址:https://tihaiku.com/zcyy/3334192.html
相关试题推荐
[originaltext]M:So,whatisyourbiologyprojectabout?W:Itisaboutmicroor
[originaltext]M:So,whatisyourbiologyprojectabout?W:Itisaboutmicroor
NarratorListentoapartofadiscussioninabiologyclass.[img]2011q1/ct
NarratorListentoapartofadiscussioninabiologyclass.[img]2011q1/ct
NarratorListentoapartofadiscussioninabiologyclass.[img]2011q1/ct
NarratorListentoalectureintheliteratureclass.[img]2011q1/ct_etoefm_
NarratorListentoalectureintheliteratureclass.[img]2011q1/ct_etoefm_
NarratorListentoalectureintheliteratureclass.[img]2011q1/ct_etoefm_
NarratorListentoalectureintheliteratureclass.[img]2011q1/ct_etoefm_
NarratorListentothelectureinbusinessclass[img]2011q1/ct_etoefm_etoef
随机试题
[originaltext]W:Goodevening,sir.Hereisthemenu.Wouldyouliketoordern
DoSomethingtoImproveYourLifeI.Wrongopinionstowards
[originaltext]W:Wow,whatavarietyofsaladsyou’vegotonyourmenu!Couldy
一般来说,海洋食品的氟含量小于陆地食品含量。( )
关于刑事责任的追究,下列表述错误的是:A.犯罪嫌疑人关某在被抓获前自杀身亡,依法
( )在很大程度上决定着企业的管理模式。A.企业的行业特征 B.企业文化
早期重商主义绝对禁止( )。A.货物外流 B.资本外流 C.货币外流 D
()应当制定完善会员落实适当性管理要求的自律规则,制定并定期更新本行业的产
个体侵犯行为的影响因素包括()。 (A)道德水准(B)情绪唤起水平 (
(2012年真题)境外某电子产品制造公司为扩展中国业务,2020年初设立上海代
最新回复
(
0
)