首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Biology Cardiac Muscle What happens when an electrical impulse generated in one part of the heart spreads to all the cardiac mu
Biology Cardiac Muscle What happens when an electrical impulse generated in one part of the heart spreads to all the cardiac mu
admin
2012-01-14
66
问题
Biology Cardiac Muscle
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://kaotiyun.com/show/zLyO777K
0
托福(TOEFL)
相关试题推荐
Completetheflowchartbelow.ChooseNOMORETHANTHREEWORDSfromthepassageforeachanswer.Writeyouranswersinboxes7-1
Matchinginformationandfeature.OutofAfrica:solarenergyfromSaharaVivienneWaltreportsonhowtheSaharaDesertcouldo
ThePearlA.Thepearlhasalwayshadaspecialstatusintherichandpowerfulallthroughthehistory.Forinstance,women
HowdesertsareformedA.Adesertreferstoabarrensectionofland,mainlyinaridandsemi-aridareas,wherethereisal
Betweenwhattimesistheroadtrafficlightest?Thenoiselevelsatthesitecanreach
SECTION3Questions21-30Questions21-23CompletethenotesonwhatMikasaysatthebeginningofthediscussion.Mikasays
He/Shethinksanoverheadprojectorisusuallyneeded.He/Shementionsthatjokescanbeusefulincontext.
TicktheTHREEotheritemswhicharementionedinthenewsheadlines.
Completethelecturenotes.UseNOMORETHANTHREEWORDSforeachanswer.PurposeoftheminilectureToexperience【T32】______
随机试题
行政机关将查封、扣押的财产或者划拨的存款、汇款以及拍卖和依法处理所得的款项,截留、私分或者变相私分的,对直接负责的主管人员和其他直接责任人员依法给予记过、记大过、降级、撤职或者开除的处分。()
我国公民道德建设的基本原则是()。
属于丙类传染病的病种是()
下列哪些建设用地可由有批准权的人民政府依法批准,划拨土地使用权()。
背景资料:某城市给水工程项目,通过招标投标确定了本市一家具有工程项目资质的施工企业承担该施工任务。施工企业在给水厂站工程施工时制定了以下施工技术要求:(1)水池底板混凝土应分层分次浇筑完成;(2)水池底板混凝土浇筑采
当某项投资期望收益率大于无风险收益率时,则风险收益率会小于零。()
王某因不服区公安分局行政拘留10天的处罚申请复议,市公安局认为处罚过轻,遂改为行政拘留15天的处罚,王某以市公安局为被告提起行政诉讼。对王某的诉讼请求,法院应当如何处理?()
在矩形ABCD的边CD上随机取一点P,使得AB是△APB的最大边的概率大于.
D公司预期未来每年产生的永续现金流量在经济状况好的情况下为1500万元,经济状况不好的情况下只有500万元,预计经济状况好的可能性为60%,经济状况不好的可能性为40%。要求:假设企业处于完美资本市场中,如果企业借入了5000万元的债务,债务的期望报
Readthefollowingarticleandchoosethebestwordforeachspace.Forquestions26~45,markoneletterA,B,CorDonyou
最新回复
(
0
)