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 Listen again to part of the lecture. Then answer the question. What can be inferred about the contractio
Biology Cardiac Muscle Listen again to part of the lecture. Then answer the question. What can be inferred about the contractio
admin
2012-01-14
39
问题
Biology Cardiac Muscle
Listen again to part of the lecture. Then answer the question. What can be inferred about the contraction of cardiac muscle?
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、Cardiac muscle contracts automatically because it contains motor neurons.
B、The contraction depends on the action of sodium, calcium, and potassium.
C、The nervous system tells cardiac muscle cells when to contract.
D、Cardiac muscle cells will live for several weeks in a laboratory dish.
答案
B
解析
Listen again to part of the lecture. Then answer the question.
"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 can be inferred about the contraction of cardiac muscle?
The professor says Electrically, they’re set up so, so that sodium and calcium-positive ions-change places with potassium-a negative ion-across the cell membrane; When sodium, calcium, and potassium ions move into or out of a cardiac cell, it causes the muscle to contract. You can infer that the contraction of cardiac muscle depends on the action of sodium, calcium, and potassium. (2.4)
转载请注明原文地址:https://kaotiyun.com/show/7QyO777K
0
托福(TOEFL)
相关试题推荐
Completethediagrambelow.ChooseNOMORETHANTHREEWORDSfromthepassageforeachanswer.Writeyouranswersinboxes18-21
DothefollowingstatementsagreewiththeinformationgiveninReadingPassage3?Inboxes35-38onyouranswersheetwriteTRU
Matchinginformationandfeature.OutofAfrica:solarenergyfromSaharaVivienneWaltreportsonhowtheSaharaDesertcouldo
Matchinginformationandfeature.OutofAfrica:solarenergyfromSaharaVivienneWaltreportsonhowtheSaharaDesertcouldo
AncientPeopleinSaharaOnOct.13,2000,PaulSereno,aprofessorfromtheUniversityofChicago,guidedateamofpalaeon
Whatpercentageofthestudentsaremature?Theuniversityaccommodationserviceshavea______thatstudentscanlookthrough
Theprofessorsaysthatsuperhighways______.【27】
Reducingspeedandfollowing______doesalottomaketheroadssafer.Youcancall911toreportanaggressivedriverifthe
WhatisthepurposeofJaneandRick’smeetingwiththetutor?
A、CurrentissuesineconomicsB、ChoicesfacedbyconservationistsC、ArecentbiologylectureD、TopicsforaresearchpaperBWhat
随机试题
试述新旧民主主义革命的区别与联系。
A.风痰阻络B.阴虚火旺C.热入心包D.心脾热盛E.中风先兆舌体强硬而胖大,舌苔厚腻的临床意义是
案情:四川成都的一名退休职工把某电视台主持人赵某告上了法庭。他以赵某在接受某杂志专访时的言论有一句“他有一个团伙”为由,向法院提起侵犯名誉权之诉;而且索赔的标的就是一分钱,此案被法院裁定不予受理。最近,除了有“一分钱官司”,还有“一元钱官司”。例如,北京市
关于合伙企业积累财产的性质,下列哪一表述是正确的?
图示高层建筑由防震缝分成Ⅰ、Ⅱ两部分,当Ⅰ、Ⅱ两部分各为下列何种结构时,要求的防震缝宽度最大?
对于渐变折射率光纤,光波在纤芯中产生连续折射,形成穿过光纤轴线的()的光折射线,引导光波沿纤芯向前传播。
美术教材是唯一的美术课程资源。()
简述幼儿教师的专业素养结构。
为深入开展“法治大讲堂”活动:龙泉驿区充分结合自身实际,形成了具有地方特色的工作思路。139个村(社区)都配备有专职人民调解员和法律顾问是龙泉驿区法治建设的一大优势和特色。龙泉驿区抓住自身优势,将定期专项法制宣传(如“3.8”节、综治宣传月、“6.26"禁
"HasEnronbecomeariskyplacetowork?"ThatwasaprettydumbthingtoaskatEnroninAugust2001.Risky?Thefirmwasappar
最新回复
(
0
)