单选题
How does the professor develop the topic of cardiac muscle?
【正确答案】
【答案解析】
[听力原文]
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, the 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 banding"s 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.
How does the professor develop the topic of cardiac muscle?
The professor compares cardiac muscle and skeletal muscle. She says ...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; Like skeletal muscle, cardiac muscle is striated; 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. (2.6)
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, the 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 banding"s 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.
How does the professor develop the topic of cardiac muscle?
The professor compares cardiac muscle and skeletal muscle. She says ...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; Like skeletal muscle, cardiac muscle is striated; 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. (2.6)
单选题
Why does the professor say this:
【正确答案】
【答案解析】
[听力原文]
Why does the professor say this:
"How can your heart keep beating and beating, never stopping, and rarely getting out of sync?"
The professor"s purpose is to introduce the topic of cardiac muscle, which the rest of the lecture develops. The professor answers her own question by saying It"s possible because of the specialized type of muscle—cardiac muscle—that makes up the heart tissue... (2.3)
Why does the professor say this:
"How can your heart keep beating and beating, never stopping, and rarely getting out of sync?"
The professor"s purpose is to introduce the topic of cardiac muscle, which the rest of the lecture develops. The professor answers her own question by saying It"s possible because of the specialized type of muscle—cardiac muscle—that makes up the heart tissue... (2.3)
单选题
Why does the professor say this:
【正确答案】
【答案解析】
[听力原文]
14. Why does the professor say this:
"Before I go into cardiac muscle, let"s back up a bit."
The professor"s purpose is to review material the class has already studied. She says ...let"s back up a bit, indicating that what she says next will review something that they have already discussed. (2.3)
"Before I go into cardiac muscle, let"s back up a bit."
The professor"s purpose is to review material the class has already studied. She says ...let"s back up a bit, indicating that what she says next will review something that they have already discussed. (2.3)
填空题
Based on the information in the lecture, indicate whether each sentence below describes skeletal muscle or cardiac muscle.
For each sentence, click in the correct box.
For each sentence, click in the correct box.
|
Skeletal
muscle |
Cardiac
muscle |
|
|
These muscles are connected to the
bones, which move when the muscles contract. |
||
|
When this type of muscle contracts,
blood moves throughout the body. |
||
|
To contract, this type of muscle must
be stimulated by a motor neuron. |
||
|
These muscle cells can generate
electrical impulses without input from the nervous system. |
||
|
This muscle cannot stop to rest
without serious consequences for the body. |
||
单选题
What happens when an electrical impulse generated in one part of the heart spreads to all the cardiac muscle cells?
【正确答案】
【答案解析】
[听力原文]
What happens when an electrical impulse generated in one part of the heart spreads to all the cardiac muscle cells?
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)
What happens when an electrical impulse generated in one part of the heart spreads to all the cardiac muscle cells?
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)
单选题
Listen again to, art of the lecture. Then answer the question.
What can be inferred about the contraction of cardiac muscle?
What can be inferred about the contraction of cardiac muscle?
【正确答案】
【答案解析】
[听力原文]
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)
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)