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Questions and Answers
What are the three major types of muscles in the body?
What are the three major types of muscles in the body?
Which physiological characteristic allows muscle cells to be stimulated by a nerve?
Which physiological characteristic allows muscle cells to be stimulated by a nerve?
Which type of muscle is under voluntary control?
Which type of muscle is under voluntary control?
What is a common function of smooth muscle?
What is a common function of smooth muscle?
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Which muscle type primarily makes up the heart?
Which muscle type primarily makes up the heart?
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What is the size comparison of a muscle fiber?
What is the size comparison of a muscle fiber?
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What type of muscle is involuntary and found in the walls of hollow organs?
What type of muscle is involuntary and found in the walls of hollow organs?
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Which of the following is NOT a physiological characteristic of muscle tissue?
Which of the following is NOT a physiological characteristic of muscle tissue?
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What is the primary function of the diaphragm?
What is the primary function of the diaphragm?
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Which of the following statements about the diaphragm is true?
Which of the following statements about the diaphragm is true?
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What component of a muscle fiber contains many nuclei and mitochondria?
What component of a muscle fiber contains many nuclei and mitochondria?
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How long can a muscle fiber be?
How long can a muscle fiber be?
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What forms the basic unit of a muscle segment?
What forms the basic unit of a muscle segment?
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What are the two types of myofilaments found in sarcomeres?
What are the two types of myofilaments found in sarcomeres?
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Which band in a sarcomere is primarily made up of thin actin filaments?
Which band in a sarcomere is primarily made up of thin actin filaments?
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In what way does the diaphragm operate?
In what way does the diaphragm operate?
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What causes the shortening of a sarcomere during muscle contraction?
What causes the shortening of a sarcomere during muscle contraction?
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Which of the following muscle types is the diaphragm primarily comprised of?
Which of the following muscle types is the diaphragm primarily comprised of?
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What are the thread-like structures found within the sarcoplasm of muscle fibers?
What are the thread-like structures found within the sarcoplasm of muscle fibers?
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What role does ATP play in muscle contraction?
What role does ATP play in muscle contraction?
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Which structure defines the boundaries of a sarcomere?
Which structure defines the boundaries of a sarcomere?
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What happens to sarcomeres during muscle relaxation?
What happens to sarcomeres during muscle relaxation?
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What connects the myosin heads to actin during muscle contraction?
What connects the myosin heads to actin during muscle contraction?
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Which of the following is NOT a type of band observed in sarcomeres?
Which of the following is NOT a type of band observed in sarcomeres?
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What is the primary function of sphincter muscles in the digestive system?
What is the primary function of sphincter muscles in the digestive system?
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Which type of muscle is referred to as myocardium?
Which type of muscle is referred to as myocardium?
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What feature distinguishes cardiac muscle fibers from other muscle types?
What feature distinguishes cardiac muscle fibers from other muscle types?
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What happens when cardiac muscle fibers contract?
What happens when cardiac muscle fibers contract?
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What role does calcium play in muscle contraction?
What role does calcium play in muscle contraction?
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What is the role of intercalated discs in cardiac muscle?
What is the role of intercalated discs in cardiac muscle?
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Which structure stores calcium in skeletal muscle cells?
Which structure stores calcium in skeletal muscle cells?
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What is a consequence of damage to cardiac muscle?
What is a consequence of damage to cardiac muscle?
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How does a motor neuron initiate muscle contraction?
How does a motor neuron initiate muscle contraction?
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What happens when calcium is pumped back into the sarcoplasmic reticulum?
What happens when calcium is pumped back into the sarcoplasmic reticulum?
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How does the contraction of one cardiac muscle fiber affect adjacent fibers?
How does the contraction of one cardiac muscle fiber affect adjacent fibers?
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What is the primary energy source muscles utilize when glycogen is converted?
What is the primary energy source muscles utilize when glycogen is converted?
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Why does cardiac muscle not repair itself effectively?
Why does cardiac muscle not repair itself effectively?
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In muscles with high demand, what contributes to their darker color?
In muscles with high demand, what contributes to their darker color?
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What is the process that occurs when muscles require energy from stored fat?
What is the process that occurs when muscles require energy from stored fat?
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What occurs at the neuromuscular junction after acetylcholine is released?
What occurs at the neuromuscular junction after acetylcholine is released?
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Study Notes
The Diaphragm
- The diaphragm is the primary mover of breathing.
- This dome-shaped muscle separates the abdominal cavity from the thoracic cavity.
- The diaphragm is responsible for bringing atmospheric air into the lungs.
- The diaphragm is under both voluntary and involuntary control.
Muscle Fibers
- Each muscle cell is an elongated fiber, known as a muscle fiber, and can be up to 12 inches (app. 30.5cm) in length.
- Muscle fibers are composed of several hundred to several thousand thread-like myofibrils.
- Muscle fibers bundle together to form a specific muscle segment.
Sarcomeres
- Sarcomeres are the functional contractile units of a muscle fiber.
- Sarcomeres are made up of two types of threadlike structures: thick myofilaments made up of myosin and thin myofilaments made up of actin.
- Z lines are made up of thin actinin and define the boundaries of sarcomeres.
Muscle Contraction
- Contraction of a muscle causes the myofilaments to slide toward each other, which shortens the sarcomere and the entire muscle.
- Muscle contraction requires the temporary connections of cross-bridges between the myosin head and the actin, pulling the sarcomere together.
ATP and Calcium
- Energy for muscle contraction and relaxation comes from ATP (adenosine triphosphate).
- ATP helps the myosin heads form and break the cross-bridges with actin.
Types of Muscles
- Muscle is a general term for all contractile tissues.
- Muscle tissue contains muscle fibers, each about the size of a human hair.
- The three major types of muscles in the body are skeletal, smooth, and cardiac.
Characteristics of Muscles
- Muscle tissues display five physiological characteristics: excitability, contractility, extensibility, elasticity, and conductivity.
- Calcium triggers contraction by reacting with regulatory proteins, which allow interaction of actin and myosin.
- During relaxation, calcium is stored away from the actin and myosin in the sarcoplasmic reticulum (SR).
ATP and Calcium (2)
- The motor neuron instructs a muscle to contract by releasing a neurotransmitter called acetylcholine (ACh).
- Acetylcholine causes the muscle fiber to open sodium ion channels.
- Sodium ions flow into the muscle fiber, exciting it and causing calcium to be released from the SR.
- When calcium is pumped back into the SR, the cross-bridge attachments are broken, and the muscle relaxes.
Muscular Fuel
- Muscles need fuel in the form of food and oxygen.
- The body stores glycogen in the muscle, where it is converted to glucose, which releases energy.
- Muscles with very high demands also store fat and use it as energy.
- Energy release causes heat production.
Muscular Fuel (2)
- Higher demand muscles have a greater blood supply to carry oxygen.
- The greater blood supply gives these muscles a darker color.
Smooth Muscle
- A special type of smooth muscle is called a sphincter.
- Sphincters are found throughout the digestive system and act as doorways to let material in and out.
- Contraction closes the door, while relaxation, opens it.
Cardiac Muscle
- Cardiac muscle is a specialized striated and involuntary muscle also called myocardium.
- It is located in the middle layer of the heart wall.
- Cells of the cardiac muscle are the cardiocytes.
- Cardiac muscle fibers are shorter and receive a richer supply of blood than any other muscle in the body.
- When cardiac muscle fibers contract, they force blood to circulate throughout the body.
- Contraction causes the heart to beat.
Cardiac Muscle (2)
- Membranes of cardiac muscle cells are interlocking and linked by gap junctions, forming intercalated discs.
- When one fiber contracts, it pulls the next one into a contraction, creating a domino effect.
- Cardiac muscle does not repair itself.
- Damage to cardiac muscle always leaves a scar.
- Scar tissue does not contract like normal tissue; it is rigid, which decreases cardiac output.
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