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Questions and Answers
What are the three major types of muscles in the body?
Which physiological characteristic allows muscle cells to be stimulated by a nerve?
Which type of muscle is under voluntary control?
What is a common function of smooth muscle?
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Which muscle type primarily makes up the heart?
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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?
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Which of the following is NOT a physiological characteristic of muscle tissue?
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What is the primary function of the diaphragm?
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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?
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How long can a muscle fiber be?
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What forms the basic unit of a muscle segment?
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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?
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In what way does the diaphragm operate?
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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?
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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?
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Which structure defines the boundaries of a sarcomere?
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What happens to sarcomeres during muscle relaxation?
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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?
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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?
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What feature distinguishes cardiac muscle fibers from other muscle types?
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What happens when cardiac muscle fibers contract?
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What role does calcium play in muscle contraction?
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What is the role of intercalated discs in cardiac muscle?
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Which structure stores calcium in skeletal muscle cells?
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What is a consequence of damage to cardiac muscle?
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How does a motor neuron initiate muscle contraction?
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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?
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What is the primary energy source muscles utilize when glycogen is converted?
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Why does cardiac muscle not repair itself effectively?
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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?
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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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