Muscle Physiology Chapter 6 Flashcards

Questions and Answers

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?

Arrival of an action potential.

The binding of calcium to which molecule causes the myosin binding sites to be exposed?

Protein complex.

A myosin head binds to which molecule to form a cross bridge?

Actin.

What causes the myosin head to disconnect from actin?

Binding of ATP. Signup and view all the answers

What energizes the power stroke?

Hydrolysis of ATP. Signup and view all the answers

Which of the following proteins makes up the thick filament of the sarcomeres?

Myosin. Signup and view all the answers

Which statement describes the sliding-filament theory?

The actin and myosin interact and the actin is pulled over the myosin, shortening the sarcomere. Signup and view all the answers

T tubules are an invagination of the ________.

Plasma membrane. Signup and view all the answers

What is the function of calcium ions in the contraction of a muscle (sarcomere)?

Calcium binds to the troponin-tropomyosin complex so that the actin and myosin can interact and the sarcomere can contract. Signup and view all the answers

Complete this sentence: As the sarcomere contracts, ________.

ADP is released and is replaced by ATP. Signup and view all the answers

Which of the following choices arranges the structures (1) muscle fiber, (2) fascicle, (3) myofibril, and (4) muscle from largest (most inclusive) to smallest?

4-2-1-3 Signup and view all the answers

What is the first and most direct energy source for muscle contraction?

ATP. Signup and view all the answers

Which of the following best describes the action of sarcomeres within a muscle cell during a contraction?

Each sarcomere shortens a little. Signup and view all the answers

Which term describes the subunits of a myofibril?

Sarcomere. Signup and view all the answers

Which of the following structures is not contained within a muscle fiber?

Tendon. Signup and view all the answers

Muscle fibers are among the largest cells in the body and are actually fusions of hundreds of individual cells.

True Signup and view all the answers

The thick filaments of sarcomeres are composed of _____?

Myosin. Signup and view all the answers

The thin filaments of sarcomeres are composed of _____?

Actin. Signup and view all the answers

A single muscle cell is referred to as a _____.

Muscle fiber. Signup and view all the answers

What is the type of chemical reaction used to rebuild ADP into ATP?

Dehydration synthesis. Signup and view all the answers

Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products?

Glycolysis. Signup and view all the answers

Which of the following processes produces 36 ATP?

Krebs cycle and oxidative phosphorylation. Signup and view all the answers

The 'rest and recovery' period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________.

Pyruvic acid is converted back to lactic acid. Signup and view all the answers

Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?

White fast twitch fibers. Signup and view all the answers

Muscles that oppose each other and produce opposite movements are described as __________.

Antagonistic. Signup and view all the answers

All of the following are functions of the muscular system, EXCEPT __________.

Maintenance of body calcium stores. Signup and view all the answers

Which of the following happens during muscle contraction?

Sarcomeres shorten. Signup and view all the answers

When a skeletal muscle contracts, the is pulled toward the .

Insertion; origin. Signup and view all the answers

Arrange the following components of a muscle in order of increasing size.

Myofibril = Fiber Fiber = Fascicle Fascicle = Muscle Signup and view all the answers

When a muscle contracts, shortening of the muscle occurs because __________.

Sarcomeres shorten. Signup and view all the answers

In a muscle cell, contain .

Myofibrils; actin and myosin filaments. Signup and view all the answers

During the course of muscle contraction, the potential energy stored in ATP is transferred to potential energy stored in _____?

The myosin head. Signup and view all the answers

The release of _____ ions from the sarcoplasmic reticulum is required for skeletal muscle contraction.

Calcium. Signup and view all the answers

Myosin heads bind to _____, which they then pull and cause to slide toward the center of the sarcomere.

Thin filaments. Signup and view all the answers

Of these events, the first to occur when a motor neuron stops sending an impulse to a muscle is _____.

The pumping of calcium ions out of the cytoplasm and back into the sarcoplasmic reticulum. Signup and view all the answers

A muscle cell contains bundles of long _____?

Myofibrils. Signup and view all the answers

When a sarcomere contracts, _____?

The actin and myosin filaments do not change in length. Signup and view all the answers

Which of the following events is the direct result of an action potential in the membrane of a muscle cell?

The muscle cell's endoplasmic reticulum (ER) releases calcium ions. Signup and view all the answers

When ATP attaches to a myosin head, _____?

The myosin head detaches from actin. Signup and view all the answers

Calcium ions _____?

Bind to the protein that blocks the myosin-binding sites on actin. Signup and view all the answers

Botulism toxin inhibits the release of acetylcholine at the neuromuscular junctions. What effect does this have on the muscle activity?

Muscles will not contract because they will not receive nerve stimulation. Signup and view all the answers

The sliding filament mechanism describes the process during which __________.

Actin and myosin slide relative to each other. Signup and view all the answers

Which of the following is the site of calcium ion storage within muscles?

Sarcoplasmic reticulum. Signup and view all the answers

What is the role of ATP in muscle function?

ATP provides energy that enables myosin to form cross-bridges with actin. Signup and view all the answers

In the sliding-filament mechanism of muscle contraction, slides over .

Actin; myosin. Signup and view all the answers

Which of the following would interfere most with a muscle's ability to contract?

Absence of acetylcholine binding sites on the muscle membrane. Signup and view all the answers

When a muscle relaxes, ATP is required. The reason for this is that __________.

The myosin heads can detach from the actin only when a molecule of ATP binds to the head. Signup and view all the answers

All of the following may happen in response to exercise training, EXCEPT __________.

Increase in the number of muscle fibers. Signup and view all the answers

Which of the following is/are characteristic of slow-twitch fibers?

Both myoglobin content that enables oxygen storage and numerous mitochondria. Signup and view all the answers

Which of the following would have motor units with the smallest number of muscle cells?

Muscles in fingers. Signup and view all the answers

The all-or-none principle states that __________.

When a muscle cell is stimulated, it responds with a complete cycle of contraction and relaxation. Signup and view all the answers

Tetanic contractions result from __________.

Frequent stimulation preventing a muscle from relaxing. Signup and view all the answers

Which of the following is the same in both slow-twitch and fast-twitch muscle fibers?

The arrangement of actin and myosin in a sarcomere. Signup and view all the answers

Which type(s) of muscle cells can contract the fastest?

Skeletal muscle cells. Signup and view all the answers

Which type(s) of muscle cells can contract spontaneously?

Both smooth muscle cells and cardiac muscle cells. Signup and view all the answers

Which of the following disorders of the muscular system is INCORRECTLY described?

Muscular dystrophy—a viral disease that causes muscle wasting. Signup and view all the answers

Steroid use in men may lead to __________.

Irreversible changes in the body. Signup and view all the answers

Study Notes

Muscle Contraction Mechanism

An action potential in the T tubule prompts calcium release from the terminal cisternae of the sarcoplasmic reticulum, initiating muscle contraction.
Calcium binds to the troponin-tropomyosin complex, exposing myosin binding sites on actin.

Myosin and Actin Interaction

Myosin heads attach to actin, forming a cross bridge and enabling the power stroke.
The power stroke is fueled by ATP hydrolysis, which transfers energy to the myosin head.
Upon ATP binding, myosin heads detach from actin.

Sarcomere Structure and Function

Thick filaments composed of myosin; thin filaments composed of actin.
Sarcomeres are the subunits of myofibrils, contracting by the sliding filament theory where actin is pulled over myosin.

Muscle Fiber Composition

Muscle fibers consist of myofibrils that contain actin and myosin filaments, localized within a single muscle fiber.
Muscle cells, known as fibers, are among the largest in the body, formed from the fusion of multiple cells.

Energy Sources in Muscle Contraction

ATP is the primary energy source for muscle contraction.
Dehydration synthesis rebuilds ADP into ATP, while glycolysis creates two pyruvic acid molecules from glucose.
Aerobic respiration through the Krebs cycle produces up to 36 ATP per glucose molecule.

Muscle Fiber Types

White fast twitch fibers are adapted for anaerobic glycolysis and have high glycogen content, which supports rapid, powerful contractions with limited oxygen supply.
Slow-twitch fibers possess high myoglobin content and numerous mitochondria, making them suited for endurance and sustained activities.

Muscle Interaction

Antagonistic muscles produce opposite movements to facilitate movement control.
The sliding filament mechanism describes actin sliding over myosin during contraction.

Calcium Ions in Muscle Function

Calcium ions are stored in the sarcoplasmic reticulum and are essential for muscle contraction.
The release of calcium triggers the interaction between actin and myosin, leading to muscle contraction.

Muscle Relaxation Process

Muscle relaxation involves the pumping of calcium ions back into the sarcoplasmic reticulum, ceasing contractions.
ATP is necessary for myosin heads to detach from actin, enabling the muscle to relax.

Motor Units and Muscle Fiber Recruitment

Smaller motor units are found in muscles like those in the fingers for fine motor control.
The all-or-none principle indicates that muscle cells respond completely or not at all when stimulated.

Effects of Exercise and Training

Muscle training can lead to adaptations such as increased myoglobin and mitochondrial content but does not increase the number of muscle fibers.

Disorders and Implications

Muscular dystrophy is characterized incorrectly as a viral disease; it is a genetic condition leading to muscle wasting.
Steroid use in men can cause irreversible changes in body composition and function.

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Test your knowledge of muscle physiology concepts with these flashcards from Chapter 6. Learn about the role of calcium in muscle contraction and how it interacts with key proteins. Use this quiz to reinforce your understanding of critical physiological processes.