Mastering Bio Muscular System

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

both smooth muscle cells and cardiac muscle cells

Which of the following processes produces 36 ATP?

Krebs cycle and oxidative phosphorylation...Yes, 36 ATPs are produced for each glucose molecule. This process, which takes place in the mitochondria, is considered aerobic respiration because oxygen is required.

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

True...Each muscle cell, called a fiber, is packed with myofibrils, which are small cylinders of contractile proteins.

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

absence of acetylcholine binding sites on the muscle membrane...Without acetylcholine binding sites, a muscle will be unable to respond to a message.

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

antagonistic

The biceps brachii and triceps brachii contribute to arm movement. These muscles are considered __________.

antagonistic...Antagonistic muscles oppose each other.

In which one of the following would one expect to find motor units made up of only a few muscle cells?

eye muscles

Unlike skeletal muscle, cardiac and smooth muscle do not respond at all to the nervous system, but contract on their own. Differences in the rate of contraction of smooth and cardiac muscle are due to the action of pacemakers in cardiac muscles.

false

Which sequence lists the structures from largest, most inclusive, to smallest?

muscle-fascicle-muscle fiber-myofibril-thick filament

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

muscular dystrophy—a viral disease that causes muscle wasting...Muscular dystrophy is a hereditary not a viral disease.

When an electrical impulse traveling along a motor neuron arrives at a neuromuscular junction

there is an increase in the secretion of acetylcholine at the neuromuscular junction

At the end of the contractile period, energy from the breakdown of ATP is used to

transport calcium back into the sarcoplasmic reticulum

Muscle contraction accounts for over 75% of the heat generated by the body.

true

The all-or-none principle states that __________.

when a muscle cell is stimulated, it responds with a complete cycle of contraction and relaxation...The all-or-none principle states that if a motor unit responds, it will respond completely.

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

white fast twitch fibers...Yes, white fast twitch fibers have high glycogen content for a readily available source of glucose for glycolysis. They appear white because of the reduced amount of myoglobin and fewer capillaries surrounding them. Because these fibers have reduced myoglobin and very few capillaries surrounding them, they have very little oxygen available for the Krebs cycle and oxidative phosphorylation. They also have fewer mitochondria (where the Krebs cycle and oxidative phosphorylation would take place).

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

ATP

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...Yes, this is NOT a part of the "rest and recovery" period. When oxygen is available, lactic acid is converted back to pyruvic acid (not vice versa) that then enters the Krebs cycle. Lactic acid is the end product of the anaerobic pathway.

Which term describes the subunits of a myofibril?

Sarcomere...Sarcomeres are the subunits of myofibrils and are composed of thin filaments and thick filaments.

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

Tendon...Tendons connect skeletal muscles to the skeleton and are not contained within muscle fibers.

Which statement describes the sliding-filament theory?

The actin and myosin interact and the actin is pulled over the myosin, shortening the sarcomere...Correct. The myosin head binds to the actin during the "power stroke" and the actin is pulled past the myosin, thereby shortening the sarcomere.

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

actin...Yes, the myosin head binds to actin, the major component of thin filaments.

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

actin; myosin...Actin slides over myosin during contraction.

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

arrival of an action potential...Yes, an action potential in the T tubule causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum.

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

myosin...Correct. Myosin makes up the thick filaments of the sarcomere.

T tubules are an invagination of the ________.

plasma membrane...Correct. The T tubule is an invagination of the plasma membrane.

Contraction of a skeletal muscle cell is initiated by the

release of acetylcholine by a neuron terminating at the neuromuscular junction

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

sarcoplasmic reticulum

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

skeletal muscle cells

Skeletal muscle groups that work together to create the same movement are referred to as

synergistic

Drag the labels onto the flowchart to identify the sequence of steps that occurs during muscle contraction. The step numbers correspond to the numbers in the diagram above.

1. action potential in the motor neurons triggers an action potential in the muscle cell 2. action potential spreads down tubules in the muscle cell 3. Endoplasmic reticulum (ER) releases calcium ions 4. Calcium ions bind to protein complex on thin (actin) filament, exposing myosin-binding sites 5. myosin heads bind to actin & shorten the sarcomere 6. when action potentials stop, calcium ions are pumped back into the ER 7. myosin-binding sites are blocked & muscle relaxes

The following events are associated with muscle contraction. Which one of the following best describes the order in which these events occur, following the initiation of a contraction by a nerve impulse? 1. T tubules transmit electrical impulses throughout the muscle cell. 2. Myosin contacts actin and pulls it toward the center of the sarcomere. 3. Acetylcholine binds to receptors on the muscle. 4. Troponin-tropomyosin complex shifts to expose myosin binding sites. 5. Calcium is released from the sarcoplasmic reticulum.

3, 1, 5, 4, 2

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

Complete this sentence. As the sarcomere contracts, ________.

ADP is released and is replaced by ATP, which is required to release the myosin from the actin...Correct. As the sarcomere contracts, ADP is released and is replaced by ATP, which is required to release the myosin from the actin.

What is the role of ATP in muscle function?

ATP provides energy that enables myosin to form cross-bridges with actin. ATP enables myosin to detach from actin. ATP provides energy to transport calcium back into storage. -All of the listed choices are correct.

Muscle cells produce lactic acid when they have an inadequate supply of

O2

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...Correct. Calcium binds to the troponin-tropomyosin complex, freeing the binding sites so that the actin and myosin can interact and the sarcomere can contract.

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

Each sarcomere shortens a little...Each sarcomere will contribute to the contraction.

Following electrical stimulation of a muscle cell, calcium functions to

bind to the protein troponin

What causes the myosin head to disconnect from actin?

binding of ATP...Yes, the binding of ATP causes the myosin head to disconnect from actin.

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

binding of calcium to the protein complex...Yes, when calcium binds to the protein complex, the myosin binding sites are exposed.

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

dehydration synthesis...Yes, a water molecule is removed, thus it is called dehydration synthesis. Building ATP from ADP requires a synthetic enzyme plus a source of energy to rebuild the high energy bond.

Tetanic contractions result from __________.

frequent stimulation, preventing a muscle from relaxing...Tetany occurs when a muscle is unable to relax.

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

glycolysis...Yes, glucose is broken down in the process called glycolysis. This process takes place in the cytoplasm and does not require oxygen - hence it is called anaerobic respiration. If oxygen is available, the pyruvic acid moves into the mitochondria and glycolysis contributes to aerobic respiration.

What energizes the power stroke?

hydrolysis of ATP...Yes, the hydrolysis of ATP provides the energy for the power stroke. Energy is transferred from ATP to the myosin head.

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

increase in the number of muscle fibers

Steroid use in men may lead to __________.

irreversible changes in the body...Changes that occur with steroid use may be irreversible