Ch. 11 AP1

Where would you expect to find numerous gap junctions in muscular tissue?

• The sarcoplasmic reticulum of skeletal muscle

• The A bands of skeletal and cardiac muscle

• The sarcolemma of skeletal muscle

• The intercalated discs of cardiac muscle

• Multiunit smooth muscle

Answer explanation

Numerous gap junctions are found in the intercalated discs of cardiac muscle, allowing for rapid communication and coordination of contractions between adjacent cardiac cells.

Skeletal muscle is called ___________, because it is usually subject to conscious control.

• excitable

• contractile

• striated

• voluntary

• isometric

Answer explanation

Skeletal muscle is called voluntary because it is under conscious control, allowing us to move and perform actions intentionally. This distinguishes it from involuntary muscles, which operate without conscious thought.

The triads of a muscle fiber consist of __________.

• two A bands and one I band

• two T tubules and one terminal cistern

• two terminal cisterns and one T tubule

• two thin myofilaments and one thick myofilament

• two thick myofilaments and one thin myofilament

Answer explanation

The triads of a muscle fiber consist of two terminal cisterns and one T tubule, which are essential for muscle contraction by facilitating calcium release and transmission of action potentials.

Cardiac muscle has very little capacity for regeneration because it lacks __________.

• satellite cells

• an endomysium

• sarcomeres

• dense bodies

• somatic nerve fibers

Answer explanation

Cardiac muscle has very little capacity for regeneration because it lacks satellite cells, which are essential for muscle repair and regeneration. Without these cells, cardiac tissue cannot effectively regenerate after injury.

An isometric contraction does not change muscle length.

• True

• False

Answer explanation

An isometric contraction occurs when a muscle generates force without changing its length. Therefore, the statement that an isometric contraction does not change muscle length is true.

The training regimen of a competitive weight lifter is designed partly to __________.

• convert certain parallel muscles into stronger pennate muscles

• increase the average number of myofibrils per muscle fiber

• convert white muscle tissue to red muscle

• increase the size of his motor units

• lower the threshold for muscle excitation

Answer explanation

The correct choice, 'increase the average number of myofibrils per muscle fiber', reflects the goal of a weight lifter's training to enhance muscle strength and size by promoting myofibril hypertrophy.

Which of the following is true concerning isotonic concentric contraction?

• The muscle shortens but tension remains constant.

• The muscle lengthens but tension remains constant.

• The muscle tenses and shortens.

• The muscle tenses but length remains unchanged.

• The muscle lengthens and tension declines.

Answer explanation

In isotonic concentric contraction, the muscle shortens while maintaining a constant tension. This distinguishes it from other types of contractions where muscle length or tension changes differently.

Which of the following contains overlapping thick and thin filaments?

• A band

• H band

• I band

• M line

• Z discs

Answer explanation

The A band contains overlapping thick (myosin) and thin (actin) filaments, which is crucial for muscle contraction. In contrast, the H band and I band do not have this overlap, making the A band the correct choice.

In order formuscle to continue contracting during anaerobic fermentation, which of the following is essential?

• Cholinesterase inhibitors

• Protease

• Myokinase

• Acetylcholinesterase

• Acid phosphatase

Answer explanation

Myokinase is essential for muscle contraction during anaerobic fermentation as it helps regenerate ATP from ADP, allowing continued energy supply for muscle activity.

If one nerve stimulus arrives at a muscle fiber so soon that the fiber does NOT relax at all from the previous twitch, the most likely result will be __________. This can only be achieved in the laboratory.

• fatigue

• spasm

• incomplete tetanus

• complete tetanus

• wave summation

Answer explanation

Complete tetanus occurs when stimuli are so frequent that the muscle fiber does not relax between twitches, resulting in a sustained contraction. This phenomenon can be achieved in a laboratory setting.