Physiology chapter 12

A motor unit consists of A) one neuron and all the skeletal muscle fibers it controls. B) one skeletal muscle fiber and all the neurons that control that fiber. C) one skeletal muscle fiber and the neuron that controls that fiber. D) one axon terminal branch and the myofibrils it controls.

A

An important difference between single-unit and multiunit smooth muscle is the A) numerous gap junctions in single-unit smooth muscle, which allow many cells to work together as a sheet. B) longer actin and myosin filaments in multiunit smooth muscle, which allow coordination of contraction. C) ability of single-unit fibers to change into multiunit fibers when advantageous. D) closely controlled individual fibers in single-unit smooth muscle to allow fine control and graded contractions by selective activation.

A

As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately A) detaches from actin. B) initiates binding with actin. C) tightens its bond to actin. D) swivels.

A

In order for the bicep muscle to shorten, the force applied by the muscle must be ________ the load applied at the hand. A) greater than B) less than C) equal to

A

In the lever system that characterizes the interaction between bones and muscle, the bones act as the ________ whereas the joints form the ________. A) lever, fulcrums B) fulcrum, levers C) lever, pulleys D) fulcrum, pulleys

A

Match from the following list. ​A. A band ​B. I band ​C. Z disk ​D. H zone ​E. M line The band with the most overlap between thick and thin filaments, which unevenly scatters light leading to its' dark appearance

A

Match the structures with the accurate description. ​A. muscle fiber ​B. fascicle ​C. sarcolemma ​D. myofibril ​E. t-tubules A single muscle cell

A

The H zone contains A) thick filaments. B) thin filaments only. C) actin only. D) thick and thin filaments.

A

The calcium release channel in the smooth muscle sarcoplasmic reticulum that is opened by increases in phospholipase C activity is the A) inositol trisphosphate (IP3) receptor channel. B) ryanodine receptor. C) dihydropyridine (DHP) receptor. D) voltage-gated Ca2+ channel. E) Ca2+-ATPase.

A

The cause of skeletal muscle fatigue during extended submaximal exercise is primarily a(n) A) depletion of glycogen stores. B) depletion of creatine stores. C) increased inorganic phosphate (Pi) concentration. D) depletion of K+ stores.

A

The factor(s) that determine the duration of a twitch in various types of fibers is the speed of the A) removal of Ca2+ ions from the sarcoplasm only. B) hydrolysis of ATP only. C) movement of Na+ across their membranes only. D) removal of Ca2+ ions from the sarcoplasm and hydrolysis of ATP. E) removal of Ca2+ ions from the sarcoplasm and hydrolysis of ATP and movement of Na+ across their membranes.

A

The force generated by a single muscle fiber can be increased by A) increasing frequency of action potentials only. B) increasing muscle length beyond optimal only. C) increasing the asynchrony of recruitment only. D) increasing frequency of action potentials and increasing muscle length beyond optimal only.

A

The function of the titin protein is to A) stabilize the position of the contractile filaments. B) pull Z lines together during contraction. C) interact with actin during contraction. D) release calcium during contraction. E) cover the myosin binding site on the actin molecule.

A

The origin is the end of the skeletal muscle that attaches to the A) more stationary bone. B) more mobile bone. C) tendon. D) ligament.

A

Which fibers fatigue sooner? A) fast-twitch fibers B) slow-twitch fibers

A

Which fibers generate more force? A) fast-twitch fibers B) slow-twitch fibers

A

_______ is composed of multiple globular molecules polymerized to form long chains or filaments. A) Actin B) Tropomyosin C) Troponin D) Myosin E) Titin

A

In order to contract and relax, muscle cells require energy in the form of ________. The immediate backup energy source is ________ that requires the enzyme ________.

ATP, phosphocreatine, creatine kinase

The heavy chain of myosin contains 2 important regions: the first acts as ________ to convert energy into movement whereas the second binds to ________.

ATPase, actin

A flexor is a skeletal muscle whose shortening moves attached bones A) away from one another. B) towards one another. C) medially D) latera

B

For antagonistic muscle groups to move a limb, flexor contraction occurs coincident with A) contraction of the extensor. B) relaxation of the extensor. C) no changes in the extensor. D) contraction of the tendon.

B

Match from the following list. ​A. A band ​B. I band ​C. Z disk ​D. H zone ​E. M line The lightest color bands of the sarcomere, comprised only of thin filaments

B

Match the structures with the accurate description. ​A. muscle fiber ​B. fascicle ​C. sarcolemma ​D. myofibril ​E. t-tubules A bundle of adjacent muscle cells

B

Most of the time, the parallel thick and thin filaments of the myofibrils are connected by ________ that span the space between myosin and actin molecules. A) tropomyosin molecules B) crossbridges C) nebulin molecules D) sarcomeres E) calcium ions

B

Motor units that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ________ muscle fibers than motor units that control more gross movements (gastrocnemius muscle of the lower leg). A) more B) fewer C) the same number of

B

Put these events in the correct chronological sequence: 1. End-plate potentials trigger action potentials. 2. Transverse tubules convey potentials into the interior of the cell. 3. Acetylcholine binds to receptors on the motor end plate. 4. Ca2+ is released from the sarcoplasmic reticulum. A) 1, 2, 3, 4 B) 3, 1, 2, 4 C) 2, 1, 4, 3 D) 3, 1, 4, 2 E) 4, 3, 2, 1

B

Skeletal muscle fibers with the greatest endurance rely on ________ for energy. A) anaerobic glycolysis B) oxidative phosphorylation C) lactic acid accumulation D) ketone body degradation

B

The I band contains A) thick filaments only. B) thin filaments only. C) myosin only. D) thick and thin filaments.

B

The action potential traveling along the t-tubule is detected by the A) ryanodine receptor. B) dihydropyridine (DHP) receptor (L-type calcium channel). C) acetylcholine receptor. D) Ca2+ ATPase.

B

The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a A) Na+ channel. B) channel for both Na+ and K+. C) calcium channel. D) ryanodine receptor.

B

The brief period of time between the beginning of the action potential in the muscle and the beginning of contraction is referred to as the A) refractory period. B) latent period. C) relaxation phase. D) depolarization period. E) repolarization period.

B

The function of transverse tubules is to A) store Ca2+ ions inside the muscle fiber. B) rapidly conduct action potentials to the interior of the muscle fiber. C) ensure a supply of glycogen throughout the muscle sarcoplasm. D) conduct ATP molecules out of the mitochondria throughout the sarcoplasm.

B

The nervous system avoids muscle fatigue during submaximal contraction by A) always recruiting slow-twitch motor units. B) asynchronous recruitment. C) synchronous recruitment. D) always recruiting fast-twitch motor units.

B

When comparing complete tetanus with unfused (incomplete) tetanus, which is true? A) Complete tetanus involves some relaxation between twitches. B) Complete tetanus involves development of maximum tension. C) Complete tetanus occurs at a lower frequency of stimulation than unfused tetanus. D) Complete tetanus would occur when there is more time between twitch contractions.

B

Within a single fiber, the tension developed during a twitch depends upon the A) amplitude of the action potential. B) length of the sarcomeres prior to contraction. C) length of the thick filament. D) duration of the stimulus.

B

A change in smooth muscle cell tension in the absence of a change in electrical potential of the cells is described as a A) pacemaker potential. B) slow wave potential. C) pharmacomechanical coupling. D) electromechanical coupling.

C

A contraction that generates enough force to move a load is known as ________, whereas one that generates force that equals the load is known as ________. A) isotropic, isometric B) isometric, eccentric C) isotonic, isometric D) isometric, isotonic E) isotonic, eccentric

C

After death, when metabolism stops, in which step of the contractile cycle must skeletal muscles remain? A) It depends on what part of the contractile cycle they were in at the time of death. B) the power stoke phase C) the rigor state D) a weak binding state

C

Before the entire muscle can change length, the force generated by the muscle must stretch the A) eccentric contractile elements. B) parallel elastic elements. C) series elastic elements. D) contractile elements.

C

During heavy exercise, the ATP requirements of active muscle are likely to be met by metabolism of A) protein. B) fatty acids. C) carbohydrates. D) nucleotides.

C

Match from the following list. ​A. A band ​B. I band ​C. Z disk ​D. H zone ​E. M line The structures that serve as the attachment site for the thin filaments and mark the boundaries for one sarcomere

C

Match from the following list. ​A. A band ​B. I band ​C. Z disk ​D. H zone ​E. M line 56) The structures that serve as the attachment site for the thin filaments and mark the boundaries for one sarcomere.

C

Match the structures with the accurate description. ​A. muscle fiber ​B. fascicle ​C. sarcolemma ​D. myofibril ​E. t-tubules The muscle cell membrane

C

Muscle fatigue arises primarily from failure in A) neuromuscular transmission. B) initiation of contraction by the motor cortex. C) excitation-contraction coupling. D) signal relay from brain to spinal cord. E) calcium pumps in the skeletal muscles.

C

Put these myofibers in the order they would be recruited as the body moves from a weak to a strong stimulus: 1. glycolytic fast-twitch fibers 2. fatigue-resistant oxidative fast-twitch fibers 3. fatigue-resistant slow-twitch fibers A) 1, 2, 3 B) 2, 3, 1 C) 3, 2, 1 D) 1, 3, 2 E) 3, 1, 2

C

Smooth muscle cells lack which protein(s)? A) actin only B) myosin only C) troponin only D) tropomyosin only E) troponin and tropomyosin

C

The contraction cycle is triggered by the rise in ________ released from the sarcoplasmic reticulum (SR). A) Na+ B) K+ C) Ca2+

C

The molecular event that occurs immediately after the power stroke is the A) release of actin from the myosin head. B) hydrolysis of ATP by the myosin head. C) release of ADP from the myosin. D) binding of tropomyosin to the myosin. E) binding of actin to the myosin.

C

The speed with which force is developed by skeletal muscles is determined by the A) Ca2+ ATPase activity. B) sarcoplasmic calcium concentration. C) myosin ATPase isoform. D) Ca2+ ATPase activity and sarcoplasmic calcium concentration. E) Ca2+ ATPase activity, myosin ATPase isoform, and sarcoplasmic calcium concentration.

C

The tension generated in a skeletal muscle fiber is directly proportional to the number of A) thick and thin filaments present. B) nebulin and titin molecules present. C) high energy crossbridges formed. D) low energy crossbridges formed. E) active sarcomeres.

C

This protein is activated by the Ca2+-calmodulin complex to phosphorylate the myosin light chain protein. A) tropomyosin B) myosin heavy chain C) myosin light chain kinase D) myosin light chain phosphatase

C

When a skeletal muscle cell contracts and the muscle shortens, A) myosin heads generate a single power stroke. B) the position of an actin molecule relative to a myosin molecule does not change. C) some myosin heads are forming crossbridges as others are releasing them. D) the actin ATPase allows the actin molecule to swivel. E) the actin molecule swivels during the power stroke.

C

Which of the following statements is NOT correct regarding the motor units and their activation? A) A motor unit in muscles of gross movement can have thousands of muscle cells. B) All muscle fibers in a single motor unit are of the same fiber type. C) A weak contractile stimulus activates fast-twitch motor units. D) The metabolic capacity of muscle fibers within a motor unit can be altered. E) At its peak intensity, a contractile stimulus will activate muscle fibers that are easily fatigued.

C

Which of the following would cause the crossbridge to transition from a high force state to a low force state? A) increasing myosin ATPase activity B) increasing intracellular calcium C) decreasing intracellular calcium D) energizing the myosin head E) decreasing myosin ATPase activity

C

Compared to skeletal muscle, contraction of smooth muscle cells is A) only a slower response to a stimulus. B) only sustained without fatigue. C) only controlled by the somatic nervous system. D) a slower response to a stimulus and sustained without fatigue. E) a slower response to a stimulus, sustained without fatigue, and controlled by the somatic nervous system.

D

Match the structures with the accurate description. ​A. muscle fiber ​B. fascicle ​C. sarcolemma ​D. myofibril ​E. t-tubules Highly organized bundles of contractile proteins within a skeletal muscle cell

D

Skeletal muscle cells are usually attached to bone by A) fascicles. B) ligaments. C) tendons. D) flexors.

D

Striated muscles are so-called because of a repeating pattern of light and dark bands. One repeating unit of the banding pattern is called a A) myofilament. B) myomere. C) sarcofibril. D) sarcomere. E) crossbridge.

D

The hydrolysis of ATP causes myosin to immediately A) swivel, moving the actin molecule. B) release of ADP. C) release from the actin. D) rotate into a position (cocked) to bind to actin. E) bind more tightly to the actin (rigor).

D

The relaxation of skeletal muscle relies on the activity of the ________, which decreases cytoplasmic calcium concentration. A) ryanodine receptor B) dihydropyridine (DHP) receptor (L-type calcium channel) C) acetylcholine receptor D) Ca2+ ATPase

D

When a skeletal muscle generates enough force during contraction to shorten, A) only the sarcomere will shorten. B) only the A band will shorten. C) only the I band will shorten. D) the sarcomere and the I band will shorten. E) the sarcomere, the A band and the I band will shorten.

D

Which of the following is NOT a correct comparison of cardiac myocytes to other muscle cell types? A) Like smooth muscle cells, some cardiac myocytes have pacemaker potentials. B) Like some smooth muscle cells, cardiac myocytes are electrically coupled. C) Like skeletal muscle cells, actin and myosin are organized into sarcomeres. D) Like skeletal muscle, contraction of cardiac muscle is under autonomic nervous control. E) Like smooth muscle cells, cardiac muscle is under hormonal control.

D

Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers? A) long contraction duration only B) few mitochondria only C) high capillary density only D) long contraction duration and high capillary density E) long contraction duration, few mitochondria, and high capillary density

D

_______ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle. A) Protein B) Glucose C) Fatty acid D) Phosphocreatine

D

Each myosin head has a binding site for A) calcium only. B) actin only. C) ATP only. D) calcium and ATP. E) actin and ATP.

E

In order for high force crossbridges to form in contracting skeletal muscle, calcium must A) bind to calmodulin to phosphorylate the myosin. B) phosphorylate the tropomyosin which moves it. C) phosphorylate the troponin to move the tropomyosin. D) bind to tropomyosin which moves the troponin. E) bind to troponin which moves the tropomyosin.

E

Match from the following list. ​A. A band ​B. I band ​C. Z disk ​D. H zone ​E. M line The letter assigned to this structure stands for the German word for middle; it is the attachment site for the thick filaments

E

Match the structures with the accurate description. ​A. muscle fiber ​B. fascicle ​C. sarcolemma ​D. myofibril ​E. t-tubules 51) inward extensions of the muscle cell membrane

E

Relative to skeletal muscle, smooth muscle A) only uses less energy to generate a given amount of force. B) only can sustain contractile force without fatigue. C) only uses calcium from the sarcoplasmic reticulum and extracellular space. D) uses less energy to generate a given amount of force and can sustain contractile force without fatigue. E) uses less energy to generate a given amount of force, can sustain contractile force without fatigue and uses calcium from the sarcoplasmic reticulum and extracellular space.

E

Which of the following is NOT a property of single-unit smooth muscles? A) All smooth muscle cells are connected by gap junctions. B) Their contraction occurs in a coordinated manner. C) Electrical responses travel directly between cells. D) Only a proportion of the smooth muscle cells receive autonomic nervous input. E) Each cell functions independent of its neighbor.

E

Groups of adjacent fibers bundled together into units are called ________. These bundles are surrounded by the proteins ________ and elastin as well as ________ that deliver nutrients to the muscle cells.

fascicles, collagen, blood vessels

As a muscle cell undergoes an eccentric contraction, sarcomere length will ________ as the length of the A band ________.

increase, does not change

The thick filament of the myofibril is composed of ________ molecules whereas ________ is a protein that makes up the thin filaments.

myosin and actin

Asynchronous activation of motor units is important because it functions to ________.

prevent fatigue

Calcium, released by the sarcoplasmic reticulum, binds to ________ to move the ________, which allows actin to form of a ________ with myosin.

troponin C, tropomyosin, high-force crossbridge