Chapter 12 Multiple Choice

Skeletal muscle cells are striated that is, they have alternating dark and light bands called ____, respectively. a. A and I bands b. H and M bands c. Z and M lines d. I and H bands

a. A and I bands Feedback: The A bands are the darker bands and the I bands are the lighter bands.

At what stage of muscle contraction is ATP split into ADP and Pi? a. Before the cross bridges of myosin can attach to actin b. During the power stroke when the myosin cross bridge flexes c. At the end of the power stroke before myosin lets go of the actin filament d. At the end of the power stroke after myosin lets go

a. Before the cross bridges of myosin can attach to actin Feedback: ATP is hydrolyzed to change the shape of the myosin head to allow it to attach to actin.

The ability of myosin to interact with actin is regulated by the binding of a. Ca2+ to troponin. b. ATP to actin. c. Ca2+ to tropomyosin. d. the binding of titin to ATP.

a. Ca2+ to troponin. Feedback: When Ca2+ binds to troponin the binding sites on actin for myosin are uncovered allowing the interaction between actin and myosin to occur.

Abductor and adductor muscles make up pairs, that together are called a. antagonistic. b. agonistic. c. complementary.

a. antagonistic.

Groups of nerve fibers that cross over from the right to the left side of the spinal cord, or vice versa, are called a. commissural tracts. b. ascending tracts. c. ipsilateral tracts. d. contralateral tracts.

a. commissural tracts.

Fatty acids provide the majority of the energy for muscle metabolism when a person is: a. exercising at less than 35% of VO2 max. b. exercising at 65% of VO2 max. c. exercising at 85% of VO2 max. d. exercising at 100% of VO2 max.

a. exercising at less than 35% of VO2 max. Feedback: The lower intensity of exercise, the lower the % of VO2 max, and the more aerobic the metabolism.

The Ca2+ required for sustained contraction of smooth muscle fibers comes mainly from the a. extracellular fluid surrounding the fibers. b. cisternae of the rough endoplasmic reticulum. c. varicosities of the autonomic nerve fibers. d. sarcoplasmic reticulum.

a. extracellular fluid surrounding the fibers. Feedback: During the sustained contraction of smooth muscles voltage regulated ion channels open and Ca2+ enters from the extracellular fluid.

Intercalated discs are a. gap junctions between cardiac muscle cells. b. a unique type of motor end plate found in smooth muscle. c. found in place of the Z lines in cardiac muscle.

a. gap junctions between cardiac muscle cells.

The term ____ is synonymous with muscle cell. a. myofiber b. sarcomere c. myofibril d. fascicle

a. myofiber

The contraction strength of a whole muscle varies in accordance with the a. number of motor units activated. b. innervation ratio. c. amount of calcium released from the sarcoplasmic reticulum. d. amplitude of the arriving action potentials.

a. number of motor units activated.

Golgi tendon organs serve to a. prevent excessive stretching of the tendon produced by too great a contraction of a muscle. b. enable a muscle to contract more forcibly. c. prevent painful muscle spasms. d. maintain muscle tone.

a. prevent excessive stretching of the tendon produced by too great a contraction of a muscle. Feedback: Golgi tendon organs monitor the tension that a muscle is generating and when the tension is too great stimulates muscle relaxation by inhibiting contraction.

Dense bodies are characteristic of a. smooth muscle. b. cardiac muscle. c. skeletal muscle.

a. smooth muscle.

When an isolated muscle is first stimulated with successive shocks at constant voltage, the increased strength of the muscle twitches is known as a. treppe. b. complete tetanus. c. isotonic contraction. d. summation.

a. treppe.

When the contractile behavior of a muscle is studied in vitro, this means the studies were done a. with the muscle removed from the body. b. with the muscle in place in the body. c. under the microscope to observe the fibers better. d. with artificial stimulation of the muscle.

a. with the muscle removed from the body.

Following muscle contraction and the cessation of action potential generation in a motor neuron, muscle relaxation takes place because of the activity of which transporter? a. Na+-K+ ATPase b. Ca++-ATPase c. Na+-Ca++ cotransporter d. K+-Ca+ exchanger

b. Ca++-ATPase Feedback: The Ca++-ATPase pumps calcium from the cytosol into the sarcoplasmic reticulum, lowering the cytosolic concentration of calcium

The nervous system must monitor the behavior of muscles. The receptor that provides information about the amount of tension being exerted on a given tendon is the a. extrafusal fiber. b. Golgi tendon organ. c. gamma motoneuron. d. muscle spindle.

b. Golgi tendon organ.

During contraction the a. actin filaments bind to the myosin filaments. b. I bands shorten. c. sarcomeres do not change in length. d. size of the H zone increases.

b. I bands shorten.

Slow-twitch muscle fibers a. have a relatively low oxidative capacity. b. are very resistant to fatigue. c. have a high glycogen content. d. have a high myosin ATPase content.

b. are very resistant to fatigue.

Muscles which decrease the angle at a joint are called: a. extensor muscles. b. flexor muscles. c. abductor muscles. d. adductor muscles.

b. flexor muscles.

A motor neuron and its associated myofibers is called a a. filament unit b. motor unit c. muscle fiber d. neuromuscular junction

b. motor unit Feedback: A motor neuron will innervate many myofibrils, and they operate as a unit called a motor unit.

The thin filaments of a muscle fiber consist of all of the following except a. tropomyosin. b. myosin. c. troponin. d. actin.

b. myosin. Feedback: The thin filament is composed of actin, tropomyosin, and troponin.

A motor unit is a. the motor end plate where a nerve fiber synapses with a muscle fiber. b. one motor neuron and all muscle fibers to which it leads. c. a spinal reflex arc. d. a sarcomere.

b. one motor neuron and all muscle fibers to which it leads. Feedback: The motor unit is the motor neuron and the skeletal muscle fibers that it innervates.

Sustained muscle activity may consume ATP faster than aerobic respiration can produce it. In such circumstances, ATP can be made by combining ADP with phosphate groups borrowed from a. creatine kinase. b. phosphocreatine. c. cyclic AMP. d. phospholipids.

b. phosphocreatine. Feedback: Phosphocreatine "stores" phosphate in the muscle cells for use when aerobic respiration is unable to supply adequate ATP.

Skeletal muscle is connected to bones by: a. ligaments. b. tendons. c. adipose tissue. d. loose areolar connective tissue.

b. tendons.

The basic unit of muscle contraction is the sarcomere, which is a. one A band and the adjacent I band. b. the distance from one Z line to the next. c. equivalent to a fascicle of muscle fibers. d. equivalent to one of the myofibrils within a muscle fiber.

b. the distance from one Z line to the next.

Terminal cisternae of the sarcoplasmic reticulum release Ca2+ when signaled by the a. motor end plate. b. sarcomeres. c. T tubules. d. motor nerve fibers.

c. T tubules. Feedback: The T tubules stimulate the release of Ca2+ from the terminal cisternae by an undefined process.

The I bands of skeletal muscle fibers each have a dark line in the middle called a a. D line. b. H line. c. Z line. d. X line.

c. Z line. Feedback: The Z line anchors the thin filaments in the skeletal muscle fiber.

Suppose you are sitting in the middle of a sofa and move both of your hands to your stomach. This action of the arms is known as a. extension. b. abduction. c. adduction. d. flexion.

c. adduction.

The strength with which a given muscle contracts is affected by all of the following except the a. frequency of stimulation to the muscle. b. thickness of each muscle fiber. c. amount of rest given to the muscle. d. initial length of the muscle fibers when resting.

c. amount of rest given to the muscle.

In skeletal muscle contraction Ca2+ must bind to troponin for contraction to occur and in order for the muscle to relax the Ca2+ must a. diffuse out of the cell. b. be actively transported into the cell. c. be actively transported into the sarcoplasmic reticulum. d. be bound to tropomyosin until the next contraction.

c. be actively transported into the sarcoplasmic reticulum.

Excitation-contraction coupling refers especially to the a. events at the neuromuscular junction where a motor fiber excites a muscle cell. b. propagation of action potentials from the neuromuscular junction to the T tubules. c. calcium release and binding to troponin molecules. d. attachment of myosin cross bridges to the thin filaments.

c. calcium release and binding to troponin molecules.

When a muscle lengthens as it contracts, this type of contraction is known as a(n) a. isometric contraction. b. tetanic contraction. c. eccentric contraction. d. isotonic contraction.

c. eccentric contraction.

The fibrous connective tissue sheath which encloses a whole muscle is called the a. endomysium. b. perimysium. c. epimysium. d. sarcolemma.

c. epimysium.

The sensitivity of muscle spindles to stretch can be adjusted by a. further stretching of the extrafusal fibers. b. alpha motoneurons. c. gamma motoneurons. d. annulospiral nerve endings.

c. gamma motoneurons.

Skeletal muscle cells are unusual in that they a. lack smooth endoplasmic reticulum. b. have no mitochondria. c. have multiple nuclei. d. depend entirely on anaerobic respiration.

c. have multiple nuclei.

A person continues breathing heavily for some time after exercising in order to "repay an oxygen debt". This oxygen debt includes all of the following except the oxygen that was a. taken from hemoglobin in the blood. b. taken from myoglobin in the muscle. c. needed to replenish the store of glycogen in the muscle. d. needed to metabolize the lactic acid produced by exercise.

c. needed to replenish the store of glycogen in the muscle.

Which of the following is not a factor in muscle fatigue? a. a drop in intracellular pH b. accumulation of lactic acid c. production of IPSPs by motor neurons d. accumulation of extracellular K+

c. production of IPSPs by motor neurons

As opposed to the upper motor neurons, the lower motor neurons have their cell bodies located in the a. thalamus as opposed to the cerebral cortex. b. medulla oblongata as opposed to higher brain centers. c. spinal cord as opposed to the brain. d. lumbar and sacral regions as opposed to cervical and thoracic.

c. spinal cord as opposed to the brain.

A muscle is stimulated and exhibits a contraction (twitch). Before this twitch is over, it is stimulated again, and a second twitch occurs "piggyback" on the first one and causes a higher contraction strength. This phenomenon is called a. tetanus. b. graded contraction. c. summation. d. isometric contraction.

c. summation.

If a muscle is already at about 60% of its resting length, it cannot be stimulated to contract any more because a. there is no more ATP. b. the myosin cross bridges cannot reach the actin filaments. c. the Z lines abut against the thick filaments and cannot go any farther. d. muscle fibers obey an all-or-none law.

c. the Z lines abut against the thick filaments and cannot go any farther.

The rigor mortis in a corpse results from the fact that a. all the neurotransmitter is used up. b. all the calcium ion is used up. c. thick filaments cannot let go of the thin filaments without ATP. d. motor neurons can no longer function.

c. thick filaments cannot let go of the thin filaments without ATP.

Contraction in a muscle occurs because the a. thin filaments get shorter. b. thick filaments get shorter. c. thin filaments slide between the thick filaments. d. titin proteins pull on opposite ends of the sarcomere.

c. thin filaments slide between the thick filaments.

Which of the following will be increased by endurance training? a. VO2 max b. lactate threshold c. mitochondrial density d. All of the above.

d. All of the above. Feedback: Endurance training increases the aerobic metabolic capacity and will increase VO2 max, lactate threshold, and mitochondrial density.

Single-unit (SU) smooth muscles differ from multi-unit (MU) smooth muscles in all of the following ways, except a. SU muscles are myogenic and MU muscles are neurogenic. b. SU muscle cells are joined by gap junctions, while MU cells are not. c. MU muscles contract only in response to nervous stimulation while SU muscles can contract in response to stretch. d. MU muscle fibers contract independently while SU fibers contract in unison.

d. MU muscle fibers contract independently while SU fibers contract in unison.

What is the neurotransmitter released at the motor end plate? a. epinephrine b. norepinephrine c. dopamine d. acetylcholine

d. acetylcholine Feedback: The receptor on the muscle cell in the motor end plate, or neuromuscular junction, is a nicotinic cholinergic receptor, so acetylcholine is the neurotransmitter.

The basal nuclei normally inhibit lower motor neurons. Therefore, damage to the basal nuclei can cause a. clonus. b. paraplegia. c. intention tremor. d. chorea.

d. chorea.

The region of the resting sarcomere where the thin and thick filaments are overlapping is seen in the a. narrow dark line known as the Z line. b. dark color of the I bands. c. lighter region of the I bands. d. dark color of the A bands.

d. dark color of the A bands.

Within a muscle the fibers are divided into larger bundles called ____, each surrounded by its own connective tissue sheath. a. sarcomeres b. sarcolemmas c. myofibers d. fascicles

d. fascicles

Myosin light-chain kinase a. is activated by cAMP. b. phosphorylates myosin to regulate muscle contraction in cardiac muscles. c. phosphorylates myosin to stimulate relaxation in smooth muscle. d. is antagonized by the actions of myosin phosphatase.

d. is antagonized by the actions of myosin phosphatase.

If enough muscle fibers contract to make the muscle as a whole shorten in length, the muscle is said to exhibit a. complete tetanus. b. graded contraction. c. isometric contraction. d. isotonic contraction.

d. isotonic contraction. Feedback: An isotonic contraction results in shortening of the muscle to produce tension on a constant load.

The ability to hydrolyze ATP during muscle contraction is due to the fact that a. tropomyosin contains an ATPase. b. actin contains an ATPase. c. titin contains an ATPase. d. myosin contains an ATPase.

d. myosin contains an ATPase.

The thick filaments of muscle are composed of a. tropomyosin. b. actin. c. troponin. d. myosin.

d. myosin.

When a skeletal muscle contracts, it usually moves the bone at one end much more than the bone at its other end. The attachment of the muscle to the less movable bone is called its a. ligament. b. insertion. c. flexor. d. origin.

d. origin

ATP is required by two different processes that are necessary to the contraction and relaxation of a muscle: the interaction between the thick and thin filaments of the sarcomeres, and the a. binding of acetylcholine to the motor end plate. b. release of calcium from the sarcoplasmic reticulum. c. movement of the troponin-tropomyosin complex. d. reuptake of calcium by the sarcoplasmic reticulum.

d. reuptake of calcium by the sarcoplasmic reticulum. Feedback: To remove all the Ca2+, energy must be expended by a specific transport protein in the sarcoplasmic reticulum.

The calcium that binds to troponin to activate muscle contraction comes from storage sites located in the a. T tubules. b. extracellular fluid. c. synaptic vesicles of the motor neuron. d. sarcoplasmic reticulum.

d. sarcoplasmic reticulum.