Phys Ch 12

A flexor is a skeletal muscle whose shortening moves attached bones ANSWER: towards one another. laterally. medially away from one another.

Skeletal muscle cells are usually attached to bone by ANSWER: ligaments. tendons. flexors. fascicles.

The origin is the end of the skeletal muscle that attaches to the ANSWER: tendon. ligament. more stationary bone. more mobile bone.

For antagonistic muscle groups to move a limb, flexor contraction occurs coincident with ANSWER: relaxation of the extensor. contraction of the extensor. no changes in the extensor. contraction of the tendon.

The function of transverse tubules is to ANSWER: -rapidly conduct action potentials to the interior of the muscle fiber. -conduct ATP molecules out of the mitochondria throughout the sarcoplasm. -ensure a supply of glycogen throughout the muscle sarcoplasm. -store Ca2+ ions inside the muscle fiber.

________ is composed of multiple globular molecules polymerized to form long chains or filaments. ANSWER: Troponin Tropomyosin Actin Titin Myosin

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. ANSWER: crossbridges nebulin molecules tropomyosin molecules calcium ions sarcomeres

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 ANSWER: myomere. myofilament. crossbridge. sarcofibril. sarcomere.

The I band contains ANSWER: myosin only. thin filaments only. thick filaments only. thick and thin filaments.

The H zone contains ANSWER: actin only. thick and thin filaments. thick filaments. thin filaments only.

The function of the titin protein is to ANSWER: -stabilize the position of the contractile filaments. -release calcium during contraction. -pull Z lines together during contraction. -interact with actin during contraction. -cover the myosin binding site on the actin molecule.

When a skeletal muscle generates enough force during contraction to shorten, ANSWER: -the sarcomere, the A band and the I band will shorten. -the sarcomere and the I band will shorten. -only the A band will shorten. -only the sarcomere will shorten. -only the I band will shorten.

The tension generated in a skeletal muscle fiber is directly proportional to the number of ANSWER: low energy crossbridges formed. thick and thin filaments present. active sarcomeres. nebulin and titin molecules present. high energy crossbridges formed.

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

In order for high force crossbridges to form in contracting skeletal muscle, calcium must ANSWER: -phosphorylate the troponin to move the tropomyosin. -bind to troponin which moves the tropomyosin. -phosphorylate the tropomyosin which moves it. -bind to calmodulin to phosphorylate the myosin. -bind to tropomyosin which moves the troponin.

Each myosin head has a binding site for ANSWER: calcium and ATP. calcium only. ATP only. actin and ATP. actin only.

As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately ANSWER: swivels. tightens its bond to actin. initiates binding with actin. detaches from actin.

The molecular event that occurs immediately after the power stroke is the ANSWER: binding of tropomyosin to the myosin. binding of actin to the myosin. hydrolysis of ATP by the myosin head. release of ADP from the myosin. release of actin from the myosin head.

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

Which of the following would cause the crossbridge to transition from a high force state to a low force state? ANSWER: increasing intracellular calcium energizing the myosin head decreasing myosin ATPase activity increasing myosin ATPase activity decreasing intracellular calcium

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

The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a ANSWER: channel for both Na+ and K+. ryanodine receptor. Na+ channel. calcium channel.

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

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

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 ANSWER: refractory period. latent period. depolarization period. repolarization period. relaxation phase.

________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle. ANSWER: Phosphocreatine Fatty acid Glucose Protein

During heavy exercise, the ATP requirements of active muscle are likely to be met by metabolism of ANSWER: fatty acids. nucleotides. protein. carbohydrates.

Muscle fatigue arises primarily from failure in ANSWER: initiation of contraction by the motor cortex. signal relay from brain to spinal cord. neuromuscular transmission. calcium pumps in the skeletal muscles. excitation-contraction coupling.

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

Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers? ANSWER: -long contraction duration, few mitochondria, and high capillary density -few mitochondria only -long contraction duration only -high capillary density only -long contraction duration and high capillary density

The speed with which force is developed by skeletal muscles is determined by the ANSWER: -Ca2+ ATPase activity. -myosin ATPase isoform. -Ca2+ ATPase activity and sarcoplasmic calcium concentration. -sarcoplasmic calcium concentration. -Ca2+ ATPase activity, myosin ATPase isoform, and sarcoplasmic calcium concentration.

Within a single fiber, the tension developed during a twitch depends upon the ANSWER: duration of the stimulus. amplitude of the action potential. length of the thick filament. length of the sarcomeres prior to contraction.

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

A motor unit consists of ANSWER: -one axon terminal branch and the myofibrils it controls. -one neuron and all the skeletal muscle fibers it controls. -one skeletal muscle fiber and the neuron that controls that fiber. -one skeletal muscle fiber and all the neurons that control that fiber.

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). ANSWER: more fewer the same number of

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

Which fibers generate more force? ANSWER: slow-twitch fibers fast-twitch fibers

Which fibers fatigue sooner? ANSWER: slow-twitch fibers fast-twitch fibers

The nervous system avoids muscle fatigue during submaximal contraction by ANSWER: always recruiting slow-twitch motor units. asynchronous recruitment. synchronous recruitment. always recruiting fast-twitch motor units.

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 ________. ANSWER: isometric, isotonic isotonic, isometric isotonic, eccentric isotropic, isometric isometric, eccentric

Before the entire muscle can change length, the force generated by the muscle must stretch the ANSWER: series elastic elements. eccentric contractile elements. contractile elements. parallel elastic elements.

In the lever system that characterizes the interaction between bones and muscle, the bones act as the ________ whereas the joints form the ________. ANSWER: lever, pulleys fulcrum, levers fulcrum, pulleys lever, fulcrums

In order for the bicep muscle to shorten, the force applied by the muscle must be ________ the load applied at the hand. ANSWER: less than equal to greater than

Compared to skeletal muscle, contraction of smooth muscle cells is ANSWER: -a slower response to a stimulus, sustained without fatigue, and controlled by the somatic nervous system. -a slower response to a stimulus and sustained without fatigue. -only a slower response to a stimulus. -only controlled by the somatic nervous system. -only sustained without fatigue.

Smooth muscle cells lack which protein(s)? ANSWER: myosin only troponin and tropomyosin troponin only tropomyosin only actin only

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

This protein is activated by the Ca2+-calmodulin complex to phosphorylate the myosin light chain protein. ANSWER: myosin light chain kinase myosin light chain phosphatase tropomyosin myosin heavy chain

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

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

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