A&P ch 9

constriction of organs

Which of the following is NOT a function of skeletal muscle? A. body movement B. maintenance of posture C. respiration D. constriction of organs E. production of heat

moving your feet in walking

Which of the following actions is caused by contraction of skeletal muscle? A. contraction of the heart B. moving your feet in walking C. movement of food through the digestive tract D. emptying of the urinary bladder E. vasoconstriction

are under involuntary contro

Smooth muscle and cardiac muscle are similar in that they both A. are under involuntary control. B. are striated. C. are widely distributed in the body. D. have multiple nuclei. E. are under voluntary control.

contractility

The capacity of a muscle cell to shorten forcefully is known as A. contractility. B. excitability. C. extensibility. D. elasticity. E. flexibility.

responds to stimulation by the nervous system

Muscles exhibit the property of excitability. This means that the muscle A. shortens its length. B. recoils to its original resting length. C. stretches beyond its normal length. D. responds to stimulation by the nervous system. E. excites itself

Muscle tissue shortens forcefully but lengthens passively

Identify the statement concerning general functional characteristics of muscle that is true. A. Muscle tissue shortens forcefully but lengthens passively. B. Muscle tissue shortens passively but lengthens forcefully. C. Muscle tissue can get shorter, but can not get longer. D. Muscle tissue can get longer, but can not get shorter. E. None of these statements are true.

It is responsible for locomotion

Identify the statement concerning skeletal muscle that is true. A. It comprises about 20% of the body’s weight. B. It propels urine through the urinary tract. C. Its function is largely under involuntary control. D. It is a kind of connective tissue. E. It is responsible for locomotion.

Smooth muscle is found in the walls of hollow organs

Which of the following is true? A. Skeletal muscle is capable of spontaneous contraction. B. Smooth muscle is found in the walls of hollow organs. C. Cardiac muscle cells have multiple nuclei. D. Smooth muscle cells are long and cylindrical. E. There is a small amount of smooth muscle in the heart.

possess striations

Skeletal muscle fibers A. possess striations. B. can contract but are not extensible or excitable. C. do not require nerve innervation to contract. D. increase dramatically in number after birth. E. are found in the walls of the stomach.

smooth muscle

Which type of muscle tissue has spindle-shaped cells? A. skeletal muscle B. smooth muscle C. cardiac muscle D. both skeletal and cardiac muscle E. both cardiac and smooth muscle

both skeletal and cardiac muscle

Which type of muscle tissue possesses striations? A. skeletal muscle B. smooth muscle C. cardiac muscle D. both skeletal and cardiac muscle E. both cardiac and smooth muscle

both cardiac and smooth muscle

Which type of muscle tissue is autorhythmic? A. skeletal muscle B. smooth muscle C. cardiac muscle D. both skeletal and cardiac muscle E. both cardiac and smooth muscle

skeletal muscle

Which type of muscle tissue is multinucleated? A. skeletal muscle B. smooth muscle C. cardiac muscle D. both skeletal and cardiac muscle E. both cardiac and smooth muscle

cardiac muscle

Which type of muscle tissue has cells that branch? A. skeletal muscle B. smooth muscle C. cardiac muscle D. both skeletal and cardiac muscle E. both cardiac and smooth muscle

skeletal muscle

Which type of muscle tissue would cause flexion and extension of the arm? A. skeletal muscle B. smooth muscle C. cardiac muscle

cardiac muscle

Which type of muscle tissue causes contraction of the heart? A. skeletal muscle B. smooth muscle C. cardiac muscle

smooth muscle

What type of muscle tissue causes vasoconstriction? A. skeletal muscle B. smooth muscle C. cardiac muscle

smooth muscle

What type of muscle tissue causes peristalsis? A. skeletal muscle B. smooth muscle C. cardiac muscle

skeletal muscle

What type of muscle tissue has neuromuscular junctions? A. skeletal muscle B. smooth muscle C. cardiac muscle

size of muscle fibers

Hypertrophy of skeletal muscles from weight lifting is caused by an increase in the A. number of muscle fibers. B. size of muscle fibers. C. number of striations. D. number of nuclei within the muscle fibers. E. number of muscle cells.

myoblasts

Skeletal muscle develops from multinucleated cells called A. fascicles. B. myoblasts. C. myofibrils. D. myotomes. E. fasciculi.

is surrounded by perimysium

A fasciculus A. is a bundle of reticular fibers. B. is surrounded by perimysium. C. is only found in smooth muscle. D. possesses an external lamina. E. is a bundle of collagen fibers.

surrounds individual muscles

Epimysium A. surrounds individual muscles. B. separates muscle fibers. C. connects muscles to bone. D. is a type of muscle tissue. E. is a type of nerve tissue.

surrounds each muscle fiber

Endomysium is a delicate network of loose connective tissue that A. surrounds each muscle fiber. B. forms a sheath around a fasciculus. C. is composed of elastic fibers. D. separates individual muscles. E. penetrates muscle fibers

epimysium

Which of the following connective tissue layers is outside all the others? A. perimysium B. endomysium C. epimysium D. paramysium E. sarcolemma

Every muscle fiber receives a branch of an axon from the nerve.

Which of the following is true about skeletal muscle? A. Sensory neurons stimulate muscles to contract. B. There are very few blood vessels in skeletal muscle. C. Every muscle fiber receives a branch of an axon from the nerve. D. There are very few nerve fibers in a muscle. E. All of these are true.

2, 3, 1, 4

List the following structures in order from smallest to largest. (1) muscle fiber (2) myofilament (3) myofibril (4) muscle fasciculus A. 4, 2, 3, 1 B. 2, 1, 4, 3 C. 3, 1, 4, 2 D. 2, 3, 1, 4 E. 1, 2, 3, 4

contain myosin and actin myofilaments.

. Muscle myofibrils A. are found in the sarcolemma. B. extend from the sarcolemma to the T-tubule. C. contain myosin and actin myofilaments. D. hold muscle cells together. E. do not appear striated

thick myofilament.

Myosin is also known as the A. thick myofilament. B. thin myofilament. C. intermediate myofilament. D. short myofilament. E. sarcomere.

contain strands of fibrous actin.

Actin myofilaments A. resemble bundles of minute golf clubs. B. contain both myosin and tropomyosin. C. are held in place by the M line. D. contain strands of fibrous actin. E. are the thickest proteins in muscle.

globular (G) actin

. Which of the following is part of a thin myofilament? A. ATP-binding site B. globular (G) actin C. calcium D. myosin E. sarcolemma

has a calcium-binding site

Troponin A. has two subunits. B. is part of the myosin myofilament. C. is a long, flexible protein. D. has a calcium-binding site. E. binds to ATP

thick myofilaments

Which of the following is composed of myosin molecules? A. thick myofilaments B. I Bands C. Z disks D. sarcolemma E. tropomyosin

actin myofilaments

. The active sites to which cross-bridges attach are found on the A. sarcoplasmic reticulum. B. actin myofilaments. C. Z disks. D. T tubules. E. myosin myofilaments.

myosin heads.

ATPase is found in A. F-actin strands. B. G-actin globular units. C. myosin heads. D. tropomyosin grooves. E. troponin molecules.

They bind to troponin

Which of the following is NOT a property of the myosin head? A. They form cross-bridges with the active sites of actin. B. They have a hinge region to bend and straighten. C. They bind to troponin. D. They have ATPase activity. E. They bind to ATP.

A band.

The region of the sarcomere that contains both actin and myosin myofilaments is called the A. I band. B. A band. C. Z disk. D. H zone. E. M line.

one Z disk to an adjacent Z disk

A sarcomere extends from A. one Z disk to an adjacent Z disk. B. one T tubule to the next T tubule. C. the middle of the I band to the middle of the A band. D. the H zone to the I band. E. the M line to the next M line.

myosin myofilaments – thin myofilaments

Which of the following is mismatched? A. I band – contains only actin B. M line – middle of the H zone C. Z disk – structure between adjacent sarcomeres D. myosin myofilaments – thin myofilaments E. actin myofilaments – thin myofilaments

structural and functional unit of the skeletal muscle cell.

A sarcomere is the A. cell membrane of a muscle fiber. B. cytoplasm of muscle cells. C. structural and functional unit of the skeletal muscle cell. D. contractile thread that extends the length of the muscle fiber. E. protein strand composed of actin or myosin.

cytoplasm of muscle cells

Sarcoplasm is the A. cell membrane of a muscle fiber. B. cytoplasm of muscle cells. C. structural and functional unit of the skeletal muscle cell. D. contractile thread that extends the length of the muscle fiber. E. protein strand composed of actin or myosin.

protein strand composed of actin or myosin

A myofilament is the A. cell membrane of a muscle fiber. B. cytoplasm of muscle cells. C. structural and functional unit of the skeletal muscle cell. D. contractile thread that extends the length of the muscle fiber. E. protein strand composed of actin or myosin

cell membrane of a muscle fiber.

The sarcolemma is the A. cell membrane of a muscle fiber. B. cytoplasm of muscle cells. C. structural and functional unit of the skeletal muscle cell. D. contractile thread that extends the length of the muscle fiber. E. protein strand composed of actin

contractile thread that extends the length of the muscle fiber

A myofibril is the A. cell membrane of a muscle fiber. B. cytoplasm of muscle cells. C. structural and functional unit of the skeletal muscle cell. D. contractile thread that extends the length of the muscle fiber. E. protein strand composed of actin

Both actin and myosin myofilaments shorten during contraction.

Which of the following statements regarding the sliding filament model is false? A. Actin and myosin do not shorten during contraction. B. Both actin and myosin myofilaments shorten during contraction. C. The sarcomere shortens. D. The I band and H zones become narrower during contraction. E. The A band remains constant in length.

longer than the length of a contracted sarcomere.

The length of the resting sarcomere is A. longer than the length of a contracted sarcomere. B. shorter than the length of a contracted sarcomere. C. the same length as a contracted sarcomere. D. the same length as the muscle fiber. E. the same length as the myofibril

sliding filament model

The model that describes the contraction of the muscle is called the A. contraction cycle. B. power stroke. C. sliding filament model. D. slipping fibril mechanism. E. paddle model.

ion concentration differences across the plasma membrane

The electrical properties of cells are the result of A. ion concentration differences across the plasma membrane. B. receptor sites that are present on the plasma membrane. C. phosphorylation reactions within the cytoplasm. D. phospholipids in the cell membrane. E. None of these choices is correct.

negatively charged proteins do not readily diffuse across the plasma membrane

Which of the following causes an unequal ion concentration across the resting plasma membrane? A. the functioning of the sodium-chloride pump B. negatively charged proteins do not readily diffuse across the plasma membrane C. the attraction of chloride ions to other intracellular anions D. the repulsion of potassium ions by the intracellular anions E. the attraction of sodium ions to chloride ions

Potassium is concentrated primarily inside the cell.

Which of the following is true during the resting membrane potential? A. Sodium ion concentration is greater inside cells. B. Negatively charged proteins are more concentrated outside the cell. C. A greater concentration of calcium ions is found inside the cell. D. Potassium is concentrated primarily inside the cell. E. None of these choices reflect what occurs during the resting membrane potential.

positively charged

The outside of the resting plasma membrane is __________ relative to the inside of the resting plasma membrane. A. positively charged B. negatively charged C. electrically neutral D. recharged E. None of these choices is correct.

there are more leak ion channels for K+ than Na+.

. The plasma membrane of an excitable cell is more permeable to potassium ions because A. of its positive electrical charge. B. there are more leak ion channels for K+ than Na+. C. protein molecules cannot exit through the cell membrane. D. calcium ions block Na+ and Cl- channels. E. there are more gated channels for K+.

a relaxed muscle fiber

In which of the following situations does a resting membrane potential exist? A. a relaxed muscle fiber B. a conducting neuron C. a stimulated sensory receptor in the skin D. a contracting cardiac muscle cell E. the eye seeing an image

voltage-gated ion channels.

. Channels that open or close in response to changes in the electrical charge or voltage across the plasma membrane are called A. ligand-gated ion channels. B. leak ion channels. C. relegated ion channels. D. voltage-gated ion channels. E. obligated ion channels.

increased permeability of the membrane to sodium ions and increased intracellular concentration of potassium ions

Which of the following changes have the potential to dramatically affect the potential difference across the plasma membrane? A. increased permeability of the membrane to sodium ions B. increased intracellular concentration of potassium ions C. any change in the rate at which the sodium-potassium pump works D. increased permeability of the membrane to sodium ions and increased intracellular concentration of potassium ions E. increased permeability of the membrane to sodium ions, increased intracellular concentration of potassium ions and any change in the rate at which the sodium-potassium pump works

Depolarization causes voltage-gated sodium ion channels to open.

Which of the following situations occurs in electrically excitable cells? A. When Na+ ion channels open, K+ ion channels close. B. The sodium-potassium pump moves sodium into the cell. C. Depolarization causes voltage-gated sodium ion channels to open. D. Sodium ion channels are opened by high extracellular calcium levels. E. The opening and closing of ligand-gated channels cause depolarization.

sodium ions.

. Depolarization of the cell membrane occurs when there is a rapid influx (inflow) of A. potassium ions. B. chloride ions. C. calcium ions. D. sodium ions. E. amino acids.

occurs when the local potential reaches threshold level.

An action potential A. occurs when the local potential reaches threshold level. B. is not propagated. C. has no repolarization phase. D. is an example of negative feedback. E. can be of varying strengths depending on strength of the stimulus.

an all-or-none response.

A stimulus either causes an action potential or it doesn’t. This is called A. an all-or-none response. B. a graded response. C. a latent period response. D. a relative refractory response. E. an arbitrary response.

original polarity of the cell is restored

When repolarization of the cell membrane is complete, the A. cell dies. B. cell regenerates. C. cell no longer has a potential difference across its membrane. D. cell is no longer responsive. E. original polarity of the cell is restored.

threshold

A muscle fiber will respond to a stimulus when that stimulus reaches the _____ level. A. threshold B. relaxation C. rigor mortis D. recruitment E. resting

neuromuscular junctions

The sites where a chemical substance is transmitted from the presynaptic terminal of an axon to the postsynaptic membrane of a muscle fiber are called A. neuromuscular junctions. B. sarcomeres. C. myofilaments. D. Z disks. E. cell body of neuron.

acetylcholine.

Synaptic vesicles in the neuromuscular junction contain A. calcium. B. ATP. C. acetylcholine. D. acetylcholinesterase. E. sodium.

neuromuscular junction

Which of the following structures contains the other four items listed? A. postsynaptic membrane B. presynaptic terminal C. synaptic cleft D. neuromuscular junction E. receptors on postsynaptic membrane

depolarization

Acetylcholine binds to a membrane bound receptor and causes ligand-gated sodium channels to open and results in A. hyperpolarization. B. depolarization. C. hypoplarization. D. no change in membrane potential. E. There is not enough information to predict the outcome

calcium ions diffuse into the presynaptic terminal through voltage-gated ion channels

When an action potential reaches the presynaptic terminal, A. calcium ions diffuse into the presynaptic terminal through voltage-gated ion channels. B. acetylcholine moves into the presynaptic terminal. C. a local potential is generated in the presynaptic terminal. D. ligand-gated ion channels in the presynaptic terminal are opened. E. nothing else happens.

continuous stimulation of the postsynaptic membrane.

Lack of acetylcholinesterase in the synaptic cleft would result in A. a decrease in acetylcholine production by the motor neuron. B. continuous stimulation of the postsynaptic membrane. C. rapid degradation of acetylcholine. D. relaxation of the muscle. E. continuous stimulation of the presynaptic membrane.

exocytosis

. Acetylcholine is released from the presynaptic terminal by the process of A. exocytosis. B. diffusion. C. phagocytosis. D. active transport. E. endocytosis.

rapid degradation of acetycholine

Too much acetylcholinesterase causes A. continuous stimulation of the muscle fiber. B. rapid degradation of acetycholine. C. voltage-gated calcium ion channels opening in the presynaptic terminal. D. an increase in sodium uptake by the muscle fiber. E. exocytosis of synaptic vesicles.

neurotransmitter combines with a receptor molecule

Which of the following events occurs on the postsynaptic membrane? A. acetylcholine production B. rapid degradation of acetylcholine C. release of neurotransmitter D. neurotransmitter combines with a receptor molecule E. release of calcium ions

contraction cannot occur

. If sodium ions cannot enter a muscle fiber in response to a stimulus, A. contraction cannot occur. B. relaxation cannot occur. C. sodium ions will be released from the sarcoplasmic reticulum instead. D. the active sites are left exposed. E. the action potential travels into the muscle anyway.

sarcolemma

. T tubules are invaginations of the A. sarcoplasmic reticulum. B. sarcomere. C. myofibril. D. sarcoplasm. E. sarcolemma

conduct action potentials deep into the muscle cell.

. T tubules A. provide nutrients to the muscle fiber. B. generate new muscle fibers. C. conduct action potentials deep into the muscle cell. D. release acetylcholine. E. store calcium ions.

stores calcium ions

. The sarcoplasmic reticulum A. stores calcium ions. B. shortens during muscle contraction. C. transmits nerve impulses to the myofibrils. D. connects adjacent sarcomeres. E. covers the muscle fiber

sarcolemma, T tubules, sarcoplasmic reticulum, calcium ions

Arrange these structures as they participate in excitation-contraction. A. T tubules, sarcolemma, calcium ions, sarcoplasmic reticulum B. calcium ions, T tubules, sarcolemma, sarcoplasmic reticulum C. sarcolemma, T tubules, sarcoplasmic reticulum, calcium ions D. sarcoplasmic reticulum, calcium ions, T tubules, sarcolemma E. sarcolemma, sarcoplasmic reticulum, calcium ions, T tubules

1, 3, 4, 2, 5

Arrange the following list of biochemical events in the correct sequence. (1) An action potential is conducted deep into the muscle fiber by the T tubule. (2) Calcium ions bind to troponin. (3) The membranes of the sarcoplasmic reticulum become more permeable to calcium ions. (4) Calcium ions diffuse into the sarcoplasm around the myofibril. (5) The troponin-tropomyosin complex moves exposing active sites. A. 1, 5, 2, 3, 4 B. 1, 3, 4, 2, 5 C. 1, 2, 3, 4, 5 D. 1, 3, 2, 5, 4 E. 1, 4, 3, 2, 5

myosin heads bind to exposed active sites on actin

. In excitation-contraction coupling, A. calcium ions must bind with myosin to expose active sites on actin. B. myosin heads bind to exposed active sites on actin. C. cross-bridges form between myosin heads and calcium ions. D. movement of the troponin-tropomyosin complex causes actin myofilaments to slide. E. ATP binds to actin myofilaments

power stroke.

When the myosin head flexes into a bend, pulling the actin filament along with it, this is called the A. action reaction. B. power stroke. C. recovery stroke. D. muscle tone. E. action potential.

formation of the cross-bridge, for movement of the cross-bridge, and for release of the cross-bridge

One ATP molecule is required for A. formation of the cross-bridge. B. movement of the cross-bridge. C. release of the cross-bridge. D. formation of the cross-bridge and for movement of the cross-bridge. E. formation of the cross-bridge, for movement of the cross-bridge, and for release of the cross-bridge.

the active sites on actin must be blocked.

In order for muscle relaxation to occur, A. calcium ions must be transported to troponin. B. power strokes slow down. C. the active sites on actin must be blocked. D. sodium ions must be actively transported to troponin. E. the active sites on myosin must be uncovered.

contraction with no relaxation

A drug that interferes with the active transport of calcium ions from the sarcoplasm back into the sarcoplasmic reticulum would result in A. relaxation of the muscle fiber. B. contraction with no relaxation. C. muscle hypertrophy. D. fibrosis of the muscle. E. an imbalance of blood calcium.

released from troponin.

. After contraction has occurred, the calcium is A. destroyed by cholinesterase. B. chemically bound to the cross bridges. C. secreted by the Golgi apparatus to the outside of the cell. D. released from troponin. E. returned to the sarcolemma.

actin-myosin cross-bridges form.

During the contraction phase of a muscle twitch, A. acetylcholine stimulates the pre-synaptic terminal. B. sodium ions diffuse into the muscle fiber. C. actin-myosin cross-bridges form. D. calcium ions are transported back to the sarcoplasmic reticulum. E. the action potential travels down the T tubule.

The action potential is propagated from presynaptic to postsynaptic membrane.

Which of the following events occurs during the lag phase of a muscle twitch? A. Muscle fibers shorten. B. Cross-bridges form, move, release, and reform many times. C. The action potential is propagated from presynaptic to postsynaptic membrane. D. Calcium is pumped back into the sarcoplasmic reticulum. E. All of these events occur in the lag phase.

latent or lag

The time between application of the stimulus to a motor neuron and the beginning of contraction is called the _____ phase. A. contraction B. relaxation C. latent or lag D. refractory E. threshold

twitch

. Which of the following would occur as a result of a single muscle contraction? A. tetanus B. tone C. treppe D. twitch E. paralysis

a single muscle fiber and a single motor unit

Which of the following will respond to a threshold stimulus with an all-or-none contraction? A. a single muscle fiber B. a single motor unit C. a whole muscle D. a single muscle fiber and a single motor unit E. a single muscle fiber, a single motor unit, and a whole muscle

A threshold stimulus will cause contraction of a muscle fiber.

Which of the following is true? A. Muscle fatigue has no influence on the force of contractions. B. A threshold stimulus will cause contraction of a muscle fiber. C. A subthreshold stimulus causes a muscle contraction. D. Motor units do not obey the "all or none" law. E. A threshold stimulus will not affect motor units

the number of motor units recruited

Whole muscles can respond in a graded fashion to stimuli by varying A. the force of contraction of individual muscle fibers. B. the number of motor units recruited. C. the amplitude of the action potential. D. the frequency of stimulus. E. thresholds

tetanus

A sustained muscle contraction is known as A. tetanus B. tone C. treppe D. twitch E. paralysis

high calcium ion concentrations in the sarcoplasm.

. Tetanus of a muscle is thought to be caused by A. high calcium ion concentrations in the sarcoplasm. B. the rapid movement of sodium ions back into the sarcoplasmic reticulum. C. an increase in stimulus strength. D. increased temperature in the active muscle. E. decreased amounts of calcium ions in muscle tissue.

increased concentration of calcium ions around the myofibrils

Which of the following helps explain the increased tension seen in multiple wave summation? A. increased motor unit recruitment B. increased concentration of calcium ions around the myofibrils C. exposure of more active sites on myosin myofilaments D. the breakdown of elastic elements in the cell E. decreased stimulus frequency

complete tetanus

A condition in which stimuli occur so rapidly that there are no intervening relaxations between contractions is called A. complete tetanus. B. incomplete tetanus. C. involuntary paralysis. D. all or none tetanus. E. treppe.

All of these choices are correct

. Treppe A. can contribute to improved muscle efficiency. B. may be due to an increase in the level of calcium ions around the myofibril. C. is an example of a graded response. D. is achieved during warm-up exercises. E. All of these choices are correct.

multiple wave summation

. The stretch of elastic components of a muscle adds to the increased tension during A. incomplete tetanus. B. twitch. C. multiple wave summation. D. all or none response. E. none of these.

is the condition in which stimuli occur so rapidly that there are no intervening relaxations

. Incomplete tetanus A. is the time during which the tissue cannot respond again. B. results in complete and incomplete tetanus. C. is the condition in which the muscle fiber only partially relaxes between contractions. D. is the condition in which stimuli occur so rapidly that there are no intervening relaxations. E. is the constant tension produced by muscles for long periods of time.

is a constant tension produced by muscles for long periods of time

Muscle tone A. is a time during which the tissue cannot respond again. B. results in complete and incomplete tetanus. C. is a condition in which the muscle fiber only partially relaxes between contractions. D. is a condition in which stimuli occur so rapidly that there are no intervening relaxations. E. is a constant tension produced by muscles for long periods of time.

is the time during which the tissue cannot respond again.

. The refractory period A. is the time during which the tissue cannot respond again. B. results in complete and incomplete tetanus. C. is the condition in which the muscle fiber only partially relaxes between contractions. D. is the condition in which stimuli occur so rapidly that there are no intervening relaxations. E. is the constant tension produced by muscles for long periods of time

results in complete and incomplete tetanus.

. Multiple wave summation A. is a time during which the tissue cannot respond again. B. results in complete and incomplete tetanus. C. is a condition in which the muscle fiber only partially relaxes between contractions. D. is a condition in which stimuli occur so rapidly that there are no intervening relaxations. E. is a constant tension produced by muscles for long periods of time.

is the condition in which stimuli occur so rapidly that there are no intervening relaxations

Complete tetanus A. is the time during which the tissue cannot respond again. B. results in complete and incomplete tetanus. C. is the condition in which the muscle fiber only partially relaxes between contractions. D. is the condition in which stimuli occur so rapidly that there are no intervening relaxations. E. is the constant tension produced by muscles for long periods of time.

constant tension produced by muscles for long periods of time

A proper definition of muscle tone is A. constant tension produced by muscles for long periods of time. B. a feeling of well-being following exercise. C. the ability of a muscle to maintain a contraction against an outside force. D. muscles contracting together. E. warm-up of muscle tissue.

motor units contract out of phase at their own particular rates.

Movements of the body are usually smooth and occur at differing rates because A. they are a mixture of isotonic and isometric contractions. B. motor units contract out of phase at their own particular rates. C. most muscle contractions closely resemble individual muscle twitches. D. muscles of different sizes contract at different rates. E. of the all or none principle.

In isometric contractions, the amount of tension produced by the muscle is constant.

Which of the following statements concerning types of muscle contractions is false? A. In isometric contractions, the amount of tension produced by the muscle is constant. B. In isotonic contractions, the muscle fibers shorten. C. The contractile processes in isometric and isotonic contractions are the same. D. Most skeletal muscle contractions are a combination of isometric and isotonic contractions. E. In isotonic contractions, the amount of tension produced by the muscle fibers is constant during the contraction.

the muscle produces increasing tension as it shortens.

. Concentric contractions occur when A. the muscle produces increasing tension as it shortens. B. the tension and length of the muscle remain constant during a contraction. C. tension in a muscle is maintained while the muscle increases in length. D. the muscle produces tension while the length of the muscle increases. E. isometric contractions occur.

a muscle produces constant tension during contraction.

An isotonic contraction is described as A. action potential frequency is high enough that no relaxation of muscle fibers occurs. B. a muscle produces constant tension during contraction. C. a muscle produces an increasing tension during contraction. D. a muscle produces increasing tension as it shortens. E. a muscle produces tension, but the length of the muscle is increasing.

action potential frequency is high enough that no relaxation of muscle fibers occurs.

Tetanus of muscles is described as A. action potential frequency is high enough that no relaxation of muscle fibers occurs. B. a muscle produces constant tension during contraction. C. a muscle produces an increasing tension during contraction. D. a muscle produces increasing tension as it shortens. E. a muscle produces tension, but the length of the muscle is increasing.

a muscle produces tension, but the length of the muscle is increasing

. An eccentric contraction is described as A. action potential frequency is high enough that no relaxation of muscle fibers occurs. B. a muscle produces constant tension during contraction. C. a muscle produces an increasing tension during contraction. D. a muscle produces increasing tension as it shortens. E. a muscle produces tension, but the length of the muscle is increasing

a muscle produces an increasing tension as the length remains constant.

An isometric contraction is described as A. action potential frequency is high enough that no relaxation of muscle fibers occurs. B. a muscle produces constant tension during contraction. C. a muscle produces an increasing tension as the length remains constant. D. a muscle produces increasing tension as it shortens. E. a muscle produces tension, but the length of the muscle is increasing

a muscle produces increasing tension as it shortens.

. A concentric contraction is described as A. action potential frequency is high enough that no relaxation of muscle fibers occurs. B. a muscle produces constant tension during contraction. C. a muscle produces an increasing tension during contraction. D. a muscle produces increasing tension as it shortens. E. a muscle produces tension, but the length of the muscle is increasing

Optimal actin and myosin overlap will produce maximal contraction.

Which of the following is true? A. The greater the overlap of actin and myosin, the stronger the contraction. B. Overstretching a muscle will increase its tension. C. Optimal actin and myosin overlap will produce maximal contraction. D. The greatest amount of tension is achieved when actin and myosin do not overlap. E. Tension is great when actin and myosin overlap as much as they can.

depletion of ATP reserves

Which of the following would contribute to muscular fatigue in the muscle fiber? A. the emotional state of an individual B. depletion of ATP reserves C. inability of the motor neuron to produce sufficient quantities of acetylcholine D. depletion of neurotransmitter E. blocked receptors in the postsynaptic membrane

the emotional state of an individual

The type of muscle fatigue known as "psychological fatigue" is the result of A. depleted ATP reserves. B. increased calcium ion concentration in the sarcoplasm. C. decreased levels of acetylcholine. D. the emotional state of an individual. E. None of these choices is correct.

is a condition in which cross-bridges cannot release.

. Physiological contracture A. occurs when muscles are resting. B. is a condition in which cross-bridges cannot release. C. is caused by an abundance of ATP in muscle fibers. D. results when muscles are well exercised. E. results when the neurotransmitter remains in the receptor.

cross-bridges form but can’t release.

. Rigor mortis occurs after death because A. cross-bridges form but can’t release. B. calcium is actively transported back to the sarcoplasmic reticulum. C. anaerobic respiration is occurring. D. myosin levels decline at death. E. cross-bridges never form.

creatine phosphate

During resting conditions, _________ is synthesized to store energy? A. calcium B. creatine phosphate C. creatine D. lactic acid E. pyruvic acid

ATP

You are hired to work in a laboratory to measure the rate of human muscle contraction. Which of the following might decrease in quantity in muscle cells undergoing contractions? A. ATP B. carbon dioxide C. water D. lactic acid E. sodium

lactic acid.

. A waste product of anaerobic respiration in muscle cells is A. uric acid. B. hydrochloric acid. C. lactic acid. D. carbonic acid. E. pyruvic acid.

both anaerobic respiration and creatine phosphate breakdown

Alex is participating in a 50 meter dash. Predict the most important chemical process his muscles will rely on during this race. A. aerobic respiration. B. anaerobic respiration. C. creatine phosphate breakdown. D. nuclear reactions. E. both anaerobic respiration and creatine phosphate breakdown

yields as many as 36 ATP per glucose molecule metabolized

. Aerobic respiration A. produces ATP molecules faster than anaerobic respiration. B. yields as many as 36 ATP per glucose molecule metabolized. C. occurs whether oxygen is present or not. D. occurs entirely in the cytoplasm. E. occurs in the ribosomes.

both anaerobic and aerobic respiration

A lack of glycolytic enzymes within skeletal muscle cells would impair which type of ATP-yielding process? A. anaerobic respiration B. aerobic respiration C. both anaerobic and aerobic respiration

aerobic respiration

A lack of mitochondria within skeletal muscle would impair which ATP-yielding chemical process? A. anaerobic respiration B. aerobic respiration C. both anaerobic and aerobic respiration

aerobic respiration

Heather is watching a movie. What type of chemical pathway do her muscles depend upon at this time? A. anaerobic respiration B. aerobic respiration C. both anaerobic and aerobic respiration

anaerobic respiration

Randy is participating in a strong man competition and is required to pull a yacht as far as he can. Which type of chemical process will his skeletal muscles rely on during this competition? A. anaerobic respiration B. aerobic respiration C. both anaerobic and aerobic respiration

anaerobic respiration

Which type of respiration rapidly produces ATP for short time periods? A. anaerobic respiration B. aerobic respiration C. both anaerobic and aerobic respiration

aerobic respiration

When skeletal muscle is producing carbon dioxide and water while making ATP, which chemical processes could be active at this time? A. anaerobic respiration B. aerobic respiration C. both anaerobic and aerobic respiration

the amount of oxygen that cells need to replenish ATP supplies after exercise

Oxygen deficit represents A. the amount anaerobic metabolism must increase after exercise. B. the amount of oxygen converted to lactic acid during exercise. C. the amount of carbon dioxide that cells need to eliminate. D. conversion of pyruvic acid to lactic acid. E. the amount of oxygen that cells need to replenish ATP supplies after exercise

recovery oxygen consumption

The elevated oxygen consumption relative to activity level after exercise has ended is called A. oxygen deficit. B. oxygen debt. C. oxygen repayment. D. recovery oxygen consumption. E. anaerobic recovery.

They are well adapted to anaerobic activity

Callie is a world class marathon runner. Which of the descriptions about her dominant type of skeletal muscle is FALSE? A. They split ATP slowly. B. They have large deposits of myoglobin. C. They are well adapted to anaerobic activity. D. They have a well developed blood supply. E. They have low glycogen stores.

the combination of myosin heads with active sites on actin molecules

. What is a cross-bridge? A. a protein found along the groove of the F-actin double helix B. a T tubule and two adjacent terminal cisternae C. the combination of myosin heads with active sites on actin molecules D. the movement of myosin head while attached to actin myofilament E. after exercise, the oxygen taken in that exceeds the oxygen required for resting metabolism

the movement of myosin head while attached to actin myofilament

What is the power stroke? A. a protein found along the groove of the F-actin double helix B. a T tubule and two adjacent terminal cisternae C. the combination of myosin heads with active sites on actin molecules D. the movement of myosin head while attached to actin myofilament E. after exercise, the oxygen taken in that exceeds the oxygen required for resting metabolism

a protein found along the groove of the F-actin double helix

. What is tropomyosin? A. a protein found along the groove of the F-actin double helix B. a T tubule and two adjacent terminal cisternae C. the combination of myosin heads with active sites on actin molecules D. the movement of myosin head while attached to actin myofilament E. after exercise, the oxygen taken in that exceeds the oxygen required for resting metabolism

a T tubule and two adjacent terminal cisternae

What is a triad? A. a protein found along the groove of the F-actin double helix B. a T tubule and two adjacent terminal cisternae C. the combination of myosin heads with active sites on actin molecules D. the movement of myosin head while attached to actin myofilament E. after exercise, the oxygen taken in that exceeds the oxygen required for resting metabolism

after exercise, the oxygen taken in that exceeds the oxygen required for resting metabolism

What is an oxygen deficit? A. a protein found along the groove of the F-actin double helix B. a T tubule and two adjacent terminal cisternae C. the combination of myosin heads with active sites on actin molecules D. the movement of myosin head while attached to actin myofilament E. after exercise, the oxygen taken in that exceeds the oxygen required for resting metabolism

acts as a reservoir for oxygen

Which of the following correctly describes myoglobin’s special function in muscle tissue? A. breaks down glycogen B. synthesizes ATP C. acts as a reservoir for oxygen D. produces action potentials E. stores glucose

fuels runner in a marathon

. Consider the following four phrases and select the one that does not belong with the others. A. anaerobic metabolism B. lactic acid production C. fast twitch fibers D. fuels runner in a marathon E. muscle fibers split ATP rapidly

They split ATP rapidly.

Which of the following statements concerning fast-twitch muscle fibers is true? A. They split ATP rapidly. B. They have large deposits of myoglobin. C. They are well adapted to aerobic metabolism. D. They have a well-developed blood supply. E. They have many mitochondria.

increases muscular strength and mass.

. Intense exercise that results in a great deal of anaerobic activity A. converts some slow-twitch fibers into fast-twitch fibers. B. increases muscular strength and mass. C. enlarges slow-twitch fibers. D. decreases the efficiency of fast-twitch fibers. E. decreases muscle strength and mass.

All of these choices are correct.

Aerobic exercise A. increases vascularity of muscle. B. develops fatigue-resistant fast-twitch fibers. C. can increase the efficiency of slow-twitch fibers. D. can increase the number of mitochondria in muscle cells. E. All of these choices are correct.

myofibrils and sarcomeres.

Muscle hypertrophy results from increased numbers of A. myofibrils and sarcomeres. B. muscle fibers. C. motor units. D. muscles. E. muscle cells.

the nervous system’s ability to recruit a large number of motor units simultaneously.

Increased strength of a trained muscle is due to A. an increased number of muscle fibers. B. the nervous system’s ability to recruit a large number of motor units simultaneously. C. elimination of unnecessary enzymes and metabolic pathways. D. elimination of all fat deposits. E. elimination of unnecessary connective tissue.

had undergone atrophy.

Betsy took a fall, broke her arm, and when she took the cast off she was alarmed to see that her muscles A. looked the same as they did before the fall. B. had undergone atrophy. C. undergone hypertrophy. D. seemed to have an increase in blood flow

increased vascularity

. Select the term that does not belong with the others. A. muscle atrophy B. immobilization C. decrease in number of myofibrils D. loss of nerve stimulation E. increased vascularity

Susan was more cold than usual because her inactivity prevented her muscles from helping to regulate her body temperature.

Susan slipped on the ice and was unable to be fully mobile for several days. What disruption to homeostasis would you predict she experienced during her immobile period in terms of her muscular system? A. Susan’s metabolic rate was raised and it initiated sweating. B. Susan was more cold than usual because her inactivity prevented her muscles from helping to regulate her body temperature. C. Susan’s uninjured muscles overcompensate for the inactive ones by contracting spontaneously.

shiver.

Maureen is hiking in the cold, and to maintain homeostasis her body begins to A. increase heat loss from the skin. B. release chemicals to initiate a high fever. C. shiver. D. reduce her blood pressure. E. vasodilate vessels in her head and neck.

The myofilaments in smooth muscle do not form sarcomeres.

When comparing smooth and skeletal muscle cells, which of the following statements is true? A. Smooth muscle cells have striations. B. The myofilaments in smooth muscle do not form sarcomeres. C. Smooth muscle cells are larger than skeletal muscle cells. D. Smooth muscle has a lot of actin and myosin. E. Smooth muscle cells are multinucleated.

A calcium-calmodulin complex initiates cross-bridge formation

Which of the following statements concerning smooth muscle is true? A. It contains many sarcomeres. B. Caveolae seem to take the place of the myofibrils. C. A calcium-calmodulin complex initiates cross-bridge formation. D. The cells are large and multinuclear. E. It has a well developed sarcoplasmic reticulum

enters from extracellular fluid.

. In smooth muscle, most of the calcium needed for muscle contraction A. is in the dense bodies. B. enters from extracellular fluid. C. is attached to the intermediate filaments. D. must be activated by myosin kinase. E. is stored in the sarcoplasmic reticulum.

both calcium binding to calmodulin and myosin kinase adding a phosphate to myosin heads.

In smooth muscle, cross-bridging occurs due to A. calcium binding to troponin. B. calcium binding to calmodulin. C. myosin kinase adding a phosphate to myosin heads. D. both calcium binding to troponin and calmodulin. E. both calcium binding to calmodulin and myosin kinase adding a phosphate to myosin heads.

It occurs when the phosphate is removed while the cross-bridges are not attached to actin.

Which of the following is NOT true of the latch state of smooth muscle contraction? A. Myosin phosphatase removes the phosphate group from myosin. B. It explains why smooth muscle can sustain tension for long periods of time. C. It occurs when the phosphate is removed while the cross-bridges are attached to actin. D. It occurs when the phosphate is removed while the cross-bridges are not attached to actin. E. It allows contraction without a large energy expenditure.

removes phosphate from myosin.

. Myosin phosphatase A. activates myosin kinase. B. forms the cross-bridge. C. removes phosphate from myosin. D. binds to calcium-calmodulin complex. E. opens calcium channels.

occurs in sheets and exhibits numerous gap junctions.

Visceral smooth muscle A. may contain groups of cells that function as an independent unit. B. occurs in sheets and exhibits numerous gap junctions. C. contracts only when stimulated. D. does not function as a unit. E. All of these choices are correct.

wall of blood vessels

Multiunit smooth muscle is located in the A. gastrocnemius. B. wall of the GI tract. C. wall of blood vessels. D. wall of the heart. E. reproductive system.

depolarizes when both sodium and calcium ions diffuse into the cell.

Smooth muscle A. responds in an all-or-none fashion. B. depolarizes when both sodium and calcium ions diffuse into the cell. C. has fast waves of depolarization. D. has fast waves of repolarization. E. has a resting membrane potential that is more negative than skeletal muscle fibers.

exhibits autorhythmic contractions.

Functionally, smooth muscle A. is well adapted to anaerobic metabolism. B. exhibits autorhythmic contractions. C. contracts in response to slow increases in length. D. is unable to maintain tone. E. rapidly develops an oxygen debt.

hyperpolarization

In a laboratory experiment, the resting membrane potential of a muscle is measured and is found to be more negative. Which of the following has occurred? A. hyperpolarization B. repolarization C. depolarization D. isopolarization E. hypopolarization

the somatic nervous system.

. Smooth muscle is regulated by all of the following except A. the autonomic nervous system. B. neurotransmitters. C. the somatic nervous system. D. hormones. E. prostaglandins.

FALSE

true/false The type of neurotransmitter or hormone that binds to receptors on smooth muscle plasma membranes determines the response of the muscle.

TRUE

true/false The diffusion of calcium ions into a smooth muscle cell does not depolarize the membrane so no action potential occurs.

part of the intracellular cytoskeleton

An antibody test on smooth muscle reveals fewer dense bodies and intermediate filaments in a patient with a colon disorder. What is the purpose of these structures? A. can rapidly develop action potentials in smooth muscle cells B. shallow invaginations of cell membrane C. maintain relatively constant tension in smooth muscle for a period of time D. part of the intracellular cytoskeleton E. act as enzymes that remove phosphate from myosin

shallow invaginations of cell membrane

What are caveolae? A. can rapidly develop action potentials B. shallow invaginations of cell membrane C. relatively constant tension maintained for a period of time D. intracellular cytoskeleton E. enzyme that removes phosphate from myosin

enzyme that removes phosphate from myosin

What is the role of myosin phosphatase? A. can rapidly develop action potentials B. shallow invaginations of cell membrane C. relatively constant tension maintained for a period of time D. intracellular cytoskeleton E. enzyme that removes phosphate from myosin

can rapidly develop action potentials

162. What is the role of pacemaker cells? A. can rapidly develop action potentials B. shallow invaginations of cell membrane C. relatively constant tension maintained for a period of time D. intracellular cytoskeleton E. enzyme that removes phosphate from myosin

The colon is unable to maintain constant tension for sustained periods of time.

A cancer patient is told by their physician that their colon is lacking smooth muscle tone. What does this mean? A. The colon is developing action potentials too rapidly. B. The colon has too many shallow invaginations of cell membranes. C. The colon is unable to maintain constant tension for sustained periods of time. D. The intracellular cytoskeleton is overactive.

have striations.

. Cardiac muscle cells are like skeletal muscle cells in that they both A. have striations. B. depolarize as a result of sodium and calcium influxes. C. possess intercalated disks. D. lack sarcomeres. E. are multinucleated

decreased recovery time

Which of the following is NOT an age related change in skeletal muscle? A. loss of muscle strength B. loss of synapse surface area C. loss of fast-twitch fibers D. decreased recovery time E. decrease in motor units

inability of the muscle fiber to respond to nervous stimulation.

Curare blocks acetylcholine receptors at the motor end plate. This would result in A. increased stimulation of the muscle. B. more acetylcholinesterase production. C. lack of calcium uptake by the muscle fiber. D. inability of the muscle fiber to respond to nervous stimulation. E. sustained contraction of the muscle.

increased accumulation of acetylcholine in the synapse

. A child ingested an organophosphate poison used to kill insects. Soon the child’s muscles began spastic contractions. Predict what occurred at the synaptic cleft. A. decreased release of acetylcholine from presynaptic neurons B. increased accumulation of acetylcholine in the synapse C. the poison binds to acetylcholine receptors and stimulates them D. increased breakdown of acetylcholine in the synaptic cleft E. Both increased accumulation of acetylcholine in the synapse and increased breakdown of acetylcholine in the synaptic cleft.

inhibition of acetylcholinesterase.

One cause of spastic paralysis might be A. inhibition of acetylcholine molecules. B. blockage of acetylcholine receptors. C. inhibition of acetylcholinesterase. D. destruction of synaptic vesicles. E. increase in the amount of acetylcholinesterase.

conversion of excess lactic acid to glucose

Which of the following occurs during recovery from oxygen deficit? A. an elevated level of anaerobic metabolism B. depletion of reserves of creatine phosphate C. conversion of excess lactic acid to glucose D. glycogen degradation to provide creatine E. depressed level of aerobic respiration

increase the number of muscle fibers

Anabolic steroids can do all of the following except A. increase muscle size and strength. B. cause testicular atrophy. C. cause cardiovascular disease. D. increase the number of muscle fibers. E. increase total muscle mass

cramps

The condition of painful, spasmodic contractions of muscles is referred to as A. cramps. B. fibrositis. C. fibromyalgia. D. muscular dystrophy. E. paralysis

fibrositis.

Inflammation of the fibrous connective tissue resulting in stiffness and soreness is A. cramps. B. fibrositis. C. fibrosis. D. muscular dystrophy. E. paralysis.

replacement of muscle cells by connective tissue

Muscular dystrophy is characterized by A. chronic muscle pain. B. decreased size of muscle fibers. C. spastic contractions of muscles. D. replacement of muscle cells by connective tissue. E. hypertrophy of muscle tissue.

It is irreversible

Which of the following is NOT true of muscular atrophy? A. It is irreversible. B. It can be caused by disuse. C. It can be caused by denervation. D. Transcutaneous stimulation can help prevent it. E. Muscle fibers are replaced by connective tissue.

increased cardiovascular fitness

Which of the following is NOT a known effect of illegal use of anabolic steroids in large dosages? A. increased muscle size B. kidney damage C. diminished testosterone secretion D. increased cardiovascular fitness E. sterility

Synaptic vesicles would fail to fuse and ACh would not be released.

What would result from a lack of extracellular calcium ions at the neuromuscular junction? A. Excessive synaptic vesicles would fuse and release too much ACh, overstimulating the myofiber. B. Synaptic vesicles would fail to fuse and ACh would not be released. C. Nothing would happen because extracellular calcium does not play a role in muscle stimulation. D. The neuron must use its intracellular calcium to make the vesicles fuse. E. Potassium ions are used in place of calcium to ensure the vesicles fuse

The muscle would have no way to relax, and spastic contractions would result.

Consider a chemical that blocks the action of acetylcholinesterase. What effect does this have on muscles? A. It would cause paralysis. B. It would cause action potentials to be inhibited, thereby rendering the muscle useless. C. The body would increase it’s production of acetylcholine to compensate. D. The axons of the motor neurons would atrophy and the muscle would weaken. E. The muscle would have no way to relax, and spastic contractions would result.

It causes flaccid paralysis, and if it affects the respiratory muscles, can result in death.

A toxin released by the anaerobic bacterium Clostridium botulinum causes the food-borne illness known as botulism, which inhibits the release of ACh at the neuromuscular junction. What effect does this have on the person? A. It causes flaccid paralysis, and if it affects the respiratory muscles, can result in death. B. It disrupts the balance between ACh and acetylcholinesterase, leading to spastic contractions. C. The brain compensates by producing more ACh, limiting the illness to only a few hours. D. The jaws are most affected, and it results in "lockjaw." E. Problems only result when the individual has low immunity.

It would decrease the number of action potentials sent to the myofiber.

Atrophy at the neuromuscular junction that naturally occurs with age would have what effect on muscles? A. It would stimulate the nervous system to increase the speed in which it sends action potentials to the myofiber. B. It would stimulate muscle cramps. C. It would decrease the number of action potentials sent to the myofiber. D. It would cause an increase in the amount of ACh released by the neurons to compensate. E. It would have no effect on the muscles.

entire sarcomere, H zone, I band

choose all that apply: During a muscle fiber contraction, which of the following decreases in size? A band entire sarcomere H zone I band

false

true/false: In a contracted muscle, the A bands do narrow because the length of the myosin myofilaments changes,.

it increases heat production up to 18 times that of resting levels, the process of muscle contraction produces heat

choose all that apply: Shivering raises body temperature because: it decreases warm blood flow to the core while increasing flow to the muscles it depresses metabolism it increases heat production up to 18 times that of resting levels the process of muscle contraction produces heat

The rate of chemical reactions increases in muscle fibers during contraction, so the rate of heat production also increases.

Why does muscle activity affect the temperature of the body? A. The rate of chemical reactions increases in muscle fibers during contraction, so the rate of heat production also increases. B. Muscle contraction generates pyrogens which reset the body’s internal thermostat to a higher temperature. C. Muscle activity directs more warm blood to the muscles away from the central core causing a cooling effect on your internal organs. D. Increased muscle activity causes a rise in adipose stores which increases the insulation value of the body.

increase

As muscle activity increases, the body temperature _____. A. decreases B. increase

isotropic band or I band

Each _____ includes a Z disk and extends from each side of the Z disk to the ends of the myosin myofilaments. A. isotropic band or I band B. anisotropic band or A band C. muscle fiber D. sarcomere

contains both myosin and actin myofilaments

Describe the H zone of the sarcomere. The H zone: A. contains both myosin and actin myofilaments B. contains only actin myofilaments C. contains only myosin myofilaments

Accounts for muscle’s extensibility and elasticity, Allows the sarcomere to recoil and stretch

choose all that apply: List some of titin’s roles in muscle contraction. Accounts for muscle’s excitability Accounts for muscle’s extensibility and elasticity Allows the sarcomere to recoil and stretch Helps to hold the actin myofilaments in position

the production of an action potential in the sarcolemma

Excitation-contraction coupling begins with: A. the release of calcium from the sarcoplasmic reticulum B. the production of an action potential in the sarcolemma C. the release of the cross-bridge D. the depolarization of the transverse tubules

sarcolemma

In order for the excitation-contraction coupling to occur, the production of an action potential must occur within the ______ of a muscle fiber. A. contraction B. sarcolemma C. junction

The heads of the myosin molecules return to their resting position and the recovery stroke occurs.

choose all that apply: If all of the calcium within a muscle fiber was removed, which of the following could still occur? The heads of the myosin myofilaments bind to G-actin to form cross-bridges. An action potential that was produced at the neuromuscular junction is propagated along the sarcolemma. The troponin molecules bound to G actin molecules are released, causing tropomyosin to move. The heads of the myosin molecules return to their resting position and the recovery stroke occurs.