Which of the following is true concerning the anatomy of a skeletal muscle fiber?

Myofibrils contain thick and thin filaments.

A triad consists of a T tubule and the nearby sarcolemma.

T tubules are extensions of the sarcoplasmic reticulum.

The sarcolemma is the muscle fiber’s cytoplasm

What event most directly triggers the release of calcium from the terminal cisternae?

action potential propagating down the T tubule

movement of tropomyosin away from the active sites on actin

action potential propagating toward the axon terminal

cross bridge formation between the thick and thin filaments

How do calcium ions initiate contraction in skeletal muscle fibers?

Calcium ions bind to troponin, changing troponin’s shape.

Calcium ions provide the energy necessary for the myosin head power stroke.

Calcium ion movement depolarizes the sarcolemma at the synaptic cleft.

Calcium ions bind to tropomyosin, exposing the active sites on actin.

Which of the following best describes the events of “excitation” in “excitation-contraction coupling”?

propagation of the action potential along the sarcolemma

release of calcium from the terminal cisternae

movement of tropomyosin away from the active sites on actin

Which of the following best describes the events of “contraction” in “excitation-contraction coupling”?

propagation of the action potential along the sarcolemma of the muscle fiber

release of calcium from the terminal cisternae

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?

Acetylcholine is degraded by acetylcholinesterase.

Acetylcholine diffuses away from the cleft.

Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis.

Acetylcholine is transported back into the axon terminal by a reuptake mechanism.

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

Acetylcholine is released by axon terminals of the motor neuron.

Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein.

When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.

Acetylcholine is released and moves across the synaptic cleft bound to a transport protein.

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.

extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber

arise in the epimysium of a skeletal muscle and extend to individual skeletal muscle fibers

extend from the brain to the sarcolemma of a skeletal muscle fiber

extend from the spinal cord to the sarcolemma of a skeletal muscle fiber

Calcium entry into the axon terminal triggers which of the following events?

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.

Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal.

Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal.

Acetylcholine binds to its receptor.

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

the opening of ligand-gated cation channels

the opening of calcium-release channels

the opening of voltage-gated calcium channels

the opening of ligand-gated anion channels

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Potassium ions diffuse inward along favorable chemical and electrical gradients.

The outside surface of the sarcolemma is negatively charged compared to the inside surface. Potassium ions diffuse outward along favorable chemical and electrical gradients.

The outside surface of the sarcolemma is negatively charged compared to the inside surface. Sodium ions diffuse outward along favorable chemical and electrical gradients.

What part of the sarcolemma contains acetylcholine receptors?

part adjacent to another muscle cell

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.

Excitation refers to the propagation of action potentials along the axon of a motor neuron.

Excitation refers to the release of calcium ions from the sarcoplasmic reticulum.

Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma. Submit

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?

Calcium release from the sarcoplasmic reticulum initiates the contraction.

Sodium release from the sarcoplasmic reticulum initiates the contraction.

Action potentials propagate into the interior of the skeletal muscle fiber.

Voltage-sensitive proteins change shape.

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?

A series of proteins that control calcium release.

Myosin cross-bridge binding sites.

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.

A skeletal muscle fiber is innervated by multiple motor neurons.

A motor neuron typically innervates only one skeletal muscle fiber.

Motor neurons always innervate thousands of skeletal muscle fibers.

What is the functional role of the T tubules?

enhance cellular communication during muscle contraction

synthesize ATP to provide energy for muscle contraction

hold cross bridges in place in a resting muscle Submit

What is a cross bridge cycle?

It is the cycle in which an energized myosin head binds to actin and performs a power stroke, then binds to ATP in order to detach and re-energize.

It is the cycle by which the sarcolemma is repeatedly depolarized and repolarized.

It is a cycle of repeated stimuli resulting in summation of muscle twitches.

It is the cycle in which motor units are recruited from small to large, in order to produce gradual increases in force.

What structure is the functional unit of contraction in a skeletal muscle fiber?

The junctional folds of the sarcolemma

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?

Calcium ions are stored in the sarcoplasmic reticulum.

Calcium ions are stored in the nuclei.

Calcium ions are stored in the transverse tubules.

Calcium ions are stored in the mitochondria. Submit

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

ADP and inorganic phosphate are bound to the myosin head.

Acetylcholine binds to receptors in the junctional folds of the sarcolemma.

How does the myosin head obtain the energy required for activation?

The energy comes from the hydrolysis of ATP.

The energy comes from the hydrolysis of GTP.

The energy comes from oxidative phophorylation.

The energy comes from the direct phosphorylation of ADP by creatine phosphate.

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape.

Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm.

Sodium ions bind to troponin and change its shape.

Calcium ions bind to tropomyosin and change its shape. Submit

When does cross bridge cycling end?

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.

Cross bridge cycling ends when calcium ions are passively transported back into the sarcoplasmic reticulum.

Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open.

Cross bridge cycling ends when ATP binds to the myosin head.

Which of the following is the correct sequence of events for muscle contractions?

motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments

muscle cell action potential, neurotransmitter release, ATP-driven power stroke, calcium ion release from SR, sliding of myofilaments

neurotransmitter release, muscle cell action potential, motor neuron action potential, release of calcium ions from SR, sliding of myofilaments, ATP-driven power stroke

neurotransmitter release, motor neuron action potential, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke

Cross bridge formation between myosin heads and actin molecules is caused by the elevation of calcium ion concentration in the cytosol. During rigor mortis, this elevation of calcium ion concentration in the cytosol is permanent because ________.

mitochondria stop producing ATP molecules required by the sarcoplasmic reticulum's calcium ion pumps

troponin molecules bind irreversibly to calcium ions to prevent them from being removed from the cytosol

tropomyosin molecules bind irreversibly to calcium ions to prevent them from being removed from the cytosol

acetylcholine continues to stimulate the release of calcium ions from the sarcoplasmic reticulum Submit

The sliding filament model of contraction states that ________.

during contraction the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree

during contraction the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments no longer overlap

during contraction the thin myofilaments slide past T tubules so that the Z discs are overlapping

during contraction the thin myofilaments slide past the thick myofilaments so that calcium ions can be released from the sarcoplasmic reticulum Submit

In an isotonic contraction, the muscle ________.

changes in length and moves the "load"

never converts pyruvate to lactate

does not change in length but increases tension

rapidly resynthesizes creatine phosphate and ATP

Creatine phosphate functions in the muscle cell by ________.

storing energy that will be transferred to ADP to resynthesize ATP

inducing a conformational change in the myofilaments

forming a temporary chemical compound with myosin

forming a chemical compound with actin

The strongest muscle contractions are normally achieved by ________.

increasing the stimulation up to the maximal stimulus

increasing stimulus above the threshold

recruiting small and medium muscle fibers

increasing stimulus above the treppe stimulus

What is the primary function of wave summation?

produce smooth, continuous muscle contraction

Most skeletal muscles contain ________.

a predominance of fast oxidative fibers

a predominance of slow oxidative fibers

A&P - muscles

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MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Muscle tissue has all of the following properties except ________.

secretion

excitability

extensibility

contractility

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Muscle tissue does NOT ________.

produce blood cells

produce movement

generate heat

stabilize joints

maintain posture

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Which of the following is CORRECTLY paired?

skeletal muscle: voluntary control

cardiac muscle: voluntary control

smooth muscle: striated

cardiac muscle: nonstriated

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Which of the following surrounds the individual muscle cell?

endomysium

epimysium

fascicle

perimysium

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Myoglobin ________.

stores oxygen in muscle cells

produces the end plate potential

is a protein involved in the direct phosphorylation of ADP

breaks down glycogen

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

The term aponeurosis refers to ________.

a sheetlike indirect attachment to a skeletal element

the tropomyosin-troponin complex

the rough endoplasmic reticulum

the bands of myofibrils

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

The connective tissue sheaths of skeletal muscle, in order from internal to external, are the ________.

endomysium, perimysium, and epimysium

endomysium, epimysium, and perimysium

perimysium, endomysium, and epimysium

epimysium, endomysium, and perimysium

epimysium, perimysium, and endomysium

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A&P - muscles

Muscle tissue has all of the following properties except ________.

Muscle tissue does NOT ________.

Which of the following is CORRECTLY paired?

Which of the following surrounds the individual muscle cell?

Myoglobin ________.

The term aponeurosis refers to ________.

The connective tissue sheaths of skeletal muscle, in order from internal to external, are the ________.

Which of the following is true concerning the anatomy of a skeletal muscle fiber?

The calcium that initiates skeletal muscle contraction is released from what structure(s)?

Which of the following are composed of myosin?

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