Chapter 9 Muscle

Which of the following is true? Skeletal muscle cells have one nucleus, but smooth muscle cells are multinucleated. Skeletal muscle fibers tend to be shorter than smooth muscle fibers. Skeletal muscle fibers contain sarcomeres; smooth muscle fibers do not. Skeletal muscle lacks the coarse connective tissue sheaths that are found in smooth muscle

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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 refers to the release of calcium ions from the sarcoplasmic reticulum. Excitation refers to the propagation of action potentials along the axon of a motor neuron. Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma

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

During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases? The cross bridge remains in place, preventing the actin myofilament from sliding. There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching. Calcium blocks the active sites on actin. The actin myofilament can only move in one direction relative to the myosin filament.

There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? acetylcholine (ACh) norepinephrine serotonin dopamine

acetylcholine (ACh)

How is acetylcholine (ACh) removed from the synaptic cleft? a reuptake pump on the axon terminal acetylcholinesterase (AChE; an enzyme) diffusion away from the synaptic cleft

acetylcholinesterase (AChE; an enzyme)

A myosin head binds to which molecule to form a cross bridge? tropomyosin actin troponin

actin

Which energy production process provides the majority of the energy for muscle activity? anaerobic glycolysis aerobic respiration direct phosphorylation of ADP by creatine phosphate use of stored ATP

aerobic respiration

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? arrival of an action potential troponin calcium ion pump ATP

arrival of an action potential

The connective tissue sheaths of skeletal muscle, in order from internal to external are the: endomysium, perimysium, and epimysium. epimysium, perimysium, and endomysium. endomysium, epimysium, and perimysium. perimysium, endomysium, and epimysium.

endomysium, perimysium, and epimysium

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? exocytosis a channel a protein carrier

exocytosis

What energizes the power stroke? hydrolysis of ATP calcium binding of ATP

hydrolysis of ATP

Which organelle contains the contractile elements found in skeletal muscle? sarcolemma myofibril sarcoplasmic reticulum glycosome

myofibril

What, specifically, is a cross bridge? ATP binding to the myosin head tropomyosin covering the active sites on actin calcium binding to troponin myosin binding to actin

myosin binding to actin

What is name given to the regularly spaced infoldings of the sarcolemma? transverse or T tubules sarcoplasmic reticulum terminal cisternae motor endplates

transverse or T tubules

In muscle fibers, which regulatory protein blocks the attachment of myosin heads to actin? thick filaments tropomyosin acetylcholinesterase calcium

tropomyosin

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? chemically gated calcium channels voltage-gated sodium channels voltage-gated potassium channels voltage-gated calcium channels

voltage-gated calcium channels

Which protein inhibits skeletal muscle contraction, and what ion removes the inhibition? myosin; sodium ions actin; chloride ions Tropomyosin; calcium ions troponin; sodium ions

Tropomyosin; calcium ions

What causes the myosin head to disconnect from actin? binding of ATP binding of troponin hydrolysis of ATP binding of calcium

binding of ATP

Which of the following factors influence the velocity and duration of muscle contraction? frequency of stimulation muscle fiber size length of muscle fibers activated load placed on the muscle

load placed on the muscle

The calcium calmodulin system of contraction regulation is found in: skeletal muscle only. cardiac and skeletal muscle. smooth muscle only. cardiac muscle only.

smooth muscle only

The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell? cytosol T tubule terminal cisternae of the sarcoplasmic reticulum sarcolemma

terminal cisternae of the sarcoplasmic reticulum

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected? Myosin cross-bridge binding sites. A series of proteins that control calcium release. Potassium leak channels. Voltage-gated sodium channels

A series of proteins that control calcium release

Calcium entry into the axon terminal triggers which of the following events? Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal. Acetylcholine binds to its receptor.

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

the binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur? Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate. Binding causes potassium voltage-gated channels to open in the motor endplate. Binding causes voltage-gated sodium channels to open in the motor endplate. Binding causes chemically gated potassium channels to open in the motor end plate.

Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? Motor neurons always innervate thousands of skeletal muscle fibers. A motor neuron typically innervates only one skeletal muscle fiber. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. A skeletal muscle fiber is innervated by multiple motor neurons.

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

Acetylcholine binds to its receptor in the sarcolemma and triggers __________. the opening of calcium-release channels the opening of ligand-gated cation channels the opening of ligand-gated anion channels the opening of voltage-gated calcium channels

the opening of ligand-gated cation channels

The binding of calcium to which molecule causes the myosin binding sites to be exposed? actin troponin tropomyosin

troponin

Which event causes cross bridge detachment? release of ADP and inorganic phosphate from the myosin head release of calcium from troponin nervous input ends ATP binding to the myosin head

ATP binding to the myosin head

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following meAction 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 diffuses away from the cleft. Acetylcholine is transported back into the axon terminal by a reuptake mechanism. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis. Acetylcholine is degraded by acetylcholinesterase

Acetylcholine is degraded by acetylcholinesterase

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? 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 by axon terminals of the motor neuron. Acetylcholine is released and moves across the synaptic cleft bound to a transport protein. Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein.

Acetylcholine is released by axon terminals of the motor neuron

How/when does the myosin head cock back to store energy for the next cycle? The power stroke cocks the myosin head. After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head. when ADP is released from the myosin head The sliding of the actin myofilament during the power stroke re-cocks myosin heads that have previously delivered their power stroke.

After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.

What is the role of calcium in the cross bridge cycle? Calcium binds to troponin, altering its shape. Calcium binds to myosin, causing the myosin head to release from the actin myofilament. Calcium binds to troponin, exposing the active site on troponin. Calcium binds to active sites on actin, forming the cross bridge

Calcium binds to troponin, altering its shape

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? Sodium ions. Calcium ions. Action potentials. Acetylcholine.

Calcium ions.

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.

Calcium release from the sarcoplasmic reticulum initiates the contraction

Which of the following is true concerning the anatomy of a skeletal muscle fiber? A triad consists of a T tubule and the nearby sarcolemma. Myofibrils contain thick and thin filaments. The sarcolemma is the muscle fiber's cytoplasm. T tubules are extensions of the sarcoplasmic reticulum.

Myofibrils contain thick and thin filaments.

BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle? Myosin heads would remain attached to actin, unable to detach. Tropomyosin would not move, and the active sites on actin would not be exposed. Myosin heads would remain detached, unable to cock. Myosin heads would remain attached to actin, unable to perform the power stroke.

Myosin heads would remain detached, unable to cock.

What role does tropomyosin play in the cross bridge cycle? Tropomyosin moves the actin filament relative to the myosin filament. The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form. Tropomyosin binds to calcium, causing muscle relaxation. Tropomyosin pushes the myosin head away, causing cross bridge detachment

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.

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

How does troponin facilitate cross bridge formation? Troponin gathers excess calcium that might otherwise block actin's progress. Troponin moves away from the active sites on actin, permitting cross bridge formation. Troponin hydrolyzes ATP, which provides the energy necessary for cross bridges to form. Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.

Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.

The sliding filament model of contraction states that: during contraction, the thin filaments slide past T-tubules so that the Z disks are overlapping. during contraction, the thin filaments slide past the thick filaments so that actin and myosin filaments overlap. during contraction, the thin filaments slide past the thick filaments so that actin and myosin filaments do not overlap. during contraction, the thin filaments slide past the thick filaments so that calcium ions can be released from the sarcoplasmic reticulum

during contraction, the thin filaments slide past the thick filaments so that actin and myosin filaments overlap.

Where in the cross bridge cycle does ATP hydrolysis occur? during the power stroke during the removal of calcium from troponin during the movement of tropomyosin to expose the active sites on actin during the cocking of the myosin head

during the cocking of the myosin head

action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________. 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 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 or spinal cord to the sarcolemma of a skeletal muscle fiber

Muscle tissue does not:generate heat. generate nerve impulses. maintain posture. produce movement. stabilize joints

generate nerve impulses.

The major role of the sarcoplasmic reticulum is to regulate: intracellular levels of Na+. extracellular levels of Ca2+. extracellular levels of Na+. intracellular levels of Ca2+.

intracellular levels of Ca2+.

When muscles are contracting under oxygen deficient conditions, they will form ________ to ensure they maintain a supply of ATP. glycogen glucose creatine phosphate lactic acid

lactic acid

Thick myofilaments are made of: troponin. tropomyosin myosin. actin.

myosin.

The smallest contractile unit of a muscle fiber is the: troponin. elastic filament. myofilament. sarcomere.

sarcomere

The calcium that initiates skeletal muscle contraction is released from what structure(s)? terminal cisternae sarcolemma sarcomeres T tubules

terminal cisternae

Which of the following are composed of myosin? thick filaments intermediate filaments tropomyosin thin filaments

thick filaments