Quiz and poll for midterm 2 Flashcards
Thick filaments are made up of __________.
a) titin
b) actin
c) nebulin
d) myosin
d
__________ occurs when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere.
Hydrolysis
A power stroke
Myosin head rotation
An action potential
b
A patient has damage to one somatic motor neuron. What will this affect?
Many muscles
One muscle fiber
One motor unit
Many muscle fiber types
c
Which of the following best summarizes the events of excitation-contraction coupling? Choose the best answer.
a. Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle.
b. The actin filament slides towards the sarcomere and the muscle contracts.
c. Cross-bridges release and the muscle relaxes.
d. An acetylcholine signal from the motor neuron is converted into an electrical signal in the muscle fiber.
a
Which of the following statements best describes the neuromuscular junction? Choose the best answer.
the release of acetylcholine from the axon terminal of the motor neurons
the release of calcium from the sarcoplasmic reticulum as a result of the action potential traveling down the t-tubule
the act of myosin and actin sliding past each other in order to produce a contraction
the point of synapse between a motor neuron and the muscle fiber that it innervates
d
Which of the following structures is/are necessary to initiate the muscle action potential?
Select all that apply.
muscle fiber
motor end plate
ryanodine receptor
acetylcholine
motor neuron
actin
Ca Superscript 2+-ATPase
t-tubule
calcium
troponin
myosin
ACh receptor-channels
tropomyosin
a,b,d,e,L
Which of the following best describes the contraction phase of the excitation-contraction coupling reaction? Choose the best answer.
An action potential travels down the t-tubule in order to release Ca Superscript 2+ from the sarcoplasmic reticulum.
Actin pushes on myosin to shorten its length, thereby shortening the muscle.
Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together.
An action potential travels down the axon of a motor neuron in order to release acetylcholine onto the motor end plate.
c
Which of the following best describes the role of calcium (Ca Superscript 2+ ) in the excitation-contraction coupling reaction? Choose the best answer.
Ca 2+ gives the myosin heads the energy necessary for the power stroke.
Ca 2+ binds to specific receptors which control the release of ATP into the cytoplasm of the muscle fiber.
Ca 2+ will bind directly to tropomyosin, resulting in a conformational shift which reveals the binding sites for myosin on actin.
Ca 2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach.
d
Which of the following is the most direct cause of muscle relaxation? Choose the best answer.
The cytoplasm of the muscle fiber exhausts all of its available ATP.
Ca Superscript 2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.
The delivery of action potentials from the motor neuron stops.
The voltage created along the t-tubule fades and the muscle fiber membrane returns to a resting potential value.
b
Which loss of function would occur if you introduced a chemical that functioned as an inhibitor of the ryanodine receptor channel? Choose the best answer.
The axon terminal of the motor neuron would not release acetylcholine
Na Superscript + ions would not be able to flow into the muscle cell in order to depolarize it
Myosin would not be able to bind to actin in order to cause shortening of the sarcomere
Ca Superscript 2+ ions would not be actively pumped back into the sarcoplasmic reticulum
c
Compared to fast-twitch glycolytic fibers (type IIX), slow-oxidative muscle fibers (type I) are characterized by a smaller diameter and __________.
the development of tension 2-3 times more quickly
faster pumping of Ca Superscript 2+ into the SR
fewer mitochondria
the presence of myoglobin
d
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
arrival of an action potential
troponin
ATP
calcium ion pump
a
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
myosin
actin
troponin
tropomyosin
c
A myosin head binds to which molecule to form a cross bridge?
troponin
tropomyosin
actin
d
What causes the myosin head to disconnect from actin?
binding of calcium
binding of ATP
hydrolysis of ATP
binding of troponin
b
What causes the power stroke?
calcium
binding of ATP
hydrolysis of ATP
release of ADP and Pi
d
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
serotonin
dopamine
norepinephrine
acetylcholine (ACh)
d
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
chemically gated calcium channels
voltage-gated potassium channels
voltage-gated calcium channels
voltage-gated sodium channels
c
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
a channel
exocytosis
a protein carrier
b
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell.
Binding causes voltage-gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell.
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell.
Binding causes potassium voltage-gated channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell.
c
How is acetylcholine (ACh) removed from the synaptic cleft?
simple diffusion away from the synaptic cleft and endocytosis into the muscle fiber
acetylcholinesterase (AChE; an enzyme) only
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
acetylcholinesterase (AChE; an enzyme) and endocytosis into the muscle fiber
c
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?
terminal cisterns (cisternae) of the sarcoplasmic reticulum
sarcolemma
cytosol
T tubule
a
What happens when skeletal muscle sarcomere length increases beyond about 2.3 micrometers (μm)?
Less calcium is released from the SR.
More myosin heads can bind to the thin filament.
Tension decreases.
The fiber can produce more force.
c
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 transported into the postsynaptic neuron by receptor-mediated endocytosis.
Acetylcholine is transported back into the axon terminal by a reuptake mechanism.
Acetylcholine diffuses away from the cleft.
Acetylcholine is degraded by acetylcholinesterase.
d
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 and moves across the synaptic cleft bound to a transport protein.
Acetylcholine is released by axon terminals of the motor neuron.
When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.
Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein.
b
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
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
extend from the spinal cord to the sarcolemma of a skeletal muscle fiber
c
Calcium entry into the axon terminal triggers which of the following events?
Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal.
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 binds to its receptor.
c
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
a
Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?
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 outside surface of the sarcolemma is negatively charged compared to the inside surface. Potassium ions diffuse outward 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.
d
What happens when calcium binds troponin?
Troponin binds to actin and causes sarcomere shortening.
Troponin changes shape and covers the SR calcium channel, which is a form of negative feedback.
Tropomyosin is pulled away from the myosin-binding site on actin.
Troponin releases myosin and activates actin.
c
Which is a similarity between summation and tetanus?
In both, muscle action potentials are shorter than muscle contraction.
Both occur when there are less frequent action potentials.
In both, muscle contraction is shorter than muscle action potentials.
Both reach maximum tension.
a
What immediately follows hydrolysis of ATP during muscle contraction?
The power stroke
Myosin binding to actin
Rotation of the myosin head to the cocked position
Myosin releases actin
c
Which of the following is the smallest structure?
Muscle fascicle
Myofibril
Muscle fiber
Myosin
d
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?
ATP bound to a myosin head
Troponin bound to tropomyosin
Calcium bound to troponin
A myosin head bound to actin
d
What structure is the functional unit of contraction in a skeletal muscle fiber?
The junctional folds of the sarcolemma
The sarcomere
The triad
The cross bridge
b
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 transverse tubules.
Calcium ions are stored in the nuclei.
Calcium ions are stored in the sarcoplasmic reticulum.
Calcium ions are stored in the mitochondria.
c
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?
ATP binds to the myosin head.
Calcium ions bind to troponin.
ADP and inorganic phosphate are bound to the myosin head.
Acetylcholine binds to receptors in the junctional folds of the sarcolemma.
a
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of GTP.
The energy comes from the direct phosphorylation of ADP by creatine phosphate.
The energy comes from the hydrolysis of ATP.
The energy comes from oxidative phophorylation.
c
What specific event triggers the uncovering of the myosin binding site on actin?
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 troponin and change its shape.
Calcium ions bind to tropomyosin and change its shape.
c
When does cross bridge cycling end?
Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open.
Cross bridge cycling ends when calcium ions are passively transported back into the sarcoplasmic reticulum.
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 ATP binds to the myosin head.
c
Skeletal muscle moves a bone at a joint, such as flexing the forearm at the elbow. How is the opposite action produced (for example, extension at the elbow)?
The muscle that produces flexion extends to produce extension.
An antagonistic neuron secretes a different neurotransmitter onto the same muscle to produce the opposite skeletal movement.
An antagonistic muscle produces the opposite movement.
The muscle that produces flexion relaxes to produce extension.
c
Which of the following would NOT change size during a muscle contraction?
H zone
I band
A band
Sarcomere
c
How is the energy released by ATP hydrolysis used during the contractile cycle in skeletal muscle?
It allows the release of calcium from the SR.
ATP hydrolysis stabilizes actin to prevent actin filament’s shortening during contraction.
It causes rotation of the myosin head, thus “cocking” it.
It provides energy for the myosin head to pull on the actin filament. This “uncocks” the myosin head.
c
Which of the following would stop muscle contraction?
A lack of ATP
Pumping of calcium ions into the SR
Pulling away of tropomyosin from the myosin-binding site on actin
Binding of acetylcholine to ACh receptors
b
Which type of skeletal muscle causes two bones to move away from one another?
Flexor
Extensor
Tendon
Antagonist
b
Which enzyme catalyzes the phosphorylation of ADP?
Ca2+-ATPase
Creatine kinase
Phosphocreatine
Na+-K+-ATPase
b
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.
c
Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?
Voltage-sensitive proteins change shape.
Sodium release from the sarcoplasmic reticulum initiates the contraction.
Calcium release from the sarcoplasmic reticulum initiates the contraction.
Action potentials propagate into the interior of the skeletal muscle fiber.
c
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.
Potassium leak channels.
Myosin cross-bridge binding sites.
Voltage-gated sodium channels.
a
What is name given to the regularly spaced infoldings of the sarcolemma?
motor endplates
terminal cisternae
transverse or T tubules
sarcoplasmic reticulum
c
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Action potentials.
Acetylcholine.
Sodium ions.
Calcium ions.
d
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.
c
Because of their shape, muscle cells are also known as __________.
myofibrils
fascicles
tubules
muscle fibers
d
Which is a difference between summation and tetanus?
Summation can cause tetanus, but tetanus cannot cause summation.
Sarcomeres shorten in tetanus but not in summation.
Muscles reach maximal tension in summation but not in tetanus.
Muscles relax between action potentials in summation but not in tetanus.
a
