Match from the following list.
A. A band
B. I band
C. Z disk
D. H zone
E. M line
The structures that serve as the attachment site for the thin filaments and mark the boundaries for one sarcomere.
C. Z disk
Which ion signals the beginning of skeletal muscle contraction?
Ca2+
________ is composed of multiple globular molecules polymerized to form long chains or filaments.
Actin
Match the structures with the accurate description.
A. muscle fiber
B. fascicle
C. sarcolemma
D. myofibril
E. t-tubules
a single muscle cell
A. muscle fiber
The function of the titin protein is to
stabilize the position of the contractile filaments.
After death, when metabolism stops, in which step of the contractile cycle must skeletal muscles remain?
the rigor state
A motor unit consists of
one neuron and all the skeletal muscle fibers it controls.
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 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
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.
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium ions.
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
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?
A myosin head bound to actin
What structure is the functional unit of contraction in a skeletal muscle fiber?
The sarcomere
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.
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.
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of ATP.
What specific event triggers the uncovering of the myosin binding site on actin?
Calcium ions bind to troponin and change its shape.
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.
________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle.
Phosphocreatine
What is it called when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere?
Power stroke
The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a
channel for both Na+ and K+.
Smooth muscle cells lack which protein(s)?
A. myosin only
B tropomyosin only
C. troponin and tropomyosin
D. troponin only
E. actin only
D. troponin only
The I band contains
thin filaments only.
Which of the following would cause muscle relaxation to occur?
Calcium ions pumped into the SR
Calcium, released by the sarcoplasmic reticulum, binds to ________ to move the ________, which allows actin to form a high-force crossbridge with myosin.
troponin C, tropomyosin
Which of the following best summarizes the events of excitation-contraction coupling?
Choose the best answer.
A. An acetylcholine signal from the motor neuron is converted into an electrical signal in the muscle fiber.
B. Muscle action potentials initiate
B. Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle.
Which of the following statements best describes the neuromuscular junction?
Choose the best answer.
A. the point of synapse between a motor neuron and the muscle fiber that it innervates
B. the release of calcium from the sarcoplasmic reticulum as a resu
A. the point of synapse between a motor neuron and the muscle fiber that it innervates
Which of the following structures is/are necessary to initiate the muscle action potential?
Select all that apply.
A. actin
B. t-tubule
C. tropomyosin
D. motor end plate
E. muscle fiber
F. troponin
G. acetylcholine
H. calcium
I. ACh receptor-channels
J. m
D. motor end plate
E. muscle fiber
G. acetylcholine
I. ACh receptor-channels
M. motor neuron
What is a change in membrane voltage that travels down the T-tubule to cause opening of Ca2+ channels
Action potential
What is an area that contains many synaptic vesicles filled with acetylcholine
Axon terminal of motor neuron
What is a structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+
ACh receptor-channel
What is an area of muscle fiber membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine
Motor end plate
Which of the following best describes the contraction phase of the excitation-contraction coupling reaction?
Choose the best answer.
A. An action potential travels down the axon of a motor neuron in order to release acetylcholine onto the motor end plate.
B. Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together.
Which of the following best describes the role of calcium (Ca2+) in the excitation-contraction coupling reaction?
Choose the best answer.
A. Ca2+ gives the myosin heads the energy necessary for the power stroke.
B. Ca2+ binds to specific receptors which c
D. Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach.
Which of the following is the most direct cause of muscle relaxation?
Choose the best answer.
A. Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.
B. The voltage created along the t-tubule fades and the muscle fibe
A. Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.
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.
A. Na+ ions would not be able to flow into the muscle cell in order to depolarize it
B. Myosin would
B. Myosin would not be able to bind to actin in order to cause shortening of the sarcomere
Which is the smallest structure?
A. Muscle fiber
B. Myosin
C. Myofibril
D. Myofilament
B. Myosin
Subjective feelings of tiredness and a desire to cease activity describes which phenomenon?
Central fatigue
Compared to skeletal muscle, contraction of smooth muscle cells is
a slower response to a stimulus and sustained without fatigue.
The contraction cycle is triggered by the rise in ________ released from the sarcoplasmic reticulum (SR).
Ca2+
Which of these structures would not change size during a muscle contraction?
A. A band
B. Sarcomere
C. I band
D. H zone
A. A band
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?
A. Acetylcholine is transported into the postsy
D. 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?
A. Acetylcholine is released and moves across the synaptic cleft bound to a
D. Acetylcholine is released by axon terminals of the motor neuron.
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
Calcium entry into the axon terminal triggers which of the following events?
A. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
B. Cation channels open and sodium ions enter the axon terminal while potassium i
A. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation 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.
How does the process of smooth muscle contraction differ from contraction in skeletal muscle?
Ca2+ comes from the extracellular fluid as well as the SR.
Match the structures with the accurate description.
A. muscle fiber
B. fascicle
C. sarcolemma
D. myofibril
E. t-tubules
a bundle of adjacent muscle cells
B. fascicle
What happens when calcium binds troponin?
Tropomyosin is pulled away from the actin active site.
Relative to skeletal muscle, smooth muscle
uses less energy to generate a given amount of force, can sustain contractile force without fatigue and uses calcium from the sarcoplasmic reticulum and extracellular space.
Put these events in the correct chronological sequence:
1. End-plate potentials trigger action potentials.
2. Transverse tubules convey potentials into the interior of the cell.
3. Acetylcholine binds to receptors on the motor end plate.
4. Ca2+ is releas
3, 1, 2, 4
When a skeletal muscle cell contracts and the muscle shortens,
some myosin heads are forming crossbridges as others are releasing them.
Which fibers fatigue sooner?
A. slow-twitch fibers
B. fast-twitch fibers
B. fast-twitch fibers
How is the energy released by ATP hydrolysis used during the contractile cycle in skeletal muscle?
It causes rotation of the myosin head back to 90�, thus "cocking" it.
Which enzyme catabolizes the phosphorylation of ADP by creatine phosphate?
Creatine kinase
As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately
detaches from actin
The H zone contains
thick filaments.
The function of transverse tubules is to
rapidly conduct action potentials to the interior of the muscle fiber.
In smooth muscle cells, Ca2+ binds to ________ which activates the enzyme ________ to phosphorylate myosin and increase force.
calmodulin, myosin light chain kinase
The molecular event that occurs immediately after the power stroke is the
release of ADP from the myosin.
Which protein spans the distance from one Z disk to the M line?
Titin