Chapters 10,
Aerobic metabolism normally provides ________ percent of the ATP demands of a resting muscle cell.
95
The region of the sarcomere containing the thick filaments is the
A band
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
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.
The post-synaptic reaction on the sarcolemma is short in duration. Which of the following explanations describes why the reaction of the sarcolemma is short in duration?
ACh diffuses out of the synaptic cleft., AChE acts to breakdown the ACh in the synaptic cleft.
Which of the following is/are mechanism(s) to end neural transmission at the neuromuscular junction?
ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE), ACh diffuses away from the synaptic cleft.
Which of the following events most directly occurs due to an action potential generated by the motor neuron?
ACh is released at the synapse.
Cross bridge detachment is caused by ________ binding to the myosin head.
ATP
The characteristic muscle stiffness associated with rigor mortis is due to the inability of myosin filaments to detach from the active site on actin filaments. What molecule is essential for this detachment?
ATP
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.
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.
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.
Tamara's muscle weakness and fatigue becomes progressively worse over the course of the day. This is a hallmark sign of myasthenia gravis, an autoimmune disorder that affects the ability of a motor neuron to communicate with a muscle fiber. What synaptic events must happen first for excitation to occur?
Acetylcholine is released from the axon terminal and diffuses across the synapse to bind to a receptor in the surface of the motor end plate.
The injection that dramatically improved Tamara's symptoms was Tensilon, an acetylcholinesterase inhibitor. What is acetylcholinesterase, and why was this injection effective in relieving Tamara's symptoms?
Acetylcholinesterase is the enzyme that clears acetylcholine from the synapse. Inhibiting this enzyme will enable acetylcholine to be available for a longer period to bind to receptors.
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.
The cross bridge cycle starts when _________.
Ca2+ from the sarcoplasmic reticulum binds to troponin
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium ions
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.
What specific event triggers the uncovering of the myosin binding site on actin?
Calcium ions bind to troponin and change its shape.
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.
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.
How is delayed-onset muscle soreness (DOMS) different from muscle fatigue?
Delayed-onset muscle soreness occurs a day or more after the physical exertion.
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.
The area in the center of the A band that contains no thin filaments is the
H band
The region of the sarcomere that always contains thin filaments is the
I band
Myasthenia gravis is an autoimmune disorder that results in the production of antibodies that either block or cause the destruction of the ACh receptor. Why do you think that Tamara's symptoms become worse as the day progresses?
In the morning, the neuronal reserves of acetylcholine are larger, allowing for sufficient neurotransmitter release and resulting in effective muscle signaling. As the day progresses and the stores of acetylcholine become depleted, muscle function becomes progressively worse.
How would the loss of acetylcholinesterase from the motor end plate affect skeletal muscle?
It would cause muscles to stay contracted.
Which of the following processes produces 36 ATP?
Krebs cycle and oxidative phosphorylation
In a sarcomere, the central portion of thick filaments are linked laterally by proteins of the
M line
The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________.
Pyruvic acid is converted back to lactic acid.
Which of the following statements is false?
Skeletal muscle and cardiac muscle stimulation is neural.
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.
The muscle action potentials that initiate contraction are transmitted from the sarcolemma into the interior of the muscle fiber by __________.
T tubules
steps of the contraction cycle
The contraction cycle begins with the arrival of calcium ions to the zones of overlap via excitation-contraction coupling. Then, calcium ions bind to the troponin-tropomyosin complex, causing troponin to change position. Troponin's movement rolls tropomyosin away from actin's active sites, thus allowing them to form cross-bridges with energized myosin heads. After cross-bridge formation, the energy that was stored in the resting state is released as the myosin head pivots towards the M line (coincident with the release of bound ADP and P). This is known as the power stroke. Finally, to disengage cross-bridges following the power stroke, ATP binds to the myosin head, and the bond between myosin and actin is broken. Myosin is reactivated for further cycling when ATP is converted into ADP and P, and the myosin head returns to its original conformation.
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of ATP.
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.
Malignant hyperthermia (MH) is a rare genetic disease in which the sarcoplasmic reticulum leaks calcium when the patient is put under general anesthesia. Which of the following best describes how anesthesia would affect the skeletal muscles of a patient with MH?
The muscles would contract because of calcium binding to troponin.
What happens immediately after the myosin head binds to the active site on actin?
The myosin head pivots, moving the actin strand.
Which of the following statements is true?
The neurotransmitter is stored in the presynaptic motor neuron.
What structure is the functional unit of contraction in a skeletal muscle fiber?
The sarcomere
Why do the disease tetanus and the normal sustained muscle contraction called tetanus share the same name?
They both eliminate the relaxation phase in the affected muscle fibers.
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.
Which of the following is important to increasing efficiency in tension production?
a shortened relaxation phase
The skeletal muscle complex known as the triad consists of
a transverse tubule and two terminal cisternae.
During neuromuscular transmission, the axon terminals release __________.
acetylcholine
The cytoplasm of the neuromuscular terminal contains vesicles filled with molecules of the neurotransmitter
acetylcholine
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine (ACh)
Triggering of the muscle action potential occurs after
acetylcholine binds to chemically-gated channels in the motor end plate.
How is acetylcholine (ACh) removed from the synaptic cleft?
acetylcholinesterase (AChE; an enzyme)
A myosin head binds to which molecule to form a cross bridge?
actin
Myosin molecules form cross-bridges when they attach to __________.
actin
Thin filaments are mostly made of the protein
actin
Which of the following proteins contains the active site involved in cross-bridge formation?
actin
The most important factor in decreasing the intracellular concentration of calcium ion after contraction is
active transport of calcium into the sarcoplasmic reticulum.
Creatine phosphate
acts as an energy reserve in muscle tissue.
During the recovery period the body's need for oxygen is increased because
additional oxygen is required to restore energy reserves.
A resting muscle generates most of its ATP by
aerobic metabolism of fatty acids.
What causes the vesicles inside a neuron to fuse with the plasma membrane?
an action potential in the neuron
Decreased blood flow to a muscle could result in all of the following except
an increase in intracellular glycogen.
After heavy exercise, if energy reserves in a muscle are depleted, ________ occurs.
an oxygen debt
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
arrival of an action potential
What causes the myosin head to disconnect from actin?
binding of ATP
The sarcoplasmic reticulum contains __________.
calcium
Active sites on the actin become available for binding after
calcium binds to troponin.
In response to action potentials arriving along the transverse tubules, the sarcoplasmic reticulum releases
calcium ions
In rigor mortis
calcium ions keep binding to troponin. the myosin heads are attached to actin. sustained contractions occur. ATP is depleted.
Smooth muscle contracts when calcium binds to __________ and activates __________.
calmodulin; myosin light chain kinase
The ________ nervous system is composed of the brain and spinal cord.
central
Muscle tissue, one of the four basic tissue groups, consists chiefly of cells that are highly specialized for
contraction
Fatigued muscles signify __________.
decreased pH
Physical evidence that supports the sliding filament theory of muscle contraction includes
decreased width of the H band during contraction.
What is the type of chemical reaction used to rebuild ADP into ATP?
dehydration synthesis
ATP binding leads to which of the following actions?
detaching and resetting cross-bridges
Which of the following is not a function of the nervous system?
direct long-term functions, such as growth
The dense layer of connective tissue that surrounds an entire skeletal muscle is the
epimysium.
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
exocytosis
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
Activities involving eccentric contractions more commonly lead to delayed-onset muscle soreness than concentric or isometric contractions. Which of the following activities is thus a candidate for delayed-onset muscle soreness?
extension of the biceps brachii
Inside a muscle, bundles of single muscle fibers form __________.
fascicles
Muscles that move the eyeball have ________ fibers.
fast
Which of the following is not a function of smooth muscle tissue?
forcing blood from the heart into the major arteries
In the liver, during the Cori cycle,
glucose is produced from lactic acid.
Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products?
glycolysis
A fascicle is a
group of muscle fibers that are encased in the perimysium.
Fast fibers
have low resistance to fatigue and quick twitches.
A muscle producing almost peak tension during rapid cycles of contraction and relaxation is said to be in
incomplete tetanus
Which of the following would not lead to increased oxygen consumption?
increased anaerobic respiration by muscle cells
Heat energy gained from muscle contraction is released by the ________ system.
integumentary
The type of contraction in which the muscle fibers do not shorten is called
isometric
The muscle weakness of myasthenia gravis results from
loss of acetylcholine receptors in the end-plate membrane.
Myofibrils are __________.
made of a series of sarcomeres
When acetylcholine binds to receptors at the motor end plate, the sarcolemma becomes
more permeable to sodium ions.
During activities requiring aerobic endurance,
most of the muscle's energy is produced in mitochondria.
Receptors for acetylcholine are located on the
motor end plate
Bacteria that cause tetanus release a neurotoxin called tetanospasmin. Which of the following components of the neuromuscular junction (NMJ) does this neurotoxin affect directly?
motor neurons
A single motor neuron together with all the muscle fibers it innervates is called a(n)
motor unit
Interactions between actin and myosin filaments of the sarcomere are responsible for
muscle contraction
The neuromuscular junction is a connection between a neuron and a __________.
muscle fiber
During the recovery period following exercise, all of the following are true except
muscle fibers are unable to contract.
In an isotonic contraction,
muscle tension exceeds the load and the muscle lifts the load.
In which of the following would the motor units have the fewest muscle fibers?
muscles that control the eyes
Skeletal muscle fibers are formed from embryonic cells called
myoblasts
Thick filaments are made of the protein
myosin
Which of the following is involved in the power stroke?
myosin
What area of the thick filament binds to actin once its active binding sites are exposed?
myosin cross-bridge (head)
Cross-bridges are portions of
myosin molecules.
Each skeletal muscle fiber is controlled by a motor neuron at a single
neuromuscular junction.
Acetylcholine receptors are primarily located __________.
on the motor end plate
At peak levels of muscle exertion the mitochondria can supply
only about one-third of the energy required by the muscle.
During anaerobic glycolysis,
oxygen is not consumed. ATP is produced. pyruvic acid is produced. carbohydrate is metabolized.
The ability of smooth muscle to function over a wide range of lengths is called
plasticity.
Which of the following best describes the term titin?
protein that accounts for elasticity of resting muscle
Skeletal muscle does each of these EXCEPT __________.
pump blood
You try to pick up an object and discover that it is much heavier than you expected. Which process must occur in the muscle to increase tension so you can pick up the object?
recruitment
What causes the power stroke?
release of ADP and Pi
The role of acetylcholinesterase in the neuromuscular junction is to __________.
remove acetylcholine from the synaptic cleft
The plasma membrane of a skeletal muscle fiber is called the
sarcolemma.
The repeating unit of a skeletal muscle fiber is the
sarcomere.
Z lines define the edges of which of the following?
sarcomeres
In response to an action potential along the transverse tubules, the __________ release(s) calcium ions into the sarcoplasm.
sarcoplasmic reticulum
Which organelle completely surrounds each myofibril inside a muscle fiber?
sarcoplasmic reticulum
Which type of muscle tissue has the greatest effect on the body's heat production?
skeletal
The structural theory that explains how a muscle fiber contracts is called the ________ theory.
sliding filament
The type of muscle fiber that is most resistant to fatigue is the ________ fiber.
slow
Which of the following types of muscle fibers are best adapted for prolonged contraction such as standing all day?
slow fibers
Which of the following best describes the term sarcoplasmic reticulum?
storage and release site for calcium ions
The narrow space between the synaptic terminal and the muscle fiber is the
synaptic cleft.
The end of a neuron, where acetylcholine-filled vesicles are located, is called the __________.
synaptic terminal
When comparing slow muscle fibers to fast muscle fibers, slow fibers
take about three times as long to reach peak tension. are rich in the red protein myoglobin. have much smaller fiber diameters. generate much less tension
At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium, come together to form a
tendon
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 cisternae of the sarcoplasmic reticulum
A muscle produces its highest tension when in complete
tetanus
Which of the following most correctly describes excitation in the context of excitation-contraction coupling in skeletal muscle?
the generation of an action potential in the sarcolemma
Which of the following acts as an ATPase during the contraction cycle of muscle?
the head portion of the myosin molecule
An action potential in the muscle fiber causes __________.
the muscle fiber to contract
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels
What is the synaptic cleft?
the space between the synaptic terminal and the motor end plate
Which of these statements about skeletal muscles is FALSE?
their fibers branch
Myosin molecules form what part of the sarcomere?
thick filament
Which of the following phrases best describes how excitation is coupled to contraction in skeletal muscle fibers?
through calcium release from the sarcoplasmic reticulum
All of the following proteins are part of the thin filaments except
titin
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
The action potential is conducted into a skeletal muscle fiber by
transverse tubules.
T tubules and the terminal cisternae are clustered into structures called __________.
triads
When the sarcomere is at rest, what is covering the active sites on actin?
tropomyosin
At rest, active sites on the actin are blocked by
tropomyosin molecules.
When calcium ion binds to troponin,
tropomyosin rolls away from the active site.
Which of the following causes the active site on actin to be exposed or uncovered?
tropomyosin shifting position
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
troponin
To what regulatory protein does calcium bind during the initiation of the contraction cycle in skeletal muscle fibers?
troponin
What component of the thin filament binds to calcium once calcium is released from the terminal cisternae of the sarcoplasmic reticulum?
troponin
When calcium is released inside a muscle cell, what does it bind to?
troponin
A single contraction-relaxation cycle in a muscle fiber produces a(n)
twitch
Each thin filament consists of
two actin protein strands coiled helically around each other.
Inside a neuron, acetylcholine is contained within __________.
vesicles
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels
Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?
white fast twitch fibers
