Ch. 12
The nervous system avoids muscle fatigue during submaximal contraction by always recruiting fast-twitch motor units. synchronous recruitment. asynchronous recruitment. always recruiting slow-twitch motor units.
asynchronous recruitment.
What structure is the functional unit of contraction in a skeletal muscle fiber? The cross bridge The junctional folds of the sarcolemma The sarcomere The triad
The sarcomere
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? ATP troponin calcium ion pump arrival of an action potential
arrival of an action potential
What, specifically, is a cross bridge? calcium binding to troponin tropomyosin covering the active sites on actin ATP binding to the myosin head myosin binding to actin
myosin binding to actin
An important difference between single-unit and multiunit smooth muscle is the closely controlled individual fibers in single-unit smooth muscle to allow fine control and graded contractions by selective activation. ability of single-unit fibers to change into multiunit fibers when needed. longer actin and myosin filaments in multiunit smooth muscle, which allow coordination of contraction. numerous gap junctions in single-unit smooth muscle, which allow many cells to work together as a sheet.
numerous gap junctions in single-unit smooth muscle, which allow many cells to work together as a sheet.
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? T tubule cytosol sarcolemma terminal cisterns (cisternae) of the sarcoplasmic reticulum
terminal cisterns (cisternae) of the sarcoplasmic reticulum
Put these events in the correct chronological sequence: 1. End-plate potentials trigger action potentials. 2. Transverse tubules bring potentials into the interior of the cell. 3. Acetylcholine binds to receptors on the motor end plate. 4. Ca2+ is released from the sarcoplasmic reticulum. 3, 1, 2, 4 2, 1, 4, 3 1, 2, 3, 4 4, 3, 2, 1 3, 1, 4, 2
3, 1, 2, 4
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge? Troponin bound to tropomyosin Calcium bound to troponin ATP bound to a myosin head A myosin head bound to actin
A myosin head bound to actin
__________ occurs when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere. A power stroke Myosin head rotation Hydrolysis An action potential
A power stroke
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. Voltage-gated sodium channels. Potassium leak channels. A series of proteins that control calcium release
A series of proteins that control calcium release
Which event causes cross bridge detachment? ATP binding to the myosin head release of calcium from troponin release of ADP and inorganic phosphate from the myosin head nervous input ends
ATP binding to the myosin head
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment? Calcium ions bind to troponin. ATP binds to the myosin head. ADP and inorganic phosphate are bound to the myosin head. Acetylcholine binds to receptors in the junctional folds of the sarcolemma.
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 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 diffuses away from the cleft.
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. 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. 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.
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 Ca2+ from the sarcoplasmic reticulum. Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together. Actin pushes on myosin to shorten its length, thereby shortening the muscle. An action potential travels down the axon of a motor neuron in order to release acetylcholine onto the motor end plate.
Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together.
How/when does the myosin head cock back to store energy for the next cycle? The power stroke cocks the myosin head. The sliding of the actin myofilament during the power stroke re-cocks myosin heads that have previously delivered their power stroke. when ADP is released from the myosin head After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.
After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur? Binding causes voltage-gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell. Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium 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.
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.
Match the structures with the accurate description. A. muscle fiber B. fascicle C. sarcolemma D. myofibril E. t-tubules the muscle cell membrane
C. Sarcolemma
The contraction cycle is initiated by the rise in ________ released from the sarcoplasmic reticulum (SR). Na+ Ca2+ K+
Ca2+
Which ion stimulates shape changes at the beginning of skeletal muscle contraction? K+ Acetylcholine Na+ Ca2+
Ca2+
How does the process of smooth muscle contraction differ from contraction in skeletal muscle? There is no active myosin ATPase producing energy for the myosin heads. Myosin pulls on troponin instead of actin. Ca2+ comes from the extracellular fluid and the SR. Relaxation occurs when calmodulin is released from its receptors.
Ca2+ comes from the extracellular fluid and the SR.
Which of the following is the most direct cause of muscle relaxation? Choose the best answer. Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites. The voltage created along the t-tubule fades and the muscle fiber membrane returns to a resting potential value. The cytoplasm of the muscle fiber exhausts all of its available ATP. The delivery of action potentials from the motor neuron stops.
Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.
Which of the following best describes the role of calcium (Ca2+ ) in the excitation-contraction coupling reaction? Choose the best answer. Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach. Ca2+ will bind directly to tropomyosin, resulting in a conformational shift which reveals the binding sites for myosin on actin. Ca2+ gives the myosin heads the energy necessary for the power stroke. Ca2+ binds to specific receptors which control the release of ATP into the cytoplasm of the muscle fiber.
Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach.
The relaxation of skeletal muscle relies on the activity of the ________, which decreases cytoplasmic calcium concentration. ryanodine receptor acetylcholine receptor Ca2+-ATPase dihydropyridine (DHP) receptor (L-type calcium channel)
Ca2+-ATPase
What is the role of calcium in the cross bridge cycle? Calcium binds to myosin, causing the myosin head to release from the actin myofilament. Calcium binds to active sites on actin, forming the cross bridge. Calcium binds to troponin, exposing the active site on troponin. Calcium binds to troponin, altering its shape.
Calcium binds to troponin, altering its shape.
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 mitochondria. Calcium ions are stored in the nuclei. Calcium ions are stored in the sarcoplasmic reticulum. Calcium ions are stored in the transverse tubules.
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 tropomyosin and change its shape. Sodium ions bind to troponin and change its shape. Calcium ions bind to troponin and change its shape. Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm.
Calcium ions bind to troponin and change its shape
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? Action potentials. Calcium ions. Sodium ions. 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? 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. Voltage-sensitive proteins change shape.
Calcium release from the sarcoplasmic reticulum initiates the contraction.
When does cross bridge cycling end? Cross bridge cycling ends when ATP binds to the myosin head. 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 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.
Match the structures with the accurate description. A. muscle fiber B. fascicle C. sarcolemma D. myofibril E. t-tubules inward extensions of the muscle cell membrane
E. t-tubules
Which is NOT a property of single-unit smooth muscles? Only some of the smooth muscle cells are associated with autonomic neuron axon terminals. Electrical responses travel directly between cells. Their contraction occurs in a coordinated manner. Each cell functions independent of its neighbor. Smooth muscle cells are connected by gap junctions.
Each cell functions independent of its neighbor.
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 shape change that occurs in voltage-sensitive proteins in 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, in this case, refers to the propagation of action potentials along the sarcolemma.
How is the energy released by ATP hydrolysis used during the contractile cycle in skeletal muscle? It provides energy for the myosin head to pull on the actin filament. This "uncocks" the myosin head. ATP hydrolysis stabilizes actin to prevent actin filament's shortening during contraction. It causes rotation of the myosin head, thus "cocking" it. It allows the release of calcium from the SR.
It causes rotation of the myosin head, thus "cocking" it.
Which of the following processes produces 36 ATP? Krebs cycle and oxidative phosphorylation glycolysis hydrolysis of creatine phosphate
Krebs cycle and oxidative phosphorylation
Which is NOT a correct comparison of cardiac myocytes to other muscle cell types? Like smooth muscle cells, some cardiac myocytes have pacemaker potentials. Like skeletal muscle cells, actin and myosin are organized into sarcomeres. Like smooth muscle cells, cardiac muscle is under hormonal control. Like some smooth muscle cells, cardiac myocytes are electrically coupled. Like skeletal muscle, contraction of cardiac muscle is under autonomic nervous control.
Like skeletal muscle, contraction of cardiac muscle is under autonomic nervous control.
What structure most directly stimulates a skeletal muscle fiber to contract? Acetylcholinesterase Voltage-gated calcium channels Motor neuron Synaptic cleft
Motor neuron
Which of the following best summarizes the events of excitation-contraction coupling? Choose the best answer. Cross-bridges release and the muscle relaxes. An acetylcholine signal from the motor neuron is converted into an electrical signal in the muscle fiber. The actin filament slides towards the sarcomere and the muscle contracts. Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle.
Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle.
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? Tropomyosin would not move, and the active sites on actin would not be exposed. Myosin heads would remain attached to actin, unable to perform the power stroke. Myosin heads would remain attached to actin, unable to detach. Myosin heads would remain detached, unable to cock.
Myosin heads would remain detached, unable to cock.
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. Na+ ions would not be able to flow into the muscle cell in order to depolarize it Ca2+ ions would not be actively pumped back into the sarcoplasmic reticulum The axon terminal of the motor neuron would not release acetylcholine Myosin would not be able to bind to actin in order to cause shortening of the sarcomere
Myosin would not be able to bind to actin in order to cause shortening of the sarcomere
A patient has damage to one somatic motor neuron. What will this affect? Many muscle fiber types Many muscles One muscle fiber One motor unit
One motor unit
________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle. Glucose Protein Fatty acid Phosphocreatine
Phosphocreatine
The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________. ATP is used to rephosphorylate creatine into creatine phosphate. Oxygen rebinds to myoglobin. Glycogen is synthesized from glucose molecules. Pyruvic acid is converted back to lactic acid.
Pyruvic acid is converted back to lactic acid.
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes? Breakdown of acetylcholine by acetylcholinesterase Depolarization of the junctional folds Release of acetylcholine from the synaptic vesicles Conduction of action potentials by the motor neuron
Release of acetylcholine from the synaptic vesicles
Compared with skeletal and cardiac muscle, which of the following is not in smooth muscle? ____ in skeletal and cardiac muscle but not in smooth muscle. Calcium ion are used in regulation of contraction of Actin is Sarcomeres are Myosin is
Sarcomeres are
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. Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. Acetylcholine binds to its receptor.
Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
What role does tropomyosin play in the cross bridge cycle? Tropomyosin moves the actin filament relative to the myosin filament. Tropomyosin binds to calcium, causing muscle relaxation. The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form. 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.
How does the myosin head obtain the energy required for activation? 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. The energy comes from the hydrolysis of ATP.
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. Potassium ions diffuse inward 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. 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 inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
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. 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. Calcium blocks the active sites on actin.
There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.
How are cardiac muscle cells similar to smooth muscle cells? They are branched. They lack striations. They do not contain sarcomeres. They are electrically linked to one another.
They are electrically linked to one another.
Which happens when a myofibril contracts? Thin and thick filaments slide past each other, but do not change in length. Thick filaments contract, but thin filaments slide. Thin and thick filaments contract as they slide past each other. Thin filaments contract, but thick filaments slide.
Thin and thick filaments slide past each other, but do not change in length.
What happens when calcium binds troponin? Tropomyosin is pulled away from the myosin-binding site on actin. Troponin binds to actin and causes sarcomere shortening. Troponin releases myosin and activates actin. 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.
How does troponin facilitate cross bridge formation? Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin. Troponin hydrolyzes ATP, which provides the energy necessary for cross bridges to form. Troponin moves away from the active sites on actin, permitting cross bridge formation. Troponin gathers excess calcium that might otherwise block actin's progress.
Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.
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 skeletal muscle fiber is innervated by multiple motor neurons. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. A motor neuron typically innervates only one skeletal muscle fiber.
Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? serotonin acetylcholine (ACh) norepinephrine dopamine
acetylcholine(ACh)
A myosin head binds to which molecule to form a cross bridge? actin tropomyosin troponin
actin
Each myosin head has a binding site for ATP only. calcium only. calcium and ATP. actin and ATP. actin only.
actin and ATP.
In order for high-force crossbridges to form in contracting skeletal muscle, calcium must bind to calmodulin to phosphorylate the myosin. phosphorylate the troponin to move the tropomyosin. bind to troponin which moves the tropomyosin. phosphorylate the tropomyosin which moves it. bind to tropomyosin which moves the troponin.
bind to troponin which moves the tropomyosin.
What causes the myosin head to disconnect from actin? binding of ATP binding of calcium binding of troponin hydrolysis of ATP
binding of ATP
During heavy exercise, the ATP requirements of active muscle are likely to be met by metabolism of carbohydrates. fatty acids. nucleotides. protein.
carbohydrates
The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a channel for both Na+ and K+. Ca2+ channel. Na+ channel. ryanodine receptor.
channel for both Na+ and K+.
What is the type of chemical reaction used to rebuild ADP into ATP? hydrolysis rehydration synthesis dehydration synthesis
dehydration synthesis
The action potential traveling along the t-tubule changes the conformation of the dihydropyridine (DHP) receptor (L-type calcium channel). Ca2+ ATPase. acetylcholine receptor. ryanodine receptor.
dihydropyridine (DHP) receptor (L-type calcium channel).
Where in the cross bridge cycle does ATP hydrolysis occur? during the movement of tropomyosin to expose the active sites on actin during the power stroke during the cocking of the myosin head during the removal of calcium from troponin
during the cocking of the myosin head
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? a channel a protein carrier exocytosis
exocytosis
Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________. 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 to the sarcolemma of a skeletal muscle fiber
extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber
Which fibers fatigue sooner? fast-twitch fibers slow-twitch fibers
fast-twitch fibers
Which fibers generate more force? fast-twitch fibers slow-twitch fibers
fast-twitch fibers
Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products? Krebs cycle and oxidative phosphorylation glycolysis hydrolysis of creatine phosphate
glycolysis
Within a single fiber, the tension developed during a twitch depends upon the amplitude of the action potential. duration of the stimulus. length of the sarcomeres prior to contraction. length of the thick filament.
length of the sarcomeres prior to contraction.
Which is a characteristic of slow-twitch oxidative skeletal muscle fibers? long contraction duration only high capillary density only few mitochondria only long contraction duration, few mitochondria, and high capillary density long contraction duration and high capillary density
long contraction duration and high capillary density
a single muscle cell Match the structures with the accurate description. A. muscle fiber B. fascicle C. sarcolemma D. myofibril E. t-tubules
muscle fiber
Thick filaments are made up of __________. titin myosin nebulin actin
myosin
A motor unit consists of one neuron and all the skeletal muscle fibers it controls. one skeletal muscle fiber and the neuron that controls that fiber. one axon terminal branch and the myofibrils it controls. one skeletal muscle fiber and all the neurons that control that fiber.
one neuron and all the skeletal muscle fibers it controls.
Skeletal muscle fibers with the greatest endurance rely on ________ for energy. anaerobic glycolysis ketone body degradation lactic acid accumulation oxidative phosphorylation
oxidative phosphorylation
The function of transverse tubules is to store Ca2+ ions inside the muscle fiber. rapidly move action potentials to the interior of the muscle fiber. conduct ATP molecules out of the mitochondria throughout the sarcoplasm. ensure a supply of glycogen throughout the muscle sarcoplasm.
rapidly move action potentials to the interior of the muscle fiber.
What causes the power stroke? hydrolysis of ATP calcium binding of ATP release of ADP and Pi
release of ADP and Pi
How is acetylcholine (ACh) removed from the synaptic cleft? 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 simple diffusion away from the synaptic cleft and endocytosis into the muscle fiber
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
A patient is born with a mutation in her calmodulin gene. This could affect the contraction of ________ muscles. smooth all three types of smooth and cardiac cardiac and skeletal
smooth
When a skeletal muscle cell contracts and the muscle shortens, the actin ATPase allows the actin molecule to swivel. some myosin heads are forming crossbridges as others are releasing them. the position of an actin molecule relative to a myosin molecule does not change. myosin heads generate a single power stroke. the actin molecule swivels during the power stroke.
some myosin heads are forming crossbridges as others are releasing them.
The function of the titin protein is to cover the myosin binding site on the actin molecule. release calcium during contraction. interact with actin during contraction. pull Z lines together during contraction. stabilize the position of the contractile filaments.
stabilize the position of the contractile filaments.
Acetylcholine binds to its receptor in the sarcolemma and triggers __________. the opening of ligand-gated cation channels the opening of ligand-gated anion channels the opening of voltage-gated calcium channels the opening of calcium-release channels
the opening of ligand-gated cation channels
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 point of synapse between a motor neuron and the muscle fiber that it innervates 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
Compared to fast-twitch glycolytic fibers (type IIX), slow-oxidative muscle fibers (type I) are characterized by a smaller diameter and __________. the presence of myoglobin faster pumping of Ca2+ into the SR fewer mitochondria the development of tension 2-3 times more quickly
the presence of myoglobin
What is name given to the regularly spaced infoldings of the sarcolemma? transverse or T tubules sarcoplasmic reticulum motor endplates terminal cisternae
transverse or T tubules
The binding of calcium to which molecule causes the myosin binding sites to be exposed? tropomyosin actin myosin troponin
troponin
Smooth muscle cells do not have which protein(s)? tropomyosin only troponin only myosin only troponin and tropomyosin actin only
troponin only
Relative to skeletal muscle, smooth muscle uses less energy to generate a given amount of force and can sustain contractile force without fatigue. 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. only uses calcium from the sarcoplasmic reticulum and extracellular space. only can sustain contractile force without fatigue. only uses less energy to generate a given amount of force.
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.
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 calcium channels voltage-gated potassium channels
voltage-gated calcium channels
Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP? red slow twitch fibers white fast twitch fibers
white fast twitch fibers
