Muscle I

24 July 2022
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question
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? norepinephrine dopamine serotonin acetylcholine (ACh)
answer
Ans. acetylcholine (ACh) -acetylcholine is the neurotransmitter found in neuromuscular junctions.
question
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? voltage-gated potassium channels voltage-gated sodium channels voltage-gated calcium channels chemically gated calcium channels
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Ans. voltage-gated calcium channels -Yes, the action potential opens voltage-gated calcium channels and calcium rushes into the axon terminal, leading to the release of the neurotransmitter.
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What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? exocytosis a channel a protein carrier
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Ans. exocytosis -Yes, the synaptic vesicles (where the neurotransmitter is stored) merge with the membrane and release the neurotransmitter by exocytosis.
question
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 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. Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell.
answer
ans. 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. -Yes, sodium enters the cell and causes depolarization. A small amount of potassium also leaves the motor end plate (junctional folds of the sarcolemma).
question
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) and endocytosis into the muscle fiber simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme) acetylcholinesterase (AChE; an enzyme) only
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Ans. simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme) -Acetylcholinesterase breaks down acetylcholine in the synaptic cleft.
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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? sarcolemma T tubule cytosol terminal cisterns (cisternae) of the sarcoplasmic reticulum
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Ans. terminal cisterns (cisternae) of the sarcoplasmic reticulum -Yes, calcium is stored in the terminal cisterns (cisternae) of the sarcoplasmic reticulum until it is released by an action potential.
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What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? arrival of an action potential ATP troponin calcium ion pump
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Ans. arrival of an action potential -Yes, an action potential in the T tubule causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum.
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The binding of calcium to which molecule causes the myosin binding sites to be exposed? troponin myosin tropomyosin actin
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Ans. Troponin -Yes, when calcium binds to troponin, troponin releases tropomyosin, exposing the myosin binding sites.
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A myosin head binds to which molecule to form a cross bridge? actin tropomyosin troponin
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Ans. actin -Yes, the myosin head binds to actin, the major component of thin filaments.
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What causes the myosin head to disconnect from actin? binding of ATP hydrolysis of ATP binding of calcium binding of troponin
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Ans. binding of ATP -Yes, the binding of ATP causes the myosin head to disconnect from actin.
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What causes the power stroke? calcium release of ADP and Pi hydrolysis of ATP binding of ATP
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Ans. release of ADP and Pi -Yes, the hydrolysis of ATP provides the energy for the power stroke. Energy is transferred from ATP to the myosin head.
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Which of the following best summarizes the events of excitation-contraction coupling? Choose the best answer. The actin filament slides towards the sarcomere and the muscle contracts. An acetylcholine signal from the motor neuron is converted into an electrical signal in the muscle fiber. Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle. Cross-bridges release and the muscle relaxes. Submit
answer
Ans. Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle.
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Which of the following statements best describes the neuromuscular junction? Choose the best answer. 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 release of acetylcholine from the axon terminal of the motor neurons the act of myosin and actin sliding past each other in order to produce a contraction
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Ans. the point of synapse between a motor neuron and the muscle fiber that it innervates
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Which of the following structures is/are necessary to initiate the muscle action potential? ryanodine receptor tropomyosin calcium ACh receptor-channels muscle fiber troponin myosin t-tubule motor end plate Ca2+-ATPase actin acetylcholine motor neuron
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ACh receptor-channels, muscle fiber, motor end plate, acetylcholine, motor neuron
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An area that contains many synaptic vesicles filled with acetylcholine
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Axon terminal of motor neuron
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A change in membrane voltage that travels down the T-tubule to cause opening of Ca2+ channels
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Action potential
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An area of muscle fiber membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine
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Motor end plate
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A structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+
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ACh receptor-channel
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Putting the Events at the Neuromuscular Junction in Order: rank from earliest to latest.
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1. Somatic motor neuron delivers action potential. 2. Acetylcholine is released from the axon terminal onto the motor end plate. 3. Net Na+ influx through nicotinic receptors. 4. Muscle fiber depolarizes. 5. Action potential travels down the T-tubule of the muscle fiber.
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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 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.
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Ans. Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together.
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Which of the following best describes the role of calcium (Ca2+ ) in the excitation-contraction coupling reaction? Choose the best answer. Ca2+ will bind directly to tropomyosin, resulting in a conformational shift which reveals the binding sites for myosin on actin. Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach. Ca2+ binds to specific receptors which control the release of ATP into the cytoplasm of the muscle fiber. Ca2+ gives the myosin heads the energy necessary for the power stroke.
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Ans. Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach.
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Putting the Events of Contraction in Order: Rank from earliest to latest.
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1. An action potential that travels down the T-tubule changes the structural confirmation of the DHP L-type Ca2+ channel. 2. Ryanodine receptor channels open. 3. Ca2+ leaves the sarcoplasmic reticulum. 4. Actin and myosin bind to one another. 5. Myosin heads utilize energy from ATP hydrolysis to produce the power stroke. 6. Actin filaments slide toward the M line, shortening the sarcomere.
question
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 cytoplasm of the muscle fiber exhausts all of its available ATP. The voltage created along the t-tubule fades and the muscle fiber membrane returns to a resting potential value. The delivery of action potentials from the motor neuron stops.
answer
Ans. Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.
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Putting It All Together: Put excitation-contraction coupling and muscle relaxation so that they occur in the correct sequential order. Rank from earliest to latest.
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1. Acetylcholine is release from motor neuron. 2. Action potential travels down the T-tubule. 3. Ca2+ is released from the sarcoplasmic reticulum. 4. Myosin generates the power stroke. 5. Ca2+ -ATPase channels actively pump Ca2+ back into the sarcoplasmic reticulum. 6. Ca2+ unbinds from troponin. 7. Actin filament slip back to rest position.
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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. Ca2+ ions would not be actively pumped back into the sarcoplasmic reticulum Na+ 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 The axon terminal of the motor neuron would not release acetylcholine
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Ans. Myosin would not be able to bind to actin in order to cause shortening of the sarcomere
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A patient has damage to one somatic motor neuron. What will this affect? One muscle fiber Many muscles Many muscle fiber types One motor unit
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Ans. One motor unit
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Which is a difference between summation and tetanus? Summation can cause tetanus, but tetanus cannot cause summation . Muscles relax between action potentials in summation but not in tetanus. Sarcomeres shorten in tetanus but not in summation. Muscles reach maximal tension in summation but not in tetanus.
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Ans. Summation can cause tetanus, but tetanus cannot cause summation.
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What happens when skeletal muscle sarcomere length increases beyond about 2.3 micrometers (Ξm)? More myosin heads can bind to the thin filament. Less calcium is released from the SR. Tension decreases. The fiber can produce more force.
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Ans. Tension decreases.
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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 the development of tension 2-3 times more quickly fewer mitochondria
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Ans. the presence of myoglobin
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Which enzyme catalyzes the phosphorylation of ADP? Ca2+-ATPase Phosphocreatine Creatine kinase Na+-K+-ATPase
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Phosphocreatine is the backup energy source of muscle, so it is a substrate and not an enzyme. Ans. Creatine kinase
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Which of the following would stop muscle contraction? Pulling away of tropomyosin from the myosin-binding site on actin A lack of ATP Pumping of calcium ions into the SR Binding of acetylcholine to ACh receptors
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Ans. Pumping of calcium ions into the SR
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How is the energy released by ATP hydrolysis used during the contractile cycle in skeletal muscle? 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 provides energy for the myosin head to pull on the actin filament. This "uncocks" the myosin head.
answer
Ans. It causes rotation of the myosin head, thus "cocking" it.
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What happens when calcium binds troponin? Tropomyosin is pulled away from the myosin-binding site on actin. Troponin releases myosin and activates actin. Troponin binds to actin and causes sarcomere shortening. Troponin changes shape and covers the SR calcium channel, which is a form of negative feedback.
answer
Ans. Tropomyosin is pulled away from the myosin-binding site on actin.
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__________ occurs when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere. Myosin head rotation An action potential A power stroke Hydrolysis
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Ans. A power stroke
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Which of the following would NOT change size during a muscle contraction? I band Sarcomere A band H zone
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A band
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Which of the following is the smallest structure? Myofibril Muscle fascicle Myosin Muscle fiber
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Ans. Myosin
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Which type of skeletal muscle causes two bones to move away from one another? Tendon Antagonist Flexor Extensor
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Ans. Extensor
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Which is a similarity between summation and tetanus? Both occur when there are less frequent action potentials. Both reach maximum tension. In both, muscle contraction is shorter than muscle action potentials. In both, muscle action potentials are shorter than muscle contraction.
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Ans. In both, muscle action potentials are shorter than muscle contraction. Submit
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What immediately follows hydrolysis of ATP during muscle contraction? The power stroke Rotation of the myosin head to the cocked position Myosin binding to actin Myosin releases actin
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Ans. Rotation of the myosin head to the cocked position
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Thick filaments are made up of __________. titin myosin actin nebulin
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ans. myosin
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Because of their shape, muscle cells are also known as __________. muscle fibers fascicles tubules myofibrils
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Ans. muscle fibers
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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)? An antagonistic muscle produces the opposite movement. 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. The muscle that produces flexion relaxes to produce extension.
answer
Ans. An antagonistic muscle produces the opposite movement.
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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 ATP bound to a myosin head A myosin head bound to actin Calcium bound to troponin
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Ans. A myosin head bound to actin -Yes! As soon as the activated myosin head forms a cross bridge with actin, the power stroke begins.
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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
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Ans. The sarcomere -Yes! A sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.
question
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 transverse tubules. Calcium ions are stored in the nuclei. Calcium ions are stored in the sarcoplasmic reticulum.
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Ans. Calcium ions are stored in the sarcoplasmic reticulum. -Yes! Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.
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After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment? Acetylcholine binds to receptors in the junctional folds of the sarcolemma. Calcium ions bind to troponin. ATP binds to the myosin head. ADP and inorganic phosphate are bound to the myosin head.
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Ans. ATP binds to the myosin head. -Yes! The binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next power stroke.
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How does the myosin head obtain the energy required for activation? The energy comes from the hydrolysis of ATP. The energy comes from the hydrolysis of GTP. The energy comes from the direct phosphorylation of ADP by creatine phosphate. The energy comes from oxidative phophorylation.
answer
Ans. The energy comes from the hydrolysis of ATP. -Yes! Myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activates the myosin head.
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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. Calcium ions bind to tropomyosin and change its shape. Calcium ions bind to troponin and change its shape. Sodium ions bind to troponin and change its shape.
answer
Ans. Calcium ions bind to troponin and change its shape. -Yes! The shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.
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When does cross bridge cycling end? Cross bridge cycling ends when ATP binds to the myosin head. Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open. 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 ions are passively transported back into the sarcoplasmic reticulum.
answer
Ans. Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. -Yes! The sarcoplasmic reticulum contains Ca2+-ATPases that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to its resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.
question
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 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. Excitation refers to the propagation of action potentials along the axon of a motor neuron.
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Ans. Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. -Yes! These action potentials set off a series of events that lead to a contraction.
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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. Voltage-sensitive proteins change shape. Action potentials propagate into the interior of the skeletal muscle fiber. Sodium release from the sarcoplasmic reticulum initiates the contraction.
answer
Ans. Calcium release from the sarcoplasmic reticulum initiates the contraction. -Yes! Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle cells. It is especially abundant and convoluted in skeletal muscle cells. It functions in the storage, release, and reuptake of calcium ions.
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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. Myosin cross-bridge binding sites. Potassium leak channels. Voltage-gated sodium channels.
answer
Ans. A series of proteins that control calcium release. -Yes! When action potentials propagate along T-tubules, a voltage-sensitive protein changes shape and triggers a different protein to open it's channels, resulting in the release of calcium from the terminal cisternae.
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What is name given to the regularly spaced infoldings of the sarcolemma? motor endplates transverse or T tubules sarcoplasmic reticulum terminal cisternae
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Ans. transverse or T tubules -Yes! T tubules penetrate a skeletal muscle fiber and provide a pathway for excitation into the interior.
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Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? Acetylcholine. Sodium ions. Action potentials. Calcium ions.
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Ans. Calcium ions. -Yes! Action potentials propagating down the T-tubule cause a voltage-sensitive protein to change shape. This shape change opens calcium release channels in the sarcoplasmic reticulum, allowing calcium ions to flood the sarcoplasm. This flood of calcium ions is directly responsible for the coupling of excitation to contraction in skeletal muscle fibers.
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What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? A skeletal muscle fiber is innervated by multiple motor neurons. A motor neuron typically innervates only one skeletal muscle fiber. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. Motor neurons always innervate thousands of skeletal muscle fibers.
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Ans. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. -Yes! There are many more skeletal muscle fibers than there are motor neurons. The ratio of neurons to fibers varies from approximately one to ten to approximately one to thousands.
question
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. Acetylcholine is transported back into the axon terminal by a reuptake mechanism. Acetylcholine diffuses away from the cleft. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis.
answer
Ans. Acetylcholine is degraded by acetylcholinesterase. -Yes! Acetylcholinesterase is an enzyme that degrades acetylcholine. This degradation results in a rapid cessation of the acetylcholine signal and a swift removal from the cleft.
question
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 binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein. Acetylcholine is released and moves across the synaptic cleft bound to a transport protein. When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.
answer
Ans. Acetylcholine is released by axon terminals of the motor neuron. -Yes! Acetylcholine is released into the synaptic cleft via exocytosis.
question
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 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 spinal cord to the sarcolemma of a skeletal muscle fiber
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Ans. extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber -Yes! The cell bodies of motor neurons to muscles in the head and neck are located in the brain. The cell bodies of motor neurons to the rest of our muscles are located in the spinal cord.
question
Calcium entry into the axon terminal triggers which of the following events? Acetylcholine binds to its receptor. 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.
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Ans. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. Submit -Yes! When synaptic vesicles fuse to the plasma membrane, acetylcholine is released via exocytosis.
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Acetylcholine binds to its receptor in the sarcolemma and triggers __________. the opening of calcium-release channels the opening of ligand-gated anion channels the opening of ligand-gated cation channels the opening of voltage-gated calcium channels
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Ans. the opening of ligand-gated cation channels -Yes! These channels permit sodium ions to diffuse inward and potassium ions to diffuse outward.
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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. 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. 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.
answer
Ans. The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients. -Yes! The resting membrane potential of all cells is negative (inside compared to outside). Therefore, given the direction of the chemical and electrical gradients, more sodium ions diffuse inward than potassium ions diffuse outward.
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Which of the following is a similarity between isometric and isotonic contractions? Sarcomeres lengthen. Muscles shorten. A load is moved. Tension develops.
answer
Ans. Tension develops.
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A muscle moving a load goes through two phases of contraction. Which phase occurs first, and what happens inside the muscle during this phase? Isotonic; elastic elements stretch Isotonic; sarcomeres shorten greatly Isometric; sarcomeres shorten greatly Isometric; elastic elements stretch
answer
Ans. Isometric; elastic elements stretch
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Which of the following structure(s) must always be present in order for you to have a skeletal muscle reflex arc? afferent neuron integrating center receptor target cell stimulus efferent neuron interneuron
answer
Ans. afferent neuron, integrating center, receptor, target cell, stimulus, efferent neuron
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Skeletal muscle reflexes can be either monosynaptic or polysynaptic. Which of the following statements is true regarding monosynaptic versus polysynaptic skeletal muscle reflexes? Choose the best answer. Polysynaptic reflexes are composed of only two neurons between the stimulus and target cell, while monosynaptic reflexes contain three or more neurons. Monosynaptic reflexes are composed of only two neurons between the stimulus and target cell, while polysynaptic reflexes contain three or more neurons. Both monosynaptic and polysynaptic reflexes are composed of only two neurons between the stimulus and target cell. Both monosynaptic and polysynaptic reflexes are composed of three or more neurons between the stimulus and target cell.
answer
Ans. Monosynaptic reflexes are composed of only two neurons between the stimulus and target cell, while polysynaptic reflexes contain three or more neurons.
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Below is a picture of the patellar tendon reflex arc. Use this figure to answer the following question in the coaching activity. Application of Knowledge to the Patellar Tendon Reflex.
answer
Stimulus: Stretch of the muscle Receptor: Muscle spindle Afferent neuron: Action potential travels through sensory neuron Integrator: Synapse of sensory neuron in spinal cord Target: Hamstring muscle, Quadriceps muscle, Response: Relaxation of hamstrings, Contraction of quadriceps
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Use the same figure as in Part D to answer the following question. Is the patellar tendon reflex a monosynaptic or polysynaptic reflex? Choose the best answer. polysynaptic monosynaptic both neither
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Both
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Ordering the Events of the Crossed Extensor Reflex: Rank from earliest to latest.
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1. Individual steps on thumbtack 2. Pain stimulates nociceptor 3.Sensory neurons delivers information to the spinal cord 4. Withdrawal reflex pulls limb away from tack 5. Crossed extensor reflex supports body,
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Is the cross extensor reflex a monosynaptic or polysynaptic reflex? Choose the best answer. monosynaptic polysynaptic both neither
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Ans. polysynaptic
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What would happen if a person were to sustain an injury that severed the alpha motor neurons leading to the leg muscles in the crossed extensor portion of the reflex? Choose the best answer. A person would not be able to feel a painful stimulus. A person would not be able to withdraw their leg in the presence of a painful stimulus. The sensory signal delivered by the afferent neuron would not be properly transduced at the spinal cord. Upon a painful stimulus, a person would withdraw their leg and then lose their balance and possibly fall over.
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Ans. Upon a painful stimulus, a person would withdraw their leg and then lose their balance and possibly fall over.
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The three types of proprioceptors include muscle spindles, Golgi tendon organs, and __________. spatial receptors intrafusal fibers joint capsules joint receptors
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Ans. joint receptors
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Which stimulus initiates a flexion reflex? Pain Loss of balance Touch Sound
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Ans. Pain
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What is the response of a muscle stretch reflex? Contraction of the agonist muscle Inhibition of alpha motor neuron activity Relaxation of the agonist muscle Contraction of the antagonist muscle
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Ans. Contraction of the agonist muscle
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A muscle spindle is a tonic proprioceptor. What happens to the signal on the sensory afferent neurons that come from the spindle when the muscle spindle is stretched? The signal is inhibited. The signal increases in frequency. The signal begins as the stretch begins. The signal increases in magnitude.
answer
Ans. The signal increases in frequency.
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Choose the FALSE statement about reflexes. Reflexes are useful primarily for medical diagnosis; they serve little practical purpose otherwise. The crossed extensor reflex is a postural reflex to maintain balance when one foot is lifted from the ground. The limb withdrawal that occurs during a withdrawal reflex primarily involves flexor muscles. Some reflexes involve activity in inhibitory neurons, which can cause a muscle to relax.
answer
Ans. Reflexes are useful primarily for medical diagnosis; they serve little practical purpose otherwise.
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Which structure responds to muscle stretch? Golgi tendon organ Alpha motor neuron Muscle spindle Extrafusal muscle fibers
answer
Ans. Muscle spindle
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Myasthenia gravis is a disease resulting from an autoimmune attack on the ACh receptors of the motor end plate. Binding of antibodies to the ACh receptors results in generalized muscle weakness that progresses as more ACh receptors are destroyed. Which of the following medications would help alleviate the muscle weakness? a drug that blocks the release of acetylcholine (botulinum toxin) a drug that binds to the acetylcholine receptor and prevents it from opening (curare) a drug that binds to and inactivates acetylcholinesterase (neostigmine) a drug that prevents acetylcholine from being loaded into synaptic vesicles (vesamicol)
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Ans. a drug that binds to and inactivates acetylcholinesterase (neostigmine)
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Inadequate calcium in the neuromuscular junction would directly affect which of the following processes? Breakdown of acetylcholine by acetylcholinesterase Depolarization of the junctional folds Conduction of action potentials by the motor neuron Release of acetylcholine from the synaptic vesicles
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Ans. Release of acetylcholine from the synaptic vesicles -Calcium ions enter the axon terminal when voltage-gated calcium channels open in response to the arrival of an action potential. The presence of calcium causes synaptic vesicles to release acetylcholine into the synaptic cleft.
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What structure most directly stimulates a skeletal muscle fiber to contract? Motor neuron Voltage-gated calcium channels Synaptic cleft Acetylcholinesterase
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Ans. Motor neuron -The motor neuron transmits action potentials from the brain or spinal cord to muscle fibers by releasing acetylcholine at the neuromuscular junction.
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neuromuscular junction at rest
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-No Na+ diffusion, chemically-gated channels closed, calcium channels closed, more negative charges inside sarcolemma, Ach in synaptic vesicles
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neuromuscular junction active
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Ach in synpatic cleft, chemically-gated channels open, less negative charges inside sarcolemma, Na+ diffusion, calcium channels open
question
Match the term in the left column to the blanks near their definition on the right.
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-Calcium channel : a type of voltage-gated ion channel located on the axon terminal. -Acetylcholinesterase : enzyme located in the synaptic cleft that breaks down acetylcholine. -Sodium channel : a type of voltage-gated ion channel located on the sarcolemma of the muscle fiber. -Synaptic cleft : the space between the axon terminal and junctional folds. -Acetylcholine : neurotransmitter that stimulates skeletal muscle contraction. -Acetylcholine receptor : a type of chemically-gated ion channel located on the junctional folds of the muscle fiber. -Synaptic vesicle : membranous sac located in the axon terminal that contains neurotransmitter.
question
Arrange the sequence of events at the NMJ from first to last. -Rank the sequence of events at the NMJ that initiate an action potential in the muscle fiber, from first to last.
answer
1. Action potential arrives at the axon terminal. 2. Calcium ions enter the axon terminal. 3. Synaptic vesicles fuse to membrane of axon terminal. 4. Acetylcholine is released into the synaptic cleft. 5. Acetylcholine binds to its receptors on the junctional folds. 6. Junctional folds become depolarized. 7. Action potential is initiated on the sarcolemma.
question
Drag the labels onto the diagram to label the steps of smooth muscle activation and deactivation.
answer
A) smooth muscle contraction 1. Ca++ from the ECF and sarcoplasmic reticulum increases cystolic ca++ contractions 2. Ca++ calmodulin activates myosin light chain kinase 3. myosin light chain kinase phosphorylates myosin heads increasing myosin ATPase activity 4. phosphorylated myosin forms myosin-actin crossbridges, creating muscle tension B) 1.Ca++ concentration decreases as it is pumped out of the cytosol into the ECF or into the sarcoplasmic reticulum 2. Ca++ unbinds from calmodulin, myosin light chain kinase activity decreases 3. myosin phosphatase from myosin light chains, decreasing myosin activity 4. less myosin ATPase activity results in decreased cross-bridge cycling
question
How are cardiac muscle cells similar to smooth muscle cells? They lack striations. They are branched. They do not contain sarcomeres. They are electrically linked to one another.
answer
Ans. They are electrically linked to one another.
question
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. Sarcomeres are Actin is Calcium ion are used in regulation of contraction of Myosin is
answer
Ans. Sarcomeres are
question
Which type(s) of muscle fiber is/are uninucleate? Smooth only Smooth and skeletal Skeletal and cardiac Smooth and cardiac
answer
Ans. Smooth and cardiac
question
Which of the following is a similarity between slow wave potentials and pacemaker potentials? Both involve depolarizations followed by repolarizations. Both create regular rhythms of contraction. Both always fire action potentials. Both have subthreshold depolarizations.
answer
Ans. Both involve depolarizations followed by repolarizations.
question
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. Ca2+ comes from the extracellular fluid and the SR. Relaxation occurs when calmodulin is released from its receptors. Myosin pulls on troponin instead of actin.
answer
Ans. Ca2+ comes from the extracellular fluid and the SR.
question
A patient is born with a mutation in her calmodulin gene. This could affect the contraction of ________ muscles. smooth cardiac and skeletal smooth and cardiac all three types of
answer
Ans. smooth