A&P - Chapter 9: Muscles And Muscle Tissue

25 July 2022
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question
Which of the following is CORRECTLY paired?
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skeletal muscle: voluntary control
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Muscle tissue does NOT ________.
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product blood cells
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Which type of muscle CANNOT contract without being stimulated by the nervous system?
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skeletal
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Which muscle characteristic describes the ability of muscle to respond to a stimulus?
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excitability
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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?
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Acetylcholine is degraded by acetylcholinesterase
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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?
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Acetylcholine is released by axon terminals of the motor neuron.
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Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.
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extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber
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Calcium entry into the axon terminal triggers which of the following events?
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Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
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Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
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the opening of ligand-gated cation channels
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Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?
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The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
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Which of the following best describes how ACh changes the ion permeability of the sarcolemma?
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ACh binds to receptors in the junctional folds
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Which of the following best describes the role of acetylcholinesterase molecules at the neuromuscular junction?
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Acetylcholinesterase breaks down ACh, which allows chemically gated ion channels to close.
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In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
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acetylcholine (ACh)
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When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
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voltage-gated calcium channels
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What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
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exocytosis
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The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
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Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate.
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How is acetylcholine (ACh) removed from the synaptic cleft?
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acetylcholinesterase (AChE; an enzyme)
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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?
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terminal cisternae of the sarcoplasmic reticulum
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Skeletal muscle cells are grouped into bundles called __________.
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fascicles
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Synaptic vesicles at the neuromuscular junction contain __________.
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acetylcholine
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ACh receptors are found mainly in the __________.
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sarcolemma
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What most directly causes synaptic vesicles to release acetylcholine into the synaptic cleft?
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calcium entering the axon terminal
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Acetylcholine receptors are best characterized as what type of channel?
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chemically gated Na+-K+ channels
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When the chemically gated ion channels open, which ion is mainly responsible for depolarizing the sarcolemma?
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sodium
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What is the primary mechanism by which ACh is cleared from the synaptic cleft?
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broken down by acetylcholinesterase
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What would happen if acetylcholine was not removed from the synaptic cleft?
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Multiple action potentials would occur in the muscle fiber.
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Which of the choices below correctly describes how an action potential generated at the neuromuscular junction (NMJ) is converted to excitation in the muscle fiber?
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An action potential in the motor neuron causes ACh to be released into the synaptic cleft. Binding of ACh to sarcolemma receptors initiates graded potentials.
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How does the shape change of these proteins lead to contraction?
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It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol.
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Which selection correctly describes the role of calcium in coupling?
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Calcium binds to troponin, which moves tropomyosin and exposes the myosin-binding sites on actin.
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Which best describes the initial event in contraction?
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Myosin heads bind to the newly exposed myosin-binding sites on actin to form cross bridges.
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Which of the following statements best summarizes excitation-contraction coupling?
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A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction.
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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?
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Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
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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?
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Calcium release from the sarcoplasmic reticulum initiates the contraction.
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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?
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A series of proteins that control calcium release
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What is name given to the regularly spaced infoldings of the sarcolemma?
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transverse or T tubules
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Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
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Calcium ions
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What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?
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Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
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Which of the following is true concerning the anatomy of a skeletal muscle fiber?
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Myofibrils contain thick and thin filaments.
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The calcium that initiates skeletal muscle contraction is released from what structure(s)?
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terminal cisternae
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Which of the following are composed of myosin?
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thick filaments
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In muscle fibers, which regulatory protein blocks the attachment of myosin heads to actin?
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tropomyosin
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What event most directly triggers the release of calcium from the terminal cisternae?
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action potential propagating down the T tubule
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How do calcium ions initiate contraction in skeletal muscle fibers?
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Calcium ions bind to troponin, changing troponin's shape.
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Which of the following best describes the events of "excitation" in "excitation-contraction coupling"?
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propagation of the action potential along the sarcolemma
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Which of the following best describes the events of "contraction" in "excitation-contraction coupling"?
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cross bridge formation
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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?
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A myosin head bound to actin
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What structure is the functional unit of contraction in a skeletal muscle fiber?
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The sarcomere
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Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?
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Calcium ions are stored in the sarcoplasmic reticulum.
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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?
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ATP binds to the myosin head.
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How does the myosin head obtain the energy required for activation?
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The energy comes from the hydrolysis of ATP.
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What specific event triggers the uncovering of the myosin binding site on actin?
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Calcium ions bind to troponin and change its shape.
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When does cross bridge cycling end?
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Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.
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A muscle cell runs out of ATP. Even though these are cyclic reactions, what step of the cross bridge cycle given is most directly inhibited or terminated?
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cross bridge detachment
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A person dies and within hours, the skeletal muscles develop a locked contraction known as rigor mortis. Calcium ions leak from the sarcoplasmic reticulum into cytoplasm. From your knowledge of cross-bridge cycling, what best explains this rigor?
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Cross bridge detachment cannot occur. Detachment requires ATP, which is only produced during life.
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What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
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arrival of an action potential
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The binding of calcium to which molecule causes the myosin binding sites to be exposed?
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binding of calcium to the protein complex
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A myosin head binds to which molecule to form a cross bridge?
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actin
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What causes the myosin head to disconnect from actin?
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binding of ATP
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What energizes the power stroke?
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hydrolysis of ATP
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What is the role of calcium in the cross bridge cycle?
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Calcium binds to troponin, altering its shape.
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What role does tropomyosin play in the cross bridge cycle?
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The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.
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How does troponin facilitate cross bridge formation?
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Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.
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What, specifically, is a cross bridge?
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myosin binding to actin
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Which event causes cross bridge detachment?
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ATP binding to the myosin head
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Where in the cross bridge cycle does ATP hydrolysis occur?
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during the cocking of the myosin head
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How/when does the myosin head cock back to store energy for the next cycle?
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After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.
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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?
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Myosin heads would remain detached, unable to cock.
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During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?
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There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.
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Thick myofilaments are made of ________.
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myosin
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The major role of the sarcoplasmic reticulum is to regulate ________.
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intracellular levels of Ca2+
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The type of muscle found in the walls of most hollow organs is ________.
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unitary smooth muscle
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The distance between Z discs ________ during muscle contraction.
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decreases
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The response of a motor unit to a single action potential of its motor neuron is called ________.
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a muscle twitch
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Which protein inhibits interaction between actin and myosin to prevent skeletal muscle contraction; and which ions remove the inhibition?
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tropomyosin; calcium ions
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Immediately following the arrival of the stimulus at a skeletal muscle cell there is a short period called the ________ period during which the neurotransmitter is released by exocytosis, diffuses across the synaptic cleft, and binds to its receptors.
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latent
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What is the primary function of wave summation?
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produce smooth, continuous muscle contraction
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What is the role of calcium ions in muscle contraction?
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bind to regulatory sites on troponin to remove contraction inhibition
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The mechanism of contraction in smooth muscle is different from skeletal muscle in that ________.
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the site of calcium regulation differs
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Although there are no sarcomeres, smooth muscle still possesses thick and thin filaments.
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true