Podcast
Questions and Answers
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels
When comparing complete tetanus with unfused (incomplete) tetanus, which statement is true?
When comparing complete tetanus with unfused (incomplete) tetanus, which statement is true?
Match the following structures with their descriptions:
Match the following structures with their descriptions:
A band = Contains both thick and thin filaments I band = Contains only thin filaments Z disk = Attachment site for thin filaments H zone = Contains only thick filaments M line = Middle of the sarcomere, attachment for thick filaments
What is the role of calcium in the cross bridge cycle?
What is the role of calcium in the cross bridge cycle?
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What role does tropomyosin play in the cross bridge cycle?
What role does tropomyosin play in the cross bridge cycle?
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How does troponin facilitate cross bridge formation?
How does troponin facilitate cross bridge formation?
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What, specifically, is a cross bridge?
What, specifically, is a cross bridge?
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Which event causes cross bridge detachment?
Which event causes cross bridge detachment?
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Where in the cross bridge cycle does ATP hydrolysis occur?
Where in the cross bridge cycle does ATP hydrolysis occur?
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How/when does the myosin head cock back to store energy for the next cycle?
How/when does the myosin head cock back to store energy for the next cycle?
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BMD (2,3-butanedione 2-monoxime) 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?
BMD (2,3-butanedione 2-monoxime) 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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During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?
During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?
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What happens when calcium binds to troponin?
What happens when calcium binds to troponin?
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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 (i.e., extension at the elbow)?
Skeletal muscle moves a bone at a joint, such as flexing the forearm at the elbow. How is the opposite action produced (i.e., extension at the elbow)?
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Which of the following occurs when a myofibril contracts?
Which of the following occurs when a myofibril contracts?
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What immediately follows hydrolysis of ATP during muscle contraction?
What immediately follows hydrolysis of ATP during muscle contraction?
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What is it called when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere?
What is it called when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere?
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Compared to fast-twitch glycolytic fibers (type IIb), slow-oxidative muscle fibers (type I) are characterized by a smaller diameter, less stored glycogen, and ________.
Compared to fast-twitch glycolytic fibers (type IIb), slow-oxidative muscle fibers (type I) are characterized by a smaller diameter, less stored glycogen, and ________.
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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?
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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What structure is the functional unit of contraction in a skeletal muscle fiber?
What structure is the functional unit of contraction in a skeletal muscle fiber?
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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?
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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After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?
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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How does the myosin head obtain the energy required for activation?
How does the myosin head obtain the energy required for activation?
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What specific event triggers the uncovering of the myosin binding site on actin?
What specific event triggers the uncovering of the myosin binding site on actin?
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When does cross bridge cycling end?
When does cross bridge cycling end?
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A flexor is a skeletal muscle whose shortening moves attached bones
A flexor is a skeletal muscle whose shortening moves attached bones
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The function of transverse tubules is to
The function of transverse tubules is to
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When a skeletal muscle cell contracts and the muscle shortens,
When a skeletal muscle cell contracts and the muscle shortens,
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As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately
As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately
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The molecular event that occurs immediately after the power stroke is the
The molecular event that occurs immediately after the power stroke is the
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The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a
The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a
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The relaxation of skeletal muscle relies on the activity of the ________, which decreases cytoplasmic calcium concentration.
The relaxation of skeletal muscle relies on the activity of the ________, which decreases cytoplasmic calcium concentration.
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Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers?
Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers?
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Within a single fiber, the tension developed during a twitch depends upon the
Within a single fiber, the tension developed during a twitch depends upon the
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A motor unit consists of
A motor unit consists of
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Motor units that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ________ muscle fibers than motor units that control more gross movements (gastrocnemius muscle of the lower leg).
Motor units that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ________ muscle fibers than motor units that control more gross movements (gastrocnemius muscle of the lower leg).
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Which fibers generate more force?
Which fibers generate more force?
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The nervous system avoids muscle fatigue during submaximal contraction by
The nervous system avoids muscle fatigue during submaximal contraction by
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In order for the bicep muscle to shorten, the force applied by the muscle must be ________ the load applied at the hand.
In order for the bicep muscle to shorten, the force applied by the muscle must be ________ the load applied at the hand.
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In order to contract and relax, muscle cells require energy in the form of ________. The immediate backup energy source is ________ that requires the enzyme ________.
In order to contract and relax, muscle cells require energy in the form of ________. The immediate backup energy source is ________ that requires the enzyme ________.
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Put these events in the correct chronological sequence: 1. End-plate potentials trigger action potentials. 2. Transverse tubules convey potentials into the interior of the cell. 3. Acetylcholine binds to receptors on the motor end plate. 4. Ca2+ is released from the sarcoplasmic reticulum.
Put these events in the correct chronological sequence: 1. End-plate potentials trigger action potentials. 2. Transverse tubules convey potentials into the interior of the cell. 3. Acetylcholine binds to receptors on the motor end plate. 4. Ca2+ is released from the sarcoplasmic reticulum.
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The factor(s) that determine the duration of a twitch in various types of fibers is the speed of the
The factor(s) that determine the duration of a twitch in various types of fibers is the speed of the
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The force generated by a single muscle fiber can be increased by
The force generated by a single muscle fiber can be increased by
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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?
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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A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?
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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Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
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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?
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?
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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?
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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Calcium entry into the axon terminal triggers which of the following events?
Calcium entry into the axon terminal triggers which of the following events?
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Study Notes
Cross Bridge Cycle and Muscle Contraction
- Calcium binds to troponin, altering its shape to initiate muscle contraction.
- Displacement of tropomyosin reveals active sites on actin, enabling cross bridge formation.
- Troponin controls tropomyosin positioning, facilitating myosin head binding to actin.
- The cross bridge is defined as the connection formed by myosin binding to actin.
Muscle Contraction Events
- Cross bridge detachment is triggered by ATP binding to the myosin head.
- ATP hydrolysis occurs during the cocking of the myosin head, storing energy for the next cycle.
- The power stroke involves myosin pulling actin filaments toward the sarcomere's center.
Muscle Fiber Types and Characteristics
- Slow-oxidative fibers (type I) are characterized by a smaller diameter and higher myoglobin content compared to fast-twitch fibers (type IIb).
- Fast-twitch fibers produce more force and fatigue quicker than slow-twitch fibers.
Mechanisms Involved in Muscle Fiber Contraction
- The cross bridge cycle ends when sufficient calcium is transported back to the sarcoplasmic reticulum, allowing calcium to unbind from troponin.
- Muscle contraction requires energy from ATP, and quickly uses phosphocreatine via creatine kinase for recharging ATP.
Neuromuscular Junction and Excitation-Contraction Coupling
- Acetylcholine binding at the neuromuscular junction opens channels for Na+ and K+, initiating action potentials.
- Calcium ions are crucial for coupling excitation to contraction, with main storage in the sarcoplasmic reticulum.
- Myasthenia gravis impairs muscle function due to an autoimmune response targeting acetylcholine receptors, which can be treated by inhibiting acetylcholinesterase.
Factors Influencing Muscle Contraction Strength
- The length of sarcomeres before contraction affects tension; optimal lengths increase force produced.
- Action potential frequency and asynchronous recruitment help prevent muscle fatigue during prolonged contractions.
Muscle Structure and Functional Units
- The sarcomere is the basic functional unit of skeletal muscle contraction.
- Each motor unit comprises one neuron controlling multiple muscle fibers, with fine movements coming from units with fewer fibers.
Physiological Responses and Relaxation
- Relaxation of skeletal muscle is facilitated by the action of Ca2+ ATPase, which decreases cytoplasmic calcium concentration.
- Proper sequencing of neuromuscular events, including end-plate potentials leading to action potentials, is crucial for effective contraction.
Myofilament Interaction
- The force during a contraction results from thin and thick myofilaments sliding past each other without changing in length.
- Continuous attachment of some myosin heads during contraction ensures stability, preventing actin from sliding backwards even when others detach.
Tetanus and Muscle Tone
- Complete tetanus demonstrates maximum tension development with no relaxation between twitches, contrasting with unfused tetanus that allows for some relaxation.
Summary of Key Structures and Functions
- Triads consist of T-tubules and terminal cisternae, regulating calcium release essential for muscle contraction.
- Z disks serve as anchoring points for thin filaments, marking the boundaries of sarcomeres.
Contraction Dynamics
- The dynamics of muscle contraction involve complex interactions of various proteins and ions, integrating biochemical and mechanical processes vital for movement.
Studying That Suits You
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Description
Test your knowledge of key concepts in physiology with these flashcards focused on Chapter 12. This set covers the roles of calcium and tropomyosin in the cross bridge cycle. It's a great resource for students looking to reinforce their understanding of muscle contraction mechanisms.
