Physiology Chapter 12 Flashcards

Questions and Answers

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?

Complete tetanus involves development of maximum tension. (correct)

Complete tetanus would occur when there is more time between twitch contractions.

Complete tetanus occurs at a lower frequency of stimulation than unfused tetanus.

Complete tetanus involves some relaxation between twitches.

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?

Calcium binds to troponin, altering its shape. Signup and view all the answers

What role does tropomyosin play in the cross bridge cycle?

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form. Signup and view all the answers

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. Signup and view all the answers

What, specifically, is a cross bridge?

Myosin binding to actin Signup and view all the answers

Which event causes cross bridge detachment?

ATP binding to the myosin head Signup and view all the answers

Where in the cross bridge cycle does ATP hydrolysis occur?

During the cocking of the myosin head Signup and view all the answers

How/when does the myosin head cock back to store energy for the next cycle?

After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head. Signup and view all the answers

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?

Myosin heads would remain detached, unable to cock. Signup and view all the answers

During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?

There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching. Signup and view all the answers

What happens when calcium binds to troponin?

Tropomyosin is pulled away from the actin active site. Signup and view all the answers

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)?

An antagonistic muscle produces the opposite movement. Signup and view all the answers

Which of the following occurs when a myofibril contracts?

Thin and thick filaments slide past each other, but do not change in length. Signup and view all the answers

What immediately follows hydrolysis of ATP during muscle contraction?

Rotation of the myosin head to the cocked position Signup and view all the answers

What is it called when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere?

Power stroke Signup and view all the answers

Compared to fast-twitch glycolytic fibers (type IIb), slow-oxidative muscle fibers (type I) are characterized by a smaller diameter, less stored glycogen, and ________.

The presence of myoglobin Signup and view all the answers

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?

A myosin head bound to actin Signup and view all the answers

What structure is the functional unit of contraction in a skeletal muscle fiber?

The sarcomere Signup and view all the answers

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?

Calcium ions are stored in the sarcoplasmic reticulum. Signup and view all the answers

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

ATP binds to the myosin head. Signup and view all the answers

How does the myosin head obtain the energy required for activation?

The energy comes from the hydrolysis of ATP. Signup and view all the answers

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape. Signup and view all the answers

When does cross bridge cycling end?

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. Signup and view all the answers

A flexor is a skeletal muscle whose shortening moves attached bones

Towards one another. Signup and view all the answers

The function of transverse tubules is to

Rapidly conduct action potentials to the interior of the muscle fiber. Signup and view all the answers

When a skeletal muscle cell contracts and the muscle shortens,

Some myosin heads are forming crossbridges as others are releasing them. Signup and view all the answers

As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately

Detaches from actin. Signup and view all the answers

The molecular event that occurs immediately after the power stroke is the

Release of ADP from the myosin. Signup and view all the answers

The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a

Channel for both Na+ and K+. Signup and view all the answers

The relaxation of skeletal muscle relies on the activity of the ________, which decreases cytoplasmic calcium concentration.

Ca2+ ATPase Signup and view all the answers

Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers?

Long contraction duration and high capillary density Signup and view all the answers

Within a single fiber, the tension developed during a twitch depends upon the

Length of the sarcomeres prior to contraction. Signup and view all the answers

A motor unit consists of

One neuron and all the skeletal muscle fibers it controls. Signup and view all the answers

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).

Fewer Signup and view all the answers

Which fibers generate more force?

Fast-twitch fibers Signup and view all the answers

The nervous system avoids muscle fatigue during submaximal contraction by

Asynchronous recruitment. Signup and view all the answers

In order for the bicep muscle to shorten, the force applied by the muscle must be ________ the load applied at the hand.

Greater than Signup and view all the answers

In order to contract and relax, muscle cells require energy in the form of . The immediate backup energy source is that requires the enzyme .

ATP, phosphocreatine, creatine kinase Signup and view all the answers

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.

3, 1, 2, 4 Signup and view all the answers

The factor(s) that determine the duration of a twitch in various types of fibers is the speed of the

Removal of Ca2+ ions from the sarcoplasm only. Signup and view all the answers

The force generated by a single muscle fiber can be increased by

Increasing frequency of action potentials only. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

Calcium ions. Signup and view all the answers

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 binds to and inactivates acetylcholinesterase (neostigmine). Signup and view all the answers

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. Signup and view all the answers

Calcium entry into the axon terminal triggers which of the following events?

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. Signup and view all the answers

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.

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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.