Muscle Physiology Quiz

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Questions and Answers

What is the role of ATP in the release of actin during muscle contraction?

  • ATP prevents rigor mortis by continuously binding to actin.
  • ATP hydrolysis is necessary for the myosin head to release actin. (correct)
  • ATP is produced by muscle cells during contraction to facilitate binding.
  • ATP binds to myosin, allowing it to form stronger bonds with actin.

Which statement accurately reflects the behavior of the SERCA pump?

  • It is activated by increased calcium levels in the muscle fibers.
  • It releases calcium ions into the cytoplasm during contraction.
  • It is responsible for calcium uptake into the sarcoplasmic reticulum. (correct)
  • It phosphorylates ATP to generate energy for muscle contraction.

What is rigor mortis primarily caused by?

  • Accumulation of ATP in muscle fibers.
  • Binding of actin and myosin in the absence of ATP. (correct)
  • Continuous electrical stimulation of muscle fibers.
  • A lack of calcium ions in the muscle tissue.

What contributes to maintaining the resting membrane potential in muscle cells?

<p>Potassium leak channels allowing K+ to flow out of the cell. (B)</p> Signup and view all the answers

What initiates the production of muscle action potential?

<p>A rush of sodium ions into the cell through voltage-gated channels. (D)</p> Signup and view all the answers

What initiates the exposure of active sites on actin during muscle contraction?

<p>Calcium binding to troponin (B)</p> Signup and view all the answers

During the cross bridge cycle, what happens during the power stroke?

<p>ADP is released from myosin heads (C)</p> Signup and view all the answers

What is the role of acetylcholinesterase in muscle contraction?

<p>It breaks down ACh into choline and acetic acid (C)</p> Signup and view all the answers

What occurs when myosin heads bind to the active sites on actin?

<p>Phosphate is released during binding (B)</p> Signup and view all the answers

In which part of the muscle fiber is the motor end plate typically found?

<p>In the middle of the muscle fiber (A)</p> Signup and view all the answers

What happens to calcium ions during the resting state of a muscle?

<p>Calcium is stored in the sarcoplasmic reticulum (D)</p> Signup and view all the answers

What is the function of myosin ATPase in muscle contraction?

<p>It hydrolyzes ATP to provide energy (A)</p> Signup and view all the answers

How does the motor neuron communicate with muscle fibers?

<p>Through chemical signals released to synaptic gaps (B)</p> Signup and view all the answers

What is the significance of the M-line during muscle contraction?

<p>It anchors the thin filaments (C)</p> Signup and view all the answers

What does excitation-contraction coupling refer to?

<p>The sequence of events from stimulation to muscle contraction (A)</p> Signup and view all the answers

What process occurs at the neuromuscular junction to initiate muscle contraction?

<p>Acetylcholine binds to ligand-gated channels (C)</p> Signup and view all the answers

What is the role of the sodium-potassium ATPase in muscle physiology?

<p>To re-establish resting membrane potential (D)</p> Signup and view all the answers

In the sliding filament theory, which zone or band disappears during maximal contraction?

<p>H-zone (B), I-band (D)</p> Signup and view all the answers

Which part of the muscle fiber is associated with the synaptic end bulb?

<p>Motor end plate (B)</p> Signup and view all the answers

What is the function of calcium ATPase in muscle relaxation?

<p>To transport calcium back into the sarcoplasmic reticulum (D)</p> Signup and view all the answers

What describes the asynchronous nature of cross-bridge cycling in muscle contraction?

<p>Myosin heads attach independently throughout contraction (C)</p> Signup and view all the answers

What is the effect of action potential reaching the threshold at the motor end plate?

<p>It initiates depolarization of the muscle cell (A)</p> Signup and view all the answers

Flashcards

Rigor Mortis

The state of muscle stiffness after death, caused by the lack of ATP preventing myosin heads from detaching from actin.

Troponin

The protein that binds to calcium, triggering a conformational change in tropomyosin to expose actin-binding sites for myosin.

Tropomyosin

The protein that blocks myosin binding sites on actin in a relaxed muscle, moved aside by troponin when calcium is present.

ATP (Adenosine Triphosphate)

The energy source required for the release of myosin from actin, allowing muscle relaxation.

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SERCA Pump

The pump that actively transports calcium ions back into the sarcoplasmic reticulum, causing muscle relaxation.

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Sliding Filament Theory

The process by which actin and myosin filaments slide past each other, shortening the muscle fiber.

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Neuromuscular Junction (NMJ)

The connection between a motor neuron and a muscle fiber. It's where the nervous system signals the muscle to contract.

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Acetylcholine Release

The release of acetylcholine from the synaptic vesicles at the NMJ, triggering a change in the muscle fiber.

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Motor End Plate

The region of the sarcolemma that contains acetylcholine receptors, receiving the signal from the motor neuron.

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Cross Bridge Cycle

The cycle of events that allows muscle fibers to contract. It involves the attachment, detachment, and reattachment of myosin heads to the actin filaments.

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Maximal Contraction

The state where all myosin heads are attached to actin and the sarcomere is maximally shortened.

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Sodium Potassium ATPase

The process of maintaining the resting membrane potential (RMP) of muscle fibers, requiring energy from ATP.

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Cross Bridge

The binding of a myosin head to an active site on actin.

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Myosin Preparation

The state of myosin heads in relaxed muscle, where they have stored energy and are ready to bind to actin.

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Myosin ATPase

An enzyme that breaks down ATP into ADP and phosphate, providing energy for the cross bridge cycle.

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SR Calcium Release

The release of calcium ions from the sarcoplasmic reticulum, triggering muscle contraction.

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Excitation-Contraction Coupling

The transformation of a motor action potential (MAP) into muscle contraction.

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Motor Unit

A group of muscle cells innervated by a single motor neuron.

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Acetylcholinesterase

The enzyme that rapidly breaks down acetylcholine in the synaptic cleft, ensuring a quick muscle response.

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Study Notes

Muscle Physiology

  • Sliding Filament Theory: Actin and myosin filaments slide past each other, shortening the muscle. Overlap of filaments changes, but filament lengths themselves do not change.

  • Neuromuscular Junction (NMJ): Connection between nervous system and muscle. Axon collateral of somatic motor neuron branches into synaptic end bulbs. Acetylcholine (ACh) is released from synaptic vesicles, triggering an action potential.

  • ATP Requirements: Sodium potassium ATPase re-establishes resting membrane potential. Myosin ATPase detaches and stores energy for power strokes. Sarcoendoplasmic reticulum calcium ATPase allows relaxation.

Cross Bridge Cycle

  • Cycle Process: Myosin binds to actin, moves it, and releases. Binding is part of preparation, where myosin heads (activated) store energy in upright position.

  • Hydrolysis: Myosin ATPase hydrolyzes ATP to ADP + P, storing energy in the heads.

  • Binding: Calcium binds to troponin, shifting tropomyosin, exposing active sites. Myosin binds to actin.

  • Power Stroke: Energy from myosin heads moves actin toward the M-line (center of sarcomere). ADP is released.

  • Release: ATP binds to myosin, causing it to release actin.

  • Re-Energization: ATP is hydrolyzed, re-energizing the myosin head, which returns to the starting position.

Electrical Properties

  • Resting Membrane Potential: Approximately -85 mV.

  • Potassium Leak Channels: More numerous than sodium channels, contributing to resting potential.

  • Sodium-Potassium Pump: Requires ATP, maintaining high extracellular sodium and high intracellular potassium. This pump maintains the concentration gradient between sodium and potassium.

Excitation-Contraction Coupling

  • Transformation: Action potential (MAP) transforms into muscle contraction.

  • Resting State: Calcium channels are closed, troponin is relaxed, and tropomyosin covers active sites.

  • Contraction: Action potential triggers calcium release from the sarcoplasmic reticulum, causing calcium binding to troponin. This moves tropomyosin, exposing binding sites on actin. Myosin then binds to actin, initiating the cross-bridge cycle.

  • Calcium Uptake: Calcium is taken back up into sarcoplasmic reticulum.

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