Muscle Physiology and Myofilaments
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Questions and Answers

What is Actin?

Thin filament

What does /brady mean?

Slow

What type of muscle has intercalated discs?

Cardiac

Muscle cells receive signals from the...

<p>All of the above</p> Signup and view all the answers

A myofilament is longer than a myofibril.

<p>False</p> Signup and view all the answers

What surrounds the muscle fiber?

<p>Epimysium, perimysium, endomysium</p> Signup and view all the answers

The sarcoplasmic reticulum is a site of ______ storage.

<p>calcium</p> Signup and view all the answers

What is the function of terminal cisternae?

<p>Store calcium</p> Signup and view all the answers

What runs perpendicular to the longitudinal axis of the muscle fiber?

<p>T-tubule</p> Signup and view all the answers

What is the cell membrane that encloses each muscle cell called?

<p>Sarcolemma</p> Signup and view all the answers

What is the cytoplasm of striated muscle cells called?

<p>Sarcoplasm</p> Signup and view all the answers

What forms a triad in muscle cells?

<p>T-tubule and two terminal cisternae</p> Signup and view all the answers

What regulatory protein blocks the cross-bridge binding sites on actin when the muscle is relaxed?

<p>Tropomyosin</p> Signup and view all the answers

What is the complex of regulatory proteins that interacts with tropomyosin?

<p>Troponin complex</p> Signup and view all the answers

What happens during muscle contraction according to the sliding filament model?

<p>Actin and myosin filaments slide past one another, shortening the sarcomere.</p> Signup and view all the answers

What is myosin classified as?

<p>Thick filament</p> Signup and view all the answers

What is Titin?

<p>An extremely large protein that maintains resting tension in muscles.</p> Signup and view all the answers

What do nebulin filaments regulate?

<p>Assembly of actin filaments</p> Signup and view all the answers

What anchors myosin filaments at the center of the sarcomere?

<p>M-line</p> Signup and view all the answers

What does the I-band consist of?

<p>Thin filaments only</p> Signup and view all the answers

What is found within the A-band?

<p>Thick and thin filaments overlap</p> Signup and view all the answers

What does the H-zone contain?

<p>Only myosin filaments</p> Signup and view all the answers

What is a muscle segment between two successive Z lines called?

<p>Sarcomere</p> Signup and view all the answers

What do cross bridges do in muscle cells?

<p>Attach to actin and exert force to move it.</p> Signup and view all the answers

What is triggered during the power stroke?

<p>Myosin pulls actin toward the M-line.</p> Signup and view all the answers

Define a motor unit.

<p>One neuron and all of the muscle fibers it stimulates.</p> Signup and view all the answers

What is the first step in the process of chemical synapse?

<p>Action potential arrives at axon terminal.</p> Signup and view all the answers

What are characteristics of graded potentials?

<p>Not propagated, vary in amplitude, hyperpolarizing or depolarizing.</p> Signup and view all the answers

What are the characteristics of action potentials?

<p>Propagated, all or none response, present refractory period.</p> Signup and view all the answers

Study Notes

Actin and Myofilaments

  • Actin is a thin filament key to muscle contraction.
  • Tropomyosin regulates actin, while troponin is a three-polypeptide complex that binds calcium.
  • Myofilaments consist of actin (thin) and myosin (thick) and are integral to muscle structure.

Muscle Cell Structures

  • Muscle fibers receive signals from surrounding environments and systemic signals.
  • Myofibrils are surrounded by the sarcolemma and contain sarcomeres, the functional units of muscle contraction.
  • Sarcoplasmic reticulum stores calcium and regulates muscle contraction by releasing calcium when stimulated.

Contraction Mechanism

  • Terminal cisternae, enlarged areas of the sarcoplasmic reticulum, increase calcium storage capacity for muscle contraction.
  • T-tubules allow electrical impulses to trigger calcium release, facilitating contraction.
  • The sliding filament model describes how actin and myosin interact during contraction, shortening the sarcomere.

Sarcomere Composition

  • Sarcomeres consist of thick (myosin) and thin (actin) filaments, giving muscles their striated appearance.
  • Key regions of sarcomeres include the I band (thin filaments only), A band (thick and thin filaments), and H zone (thick filaments only).
  • The Z line anchors actin filaments while the M line anchors myosin.

Muscle Fiber Types

  • Fast twitch fibers are larger in diameter, designed for quick bursts of activity, ideal for movements like sprinting.
  • Slow twitch fibers are smaller, richer in myoglobin, and suited for endurance activities like long-distance running.

Muscle Contraction Process

  • Cross bridges form between myosin and actin filaments, exerting force to enable movement.
  • The power stroke is initiated when ATP is hydrolyzed, allowing myosin heads to pull actin and shorten the sarcomere.
  • Calcium ions play a crucial role in muscle contraction by binding to troponin and allowing cross-bridge formation.

Neuromuscular Junction

  • The NMJ is where motor neurons connect with muscle fibers, facilitating contraction through neurotransmitter release.
  • Action potentials at the motor end plate trigger muscle contractions across the sarcolemma.
  • Motor units consist of a motor neuron and the muscle fibers it stimulates, working together for precise control of muscle movements.

Electrical Activity and Synaptic Transmission

  • Action potentials propagate along axons using voltage-gated Na+/K+ channels, while graded potentials occur at dendrites and cell bodies.
  • Graded potentials vary in amplitude and can be either excitatory or inhibitory, with no refractory period allowing summation.
  • Action potentials are all-or-nothing, with distinct phases of depolarization and repolarization, ensuring reliable transmission of signals.

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Description

This quiz explores the structure and function of muscle cells, focusing on critical components such as actin, myosin, and the contraction mechanism. Learn about the interaction between myofilaments and the sliding filament model that describes muscle contraction. Test your knowledge on how these elements work together to facilitate movement.

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