Muscle Physiology Module 4
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Questions and Answers

What is the primary function of skeletal muscle as described in the module?

  • To develop tension and shorten (correct)
  • To maintain posture
  • To produce heat
  • To store nutrients

What type of muscle can be described as striated and multinucleated?

  • Smooth muscle
  • Cardiac muscle
  • Connective tissue
  • Skeletal muscle (correct)

What are myofibres formed from?

  • Myoblasts that fuse together (correct)
  • Differentiated mononucleated cells
  • Undifferentiated cells
  • Adipose cells

Which connective tissue structure is mentioned to bind muscle fibers together?

<p>Epimysium (C)</p> Signup and view all the answers

How large can an adult skeletal muscle fiber (myofibre) be?

<p>20-100 µm in diameter (D)</p> Signup and view all the answers

What characteristic does not describe skeletal muscle?

<p>Involuntary control (D)</p> Signup and view all the answers

What percentage of body mass is primarily composed of skeletal muscle?

<p>35-40% (C)</p> Signup and view all the answers

What visual characteristic can be observed in skeletal muscle under a microscope?

<p>Alternating light and dark bands (D)</p> Signup and view all the answers

What is the primary role of tendons in relation to muscles?

<p>To transmit force from muscles to bones (D)</p> Signup and view all the answers

What structure within a muscle fiber primarily holds the contractile proteins?

<p>Myofibril (A)</p> Signup and view all the answers

What is the main function of the sarcomere in skeletal muscle?

<p>To contract the muscle (A)</p> Signup and view all the answers

Which component is primarily responsible for anchoring thin filaments to Z-lines?

<p>Actin (B)</p> Signup and view all the answers

What is the function of the sarcomere in muscle physiology?

<p>It is the unit of contraction in muscle fibers (D)</p> Signup and view all the answers

What is the zone within the A band where there are no overlapping thin filaments called?

<p>H zone (C)</p> Signup and view all the answers

Which layer of connective tissue binds the entire muscle structure?

<p>Epimysium (C)</p> Signup and view all the answers

How many sets of thin filaments are present in each sarcomere?

<p>Two sets at opposite ends (D)</p> Signup and view all the answers

What gives muscle its characteristic striations?

<p>The arrangement of actin and myosin filaments (A)</p> Signup and view all the answers

What is the role of tropomyosin and troponin in muscle contraction?

<p>They regulate thin actin filaments (C)</p> Signup and view all the answers

Which component binds groups of muscle fibers or fascicles?

<p>Perimysium (D)</p> Signup and view all the answers

Which of the following accurately describes a fascicle?

<p>A group of muscle fibers (C)</p> Signup and view all the answers

Which protein is considered the largest in the human body?

<p>Titin (A)</p> Signup and view all the answers

What structure defines the boundaries of a sarcomere?

<p>Z lines (D)</p> Signup and view all the answers

What is the percentage of volume that myofibrils account for in muscle tissue?

<p>80% (A)</p> Signup and view all the answers

What term describes the interaction between thick myosin filaments and thin actin filaments during contraction?

<p>Cross-bridge (A)</p> Signup and view all the answers

What occurs when myosin’s cross-bridges bind to actin during muscle contraction?

<p>Actin filaments move toward the center of the sarcomere. (C)</p> Signup and view all the answers

How many actin filaments can interact with a single myosin filament?

<p>6 (A)</p> Signup and view all the answers

Which statement about muscle contraction is correct?

<p>Contraction involves activation of cross-bridge cycling between actin and myosin. (A)</p> Signup and view all the answers

What is the role of calcium ions in muscle contraction?

<p>Calcium ions regulate the interaction between myosin and actin. (D)</p> Signup and view all the answers

What characterizes the sliding-filament mechanism?

<p>Thick and thin filaments slide past one another during contraction. (D)</p> Signup and view all the answers

What structural characteristic does the actin molecule have?

<p>It is a single globular polypeptide that forms a long filament. (A)</p> Signup and view all the answers

What is the result of cross-bridge cycling in muscle contractions?

<p>It generates force while potentially leading to muscle shortening. (D)</p> Signup and view all the answers

What happens during muscle relaxation?

<p>Calcium levels decrease, and actin-myosin interactions are inhibited. (D)</p> Signup and view all the answers

What is the main function of tropomyosin in relaxed skeletal muscle?

<p>To block the cross-bridge binding site on actin (A)</p> Signup and view all the answers

What are the three subunits of troponin?

<p>C, I, T (B)</p> Signup and view all the answers

Which of the following molecules holds tropomyosin in its inhibitory position?

<p>Troponin (C)</p> Signup and view all the answers

What role does the I subunit of troponin play?

<p>Preventing tropomyosin from moving along actin (B)</p> Signup and view all the answers

What structural components make up a myosin molecule?

<p>Two heavy chains and four light chains (D)</p> Signup and view all the answers

Which statement is true regarding the interaction of troponin and tropomyosin with actin?

<p>Both inhibit myosin from binding to actin in a resting myofibre (B)</p> Signup and view all the answers

What is the composition of the globular heads of the myosin molecule?

<p>Two globular heads and a single tail (A)</p> Signup and view all the answers

What is the primary binding site found on the globular head of myosin?

<p>Binding site for actin (C)</p> Signup and view all the answers

What is the function of the ATP binding site in myosin?

<p>Act as an ATPase for energy generation (A)</p> Signup and view all the answers

Which of the following best describes the cross-bridge cycle?

<p>The myosin head binds and detaches from the thin filament in a sequence (B)</p> Signup and view all the answers

What part of the muscle contraction cycle is referred to as the 'power stroke'?

<p>The movement of the cross-bridge (C)</p> Signup and view all the answers

How do myosin molecules within a thick filament orient themselves?

<p>Oriented in opposite directions at each end (A)</p> Signup and view all the answers

Which term can refer to the myosin head or the binding action between myosin and actin?

<p>Cross-bridge (A)</p> Signup and view all the answers

What occurs after the detachment of the cross-bridge in the muscle contraction cycle?

<p>The myosin head binds to a new site on actin (C)</p> Signup and view all the answers

What is the primary role of specialized proteins in stabilizing the myosin head?

<p>Providing a regulatory function (B)</p> Signup and view all the answers

What is the final step in the sequence of the cross-bridge cycle?

<p>Re-energizing the myosin head (A)</p> Signup and view all the answers

Flashcards

Skeletal Muscle

The largest tissue group in the human body, comprising about 35-40% of the body's total mass. It is composed of striated muscle fibers.

Myofibre

A single muscle cell, formed by the fusion of multiple mononucleated cells called myoblasts.

Muscle Fiber/Myofibre

A long, cylindrical, multinucleated muscle cell.

Striated Muscle

Muscle tissue with visible alternating light bands perpendicular to its length.

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Muscle Contraction

The ability of muscle tissue to develop tension and shorten.

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Myoblast

An undifferentiated, mononucleated cell that fuses together to form a muscle fiber.

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Muscle Composition

All the muscle fibers bound together by connective tissue.

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Muscle fiber size

Muscle fibers are 20-100 µm in diameter and up to 20 cm long in adults.

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Sarcomere

The functional unit of skeletal muscle, the smallest component capable of contraction within a muscle fiber.

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Muscle fiber structure

A muscle fiber is a single muscle cell. Multiple fibers are bundled together into fascicles, which are further grouped by connective tissue to form the whole muscle.

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A band

The wide, dark band in a sarcomere, containing thick filaments of myosin.

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I band

The light band in a sarcomere, containing thin filaments of actin.

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Sarcomere

The functional unit of a muscle, repeating segments of myofibrils.

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Actin

A protein that forms thin filaments inside myofibrils.

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Z line

Lines where thin filaments of actin are anchored within the sarcomere.

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Myosin

A protein that forms thick filaments inside myofibrils.

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Thick filament

Filaments primarily composed of myosin protein, crucial for muscle contraction.

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Muscle Striations

The striped appearance of muscles due to the organized arrangement of actin and myosin filaments.

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Cross-bridge

A portion of the myosin molecule that extends and connects to actin filaments, enabling muscle contraction.

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Fascicle

A bundle of muscle fibers.

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Connective tissue in muscle

Layers of connective tissues(epimysium, perimysium, endomysium) that surround and support muscles, muscle fascicles, and individual fibers.

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Thin filament

Filaments primarily composed of actin protein, crucial for muscle contraction.

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Sliding Filament Mechanism

The process by which muscle fibers contract, involving the movement of thin (actin) filaments over thick (myosin) filaments within a sarcomere.

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Cross-bridge Cycling

A series of steps involving the attachment, pivoting, and detachment of myosin cross-bridges to actin filaments, generating force and movement.

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What causes muscle fiber shortening?

Muscle fibers shorten as a result of the sliding filament mechanism, where actin filaments slide over myosin filaments.

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How does Calcium regulate muscle contraction?

Calcium ions bind to troponin, moving tropomyosin away from the actin binding sites, allowing myosin cross-bridges to attach and initiate the sliding filament mechanism.

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Role of Actin and Myosin in Muscle Contraction

Actin and myosin proteins interact within a sarcomere, forming cross-bridges that generate force and cause the thin filaments to slide over the thick filaments. This movement shortens the sarcomere, resulting in muscle contraction.

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Myosin Head

The globular portion of the myosin molecule that binds to actin filaments, responsible for the power stroke in muscle contraction.

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ATPase Activity

The enzymatic activity present in the myosin head that hydrolyzes ATP, providing energy for the muscle contraction process.

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Power Stroke

The movement of the myosin head, after binding to actin, that generates the force for muscle contraction.

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Regulating Myosin Head

Specialized proteins regulate the binding of myosin to actin, ensuring proper contraction and relaxation.

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Troponin

A protein complex that regulates muscle contraction by controlling the interaction between actin and myosin. It has three subunits: T, I, and C.

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Tropomyosin

A protein that covers the myosin-binding sites on actin filaments in relaxed muscle, preventing muscle contraction.

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What are the subunits of troponin?

Troponin has three subunits: T, I, and C. T interacts with tropomyosin, I inhibits the interaction between actin and myosin, and C binds calcium.

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Function of troponin in muscle contraction

Troponin acts as a calcium sensor. When calcium binds to the C subunit, it causes a conformational change in troponin, moving tropomyosin away from the myosin-binding sites on actin, allowing muscle contraction to occur.

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Myosin Molecule Structure

Myosin is a protein composed of two large polypeptide heavy chains and four smaller light chains. These combine to form a molecule with two globular heads and one long tail.

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Myosin Head Binding Sites

Each globular head of the myosin molecule has two binding sites: one for actin and one for ATP.

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Function of Myosin in Muscle Contraction

Myosin forms thick filaments that interact with actin filaments to create muscle contraction. The myosin heads bind to actin and use ATP to generate force, pulling the actin filaments towards the center of the sarcomere.

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How are myosin and actin filaments arranged?

Myosin filaments are thick and located in the center of the sarcomere, while actin filaments are thin and extend towards the Z lines. They are arranged in a highly organized pattern, creating the striated appearance of skeletal muscle.

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Study Notes

Module 4 - Muscle Physiology

  • Course: HH/KINE 2011 - Human Physiology I
  • Semester: Fall 2024
  • Instructor: Dr. Paris
  • Textbook: Human Physiology, Nelson (4th Edition), Chapter 7 (pages 297-322) / 5th Edition, Chapter 8
  • Module Overview: This module covers muscle physiology, specifically focusing on skeletal muscle.
  • Learning Objectives: By the end of this section, students should be able to describe the macro- and micro-architecture of skeletal muscle and understand the molecular basis of skeletal muscle contraction.
  • Muscle Contraction: Muscles can develop tension and shorten (muscle contraction). Skeletal muscle comprises ~35-40% of body mass.
  • Muscle Types:
    • Striated muscle: Skeletal muscle, Cardiac muscle
    • Unstriated muscle: Smooth muscle
    • Voluntary muscle: Skeletal muscle
    • Involuntary muscle: Cardiac and smooth muscle
  • Skeletal Muscle Fiber:
    • Formed by the fusion of undifferentiated, mononucleated cells (myoblasts).
    • Cylindrical and elongated.
    • Diameter ranges from 20-100µm.
    • Length can vary significantly.
    • Contains multiple nuclei.
    • Exhibit alternating light and dark bands (striations) under a microscope perpendicular to the long axis.
  • Skeletal Muscle Organization: Repeating units called sarcomeres (the structural and functional units) are organized in a repeating pattern within a muscle fiber.
  • Muscle Tissue Composition: Muscle fibers are bound together by connective tissue layers (epimysium, perimysium, endomysium).
  • Myofibrils:
    • Within skeletal muscle fibers, myofibrils represent ~80% of the fiber volume.
    • Composed of repeating proteins actin (thin filament) and myosin (thick filament).
    • The alternating patterns of actin and myosin create the visible striations.
  • Sarcomere: These structural and functional units of skeletal muscle are composed of repeating patterns along myofibrils.
  • A and I Bands:
    • A band: The central, wide dark band where thick filaments are located and thin filaments may overlap.
    • I band: The lighter bands where thin filaments are located, without overlap of thick filaments. The Z line and the H zone within the A band.
  • Z-line (Z discs): A dark line formed from proteins that connect at the ends of the sarcomere and hold thin filaments of adjacent sarcomeres together, and anchor the thin filaments.
  • M-line (M disc): A dark line located in the middle of the A band that holds the thick filaments together.
  • H-zone: A lighter area in the middle of the A band where thin filaments do not overlap thick filaments. This area shortens during muscle contraction.
  • Titin: The largest protein in the body, acting as an elastic protein component that helps muscle fibers regain their normal length after being stretched (or contracted).
  • Protein Components of Thick and Thin Filaments: Specific proteins (myosin, actin, troponin, tropomyosin) are key components in the process and organization of myofibrils. These proteins generate and regulate force, and create the sliding filament mechanism.
  • Myosin Molecule: Large molecules including two globular heads and a long tail. Each globular head has binding sites for actin and ATP.
  • Actin Molecule: Globular (G-actin) molecules polymerize to form long, fibrous actin filaments.
  • Sliding Filament Mechanism:
    • Thin filaments move toward center of sarcomere.
    • Myosin cross-bridges bind to actin and then flex, causing the actin filament to slide toward the center.
  • Regulation of Muscle Contraction: Tropomyosin and troponin block myosin binding to actin in a relaxed muscle and are critical regulatory molecules. Calcium ions initiate contraction by binding to troponin which shifts the tropomyosin away from the myosin binding sites.
  • Steps of the Cross-Bridge Cycle: Myosin head binds to actin, generates power stroke, myosin head detaches from actin, myosin head re-energizes, and the cycle repeats, leading to contraction. This process is driven by ATP hydrolysis. The ATP binding site of ATPase also has an enzymatic activity, driving the whole process.
  • Cross Bridges: Portion of myosin that reaches to the thin actin filament and enables muscle contraction.
  • Muscle Contraction Process: The sliding filament mechanism is the process that occurs during muscle contraction, where thin and thick filaments slide past each other to change the length of the sarcomere. This mechanism is caused by cross-bridge cycling.
  • How Muscles Contract: Force generation results in shortening of skeletal muscles because overlapping thick and thin filaments within each sarcomere move relative to each other.
  • Factors influencing muscle contraction: Calcium release which leads to changes in membrane potential. The amount of calcium available influences the interaction between myosin and actin which leads to contraction.

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Description

Explore the intricacies of muscle physiology in this quiz focused on skeletal muscle. Covering both the macro- and micro-architecture, this quiz will assess your understanding of muscle types and the molecular basis of muscle contraction. Prepare to enhance your knowledge essential for Human Physiology I.

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