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    Muscle Physiology

    Free practice questions for NCLEX - Muscle Physiology. Includes full solutions and score reporting.

    NCLEX : Muscle Physiology

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    NCLEX Help » General Biology » Musculoskeletal System and Anatomy » Muscle Physiology

    Example Question #11 : Muscle Physiology

    The sliding filament theory of muscle contraction involves the __________ attaching to __________ and then pulling during the power stroke.

    Possible Answers:

    actin head . . . myosin

    troponin . . . actin

    myosin . . . tropomyosin

    myosin head . . . actin

    Correct answer:

    myosin head . . . actin

    Explanation:

    The sliding filament theory of muscle contraction involves the myosin head attaching to actin and then pulling during the power stroke. Troponin is a protein attached to tropomyosin, a thin strand wrapping around the actin filament. When calcium enters the cell, troponin moves toward it, pulling the tropomyosin strand away from actin binding sites and allowing the myosin head to bind.

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    Example Question #12 : Muscle Physiology

    Which of the following molecules binds to troponin during muscle contraction, triggering tropomyosin to move away from the actin binding sites and allowing the myosin head to form a cross bridge?

    Possible Answers:

    ADP Calcium ATP Sodium

    Correct answer:

    Calcium Explanation:

    During a muscle cell action potential, calcium enters the cell via t-tubules, which are specialized invaginations of the sarcoplasmic reticulum. Calcium binds with troponin, which pulls the tropomyosin strand away from actin binding sites and allows myosin heads to bind. Neither sodium nor potassium bind to troponin, and ATP and ADP both bind to myosin, rather than troponin.

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    Example Question #13 : Muscle Physiology

    Which of the following is the name of the modified endoplasmic reticulum found in muscle cells?

    Possible Answers:

    The sarcomere

    The sarcoplasmic reticulum

    The t-tubule

    The myoplasmic reticulum

    Correct answer:

    The sarcoplasmic reticulum

    Explanation:

    Muscle cells have a specialized endoplasmic reticulum called the sarcoplasmic reticulum. The sarcoplasmic reticulum regulates the calcium ion concentration in the cytoplasm of striated muscle cells, and so plays a significant role in muscle contraction and relaxation. The T-tubule is a specialized invagination of the sarcoplasmic reticulum, and the sarcomere is the single contractile unit of a muscle fibril. There is no muscle structure called the mycoplasmic reticulum.

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    Sliding Filament Theory, Sarcomere, Muscle Contraction, Myosin

    Muscle is a specialized contractile tissue that is a distinguishing characteristic of animals. Changes in muscle length support an exquisite array of animal movements, from the dexterity of octopus tentacles and peristaltic waves of feet to the precise coordination of linebackers and ballerinas. What molecular mechanisms give rise to muscle contraction? The process of contraction has several key steps, which have been conserved during evolution across the majority of animals

    What Is a Sarcomere?

    When muscle cells are viewed under the microscope, one can see that they contain a striped pattern (striations). This pattern is formed by a series of basic units called sarcomeres that are arranged in a stacked pattern throughout muscle tissue (Figure 1). There can be thousands of sarcomeres within a single muscle cell. Sarcomeres are highly stereotyped and are repeated throughout muscle cells, and the proteins within them can change in length, which causes the overall length of a muscle to change. An individual sarcomere contains many parallel actin (thin) and myosin (thick) filaments. The interaction of myosin and actin proteins is at the core of our current understanding of sarcomere shortening. How does this shortening happen? It has something to do with a sliding interaction between actin and myosin.

    Figure 1: A gastrocnemius muscle (calf) with striped pattern of sarcomeres

    The view of a mouse gastrocnemius (calf) muscle under a microscope. The sarcomeres are artifically colored green, and appear as stacked horzontal stripes of similar lengths. (White scale bar = 25 microns.)

    © 2008 Nature Publishing Group Llewellyn, M. E. Minimally invasive high-speed imaging of sarcomere contractile dynamics in mice and humans. 454, 784-788 (2008). All rights reserved.

    The Sliding Filament Theory

    In 1954, scientists published two groundbreaking papers describing the molecular basis of muscle contraction. These papers described the position of myosin and actin filaments at various stages of contraction in muscle fibers and proposed how this interaction produced contractile force. Using high-resolution microscopy, A. F. Huxley and R. Niedergerke (1954) and H. E. Huxley and J. Hanson (1954) observed changes in the sarcomeres as muscle tissue shortened. They observed that one zone of the repeated sarcomere arrangement, the "A band," remained relatively constant in length during contraction (Figure 2A). The A band contains thick filaments of myosin, which suggested that the myosin filaments remained central and constant in length while other regions of the sarcomere shortened. The investigators noted that the "I band," rich in thinner filaments made of actin, changed its length along with the sarcomere. These observations led them to propose the sliding filament theory, which states that the sliding of actin past myosin generates muscle tension. Because actin is tethered to structures located at the lateral ends of each sarcomere called z discs or "z bands," any shortening of the actin filament length would result in a shortening of the sarcomere and thus the muscle. This theory has remained impressively intact (Figure 2B).

    Figure 2: Comparison of a relaxed and contracted sarcomere

    (A) The basic organization of a sarcomere subregion, showing the centralized location of myosin (A band). Actin and the z discs are shown in red. (B) A conceptual diagram representing the connectivity of molecules within a sarcomere. A person standing between two bookcases (z bands) pulls them in via ropes (actin). Myosin (M) is analogous to the person and the pulling arms. (z bands are also called z discs.)

    © Nature Publishing Group A) adapted from Huxley, A. F. & Niedergerke, R. Structural Changes in Muscle During Contraction: Interference Microscopy of Living Muscle Fibres. 172, 971-973 (1954). B) © Nature Education All rights reserved.

    Figure Detail

    An Analogy for Sliding Filaments in a Sarcomere Shortening Event

    Imagine that you are standing between two large bookcases loaded with books. These large bookcases are several meters apart and are positioned on rails so that they can be easily moved. You are given the task of bringing the two bookcases together, but you are limited to using only your arms and two ropes. Standing centered between the bookcases, you pull on the two ropes — one per arm — which are tied securely to each bookcase. In a repetitive fashion, you pull each rope toward you, regrasp it, and then pull again. Eventually, as you progress through the length of rope, the bookcases move together and approach you. In this example, your arms are similar to the myosin molecules, the ropes are the actin filaments, and the bookcases are the z discs to which the actin is secured, which make up the lateral ends of a sarcomere. Similar to the way you would remain centered between the bookcases, the myosin filaments remain centered during normal muscle contraction (Figure 2B).

    What Are Cross Bridges, and How Do They Relate to Sliding Filaments?

    One important refinement of the sliding filament theory involved the particular way in which myosin is able to pull upon actin to shorten the sarcomere. Scientists have demonstrated that the globular end of each myosin protein that is nearest actin, called the S1 region, has multiple hinged segments, which can bend and facilitate contraction (Hynes 1987; Spudich 2001). The bending of the myosin S1 region helps explain the way that myosin moves or "walks" along actin. The slimmer and typically longer "tail" region of myosin (S2) also exhibits flexibility, and it rotates in concert with the S1 contraction (Figure 3A).

    Source : www.nature.com

    Chapter 9 Muscle Physiology Flashcards

    Start studying Chapter 9 Muscle Physiology. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

    Chapter 9 Muscle Physiology

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    true or false? One of the important functions of skeletal muscle contraction is production of heat.

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    true

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    Which of the following statements is true?

    Skeletal muscle cells are long and cylindrical with many nuclei.

    Cardiac muscle cells are found in the heart and large blood vessels. Smooth muscle cells have t tubules. Cardiac muscle cells have many nuclei.

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    skeletal muscle cells are long and cylindrical with many nuclei

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    Terms in this set (103)

    true or false? One of the important functions of skeletal muscle contraction is production of heat.

    true

    Which of the following statements is true?

    Skeletal muscle cells are long and cylindrical with many nuclei.

    Cardiac muscle cells are found in the heart and large blood vessels. Smooth muscle cells have t tubules. Cardiac muscle cells have many nuclei.

    skeletal muscle cells are long and cylindrical with many nuclei

    Which of the following surrounds the individual muscle cell?

    endomysium

    Which term best identifies a muscle cell?

    muscle fiber

    Which of the structures is surrounded by the connective tissue sheath known as the perimysium?

    B fascicle

    A small bundle or cluster, especially of nerve or muscle fibers bounded by a perimysium

    Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped,

    no muscle tension could be generated

    the sliding filament model of contraction involves

    actin and myosin sliding past each other and partially overlapping

    which of the following is the correct sequence of events for muscle contractions?

    motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments

    what is the functional unit of a skeletal muscle called?

    a sarcomere

    rigor mortis occurs because

    no ATP is available to release attached to actin and myosin molecules

    During muscle contraction, myosin cross bridges attach to which active sites?

    actin filaments

    What structure in skeletal muscle cells functions in calcium storage?

    sarcoplasmic reticulum

    myoglobin

    protein of muscle that stores and transports oxygen

    what is the role of tropomyosin in skeletal muscles?

    tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules

    a sarcomere is the distance between two

    Z discs

    contains only the actin filaments

    I band

    the thicker filaments are the

    myosin filaments

    both actin and myosin found in the

    A band

    the myosin filaments are located in the

    A band

    The sliding filament model of contraction involves ________.

    during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin overlap to a greater degree

    sarcomere

    shorten's during muscle contraction

    A Band

    dark band, the entire length of thick myofilaments

    reduction in blood flow to a muscle fiber would have the greatest effect on

    slow oxidative fibers

    exhaustion of glycogen storage within a muscle fiber would have the biggest effect on

    fast glycolytic fibers

    after nervous stimulation stops, what prevents ACh in the synaptic cleft from continuing to stimulate contraction?

    acetylcholinesterase destroying ACh

    the interaction between which protein and ion initiates contraction of skeletal muscle?

    troponin; calcium ions

    Which step precedes all of the other listed steps?

    An action potential starts on the sarcolemma.

    ACh is released by the motor neuron.

    The sarcoplasmic reticulum is activated.

    Sodium rushes into the cell.

    ACh is released by the motor neuron

    myosin tail groups

    form the extended versions of the thick myofilaments

    actin

    the chief component of the thin myofilaments

    a toxin released by certain bacteria can block the release of neurotransmitters and a neuromuscular synapse. What would result from such a block?

    the loss of ability to contract the muscle. without acetylcholine, the muscle would not be able to contracted or even maintain tone.

    an enzyme known as acetylcholinesterase is present in the synaptic cleft. What is its role?

    to break down acetylcholine.

    exocytosis

    neurotransmitters stored in synaptic vesicles are released into the synaptic cleft

    what is the role of calcium in the cross Bridge cycle?

    calcium binds to troponin, altering its shape

    what role does triple myosin play in the cross Bridge cycle?

    the displacement of tropomyosin exposes the active site of actin, allowing cross-bridges to form

    how does troponin facilitate cross Bridge formation?

    troponin controls the position of tropomyosin on a thin filament, enabling myosin heads to bind to the active sites on actin

    What, specifically, is a cross bridge?

    myosin binding to actin

    which event causes cross Bridge detachment?

    ATP binding to the myosin head

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