Muscle Physiology and Organization
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Questions and Answers

Which of the following types of muscle is found only in the heart?

  • Smooth
  • Cardiac (correct)
  • Skeletal

    • Which of the following is a function of muscle contraction?

  • Purposeful locomotory movement
  • Manipulation of external objects
  • Propulsion of contents
  • Emptying of contents of certain organs
  • Production of heat as a metabolic by-product
  • All of the above (correct)

    • What is the functional unit of a muscle?

  • Sarcomere (correct)
  • Myofibril
  • Muscle fiber
  • Muscle

    • What is the function of the H zone in a sarcomere?

    <p>The H zone is the lighter area in the middle of the A band where thin filaments do not reach.</p> Signup and view all the answers

    Match the following muscle types with their characteristics:

    <p>Skeletal = Striated, voluntary, multinucleated Cardiac = Striated, involuntary, branched Smooth = Unstriated, involuntary, single nucleus</p> Signup and view all the answers

    Skeletal muscle cells are involuntary.

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

    Smooth muscle cells are found in the walls of hollow organs and tubes.

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

    Cardiac muscle cells are responsible for the rhythmic contraction of the heart.

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

    What is the role of calcium ions in muscle contraction?

    <p>Calcium ions are necessary for muscle contraction. When calcium ions bind to troponin, it causes a conformational change in tropomyosin, exposing the myosin-binding sites on the actin filaments. This allows myosin to bind to actin and initiate the power stroke, leading to muscle contraction.</p> Signup and view all the answers

    What is the role of ATP in muscle contraction?

    <p>ATP is the primary energy source for muscle contraction. It is used to power the myosin crossbridge cycle, which involves the attachment, detachment, and reattachment of myosin to actin, leading to the sliding of filaments and muscle shortening. ATP is also required for the active transport of calcium ions back into the sarcoplasmic reticulum, which is essential for muscle relaxation.</p> Signup and view all the answers

    Describe the sliding filament theory of muscle contraction.

    <p>The sliding filament theory states that muscle contraction occurs due to the sliding interaction between thick (myosin) and thin (actin) filaments. Myosin heads bind to actin, forming crossbridges, and use ATP to pivot, pulling the thin filaments towards the center of the sarcomere. This sliding movement shortens the sarcomere, resulting in muscle contraction.</p> Signup and view all the answers

    Which of the following is a characteristic of skeletal muscle cells?

    <p>Striated and voluntary</p> Signup and view all the answers

    What are intercalated discs, and what is their function in cardiac muscle?

    <p>Intercalated discs are specialized junctions that connect cardiac muscle cells end-to-end. They contain desmosomes, which provide structural support and hold the cells together, and gap junctions, which allow for the rapid transmission of electrical signals between cells. The rapid transmission of electrical signals via gap junctions ensures that the heart contracts as a coordinated unit, allowing for efficient pumping of blood.</p> Signup and view all the answers

    What is the role of the SA node in the heart?

    <p>To initiate and regulate the heartbeat</p> Signup and view all the answers

    Which of the following hormones can increase heart rate?

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

    What is the term for the amount of blood ejected from the heart with each beat?

    <p>Stroke volume</p> Signup and view all the answers

    What is the Frank-Starling Law of the heart?

    <p>The Frank-Starling Law of the heart states that the stroke volume of the heart increases as the end-diastolic volume increases. Essentially, the heart pumps out more blood with each beat when it is stretched more by an increased amount of venous return filling the heart.</p> Signup and view all the answers

    The cardiac cycle consists of a period of systole, when the heart contracts and pumps blood, and a period of diastole, when the heart relaxes and fills with blood.

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

    What are the heart sounds, S1 and S2, caused by?

    <p>The closing of the AV valves and the closing of the semilunar valves, respectively</p> Signup and view all the answers

    Which of the following is a condition associated with the occurrence of a heart murmur?

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

    Physiological heart murmurs are often benign and can be normal in young animals.

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

    Describe the major functions of the pulmonary circulation.

    <p>The pulmonary circulation is the loop of blood flow between the heart and the lungs. Its primary function is to carry deoxygenated blood from the heart to the lungs, where it picks up oxygen and releases carbon dioxide, and then return the oxygenated blood back to the heart.</p> Signup and view all the answers

    Describe the major functions of the systemic circulation.

    <p>The systemic circulation is the loop of blood flow between the heart and the rest of the body. It carries oxygenated blood from the heart to various tissues and organs throughout body, delivering oxygen and essential nutrients and removing waste products like carbon dioxide. Deoxygenated blood is then returned to the heart.</p> Signup and view all the answers

    Which of the following factors primarily affects the flow of blood through a vessel?

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

    Explain the relationship between blood vessel radius and blood flow.

    <p>Blood vessel radius is inversely proportional to the resistance of blood flow. A smaller radius results in higher resistance and lower flow, while a larger radius leads to lower resistance and higher flow. This is because a smaller radius presents a larger surface area for blood to rub against, leading to greater friction and resistance. This relationship plays a large role in the control of blood flow distribution to various tissues and organs.</p> Signup and view all the answers

    Capillaries are the smallest blood vessels and the site of exchange between blood and the interstitial fluid.

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

    Precapillary sphincters are smooth muscle rings that control the flow of blood through capillaries.

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

    Which of the following is a vasoconstrictor?

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

    Which of the following is a vasodilator?

    <p>Nitric oxide</p> Signup and view all the answers

    How is the heart adapted to act as an efficient pump?

    <p>The heart is structurally and functionally adapted for efficient pumping. Its four chambers, with specialized valves, ensure a unidirectional flow of blood. The muscular walls, especially the thicker left ventricular wall, generate the force needed to propel blood throughout the body. The electrical conduction system ensures coordinated contraction of the heart chambers, and the presence of intercalated discs between cardiac muscle cells facilitates rapid electrical signal transmission, ensuring synchronized contraction.</p> Signup and view all the answers

    Which of the following factors does NOT influence heart rate?

    <p>Muscle fiber type</p> Signup and view all the answers

    The function of the lymphatic system is to return excess fluid from the tissues back to the circulatory system.

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

    Which of the following is NOT a component of the lymphatic system?

    <p>All of the above are components of the lymphatic system</p> Signup and view all the answers

    Study Notes

    Muscle Physiology

    • Muscles are highly organized microfilament-based structures.
    • Muscles contract to pull external structures or squeeze fluids.
    • Muscles convert ATP (chemical energy) into mechanical energy.
    • Muscles respond to electrical signals.
    • Skeletal muscles are the largest tissue group in vertebrates, comprising 40% of male body weight, 32% of female body weight, and 25% of hummingbird body weight.
    • Three types of muscles include skeletal, cardiac, and smooth.
    • Skeletal muscle contraction performs purposeful movements, manipulating objects, propelling contents, and producing heat/sound.

    Levels of Organization in Skeletal Muscle

    • Whole muscle (organ) contains bundles of muscle fibers (cells).
    • Muscle fibers contain myofibrils.
    • Myofibrils are made of thick (myosin) and thin (actin) filaments.
    • Sarcomeres are the functional units of muscle, located between Z lines.
    • I bands contain only thin filaments.
    • A bands contain thick filaments and overlapping thin filaments.
    • H zones are regions where only thick filaments exist within an A band.
    • M lines are the central regions of the sarcomeres.
    • Myofibrils contain a network of transverse (T) tubules and sarcoplasmic reticulum.
    • Myosin molecules have tails that intertwine and globular heads (cross bridges) for binding and ATPase activity (for energy).

    Thin Filament Composition

    • Thin filaments consist of actin, tropomyosin, and troponin molecules.
    • Tropomyosin covers myosin-binding sites on actin in relaxed muscle.
    • Calcium binding to troponin moves tropomyosin, exposing binding sites.

    Skeletal Muscle vs Cardiac vs Smooth Muscle

    • Skeletal muscle: Striated, voluntary, multinucleated.
    • Cardiac muscle: Striated, involuntary, uninucleated, electrically interconnected.
    • Smooth muscle: Non-striated, involuntary, uninucleated, and contain gap junctions enabling widespread excitation.

    Role of Calcium

    • Calcium release is essential for muscle excitation.
    • Calcium binding to troponin uncovers myosin-binding sites on actin.
    • Calcium uptake into the sarcoplasmic reticulum relaxes the muscle.

    Cross-Bridge Cycle

    • Myosin cross-bridges bind to actin, causing a power stroke (pulling thin filament).
    • ATP binding causes detachment of myosin from actin.
    • ATP hydrolysis cocks the myosin head for another cycle.

    Neuromuscular Junction

    • The neuromuscular junction (NMJ) is a synapse between neuron and muscle, initiating contraction.
    • Acetylcholine (neurotransmitter) release triggers action potentials in muscle fibers.

    T-tubules and Sarcoplasmic Reticulum

    • T-tubules transmit the action potential into the muscle fiber.
    • Sarcoplasmic reticulum releases calcium in response to the action potential.

    ATP Production in Muscle

    • Creatine phosphate, oxidative phosphorylation, and glycolysis are pathways for ATP production.

    Muscle Mechanics

    • Muscle contraction depends on motor unit recruitment and the frequency of stimulation.
    • Muscle tension depends on fiber length and fatigue.
    • Isotonic contractions produce movement, while isometric contractions maintain tension.

    Muscle Disorders

    • Various diseases (e.g., tetanus, exertional rhabdomyolysis, milk fever, eclampsia) can affect muscle function.

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    Description

    Explore the fascinating world of muscle physiology and the intricate organization of skeletal muscle. This quiz delves into muscle types, contraction processes, and the structural hierarchy of muscle tissue. Test your understanding of how muscles function and how they are organized at various levels.

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