Muscular Tissue Overview
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Questions and Answers

What is the primary function of myofibrils in muscle fibers?

  • Storage of calcium ions
  • Producing energy for muscle contraction
  • Contracting and extending muscle fibers (correct)
  • Transporting oxygen to muscles
  • The I-band is formed exclusively of myosin filaments.

    False (B)

    What type of protein is myoglobin and what is its function?

    Myoglobin is an oxygen-binding pigmented protein that provides oxygen for oxidative reactions.

    The __________ is a well-developed smooth endoplasmic reticulum in muscle cells that stores calcium ions.

    <p>sarcoplasmic reticulum</p> Signup and view all the answers

    Match the muscle components with their descriptions:

    <p>A-band = Region with thick myosin filaments I-band = Region with thin actin filaments Z-line = Dense membrane dividing the I-band M-line = Middle of the A-band</p> Signup and view all the answers

    Which organelle is primarily responsible for energy production in muscle cells?

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

    The H-zone is a pale area located in the middle of the I-band.

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

    Name one of the large proteins that link thick myofilaments to the Z-line.

    <p>Titin or Dystrophin</p> Signup and view all the answers

    Which type of skeletal muscle fiber is characterized by a rich supply of myoglobin?

    <p>Red (slow twitch) (A)</p> Signup and view all the answers

    White muscle fibers are rich in mitochondria and have low levels of glycogen.

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

    What primarily composes the A-band in muscle fibers?

    <p>Both myosin and actin filaments (C)</p> Signup and view all the answers

    What is the primary source of energy for red skeletal muscle fibers?

    <p>Aerobic respiration</p> Signup and view all the answers

    The I-band becomes shorter during muscle contraction.

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

    Skeletal muscle hypertrophy occurs through the enlargement of muscle fibers due to __________.

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

    Match the following types of muscle fibers with their characteristics:

    <p>Red fibers = Slow, prolonged contraction White fibers = Fast, short contraction Intermediate fibers = Characteristics between red and white Satellite cells = Activate to regenerate muscle fibers</p> Signup and view all the answers

    What is the functional unit of contraction in muscle fibers?

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

    The __________ are invaginations of the sarcolemma that encircle myofibrils.

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

    What happens to satellite cells after muscle injury?

    <p>They become activated and proliferate. (D)</p> Signup and view all the answers

    What happens to calcium levels when depolarization stops?

    <p>Calcium is actively transported into the sarcoplasmic reticulum (B)</p> Signup and view all the answers

    Muscular dystrophy is a condition characterized by an increase in muscle function.

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

    What is the musculotendinous junction?

    <p>The junction where muscle fibers connect with tendon.</p> Signup and view all the answers

    Match the skeletal muscle types with their characteristics:

    <p>Type I = Slow-twitch fibers, endurance Type IIa = Fast-twitch, moderate endurance Type IIb = Fast-twitch, low endurance Type IIX = Fast-twitch, explosive power</p> Signup and view all the answers

    The H-zone contains both actin and myosin filaments.

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

    When the muscle contracts, the A-band __________ in length.

    <p>remains constant</p> Signup and view all the answers

    What primarily causes muscle cramps?

    <p>Dehydration and lack of potassium (B), High levels of exercise without proper warm-up (D)</p> Signup and view all the answers

    Myasthenia Gravis affects the skeletal muscles by enhancing muscle strength.

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

    What is the primary function of the cardiac muscle?

    <p>Pumping blood throughout the body</p> Signup and view all the answers

    Cardiac muscle fibers are characterized by a cylindrical shape and have a nucleus that is _____ and _____ in each cardiac myocyte.

    <p>oval, central</p> Signup and view all the answers

    Match the following terms related to cardiac muscle with their descriptions:

    <p>Myofibrils = Less abundant compared to skeletal muscles Mitochondria = Numerous and large with closely packed cristae Sarcoplasmic reticulum = Accompanies T-tubules leading to diad formation Intercalated discs = Junctions between adjacent cardiac myocytes</p> Signup and view all the answers

    Which component is NOT present in the sarcoplasm of cardiac muscle fibers?

    <p>Large amounts of sarcoplasmic reticulum (D)</p> Signup and view all the answers

    The myocardium forms the outer layer of the heart.

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

    What changes occur in cardiac myocytes with age?

    <p>Increased lipofuscin granules leading to brown atrophy.</p> Signup and view all the answers

    What structural components are found in the transverse regions of the cardiac muscle intercalated discs?

    <p>Desmosomes and Adherent junctions (C)</p> Signup and view all the answers

    Cardiac muscle fibers can regenerate after injury.

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

    What is the primary function of Purkinje muscle fibers?

    <p>To transmit impulses to ventricular muscles.</p> Signup and view all the answers

    The cardiac muscle's involuntary contraction is modulated, but not initiated, by ______ innervations.

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

    Match the following structures with their functions:

    <p>Desmosomes = Bind cardiac cells together Gap junctions = Allow contraction signals to pass Valves = Prevent backflow of blood Purkinje fibers = Transmit impulses quickly to heart muscles</p> Signup and view all the answers

    What occurs during a myocardial infarction?

    <p>Complete obstruction of a coronary artery (A)</p> Signup and view all the answers

    Angina is characterized by severe chest pain resulting from increased oxygenation of the heart muscle.

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

    What type of epithelium covers the heart valves?

    <p>Simple squamous epithelium</p> Signup and view all the answers

    What is the primary function of smooth muscles?

    <p>Produces slow, sustained involuntary contraction (D)</p> Signup and view all the answers

    Smooth muscle fibers have a striated appearance.

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

    What hormone is a potent stimulator of smooth muscle contraction?

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

    Smooth muscle cells may be affected by hormones such as __________.

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

    Where are smooth muscles primarily located?

    <p>The walls of hollow viscera and blood vessels (A)</p> Signup and view all the answers

    Match the following characteristics with their corresponding smooth muscle features:

    <p>Shape = Non-branched spindle shaped Nucleus = Single, central &amp; oval Caveolae = Invaginations controlling Ca release Desmin filaments = Abundant in smooth muscle cells</p> Signup and view all the answers

    Smooth muscle fibers are arranged in sheets, layers, or bundles.

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

    What type of connective tissue surrounds each bundle of smooth muscle fibers?

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

    Flashcards

    Sarcoplasmic Reticulum

    A network of smooth endoplasmic reticulum surrounding myofibrils in muscle cells. It plays a crucial role in storing and releasing calcium ions (Ca++) for muscle contraction.

    Myofibrils

    Cylindrical protein structures that make up muscle fibers. They are responsible for muscle contraction and are arranged in parallel bundles within each muscle cell.

    Sarcomere

    The functional unit of a myofibril, responsible for muscle contraction. It is characterized by alternating dark (A) and light (I) bands.

    A-band

    The darker band in a sarcomere, containing both thick (myosin) and thin (actin) filaments.

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    I-band

    The lighter band in a sarcomere, composed solely of thin (actin) filaments.

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    Z-line

    A dark line that bisects the I-band and serves as the attachment point for thin (actin) filaments.

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    H-zone

    The central region of the A-band where only thick (myosin) filaments are present.

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    M-line

    A thin line in the center of the H-zone, where the thick (myosin) filaments are linked together.

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    What are the characteristics of red muscle fibers?

    Red muscle fibers are characterized by their dark color due to abundant myoglobin, mitochondria, and vascularization. They utilize aerobic respiration to produce energy, allowing them to contract slowly and resist fatigue for extended periods.

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    What are the characteristics of white muscle fibers?

    White muscle fibers are pale in color due to less myoglobin and higher glycogen levels. They rely on anaerobic glycolysis for energy, leading to rapid and powerful contractions but rapid fatigue.

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    What are intermediate fibers?

    Intermediate fibers possess characteristics of both red and white fibers, exhibiting a blend of aerobic and anaerobic capabilities.

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    What are satellite cells and their function?

    Satellite cells are inactive myoblasts found in adult muscle fibers, nestled between the sarcolemma and basal lamina. They are responsible for regenerating muscle fibers after injury.

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    What is the musculotendinous junction?

    The musculotendinous junction is where muscle fibers merge with tendons. The muscle fiber gradually tapers off, while the connective tissue components of the muscle continue into the tendon.

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    What is skeletal muscle hypertrophy?

    Skeletal muscle hypertrophy refers to an increase in muscle fiber size, typically caused by exercise or physical training.

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    What is muscular dystrophy?

    Muscular dystrophy involves a progressive degeneration of skeletal muscle fibers. A key feature is the absence of dystrophin, a protein crucial for muscle function.

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    T-tubules (Transverse tubules)

    Invaginations of the sarcolemma into the muscle fiber's interior, encircling myofibrils and aiding in the transmission of nerve impulses.

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    Muscle Contraction (Role of the Tubular System)

    The process by which a nerve impulse triggers calcium release from the sarcoplasmic reticulum, leading to muscle contraction.

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    Muscle Relaxation

    The process by which calcium is actively pumped back into the sarcoplasmic reticulum after contraction, resulting in muscle relaxation.

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    Muscle Cramps

    Sudden, painful muscle contractions caused by factors like reduced blood flow, low potassium levels, or intense exercise without proper warm-up.

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    Myasthenia Gravis

    An autoimmune disease where the body's immune system attacks acetylcholine receptors in skeletal muscles, causing weakness. This starts with facial, eye, and tongue muscles and progresses to respiratory muscles, potentially leading to respiratory failure.

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    Cardiac Muscle

    The specialized muscle tissue that makes up the heart's middle layer.

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    Epicardium

    The outer layer of the heart, surrounding the myocardium.

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    Endocardium

    The inner layer of the heart, lining the chambers.

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    Cardiac Muscle Fibers

    The interconnected, branched muscle fibers that make up cardiac muscle.

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    Intercalated Discs

    The junctions between individual cardiac muscle cells (myocytes) within a fiber.

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    Cardiac Myocyte Nucleus

    Single, oval-shaped nuclei found in each cardiac myocyte.

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    Purkinje muscle fibers

    These are specialized cardiac muscle fibers found in the moderator band, atrioventricular bundle, and its branches. They transmit impulses faster than ordinary myocardium, ensuring synchronized ventricle contractions.

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    Myocardial infarction

    Irreversible injury and death of cardiac muscle cells, commonly caused by a complete blockage of a coronary artery.

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    Gap junctions

    These junctions allow for direct communication between adjacent cardiac muscle cells, facilitating the rapid spread of electrical impulses.

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    Cardiac muscle contraction

    Involuntary rhythmic contraction of cardiac muscle fibers, regulated by the autonomic nervous system and hormones.

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    Angina

    A narrowing of the coronary artery lumen due to atheroma buildup, leading to reduced oxygen supply to ventricular muscle and chest pain upon exertion.

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    Reduced oxygenation of ventricular muscle

    A condition where the ventricular muscle is inadequately oxygenated due to a slowly progressive narrowing of the coronary artery lumen.

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    What is smooth muscle?

    Smooth muscle, a type of muscle tissue found in the walls of hollow organs like the digestive, urinary, and respiratory tracts, as well as blood vessels, skin, and the eye. It contracts slowly and involuntarily, helping to move substances through organs and regulate blood flow.

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    How are smooth muscle fibers connected?

    Smooth muscle fibers, unlike skeletal muscle fibers, are connected together by gap junctions. This allows for coordinated contraction of the muscle fibers, facilitating smooth muscle movement.

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    What is the endomysium?

    Smooth muscle fibers are surrounded by a thin layer of reticular fibers called endomysium. This provides structural support and helps to organize the muscle fibers.

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    How are smooth muscle fibers arranged?

    Smooth muscle fibers are arranged in sheets, layers, or bundles, which are in turn surrounded by a thin collagenous connective tissue called perimysium. This perimysium also contains blood vessels and nerves, providing the muscle with necessary resources and control.

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    How does oxytocin affect smooth muscle?

    Oxytocin, a hormone, can directly influence smooth muscle contraction. It plays a crucial role in uterine contraction during childbirth, making it a valuable tool for inducing or enhancing labor.

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    What are caveolae and how do they affect smooth muscle contraction?

    Caveolae are invaginations on the smooth muscle cell surface, functioning in controlling calcium release and regulating muscle contraction. Unlike skeletal muscle, smooth muscle lacks T-tubules.

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    What is the shape of smooth muscle fibers?

    Smooth muscle cells are spindle-shaped, meaning they are wider in the center and taper at both ends, which allows them to fit together tightly. The tapered ends lie next to the broader parts of neighboring cells, forming sheets.

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    What are dense bodies in smooth muscle?

    Dense bodies, analogous to Z-lines in striated muscle, serve as attachment points for actin filaments. They transmit the contractile force throughout the smooth muscle, enabling coordinated movement.

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    Study Notes

    Muscular Tissue

    • The structural and functional unit is a specialized elongated cell called a muscle fiber containing contractile filaments (actin and myosin).
    • The cell membrane of muscle fibers is called the sarcolemma, and the cytoplasm is called the sarcoplasm.
    • Sarcoplasmic reticulum is the smooth ER.
    • Sarcoplasm is acidophilic and contains organelles like mitochondria, sarcoplasmic reticulum, and myofibrils, and inclusions like glycogen, myoglobin, and fat.
    • Muscle tissue originates from the Mesoderm.
    • Muscle cells (myocytes) can form all types of muscle tissue.

    Types of Muscular Tissue

    • Classified according to the shape and function of their cells:
      • Skeletal muscle
      • Cardiac muscle
      • Smooth muscle

    Skeletal Muscle

    • Attached to the skeleton.
    • Consists of muscle fibers held and supported by connective tissue:
      • Epimysium: surrounds the whole muscle.
      • Perimysium: surrounds bundles (fascicles) of muscle fibers.
      • Endomysium: surrounds each individual muscle fiber; a layer of reticular fibers containing small blood vessels and nerves.
    • Connective tissue is essential for force transmission and nourishment of the muscle fibers through diffusion.

    Skeletal Muscle Fiber

    • Cylindrical, non-branched (except in face and tongue).

    • Size: 10-100 µm in diameter and markedly variable in length.

    • Multiple, oval nuclei just under the sarcolemma.

    • Sarcoplasm is acidophilic with uniform transverse striations in longitudinal section.

    • Organelles:

      • Myofibrils: numerous cylindrical, parallel, longitudinal fibrils extending the entire muscle fiber.
      • Sarcoplasmic reticulum: a well-developed smooth endoplasmic reticulum forming networks around myofibrils. Essential for calcium storage and release during muscle contraction.
      • Mitochondria: numerous, arranged in rows between myofibrils.
      • Other organelles: few, found mainly in the perinuclear cytoplasm.
    • Inclusions:

      • Myoglobin: oxygen-binding protein.
      • Glycogen granules: energy storage.
      • Lipid droplets.

    Myofibrils

    • The myofibrils are composed of two main types of protein filaments:

      • Thin filaments (actin filaments).
      • Thick filaments (myosin filaments).
    • Thick filaments are located in the A-band, while the Thin filaments extend into and occupy the I band, and both are connected to the Z lines.

    • Dark bands (A-bands) and light bands (I-bands).

    • The A-band appears dark because it contains both actin and myosin filaments, and the I band is light because it contains only actin filaments.

    • The H zone is a pale area in the middle of the A-band, which contains only myosin filaments.

    • The M-line bisects the H zone.

    Triad Tubular System (T-system)

    • Formed of three tubules: one T-tubule (transverse tubule) in the middle, and two wide terminal cisternae of sarcoplasmic reticulum.
    • The T-tubules are invaginations of the sarcolemma.
    • The lumen of the T-tubule is continuous with the extracellular space.
    • Located at the junction between the A and I bands.

    Function of Skeletal Muscle

    • Skeletal muscle is voluntary.
    • Skeletal muscle's contraction is transmitted to the T tubules, then to the depth of the fiber and stimulate the sarcoplasmic reticulum to release calcium (Ca²⁺), which facilitates the sliding of actin filaments over myosin filaments filling the middle of the A band.

    Types of Skeletal Muscle Fibers

    • Classified based on color and function (fast twitch or slow twitch).
    • Differences: color, myoglobin content, source of energy, mitochondria number, and fatigue resistance.

    Cardiac Muscle

    • Forms the middle layer of the heart (myocardium).
    • Thicker in the ventricles than in the atria.
    • Surrounded by:
      • Epicardium (visceral layer of the pericardium) - outside
      • Endocardium - inside
    • Cardiac muscle tissue is made up of branched and interconnected muscle fibers.
    • Each fiber is surrounded by delicate connective tissue rich in capillaries (endomysium).
    • Characterized by intercalated discs, which are specialized junctions between adjacent cardiac muscle cells.

    Smooth Muscle

    • Found in the walls of hollow viscera, blood vessels, and other structures.

    • Small, non-branched spindle-shaped cells.

    • Arranged in sheets or layers.

    • Connected by gap junctions.

    • Characterized by the presence of dense bodies forming an attachment site for contractile proteins (myosin) and lack of striations.

    • Innervated by the autonomic nervous system (involuntary).

    • Function: Slow, sustained contractions, influenced by hormones and autonomic nervous system, contraction that maintains blood vessel tone in cardiovascular, respiratory, and gastrointestinal systems.

    • Regeneration: Limited ability to repair or regenerate after injury.

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