Muscle Types Overview
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Questions and Answers

What shape are smooth muscle fibers?

  • Spindle shape (correct)
  • Branched shape
  • Multi-nucleated shape
  • Cigar shape

    • Which statement about cardiac muscle is true?

  • It is striated and voluntary.
  • It has intercalated discs. (correct)
  • It is found in the walls of hollow visceral organs.
  • It contracts rapidly and can fatigue quickly.

    • What initiates muscle contraction in muscle fibers?

  • The activation of myosin's cross bridges (correct)
  • Intercalated discs signaling adjacent cells
  • Direct ATP consumption by muscle fibers
  • Calcium triggering nerve impulses

    • Which type of muscle is involuntary and does not have striations?

    <p>Smooth muscle</p> Signup and view all the answers

    What is the primary function of myosin heads during muscle contraction?

    <p>To bind to actin and generate tension</p> Signup and view all the answers

    How do skeletal muscles often respond to stimulation?

    <p>Voluntarily through conscious control</p> Signup and view all the answers

    What role does calcium play in muscle contraction?

    <p>Calcium initiates the contraction process.</p> Signup and view all the answers

    What structure holds adjacent thick filaments together within a sarcomere?

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

    What is the primary function of the iliopsoas muscle group?

    <p>Flex the thigh or trunk on thigh</p> Signup and view all the answers

    Which muscle type is primarily responsible for propelling blood throughout the body?

    <p>Cardiac muscle</p> Signup and view all the answers

    What is the function of the endomysium in skeletal muscles?

    <p>Surrounds individual muscle fibers</p> Signup and view all the answers

    Which muscle assists in flexing the vertebral column laterally in addition to flexing the thigh?

    <p>Psoas major</p> Signup and view all the answers

    Which muscle is primarily involved in achieving the cross-legged position?

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

    What is a common consequence of straining the muscle group that consists of the adductors?

    <p>Pulled groin</p> Signup and view all the answers

    Which adductor muscle primarily extends the thigh when working with the hamstrings?

    <p>Adductor magnus</p> Signup and view all the answers

    Which function is NOT associated with the adductor muscles?

    <p>Extending the thigh</p> Signup and view all the answers

    What nerve innervates the entire adductor muscle group?

    <p>Obturator nerve</p> Signup and view all the answers

    What role does the quadriceps femoris play in physical activities?

    <p>Important knee extensor</p> Signup and view all the answers

    What role do calcium ions play in excitation-contraction coupling?

    <p>They bind to troponin, exposing binding sites for myosin.</p> Signup and view all the answers

    During the cross bridge cycle, which event occurs immediately after the power stroke?

    <p>Detachment of the cross bridge.</p> Signup and view all the answers

    What conditions are necessary for the continuation of the cross bridge cycle?

    <p>Continuous presence of calcium and sufficient ATP.</p> Signup and view all the answers

    What happens to the distance between successive Z discs during muscle contraction?

    <p>It decreases.</p> Signup and view all the answers

    What is the result of the myosin head pivoting during the power stroke?

    <p>The actin filament is pulled toward the M line.</p> Signup and view all the answers

    Which ion is critical for triggering muscle contraction?

    <p>Calcium ion</p> Signup and view all the answers

    What is the role of troponin in skeletal muscles?

    <p>It acts as a bonding site for calcium ions.</p> Signup and view all the answers

    What primarily occurs at the neuromuscular junction during excitation?

    <p>Acetylcholine binds to receptor proteins on the sarcolemma.</p> Signup and view all the answers

    During the depolarization phase of action potential, which ion's concentration increases inside the muscle fiber?

    <p>Sodium ion</p> Signup and view all the answers

    What characterizes isotonic contractions?

    <p>Tension remains constant while muscle length changes.</p> Signup and view all the answers

    What occurs to the myosin head when ATP is hydrolyzed?

    <p>The myosin head returns to a cocked position.</p> Signup and view all the answers

    What happens to the A bands during muscle contraction?

    <p>Their length does not change.</p> Signup and view all the answers

    What is the resting membrane potential for muscle fibers before stimulation?

    <p>-95</p> Signup and view all the answers

    Which step follows the action potential propagation along the T tubules?

    <p>Calcium ions are released into the cytosol.</p> Signup and view all the answers

    What triggers the closing of sodium channels during action potential?

    <p>Reaching a threshold of +30mV</p> Signup and view all the answers

    What occurs after potassium exits the muscle fiber during repolarization?

    <p>Resting membrane potential is restored.</p> Signup and view all the answers

    During excitation-contraction coupling, what leads to the sliding of myofilaments?

    <p>Transmission of action potential along the sarcolemma</p> Signup and view all the answers

    What happens to the H zones during muscle contraction?

    <p>They disappear.</p> Signup and view all the answers

    Which muscle is primarily responsible for flexing and rotating the lumbar region of the vertebral column?

    <p>Rectus Abdominis</p> Signup and view all the answers

    What is the primary function of the diaphragm during respiration?

    <p>Flattens on contraction</p> Signup and view all the answers

    Which of the following muscles acts synergistically with the sternocleidomastoid and aids in rotating the head?

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

    Which muscle's action would likely result in flexing the vertebral column laterally?

    <p>Quadratus Lumborum</p> Signup and view all the answers

    Which of the following muscles is primarily responsible for drawing the scapula forward and downward?

    <p>Pectoralis Minor</p> Signup and view all the answers

    Which of these muscles is involved in forced expiration by drawing the ribs together?

    <p>Internal Intercostals</p> Signup and view all the answers

    What is the main action of the Iliocostalis muscle?

    <p>Extend and laterally flex the vertebral column</p> Signup and view all the answers

    Which of the following muscles helps maintain an erection by retarding venous drainage?

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

    What is the function of the external oblique muscle when acting individually?

    <p>Assist in lateral trunk rotation</p> Signup and view all the answers

    Which muscle is a prime mover for protracting and holding the scapula against the chest wall?

    <p>Serratus Anterior</p> Signup and view all the answers

    Which muscle is responsible for stabilizing and depressing the pectoral girdle?

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

    What function does the rectus abdominis muscle perform during activities like sit-ups?

    <p>Flexes the vertebral column</p> Signup and view all the answers

    Which muscle helps lift the anal canal during defecation?

    <p>Levator Ani</p> Signup and view all the answers

    What is a primary function of the rhomboids muscle?

    <p>Stabilize and retract the scapula</p> Signup and view all the answers

    Study Notes

    Muscle Types

    • Three types: skeletal, smooth, and cardiac; all elongated muscle cells.
    • Myofilaments (myo = muscle, sarco = flesh) enable muscle contraction by shortening.
    • Muscles are delicate; protected and bundled by connective tissues.

    Skeletal Muscle

    • Smoothly forms the body's contours with huge, cigar-shaped, multi-nucleated cells.
    • Largest muscle fibers can reach up to 30 cm in length and are striated.
    • Voluntary activation often occurs through reflexes; fibers are soft and fragile yet bundled to withstand force.
    • Enclosed in connective tissue: endomysium, perimysium, and epimysium, which blend with tendons for durability.

    Smooth Muscle

    • Involuntary muscle found in hollow visceral organs like the stomach, with no striations.
    • Characterized by spindle-shaped cells containing a single nucleus.
    • Arranged in circular and longitudinal layers; they alternate contractions for processes like peristalsis.

    Cardiac Muscle

    • Unique to the heart; striated but involuntary, responsible for pumping blood.
    • Innervated by the nervous system and cushioned by a small amount of endomysium.
    • Features branching cells connected by intercalated discs, facilitating coordinated contractions.
    • Contains a pacemaker that regulates heartbeat.

    Muscle Function

    • The M-line holds adjacent thick filaments together, while myofibrils consist of chains of sarcomeres aligned in a series.
    • Thick filaments (myosins) have ATPase enzymes essential for contraction; the heads form cross-bridges with thin filaments (actin).
    • Thin filaments are anchored at Z discs and contribute to the bonding pattern with myosin heads.
    • Calcium ions trigger contraction by interacting with troponin in skeletal muscles (calmodulin does so in smooth muscles).

    Sliding Filament Theory

    • Myosin heads generate cross-bridge tensions, allowing thin filaments to slide past thick filaments during contraction.
    • As thin filaments slide, Z discs move toward the M-line, shortening the muscle fiber.
    • Muscle fibers need to be activated for contraction, stimulated by nerve endings to generate an action potential.

    Excitation-Contraction Coupling

    • Begins at the neuromuscular junction with the release of acetylcholine, triggering action potential propagation along the sarcolemma.
    • Calcium ions are released from the sarcoplasmic reticulum, binding to troponin and exposing myosin-binding sites on actin.
    • Myosin forms cross-bridges with actin, initiating contraction.

    Cross Bridge Cycle

    • Formation: Myosin binds to actin, breaking ATP into ADP and phosphate.
    • Power Stroke: Release of ADP and phosphate allows myosin head to pivot, pulling actin filaments.
    • Detachment: ATP binding weakens the connection between myosin and actin.
    • Cocking: ATP hydrolysis returns the myosin head to a high-energy state for further cycles.

    Types of Contraction

    • Isotonic Contraction: Muscle length changes to move a load.
      • Example: External and internal intercostals assist in respiration; diaphragm acts as the prime mover for inspiration.

    Key Muscle Groups

    • Abdominal Muscles: Rectus abdominis, external and internal obliques, and transversus abdominis flex and rotate the trunk and stabilize the pelvis.
    • Pelvic Floor Muscles: Levator ani and coccygeus support pelvic viscera and resist pressure changes.
    • Urogenital Diaphragm: Deep transverse perineal muscle and external urethral sphincter support pelvic organs and control urination.
    • Pectoral Muscles: Pectoralis minor and serratus anterior play roles in scapula movement and stabilization.

    Key Muscle Functions

    • Gluteal Muscles: Extend and laterally rotate the thigh; important for walking and posture.
    • Quadriceps Femoris: Extends the knee; crucial in activities like jumping and running.

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    Muscular System PDF

    Description

    Explore the three types of muscles: skeletal, smooth, and cardiac. Learn about their similarities, structures, and functions in the human body. This quiz will test your knowledge on muscle characteristics and classifications.

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