Neuromuscular Junction and Muscle Contraction Quiz
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Questions and Answers

What is the role of acetylcholine in the neuromuscular junction?

  • It directly connects motor neurons to muscle fibers.
  • It acts as a neurotransmitter to initiate muscle contraction. (correct)
  • It provides energy for muscle fibers during contraction.
  • It stimulates the release of calcium from the sarcoplasmic reticulum.

    • Which structure separates the axonal endings and muscle fibers at the neuromuscular junction?

  • Muscle fiber membrane
  • Synaptic cleft (correct)
  • Motor end plate
  • Presynaptic terminal

    • What occurs first in the steps of muscle contraction at the neuromuscular junction?

  • Synaptic vesicles fuse with the membrane of the axonal ending.
  • Acetylcholine binds to receptors on the motor end plate.
  • The muscle fiber generates an action potential.
  • Voltage gated calcium channels open at the presynaptic terminal. (correct)

    • What is the primary function of the motor end plate in the neuromuscular junction?

    <p>To house acetylcholine receptors for signal transmission.</p> Signup and view all the answers

    Which component of the neuromuscular junction contains synaptic vesicles?

    <p>Axonal endings</p> Signup and view all the answers

    What occurs after acetylcholine binds to ligand-gated sodium channels on the motor end plate?

    <p>Sodium channels open and sodium enters the muscle fiber</p> Signup and view all the answers

    Which component of the actin myofilament prevents tropomyosin from uncovering active sites on G actin in relaxed muscle?

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

    What process initiates the release of acetylcholine from synaptic vesicles during muscle contraction?

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

    What happens to acetylcholine after it unbinds from ligand-gated channels?

    <p>It is broken down by acetylcholinesterase</p> Signup and view all the answers

    Which molecule is symported with sodium in the presynaptic terminal after acetylcholine is removed?

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

    What is the primary role of troponin in muscle contraction?

    <p>Prevents tropomyosin from uncovering active sites.</p> Signup and view all the answers

    Which of the following components are found in a myosin molecule?

    <p>Two myosin heads.</p> Signup and view all the answers

    What must occur for a skeletal muscle to contract?

    <p>Action potential must be propagated along the sarcolemma.</p> Signup and view all the answers

    What initiates muscle relaxation after contraction?

    <p>Cessation of acetylcholine release.</p> Signup and view all the answers

    How does isometric contraction differ from isotonic contraction?

    <p>Muscle does not shorten in isometric contraction.</p> Signup and view all the answers

    What happens to troponin during muscle relaxation?

    <p>Calcium diffuses away from it.</p> Signup and view all the answers

    What is the final trigger for muscle contraction?

    <p>A rise in intracellular calcium levels.</p> Signup and view all the answers

    Which statement accurately describes cross-bridge movement?

    <p>Myosin heads bind to active sites on actin.</p> Signup and view all the answers

    What occurs during eccentric contraction?

    <p>Muscle lengthens while controlling the weight.</p> Signup and view all the answers

    Which of the following describes the hinge region of myosin?

    <p>It allows for rotational movement of heads.</p> Signup and view all the answers

    Which of these is classified as a voluntary muscle?

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

    What serves as the basic structural and functional unit of a skeletal muscle?

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

    Which of the following is not a recognized function of the muscular system?

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

    Which definition accurately describes extensibility in muscles?

    <p>Ability of a muscle to be stretched beyond its normal resting length and still contract</p> Signup and view all the answers

    Which structure within the muscle fiber plays a crucial role in regulating intracellular calcium levels?

    <p>Sarcoplasmic Reticulum</p> Signup and view all the answers

    Which type of muscle is classified as voluntary?

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

    What is the basic structural and functional unit of skeletal muscle?

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

    Which function is NOT associated with the muscular system?

    <p>Sensory perception</p> Signup and view all the answers

    What is the definition of extensibility in muscles?

    <p>Ability to be stretched beyond normal resting length and still contract</p> Signup and view all the answers

    Which structure in muscle fibers is essential for regulating intracellular calcium levels?

    <p>Sarcoplasmic Reticulum</p> Signup and view all the answers

    Which function is specifically related to skeletal muscles in the context of posture?

    <p>Maintenance of posture</p> Signup and view all the answers

    What is one of the primary functions of the muscular system regarding body heat?

    <p>Regulation of body temperature</p> Signup and view all the answers

    What is the primary function of elasticity in muscle tissue?

    <p>To return to its original resting length after being stretched</p> Signup and view all the answers

    What surrounds each fascicle within a skeletal muscle?

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

    What is the role of the thick myofilament in muscle contraction?

    <p>To create cross-bridges during contraction</p> Signup and view all the answers

    What is the basic unit of contraction in a muscle fiber?

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

    How are actin and myosin filaments arranged within a sarcomere?

    <p>Myosin filaments reside in the A band without contacting Z lines</p> Signup and view all the answers

    Which component serves as the plasma membrane of a muscle cell?

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

    Which muscle type is characterized by being involuntary and non-striated?

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

    What is the primary role of tropomyosin in muscle contraction?

    <p>To hold actin filaments together</p> Signup and view all the answers

    Study Notes

    Neuromuscular Junction

    • Formed from axonal endings and motor end plate
    • Axonal endings contain synaptic vesicles with acetylcholine
    • Motor end plate contains acetylcholine receptors
    • Axonal ends and muscle fibers are separated by the synopotic cleft

    Muscle Contraction

    • Starts with action potential arriving at the presynaptic terminal
    • Voltage gated calcium channels in the presynaptic membrane open
    • Acetylcholine is released from the presynaptic terminal through exocytosis into the synaptic cleft
    • Acetylcholine binds to ligand-gated sodium channels on the motor end plate
    • Sodium enters the muscle fiber due to open ligand gated sodium channels
    • Action potential is generated if depolarization passes threshold
    • Acetylcholine unbinds and ligand gated channels close
    • Acetylcholinesterase removes acetylcholine from the synaptic cleft
    • Choline is symported with sodium in the presynaptic terminal
    • Acetylcholine is reformed within the presynaptic terminal

    Actin and Myosin Myofilament Structure

    • Actin myofilaments are made up of globular (G) actin and form fibrous (F) actin
    • Tropomyosin covers active sites on G actin subunits in a relaxed muscle
    • Troponin anchors troponin to actin
    • Troponin prevents tropomyosin from uncovering G actin active sites in a relaxed muscle
    • Troponin binds calcium
    • Myosin myofilaments consists of two myosin heavy chains
    • Myosin heads bind to active sites on actin molecules to form cross-bridges
    • Myosin heads are attached to the rod portion via a hinge region
    • Myosin heads are ATPase enzymes which break down ATP

    Excitation Contraction Coupling

    • This occurs at the triad, which links the electrical component of muscle contraction to the mechanical component
    • Skeletal muscle must be stimulated by a nerve ending and propagate an action potential along its sarcolemma
    • In order to contract, intracellular calcium levels must rise

    Cross-bridge Movement

    • Calcium binds to troponin and causes troponin to change shape
    • This pulls tropomyosin away from the active site of actin
    • Myosin binds to actin and forms a cross-bridge
    • The myosin head pivots pulling the actin filament towards the center of the sarcomere
    • ATP binds to the myosin head, causing it to detach from the active site of actin
    • The ATP is broken down which changes the shape of the myosin head and cocks it into a high-energy position
    • The cycle repeats as long as calcium is bound to troponin

    Muscle Relaxation

    • Acetylcholine is no longer released at the neuromuscular junction
    • Cessation of action potential along the sarcolemma stops calcium release
    • Calcium diffuses away from troponin molecules
    • Tropomyosin covers the G actin active sites
    • No formation of cross bridges occurs

    Types of Muscle Contractions

    • Isometric contraction: Muscle does not shorten, tension increases
    • Isotonic contractions: Muscle shortens, tone remains constant throughout contraction
    • Isotonic contractions have two types: Concentric and eccentric contractions

    Disorders of the Muscular System

    • Aging leads to muscle atrophy (physiologic and age related)
    • Loss of muscle fibers begins as early as 25 years old
    • Surface area of the neuromuscular junction and number of motor neurons decreases with aging
    • Muscle fatigue is a temporary state of reduced work capacity and can be caused by acidosis and ATP depletion
    • Muscle soreness occurs after vigorous exercise and is caused by inflammatory chemical influx into muscle fibers
    • Cramps are painful spastic contractions of skeletal muscle caused by dehydration and ion imbalance
    • Tendinitis in is an inflammation of a tendon or its attachment point due to overuse of a skeletal muscle
    • Fibromyalgia is a non-life-threatening chronic widespread pain in skeletal muscles with no known cure
    • Myasthenia Gravis is an autoimmune disease where autoantibodies bind to acetylcholine receptors this can be diagnosed by electro myography and identification of the autoantibodies
    • Duchenne Muscular Dystrophy is caused by mutations in the dystrophin gene on the X chromosome which causes progressive muscle weakness and muscle contractures and is diagnosed through serum creatinine, muscle biopsies and immunohistochemical studies

    Formative Assessment

    • The major properties of muscle are: Contractility, Elasticity, Excitability, Extensibility
    • The head of the myosin molecule binds to an active site on G actin
    • T tubule is the part of the sarcolemma that invaginates into the interior of skeletal muscle fibers
    • The type of muscle contraction used when a weight lifter attempts to lift a weight that is too heavy is an isometric contraction
    • The order of events in a muscle contraction are: Calcium ions combine with troponin, troponin pulls away from actin, myosin binds to actin

    Functions of the Muscular System

    • The muscular system allows for body movement by contracting skeletal muscles attached to bones.
    • The muscular system maintains posture through muscle tone which keeps us upright.
    • The muscular system assists in respiration through muscle contraction in the thorax and diaphragm.
    • Muscle contraction during activity produces heat as a by-product.
    • The muscular system plays a central role in communication, as muscles are involved in speech, facial expressions, and writing.
    • Smooth muscle in internal organs and vessels constricts through contraction.
    • Cardiac muscle contraction is responsible for the beating of the heart.

    Functional Properties of Muscle Tissue

    • The ability of a muscle to shorten forcibly is called contractility.
    • Muscle shortening is forceful, while lengthening is passive.
    • A muscle can be stimulated by a nerve and contract, this is known as excitability.
    • A muscle can be stretched beyond its normal resting length and still be able to contract, this is known as extensibility.
    • The ability of a muscle to return to its original resting length after it has been stretched is called elasticity.

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    Description

    Test your knowledge on the neuromuscular junction and the process of muscle contraction. This quiz covers the roles of acetylcholine, sodium channels, and the steps involved in generating an action potential. Perfect for biology students or anyone looking to reinforce their understanding of muscle physiology.

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