Muscle Contraction Mechanisms
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Questions and Answers

What triggers the contraction of a muscle fiber?

  • Inhibition of regulatory proteins
  • Decreased levels of ATP in the muscle fiber
  • Release of calcium ions from the sarcoplasmic reticulum (correct)
  • Increased temperature in the muscle fiber

    • What role does ATP play in muscle contraction?

  • Preventing actin filaments from sliding
  • Providing energy to release and recock myosin heads (correct)
  • Reinforcing the binding of actin and myosin
  • Stimulating the release of calcium ions

    • During the contraction process, what happens to the myosin heads as they attach to actin?

  • They rotate clockwise around actin
  • They remain stationary while exerting force
  • They pivot toward the center of the sarcomere (correct)
  • They detach immediately after binding

    • What change occurs to the regulatory proteins on actin when calcium binds to them?

    <p>They change shape and expose myosin-binding sites</p> Signup and view all the answers

    What is the primary effect of myosin attachments to actin during the contraction cycle?

    <p>It facilitates the sliding of thin filaments toward the center of the sarcomere</p> Signup and view all the answers

    What occurs during isotonic contractions?

    <p>Myofilaments slide past each other and the muscle shortens.</p> Signup and view all the answers

    Which of the following examples illustrates isometric contraction?

    <p>Pushing your palms together.</p> Signup and view all the answers

    What is the primary action of flexion?

    <p>Decreases the angle of the joint.</p> Signup and view all the answers

    Which statement is true about hyperextension?

    <p>It can exceed 180º extension.</p> Signup and view all the answers

    What does rotation involve?

    <p>Moving a bone around its longitudinal axis.</p> Signup and view all the answers

    What does the term 'maximus' indicate when naming a muscle?

    <p>It indicates the muscle is large.</p> Signup and view all the answers

    Which joint action is typical of extension?

    <p>Straightening the elbow or knee.</p> Signup and view all the answers

    Which of the following muscle names indicates a muscle that has two origins?

    <p>Biceps brachii</p> Signup and view all the answers

    In which joint type is rotation most commonly observed?

    <p>Ball-and-socket joints.</p> Signup and view all the answers

    What characterizes isometric contractions?

    <p>Muscle tension increases but there is no shortening.</p> Signup and view all the answers

    What does 'rectus' mean in the context of muscle fiber orientation?

    <p>Straight arrangement of fibers</p> Signup and view all the answers

    Which muscle shape is described as 'trapezoid'?

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

    In muscle naming conventions, what does 'sub' designate?

    <p>It means the muscle is underneath another structure.</p> Signup and view all the answers

    What action does the term 'extensor' refer to?

    <p>It refers to a muscle that extends a joint.</p> Signup and view all the answers

    Which of the following is the correct naming based on muscle location?

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

    The term 'longus' in muscle naming indicates what characteristic?

    <p>The muscle is longer than others.</p> Signup and view all the answers

    Which muscle is classified as a circular muscle?

    <p>Orbicularis oris</p> Signup and view all the answers

    What type of muscle is the pectoralis major?

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

    The deltoid muscle is an example of which type of muscle classification?

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

    Which muscle is classified as unipennate?

    <p>Extensor digitorum longus</p> Signup and view all the answers

    Which of the following muscle classifications refers to a muscle with fibers arranged parallel to the long axis?

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

    What type of muscle is the rectus femoris classified as?

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

    Which muscle is considered fusiform?

    <p>Biceps brachii</p> Signup and view all the answers

    What characteristic defines a bipennate muscle?

    <p>Fibers are arranged on both sides of a central tendon.</p> Signup and view all the answers

    Which muscle is positioned on the anterior trunk, primarily responsible for pushing movements?

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

    What is the primary function of the deltoid muscle?

    <p>Abduction of the shoulder</p> Signup and view all the answers

    Which muscle group includes the rectus abdominis and the internal oblique?

    <p>Abdominal muscles</p> Signup and view all the answers

    Which muscle connects the occipital bone to the shoulder region?

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

    Which muscle is classified as a major muscle of the posterior trunk?

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

    What is the primary role of the triceps brachii muscle?

    <p>Extension of the elbow</p> Signup and view all the answers

    Which of the following muscles is deep to the tendon of the triceps brachii?

    <p>Olecranon process of ulna</p> Signup and view all the answers

    Which structure is part of the abdominal muscle arrangement?

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

    Study Notes

    Relaxed vs. Contracted Sarcomere

    • In a relaxed sarcomere, regulatory proteins on actin filaments prevent myosin binding.
    • When a muscle fiber is stimulated, calcium ions are released from the sarcoplasmic reticulum.
    • Calcium binds to regulatory proteins on actin filaments, causing a shape change.
    • This change exposes myosin-binding sites on actin, allowing myosin heads to attach.
    • Myosin heads are "cocked" like oars, ready to pull towards the center of the sarcomere.
    • Myosin attachment to actin causes a power stroke, pulling the thin filaments towards the center of the sarcomere.
    • ATP provides the energy for myosin to detach and recock, enabling further movement.

    Types of Muscle Contractions

    • Isotonic contractions: Myofilaments slide past each other, resulting in muscle shortening and movement.
      • Examples: bending the knee, lifting weights.
    • Isometric contractions: Muscle filaments attempt to slide, but the muscle is against an immovable object.
      • Tension increases, but the muscle does not shorten.
      • Example: pushing palms together.

    Types of Body Movements

    • Flexion: Decreases the angle of a joint, bringing two bones closer together.
      • Common in hinge joints (knee, elbow) and ball-and-socket joints (hip).
    • Extension: Opposite of flexion, increases the angle between two bones.
      • Straightening the elbow or knee.
      • Hyperextension: Extension beyond 180 degrees.
    • Rotation: Movement of a bone around its longitudinal axis.
      • Common in ball-and-socket joints.
      • Example: Shaking your head "no".

    Naming Skeletal Muscles

    • Location: Refers to the bone or body region the muscle is associated with.
      • Examples: frontalis (frontal bone), tibialis anterior (front of tibia).
    • Shape: Describes the overall form of the muscle.
      • Examples: deltoid (triangle), trapezius (trapezoid), orbicularis (circular).
    • Size: Indicates the size of the muscle relative to other muscles.
      • Examples: maximus (largest), minimus (smallest), vastus (huge).
    • Direction of Fibers: Describes the orientation of muscle fibers relative to the muscle's long axis.
      • Examples: rectus (straight), transversus (transverse), oblique (diagonal).
    • Number of Origins: Refers to the number of distinct attachment points the muscle has.
      • Examples: biceps (two origins), triceps (three origins), quadriceps (four origins).
    • Origin and Insertion Points: Uses the names of the bones the muscle originates from and inserts onto.
      • Example: sternocleiodomastoid muscle (sternum, clavicle, mastoid process).
    • Action: Indicates the primary movement the muscle performs.
      • Examples: flexor carpi radialis (flexes wrist), abductor magnus (abducts thigh), extensor digitorum (extends fingers).

    Fascicle Arrangement

    • Different arrangements of muscle fibers within a muscle influence its power and range of motion.
      • Circular: Muscle fibers arranged in concentric rings.
        • Example: orbicularis oris.
      • Convergent: Muscle fibers converge from a wide area to a single attachment point.
        • Example: pectoralis major.
      • Fusiform: Spindle-shaped muscle with fibers running parallel to the long axis.
        • Example: biceps brachii.
      • Parallel: Muscle fibers run parallel to each other along the long axis.
        • Example: sartorius.
      • Unipennate: Muscle fibers arranged on one side of a tendon.
        • Example: extensor digitorum longus.
      • Bipennate: Muscle fibers arranged on both sides of a central tendon.
        • Example: rectus femoris.
      • Multipennate: Muscle fibers attach to a tendon at multiple angles.
        • Example: deltoid.

    Deltoid and Pelvic/Hip/Thigh Muscles

    • The deltoid muscle is a large, triangular muscle that covers the shoulder; used for intramuscular injections.
    • The pelvic, hip, and thigh muscles are:
      • Adductor muscles: Responsible for adducting the thigh.
      • Sartorius: Longest muscle in the body; flexes and rotates the thigh, flexing the knee.
      • Vastus lateralis: One of the quadriceps muscles; extends the knee.

    Muscles of the Posterior Neck, Trunk, and Arm

    • Includes trapezius, deltoid, triceps brachii, latissimus dorsi.
      • Trapezius: Elevates, depresses, retracts, and rotates the scapula.
      • Deltoid: Abducts, flexes, extends, and rotates the arm.
      • Triceps brachii: Extends the forearm.
      • Latissimus dorsi: Extends, adducts, and rotates the arm medially.

    Muscles of the Anterior Trunk, Shoulder, and Arm

    • Includes pectoralis major, serratus anterior, rectus abdominis, internal and external oblique muscles.
      • Pectoralis major: Flexes, adducts, and rotates the arm medially.
      • Serratus anterior: Protracts and rotates the scapula upward.
      • Rectus abdominis: Flexes the vertebral column.
      • Internal and external oblique muscles: Compress abdomen, flex and rotate the vertebral column.

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