Biomechanics & Surgery: Muscle Structure and Contraction
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Questions and Answers

Which muscle is considered the main or prime mover in a particular movement?

  • Synergist
  • Antagonist
  • Co-contractor
  • Agonist (correct)

    • Which type of muscle fiber is predominant in tonic or stability muscles?

  • Slow-twitch (Type I) fibers (correct)
  • Muscle fibers are not relevant for tonic or stability muscles
  • Fast-twitch (Type IIa & IIb) fibers
  • A mix of fast-twitch and slow-twitch fibers

    • What is the primary function of synergist muscles?

  • To oppose the action of the agonist
  • To produce the main force for a movement
  • To stabilize neighboring joints (correct)
  • To contract simultaneously with the agonist

    • Which relationship describes how muscle length affects the force it can produce?

    <p>Length-Tension Relationship</p> Signup and view all the answers

    What is the term used to describe the simultaneous contraction of agonist and antagonist muscles?

    <p>Co-contraction</p> Signup and view all the answers

    Which type of muscle is used primarily for short, powerful actions?

    <p>Phasic or mobility muscles</p> Signup and view all the answers

    What is the primary function of muscles?

    <p>To produce moments (rotational forces) about joints</p> Signup and view all the answers

    How are mono-articular and multi-articular muscles classified?

    <p>Mono-articular muscles cross a single joint, while multi-articular muscles cross multiple joints</p> Signup and view all the answers

    What happens when the number of cross bridges attached to actin filaments increases?

    <p>The contraction force increases</p> Signup and view all the answers

    What is the function of the tendon?

    <p>To transmit the force produced by the muscle to the bone</p> Signup and view all the answers

    Which of the following describes a twitch response in a muscle fiber?

    <p>It is a single contraction in response to a single stimulus from the motor neuron</p> Signup and view all the answers

    What is the difference between the origin and insertion of a muscle?

    <p>The origin is the proximal attachment, and the insertion is the distal attachment</p> Signup and view all the answers

    What is the role of multi-articular muscles?

    <p>They can move two or more joints in the same direction</p> Signup and view all the answers

    What happens when the frequency of stimuli to a muscle fiber increases?

    <p>The tension in the fiber increases between stimuli</p> Signup and view all the answers

    Which type of muscular contraction generates the least force when maximally stimulated?

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

    How can an understanding of muscle mechanics be applied?

    <p>To optimize an individual's performance in various activities</p> Signup and view all the answers

    In which type of muscular contraction does the joint angle remain constant?

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

    Which type of muscular contraction is produced during the use of an 'isokinetic dynamometer'?

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

    What is the primary function of a mono-articular muscle?

    <p>To generate positive work</p> Signup and view all the answers

    Which of the following is NOT a characteristic of a bi-articular muscle?

    <p>Primarily used to generate positive work</p> Signup and view all the answers

    What is the typical range of muscle cross-sectional area that affects maximal joint torque?

    <p>0.3-0.4 N/sq.mm</p> Signup and view all the answers

    What is the relationship between the $FL/ML$ ratio and the muscle's force-velocity characteristics?

    <p>A low $FL/ML$ ratio indicates high velocity, while a high ratio indicates high force generation</p> Signup and view all the answers

    Which type of muscle contraction produces the highest torque?

    <p>Eccentric contraction</p> Signup and view all the answers

    What is the primary function of the gastrocnemius muscle?

    <p>To produce plantarflexion</p> Signup and view all the answers

    In the 'real world' situation, which statement is true about muscle contraction?

    <p>The contraction may be concentric, isometric or eccentric</p> Signup and view all the answers

    How does the pennation angle of a muscle fiber affect its force generation?

    <p>Increasing the pennation angle decreases the force generation of the muscle</p> Signup and view all the answers

    Which of the following statements about muscle action in the 'real world' is incorrect?

    <p>The muscle has a single action, such as adducting the hip</p> Signup and view all the answers

    What is the main purpose of studying muscle mechanics?

    <p>To determine the length, velocity, power, and force generation of muscles</p> Signup and view all the answers

    In the 'real world' situation, how does gravity affect muscle movement?

    <p>Gravity may oppose, help or produce movement</p> Signup and view all the answers

    Which of the following statements about muscle contraction speed and torque is correct?

    <p>Both (a) and (b)</p> Signup and view all the answers

    Study Notes

    Muscle Function and Classification

    • The main or prime mover in a movement is known as the agonist muscle.
    • Tonic or stability muscles predominantly consist of slow-twitch muscle fibers (Type I), which are endurance-oriented.
    • Synergist muscles assist the prime mover by stabilizing joints and helping to produce a smoother motion.
    • The length-tension relationship describes how optimal muscle length increases the force production capability of muscles.
    • Cocontraction refers to the simultaneous contraction of agonist and antagonist muscles.

    Muscle Contraction Types

    • Fast-twitch fibers (Type II) are primarily used for short, powerful actions.
    • The primary function of muscles is to facilitate movement and provide stability.
    • Mono-articular muscles cross one joint, while multi-articular muscles span multiple joints.

    Muscle Mechanics and Forces

    • An increase in the number of cross bridges attached to actin filaments enhances muscle contraction strength.
    • Tendons connect muscles to bones, transmitting force generated by muscle contractions.
    • A twitch response in a muscle fiber is a single contraction cycle in response to a stimulus.

    Muscle Attachment and Roles

    • The origin of a muscle is the attachment point that remains stationary, while the insertion moves during contraction.
    • Multi-articular muscles are involved in complex movements, allowing them to function across different joints.
    • An increase in the frequency of stimuli to a muscle fiber leads to tetanus, a sustained contraction.

    Muscle Contraction Characteristics

    • Isometric contractions occur when the joint angle remains constant, producing tension without movement.
    • Isokinetic contractions are performed with a constant speed against resistance, often using a dynamometer.
    • Mono-articular muscles primarily function to produce movement at a single joint.

    Muscle Fiber Characteristics

    • Characteristics of bi-articular muscles include being able to cross more than one joint, allowing for versatility in movement.
    • The typical range for muscle cross-sectional area impacting maximal torque is about 30-50 cm².
    • The force-velocity relationship suggests a trade-off between force and the speed of contraction with a lower FL/ML ratio indicating higher velocity.

    Torque and Functional Insights

    • The type of muscular contraction that produces the highest torque is the eccentric contraction.
    • The primary function of the gastrocnemius muscle is to facilitate plantarflexion of the foot.
    • In real-world situations, gravity significantly influences muscle movement by providing resistance.
    • The interaction between muscle contraction speed and torque typically indicates that slower contractions yield higher torque output.

    Purpose of Studying Muscle Mechanics

    • Understanding muscle mechanics aids in optimizing performance in sports, rehabilitation strategies, and preventing injuries, thus enhancing overall movement efficacy.

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