Pathway of Voluntary Movement Quiz
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Questions and Answers

What is the role of upper motor neurons (UMNs) in the pathway of voluntary movement?

  • They send action potentials to the muscles.
  • They fire and send action potentials to the spinal cord. (correct)
  • They innervate muscle fibers directly.
  • They act as the final common pathway.

    • How long does it typically take for a response to occur from thought to action?

  • 30-35 ms (correct)
  • 40-45 ms
  • 10-15 ms
  • 20-25 ms

    • What structure is primarily responsible for relaying action potentials to muscles?

  • Lower motor neurons (correct)
  • Peripheral nerves
  • Motor cortex
  • Upper motor neurons

    • What type of feedback can modify muscle contraction output?

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

    What determines the force output of a muscle?

    <p>The motor unit and its control by the CNS</p> Signup and view all the answers

    Which type of muscle fibers can be classified based on motor neuron innervation?

    <p>All muscle fibers from one motor unit</p> Signup and view all the answers

    What characteristic of the motor unit affects how muscles are activated?

    <p>All muscle fibers are activated simultaneously</p> Signup and view all the answers

    Which of the following statements about sarcomeres is true?

    <p>They are the anatomical units of contraction.</p> Signup and view all the answers

    What happens to muscle tension when passive properties are added to active tension curves?

    <p>Total muscle tension increases</p> Signup and view all the answers

    What characterizes an isometric contraction?

    <p>It generates tension with no movement</p> Signup and view all the answers

    How does the speed of shortening in a muscle relate to resistance?

    <p>It decreases as resistance increases</p> Signup and view all the answers

    What occurs during eccentric contractions in terms of tension?

    <p>Tension can increase without risking muscle damage</p> Signup and view all the answers

    What is the relationship between peak power output and velocity?

    <p>Half of maximum velocity corresponds to peak power</p> Signup and view all the answers

    What limits maximum velocity in muscle contractions?

    <p>Resistance surpassing muscle strength</p> Signup and view all the answers

    In which scenario would passive tension take over during muscle activity?

    <p>When muscle stretches excessively with lower resistance</p> Signup and view all the answers

    What role does the passive component play at maximum isometric tension?

    <p>It increases muscle force without shortening</p> Signup and view all the answers

    What is the physiological advantage of smaller cells in the context of excitability?

    <p>They reach the threshold of excitement sooner.</p> Signup and view all the answers

    Why might the CNS need to increase its input for larger motor units (MUs)?

    <p>The CNS sends a fixed amount of input, which may not activate larger MUs sufficiently.</p> Signup and view all the answers

    What challenge is associated with recruiting larger motor units during activity?

    <p>Their activation results in quicker exhaustions of other motor pools.</p> Signup and view all the answers

    In muscle fibres, which type is predominantly used during glycogen depletion?

    <p>Fast-twitch IIB fibres.</p> Signup and view all the answers

    What is a major factor that contributes to the excitability of cell membranes?

    <p>The concentration of excitatory synaptic inputs.</p> Signup and view all the answers

    What does electromyography primarily record during muscle contraction?

    <p>The electrical activity of muscle tissue</p> Signup and view all the answers

    What is the relationship between force and electromyography (EMG) activity?

    <p>A linear relationship where more EMG corresponds to greater force</p> Signup and view all the answers

    Which type of motor units tend to have a higher innervation ratio and are associated with fast twitch fibers?

    <p>Type IIb fibers</p> Signup and view all the answers

    What is the relationship between muscle fiber size and motor control?

    <p>Fine control muscles have smaller fibers and less muscle mass.</p> Signup and view all the answers

    What method does intramuscular EMG use to gather data?

    <p>It inserts a needle directly into the muscle.</p> Signup and view all the answers

    Where are slow motor types primarily located within the muscle?

    <p>Central and deeply located in the muscle.</p> Signup and view all the answers

    Which mechanism does the CNS use for muscle force gradation?

    <p>Changing the rate or frequency of motor unit action potential trains</p> Signup and view all the answers

    Which muscle fiber type is primarily associated with endurance?

    <p>Type I fibers.</p> Signup and view all the answers

    What is generally observed about slow twitch fibers compared to fast twitch fibers?

    <p>They have a slower shortening capacity</p> Signup and view all the answers

    What happens to muscle force when shock is applied to muscle tissue?

    <p>It results in a smaller and slower twitch response</p> Signup and view all the answers

    What happens to muscle tension when the sarcomere is excessively stretched?

    <p>There will be no cross-bridges formed.</p> Signup and view all the answers

    What role does temporal summation play in muscle contraction?

    <p>It enhances the overall force by increasing the frequency of action potentials</p> Signup and view all the answers

    How does optimal sarcomere length affect muscle force generation?

    <p>It can generate force due to adequate cross-bridge formation.</p> Signup and view all the answers

    What characterizes the innervation ratio in muscles requiring fine motor control?

    <p>Low number of fibers for fewer motor neurons.</p> Signup and view all the answers

    What effect does stretching a muscle have on its tension?

    <p>Tension increases up to a certain point before decreasing.</p> Signup and view all the answers

    Which factor does NOT influence the length-tension relationship of a muscle?

    <p>The number of motor neurons innervating the muscle.</p> Signup and view all the answers

    Study Notes

    Pathway of Voluntary Movement

    • Movement begins with the upper motor neuron (UMN) in the motor cortex firing action potentials (APs).
    • These APs travel down descending pathways from the brain to the spinal cord.
    • The motor neuron system (MNS) is part of the central nervous system (CNS), but their axons are long and extend to the periphery.
    • It takes about 30-35 milliseconds for a signal to travel from thought to action.
    • The final common pathway for motor output is the lower motor neuron (LMN) in the spinal cord sending APs to muscles.
    • The LMN is the main controllable element in the motor pathway and determines the force output of the muscles.

    The Motor Unit

    • A motor unit consists of one motor neuron and all the muscle fibers it innervates.
    • One motor neuron can innervate multiple muscle fibers.
    • Muscles contain hundreds of motor units.
    • The type of muscle fiber in a motor unit is determined by the motor neuron.
    • The size of a motor unit (number of muscle fibers innervated) determines the level of fine control possible.

    Motor Unit (MU) Size and Control

    • Muscles requiring fine control have a smaller innervation ratio (fewer muscle fibers per motor unit) compared to larger muscles requiring more force.
    • Slow twitch muscle fibers are more centrally located, deep within the muscle to receive an adequate blood supply.
    • Fast twitch muscle fibers tend to be located more peripherally.

    Variability in Muscle Fiber Types

    • The proportion of slow twitch (type I) and fast twitch (type II) muscle fibers varies between individuals.
    • Humans are mostly made up of slow twitch fibers optimized for endurance.
    • It's possible to make fast twitch fibers act more like slow twitch fibers and vice versa, but not through actual type conversion.
    • Length-Tension Relationship: A muscle can produce the most force when it is at its optimal length.
      • Excessive shortening or stretching decreases force production since fewer cross-bridges can be formed.
    • Whole Muscle Length-Tension Relationship: Longer muscles generate more tension due to the contribution of passive components (elastic connective tissue).
      • These passive elements contribute to the total muscle tension curve, which is the sum of active and passive tension.
    • Load-Velocity Relationship: The speed of muscle shortening is dictated by the resistance it encounters.
      • A muscle can shorten at its maximum velocity (Vmax) with no resistance.
      • When resistance increases, the velocity of shortening decreases.
    • Power: The power of a muscle contraction is measured in watts and is calculated by multiplying force and velocity.
      • Peak power output occurs at about half of Vmax.
      • Motor units control the speed, strength, and power of muscle contractions.

    Electromyography (EMG)

    • Surface EMG: Records the electrical activity of a muscle during contraction by placing electrodes on the skin.
      • Provides an overall measure of electrical activity in the muscle.
      • Does not allow for the identification of individual motor unit activity.
    • Intramuscular EMG: Records electrical activity directly from within a muscle using a needle electrode.
      • Allows for the recording of individual motor unit activity.
      • Enables the observation of the firing rate of motor units.

    Muscle Force Gradation

    • The CNS uses two mechanisms to control muscle force:
      • Recruitment: Activating more motor units.
      • Rate Coding: Increasing the firing rate of motor units.
    • Small motor units are easier to activate (lower threshold) than large motor units.
    • Smaller motor units have a higher surface area to volume ratio, leading to concentrated excitatory currents and easier excitation.
    • Larger motor units are recruited later and do not fire for as long as smaller motor units.
    • All motor unit types are used during different phases of movement, with type IIB fibers being recruited primarily during high-intensity bursts.

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    Description

    Test your knowledge on the pathway of voluntary movement including the roles of upper and lower motor neurons, as well as motor units. This quiz covers essential concepts related to the central nervous system and how signals travel from the brain to muscles. Assess your understanding of motor output and muscle innervation.

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