Patellar Reflex Quiz: Knee-Jerk Reflex
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Questions and Answers

What is the primary function of the inverse stretch reflex?

  • Regulates muscle tone
  • Prevents excessive tension on the muscle (correct)
  • Assesses the integrity of sensory and motor reflex pathways
  • Causes muscle contraction

    • Which type of reflex is characterized by the contraction of all the flexor muscles in a limb in response to a noxious stimulus?

  • Inverse stretch reflex
  • Withdrawal reflex (correct)
  • Flexor reflex (correct)
  • Extensor reflex

    • What is the main action of the flexor reflex on the alpha motor neurons?

  • Inhibition of alpha motor neurons to extensor muscles
  • Inhibition of alpha motor neurons to flexor muscles
  • Stimulation of alpha motor neurons to extensor muscles
  • Stimulation of alpha motor neurons to flexor muscles (correct)

    • Which of the following is NOT a characteristic of the withdrawal reflex?

    <p>It is a monosynaptic reflex</p> Signup and view all the answers

    What is the role of the gamma loop in regulating muscle tone?

    <p>It is involved in the reflexes using muscle spindle and Golgi tendon organ</p> Signup and view all the answers

    Which segments of the spinal cord are involved in the withdrawal reflex of the thoracic limb?

    <p>C6-T2</p> Signup and view all the answers

    What is the term for the muscle's continuous resistance to being stretched?

    <p>Muscle tone</p> Signup and view all the answers

    What is the purpose of evaluating extensor tone during a neurological examination?

    <p>To evaluate the function of the spinal cord</p> Signup and view all the answers

    What is the relationship between the intensity of the noxious stimulus and the response of the withdrawal reflex?

    <p>The response is proportional to the intensity of the stimulus</p> Signup and view all the answers

    Where are the cell bodies of upper motor neurons located?

    <p>In the motor nucleus of the brainstem or the motor cortex of the forebrain</p> Signup and view all the answers

    What is the primary function of the upper motor neuron system?

    <p>To initiate and regulate voluntary movement</p> Signup and view all the answers

    What happens when inhibitory upper motor neurons are lost?

    <p>Muscle tone increases</p> Signup and view all the answers

    What is the result of a loss of facilitatory upper motor neurons?

    <p>Paresis or paralysis</p> Signup and view all the answers

    What is the term for uncoordinated movement?

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

    What is the term for weakness of voluntary movement?

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

    What is the role of upper motor neurons in regulating lower motor neurons?

    <p>They can either stimulate or inhibit lower motor neurons</p> Signup and view all the answers

    What is the term for the loss of motor function?

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

    What is the result of a loss of upper motor neurons on muscle tone?

    <p>Muscle tone increases</p> Signup and view all the answers

    What type of reflex is the patellar reflex primarily classified as?

    <p>Monosynaptic reflex</p> Signup and view all the answers

    Which nerve is involved in the patellar reflex?

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

    What is the cord segment involved in the patellar reflex?

    <p>L4, L5, L6</p> Signup and view all the answers

    What is the primary action of the patellar reflex?

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

    What is the receptor sensitive to in the Golgi tendon organ reflex?

    <p>Muscle tension</p> Signup and view all the answers

    What is the purpose of the reciprocal inhibition in the patellar reflex?

    <p>To prevent muscles from working against each other</p> Signup and view all the answers

    What is the name of the receptor that detects muscle stretch in the patellar reflex?

    <p>Muscle spindle</p> Signup and view all the answers

    What is the function of the Golgi tendon organ reflex?

    <p>To mitigate the force of muscle contraction</p> Signup and view all the answers

    What is the patellar reflex also known as?

    <p>Knee-jerk reflex</p> Signup and view all the answers

    What is the method to test the motor system in animals?

    <p>Applying gentle pressure to the plantar or palmar surface of the pelvic or thoracic limbs</p> Signup and view all the answers

    What is the normal response when pressure is applied to the plantar or palmar surface of the pelvic or thoracic limbs in animals?

    <p>The limb is easy to flex</p> Signup and view all the answers

    How many main components can the motor system be divided into?

    <p>2</p> Signup and view all the answers

    What is the origin of Lower Motor Neurons (LMN) in the spinal cord?

    <p>Ventral horn of the spinal cord</p> Signup and view all the answers

    Where do Upper Motor Neurons (UMN) typically originate?

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

    What is the function of Upper Motor Neurons (UMN)?

    <p>Project to and control Lower Motor Neurons (LMN)</p> Signup and view all the answers

    What is the name of the pathway that Upper Motor Neurons (UMN) belong to?

    <p>Corticomedullary pathway</p> Signup and view all the answers

    What is the direction of the green arrowheads in the diagram?

    <p>From Upper Motor Neurons to Lower Motor Neurons</p> Signup and view all the answers

    What type of synapse occurs between Upper Motor Neurons and Lower Motor Neurons?

    <p>Indirect synapse with local synapses</p> Signup and view all the answers

    What is the result of loss of facilitatory UMNs?

    <p>Paresis or paralysis</p> Signup and view all the answers

    What is the primary function of LMNs?

    <p>To initiate motor movement</p> Signup and view all the answers

    What is the characteristic of muscle tone in LMN lesions?

    <p>Decreased to absent muscle tone</p> Signup and view all the answers

    What is the characteristic of muscle atrophy in UMN lesions?

    <p>Mild and chronic</p> Signup and view all the answers

    What is the location of UMNs in the CNS?

    <p>CNS neurons that communicate with LMNs</p> Signup and view all the answers

    What is the level of the spinal cord where LMNs innervating the limbs are confined?

    <p>Cervical and lumbar intumescences</p> Signup and view all the answers

    What is the result of a high cervical lesion?

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

    What is the characteristic of reflexes in UMN lesions?

    <p>Increased reflexes</p> Signup and view all the answers

    What is the problem in a lesion that results in paresis or paralysis, with decreased to absent muscle tone and reflexes?

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

    Study Notes

    Patellar Reflex (Quadriceps, Knee-Jerk Reflex)

    • Elicited by tapping the tendon of the quadriceps femoris muscle located immediately distal to the patella
    • Tests the stretch reflex mediated by the femoral nerve
    • This is the most reliable test of the stretch reflex
    • Cord segment involved: L4, L5, L6

    Stretch Reflex

    • Main action: contraction
    • Secondary action: reciprocal inhibition, inactivation of antagonist muscle
    • Stretch reflexes and other muscle contractions often accompanied by reciprocal inhibition, which prevents muscles from working against each other

    Inverse Stretch Reflex (Golgi Tendon Organ Reflex)

    • Main action: reduced stimulation, inhibited at the level of the spinal cord
    • Secondary action: reciprocal stimulation
    • Responds to contraction, causes muscle relaxation, and prevents excessive tension on the muscle

    Flexor Reflex (Withdrawal Reflex)

    • Coordinated polysynaptic reflex in which all the flexor muscles of a limb contract in response to a noxious stimulus
    • Alpha motor neurons to the limb flexor muscles are stimulated, while those to extensor muscles are inhibited
    • Reciprocal innervation
    • The force and duration of the withdrawal reflex are proportional to the intensity of the noxious stimulus applied

    Extensor Tone

    • Muscle tone is important for maintaining normal posture and providing support for the joints to stabilize their position
    • It refers to the muscle's continuous resistance to being stretched (resting tension)
    • It is regulated by the local spinal cord reflexes and by higher levels of the brain
    • Muscle tone (extensor tone) is evaluated during neurological examination

    Motor System

    • Can be divided into 2 main components: Upper Motor Neuron (UMN) and Lower Motor Neuron (LMN)
    • Upper Motor Neurons:
      • Completely contained within the CNS
      • Cell body is located in a motor nucleus of the brainstem or the motor cortex of the forebrain
      • Their axons connect to lower motor neurons
      • Exert their effect by stimulating or inhibiting LMNs
      • UMN system is responsible for initiation of voluntary movement, maintenance of muscle tone for support against gravity, and regulation of posture
    • Lower Motor Neurons:
      • Cell body is located in the ventral horn of the spinal cord or in cranial nerve nuclei
      • Their axons directly innervate skeletal muscle
      • LMNs are responsible for the transmission of motor signals to muscles

    Upper Motor Neurons vs. Lower Motor Neurons

    • UMN signs:
      • Paresis or paralysis
      • Normal to increased reflexes
      • Normal to increased extensor muscle tone
      • Mild/chronic muscle atrophy
    • LMN signs:
      • Paresis or paralysis
      • Decreased to absent reflexes
      • Decreased to absent extensor muscle tone
      • Severe/fast muscle atrophy

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    Description

    A short quiz on the patellar reflex, a monosynaptic reflex involving the quadriceps femoris muscle and the spinal cord alpha motor neurons.

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