Neuroscience: Extrapyramidal System
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Questions and Answers

What is the main function of the lateral reticulospinal tract?

  • Provides input to the cerebellum
  • Inhibits the gamma motor neurons (correct)
  • Facilitates the gamma motor neurons
  • Facilitates the stretch reflex
  • From which part of the brain does the ventral reticulospinal tract originate?

  • Cerebellum
  • Medulla
  • Spinal cord
  • Pons (correct)
  • Which structure receives input from the basal ganglia and sends output fibers to the cerebellum?

  • Vestibular nucleus
  • Inferior olive (correct)
  • Globus pallidus
  • Ventral horn cells
  • Which tract is responsible for adjustments of head position?

    <p>Ventral vestibulospinal tract</p> Signup and view all the answers

    What is the function of the vestibulospinal tracts in relation to muscle tone?

    <p>They facilitate skeletal muscle tone</p> Signup and view all the answers

    Which nuclei are indirectly connected to the globus pallidus?

    <p>Subthalamus and tectum of the midbrain</p> Signup and view all the answers

    Which motor neurons are affected by the olivospinal tract?

    <p>Both alpha and gamma motor neurons</p> Signup and view all the answers

    What type of movements does the extrapyramidal system primarily mediate?

    <p>Gross movements involving large muscles</p> Signup and view all the answers

    Which structures are NOT part of the extrapyramidal system?

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

    What type of neurons are found in the lower part of the red nucleus?

    <p>Giant pyramidal neurons</p> Signup and view all the answers

    The rubrospinal tract influences which type of muscles?

    <p>Physiological flexor muscles of the fore- and hindlimb</p> Signup and view all the answers

    What is the primary function of the lateral tectospinal tract?

    <p>To direct the eye and turn the head towards a light source</p> Signup and view all the answers

    What does lesioning the red nucleus primarily affect?

    <p>Use of the contralateral distal limb</p> Signup and view all the answers

    Which of the following tracts originates from the inferior colliculus?

    <p>Ventral tectospinal tract</p> Signup and view all the answers

    In which areas of the brainstem does the reticular formation extend?

    <p>Throughout the medulla, pons, and mesencephalon</p> Signup and view all the answers

    What role does the reticular formation play in the nervous system?

    <p>Filtering incoming sensory information</p> Signup and view all the answers

    What is commonly referred to as stroke?

    <p>Interruption of blood supply to the motor cortex</p> Signup and view all the answers

    What is a key characteristic of upper motor neuron lesions?

    <p>Weakness or paralysis of the involved muscles</p> Signup and view all the answers

    What does spasticity indicate in upper motor neuron lesions?

    <p>Increased muscle tone</p> Signup and view all the answers

    Which of the following is NOT a sign of lower motor neuron lesions?

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

    Which statement about the extrapyramidal system is accurate?

    <p>It may lead to slowness of movements</p> Signup and view all the answers

    How do upper motor neuron lesions usually affect reflex responses?

    <p>They increase the stretch reflexes</p> Signup and view all the answers

    The presence of a positive Babinski sign indicates which condition?

    <p>Upper motor neuron lesion</p> Signup and view all the answers

    What role does the pyramidal system primarily serve in motor control?

    <p>Mediating fine and discrete movements</p> Signup and view all the answers

    Study Notes

    The Extrapyramidal System

    • Includes all brain and brainstem components contributing to motor control outside the direct pyramidal system
    • Components include basal ganglia, reticular formation, vestibular nuclei, red nuclei, substantia nigra, tectum and subthalamic nucleus

    Red Nucleus

    • Receives projections from the motor cortex (cortico-rubral tract) and collateral fibers from the corticospinal tract & globus pallidus of the basal ganglia
    • Lower part of the red nucleus contains giant pyramidal neurons (similar to Betz cells) originating the rubrospinal tract
    • Rubrospinal tract crosses to the opposite side and descends anterior to the lateral corticospinal tract
    • Exerts significant influence over physiological flexor muscles of limbs
    • Lesion or inactivation leads to contralateral distal limb deficits resembling motor cortex or corticospinal tract lesions

    Tectum of the Midbrain

    • Receives projections from the globus pallidus
    • Originates two descending extrapyramidal tracts:
      • Lateral tectospinal tract: Originates from the superior colliculus (visual reflex center), crosses to the opposite side and terminates in cervical segments of the spinal cord; responsible for directing the eye and turning the head towards a light source (visuospinal reflexes)
      • Ventral tectospinal tract: Originates from the inferior colliculus (auditory reflex center), crosses to the opposite side and terminates in cervical segments of the spinal cord; responsible for turning the head towards sound sources (audiospinal reflexes)

    Reticular Formation

    • Extends from the spinal cord's upper end throughout the brainstem (medulla, pons, mesencephalon)
    • Complex intertwining nets of small neurons
    • Receives projections from the globus pallidus
    • Originates two descending extrapyramidal tracts:
      • Lateral reticulospinal tract: Originates from the inhibitory reticular formation of the medulla, descends on both sides of the spinal cord (mostly ipsilateral) and inhibits the gamma motor neurons, thus inhibiting the stretch reflex and skeletal muscle tone
      • Ventral reticulospinal tract: Originates from the facilitatory reticular formation of the pons, descends without crossing and terminates on the gamma motor neurons of the ipsilateral side of the spinal cord; facilitates the gamma motor neurons, thus facilitating the stretch reflex and skeletal muscle tone

    Basal Ganglia

    • Receives projections from the motor cortex to the corpus striatum and then to the globus pallidus
    • Projects to brain stem nuclei including subthalamus, substantia nigra, red nucleus, tectum, reticular formation, vestibular nucleus, and inferior olive

    Vestibular Nucleus of the Medulla

    • Receives projections from the globus pallidus
    • Originates two descending extrapyramidal tracts:
      • Lateral vestibulospinal tract: Originates from the vestibular nucleus, descends without crossing to terminate on the alpha and gamma motor neurons (postural adjustments)
      • Ventral vestibulospinal tract: Originates from the vestibular nucleus, descends on both sides of the spinal cord to terminate on alpha and gamma motor neurons (adjustments of head position)
    • Facilitates the stretch reflex and skeletal muscle tone, and mediates some postural reflexes

    Inferior Olive of the Medulla

    • Receives input fibers from the motor cortex, globus pallidus and spinal cord
    • Sends output fibers to the cerebellum and projects the fibers of the olivospinal tract
    • Olivospinal tract descends in the spinal cord to terminate on the ventral horn cells of the same side
    • Facilitates the stretch reflex and skeletal muscle tone
    • Works in close association with the cerebellum to correct deviations in muscle contraction from movement plans (servocomparator function)

    General Functions of the Extrapyramidal System

    • Mediation of gross movements involving groups of large muscles
    • Providing a weaker alternative to the pyramidal system for some discrete movements
    • Mediation of fixation and positioning movements accompanying fine movements
    • Adjustment of skeletal muscle tone through facilitation or inhibition
    • Adjustment of muscle movements to match preset plans to reach a certain target

    Stroke

    • Damage to the motor cortex or pyramidal tracts due to interruption of blood supply resulting in hemiplegia
    • "Upper motor neuron" is preferred over "pyramidal tract" as the signs traditionally described include both pyramidal tract and subcorticospinal pathways
    • A single upper motor neuron with direct synaptic contact with a lower motor neuron is uncommon except for finger muscles

    Signs of Upper Motor Neuron Lesion

    • Weakness in corticospinal distribution: Shoulder abduction, finger movements, hip flexion, toe dorsiflexion
    • Spastic increase in muscle tone
    • Increased stretch reflexes
    • Extensor planter response (positive Babinski sign)
    • Little or no atrophy

    Signs of Lower Motor Neuron Lesion

    • Weakness or paralysis of the involved muscles
    • Loss of tone on passive movement (flaccidity)
    • Absence of reflexes in the involved muscles
    • A normal flexor planter response unless neurons are damaged
    • Muscle atrophy
    • Abnormal electrical excitability of peripheral nerves and muscle in association with fibrillation and fasciculation

    Lesion of the Extrapyramidal System Only

    • No muscle paralysis but slowness of movements with facial expression changes and loss of some stereotyped movements (e.g., swinging the arm while walking)
    • Muscle tone could be increased or decreased. Hypertonia of extrapyramidal type affects both gravity and antigravity muscles equally (rigidity)
    • *** (missing information from the text provided)***

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    Description

    Explore the intricacies of the extrapyramidal system, including key components such as the basal ganglia and red nucleus. Understand how these structures contribute to motor control and their interactions with other brain regions. This quiz will test your knowledge of the physiology and implications of lesions in this important neural network.

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