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?

Ventral vestibulospinal tract Signup and view all the answers

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

They facilitate skeletal muscle tone Signup and view all the answers

Which nuclei are indirectly connected to the globus pallidus?

Subthalamus and tectum of the midbrain Signup and view all the answers

Which motor neurons are affected by the olivospinal tract?

Both alpha and gamma motor neurons Signup and view all the answers

What type of movements does the extrapyramidal system primarily mediate?

Gross movements involving large muscles Signup and view all the answers

Which structures are NOT part of the extrapyramidal system?

Cerebellum Signup and view all the answers

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

Giant pyramidal neurons Signup and view all the answers

The rubrospinal tract influences which type of muscles?

Physiological flexor muscles of the fore- and hindlimb Signup and view all the answers

What is the primary function of the lateral tectospinal tract?

To direct the eye and turn the head towards a light source Signup and view all the answers

What does lesioning the red nucleus primarily affect?

Use of the contralateral distal limb Signup and view all the answers

Which of the following tracts originates from the inferior colliculus?

Ventral tectospinal tract Signup and view all the answers

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

Throughout the medulla, pons, and mesencephalon Signup and view all the answers

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

Filtering incoming sensory information Signup and view all the answers

What is commonly referred to as stroke?

Interruption of blood supply to the motor cortex Signup and view all the answers

What is a key characteristic of upper motor neuron lesions?

Weakness or paralysis of the involved muscles Signup and view all the answers

What does spasticity indicate in upper motor neuron lesions?

Increased muscle tone Signup and view all the answers

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

Increased stretch reflexes Signup and view all the answers

Which statement about the extrapyramidal system is accurate?

It may lead to slowness of movements Signup and view all the answers

How do upper motor neuron lesions usually affect reflex responses?

They increase the stretch reflexes Signup and view all the answers

The presence of a positive Babinski sign indicates which condition?

Upper motor neuron lesion Signup and view all the answers

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

Mediating fine and discrete movements 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)
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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.