Clinical Neuroscience Week 5 - Spinal Cord Descending Pathways

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Questions and Answers

Which of the following is NOT a component of the pyramidal tract?

Corticobulbar tract

Rubrospinal tract (correct)

Anterior corticospinal tract

Lateral corticospinal tract

What is the primary function of the anterior corticospinal tract?

Control of posture and balance

Control of fine motor movements in the limbs

Control of involuntary movements in the limbs

Control of voluntary movements in the axial muscles (correct)

Where do the fibers of the corticospinal tract decussate?

Medulla (correct)

Midbrain

Spinal cord

Pons

What is the consequence of a lesion in the lateral corticospinal tract?

Loss of fine motor control in the contralateral limbs (A) Signup and view all the answers

Which of the following is an example of a motor pathway that is NOT part of the pyramidal tract?

All of the above (D) Signup and view all the answers

What is the role of the internal capsule in the corticospinal tract?

It houses a dense collection of ascending and descending fibers (D) Signup and view all the answers

What percentage of corticospinal tract fibers originate from the primary motor cortex?

30-40% (D) Signup and view all the answers

What is the primary difference between the corticospinal and corticobulbar pathways?

The corticospinal pathway targets muscles in the limbs, while the corticobulbar pathway targets muscles in the head and face. (B) Signup and view all the answers

What is the significance of the corona radiata in the corticospinal tract?

It is a dense web of fibers that connect different regions of the cerebral cortex. (D) Signup and view all the answers

Why is the anterior corticospinal tract limited to impacting the cervical and thoracic regions, unlike the lateral corticospinal tract which impacts lumbar and sacral regions?

The anterior pathway is responsible for controlling axial muscles, which are primarily located in the cervical and thoracic regions. (D) Signup and view all the answers

Which of the following is NOT a characteristic of the corticobulbar tract?

Descends directly into the spinal cord (A) Signup and view all the answers

What is the MAIN function of the corticobulbar tract?

To control voluntary movement of muscles in the head and neck (D) Signup and view all the answers

Which of the following statements about the hypoglossal nerve (CN XII) is CORRECT?

It is only affected by lesions on the same side of the brain. (B) Signup and view all the answers

What is the clinical significance of bilateral influence of the corticobulbar tracts?

It allows for redundancy, meaning that damage to one side may not cause significant clinical effects. (D) Signup and view all the answers

Which of the following cranial nerves receives unilateral input from the corticobulbar tract?

Hypoglossal nerve (CN XII) (A), Facial nerve (CN VII) (C) Signup and view all the answers

Which of the following statements about the extrapyramidal pathways is CORRECT?

They are responsible for reflexes and automatic movements. (A) Signup and view all the answers

What is the primary function of the reticulospinal tract?

To maintain posture and balance during movement (A) Signup and view all the answers

Which of the following extrapyramidal tracts plays a role in head orientation in response to auditory stimuli?

Tectospinal (D) Signup and view all the answers

What is the main function of the rubrospinal tract?

To control large muscle movements, especially flexors (B) Signup and view all the answers

Which of the following is a characteristic of spasticity?

It is a state of involuntary muscle contraction and resistance to stretch. (D) Signup and view all the answers

What is the primary mechanism that causes spasticity?

Damage to the corticospinal tract (D) Signup and view all the answers

What type of stroke is MOST commonly associated with weakness in the face, hand, and arm?

MCA stroke (B) Signup and view all the answers

Which of the following is TRUE about an ACA stroke?

It is more likely to affect the lower extremities than the upper extremities. (B) Signup and view all the answers

Which descending pathway(s) is/are likely impacted by an MCA stroke?

Corticospinal tract and the cortical bulbar tract (D) Signup and view all the answers

Are the deficits resulting from an MCA stroke likely to be contralateral or ipsilateral to the lesion?

Contralateral (B) Signup and view all the answers

Which extrapyramidal pathway is directly involved in the control of posture?

Reticulospinal (A), Vestibulospinal (B) Signup and view all the answers

In an individual with a complete spinal cord injury, which of the following is NOT a characteristic finding?

Increased muscle mass below the level of injury (A) Signup and view all the answers

A patient presents with weakness primarily affecting the contralateral upper extremity, with less impact on the lower extremity. This pattern is most consistent with a stroke affecting which artery?

Middle cerebral artery (MCA) (D) Signup and view all the answers

Which of the following is a key difference between central and peripheral lesions regarding muscle strength?

Central lesions can be strengthened through direct electrical stimulation, while peripheral lesions cannot. (A) Signup and view all the answers

Which of the following is NOT a common age-related change affecting skeletal muscle in stroke patients?

Enhancement of Type I muscle fibers (A) Signup and view all the answers

Which of the following correctly describes the difference between central and peripheral fatigue?

Central fatigue is a result of reduced neural drive, while peripheral fatigue is caused by depletion of glycogen stores in the muscle. (D) Signup and view all the answers

In a patient with a stroke affecting the middle cerebral artery (MCA), what is the most likely expected pattern of sensation?

Contralateral sensory loss, more pronounced in the upper extremity compared to the lower extremity. (D) Signup and view all the answers

Which of the following accurately describes the mechanism by which a lesion in the central nervous system (CNS) affects muscle function?

The lesion blocks the outflow of neural signals from the brain to the spinal cord and ultimately to the muscle. (A) Signup and view all the answers

In an individual with a peripheral lesion affecting a motor nerve, what is the primary goal of rehabilitation?

Strengthening muscles surrounding the affected area to compensate for the weakened muscle. (A) Signup and view all the answers

Which of the following statements accurately describes the effect of a central lesion on muscle strength?

Central lesions can be partially overcome with intensive rehabilitation, but the muscle will never reach its full potential. (A) Signup and view all the answers

Why is it important to understand the difference between central and peripheral fatigue in rehabilitation?

Understanding the type of fatigue can help determine the most effective rehabilitation strategies. (B) Signup and view all the answers

Study Notes

Descending Motor Pathways

Descending pathways carry motor signals from the brain to the muscles.
Two major categories: pyramidal and extrapyramidal tracts.
Pyramidal tracts are involved in voluntary movements and include the corticospinal tract.
Extrapyramidal tracts are involved in posture, locomotion, and balance.

Corticospinal (CST) Tract

Also known as pyramidal tracts.
Two parts: lateral and anterior/ventral.
Purpose: initiate simple voluntary movements.
Pathway: Cortex → Corona Radiata → Internal Capsule → Midbrain → Spinomedullary Junction → Skeletal Muscle (α and γ motor neurons).
About 90% of corticospinal fibers decussate (cross over).
10-20% remain ipsilateral leading to some level of ipsilateral weakness observed after stroke.
CST Fibers Origin: Primary motor cortex, supplementary motor area, premotor cortex, and parietal lobe.

Anterior/Ventral CST

Located in anterior portion of the CST
Fibers do not decussate until the level of the spinal cord
Primarily innervates the cervical and thoracic regions.
Pathway: Cortex → Corona Radiata → Internal Capsule → Midbrain → Spinomedullary Junction (no decussation) → Cervical/Thoracic Skeletal Muscle (α and γ motor neurons).

Corticobulbar Pathway

Fibers homologous to cortical spinal tract fibers.
Terminates in motor nuclei of cranial nerves (e.g., CN 5, 7, 9, 10, 11).
Part of the upper motor neuron system.
Pathway: Internal Capsule → Midbrain → Brainstem nuclei.
Corticobulbar tracts generally provide bilateral influence on cranial nerve nuclei, making unilateral lesions have less effect.

Extrapyramidal Tracts

Located in the brainstem.
Four tracts: reticulospinal, tectospinal, vestibulospinal, rubrospinal.
Pathways for supporting movement, posture, and locomotion.
Rubrospinal pathway is the only extrapyramidal tract that decussates.
Not under conscious voluntary control.
Function: Reticulospinal (locomotion and posture); Tectospinal (head orientation); Vestibulospinal (head position); Rubrospinal (large muscle movements; mainly flexors).

Clinical Application - Spasticity

Involuntary resistance to passive movement in a muscle.
Mechanism: Damage to the corticospinal tract disrupts inhibitory signals to muscles leading to increased excitatory input from extrapyramidal pathways.
Outcome: Continuous muscle contraction (spasticity).
Location: Can occur in any limb, and severity varies among individuals.
Treatment: Multifactorial, including medication, physical therapy techniques, and assistive devices.
Prognosis: Spasticity can be permanent following corticospinal tract damage.

Clinical Application - Stroke (MCA vs. ACA)

MCA Stroke: Affects lateral aspects of frontal, parietal, and temporal lobes.
Impacts corticospinal tract and corticobulbar pathway influencing upper limbs, face, speech, and motor functions (contralateral).
ACA Stroke: Primarily affects the anterior parts of the brain, potentially impacting lower limbs and trunk more than upper limbs.
Motor deficits are contralateral (opposite side) to the affected area.

Clinical Application - Complete Spinal Cord Injury (SCI)

Complete SCI: No signal can pass through the injury site.
Muscle weakness, loss of sensation, hypertonicity and hyperreflexia below the injury level.
Bilateral deficits.

Central vs. Peripheral Muscle Physiology

Peripheral Lesion: Loss of specific motor unit function, atrophy and compensatory strengthening is possible.
Central Lesion: Loss of volitional control, but spinal neuron and muscle function remains possible. Compensation and strengthening methods differ.

Aging result in loss of type II (fast-twitch) muscle fibers and related motor neurons.
Atrophy, increased intramuscular fat, reinnervation of denervated fibers
Overall muscle weakness results from this combination of age related losses and stroke.

Central vs. Peripheral Fatigue

Central Fatigue results from CNS adjustments from a stroke.
Peripheral Fatigue is from muscle breakdown during exercise.

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Description

Test your knowledge on the descending motor pathways, specifically the roles of the pyramidal and extrapyramidal tracts. Explore the structure and function of the corticospinal tract, including its pathway and significance in voluntary movements. This quiz encompasses key concepts vital for understanding motor control in the nervous system.