Descending Motor Tracts

Question 1

What are the 3 descending motor tracts from the cortex?

Answer 1

1. Lateral corticospinal tract (LCT)
2. Anterior corticospinal tract (ACT)
3. Corticobulbar tract (CBT)

Question 2

What are the 4 extrapyramidal tracts? What are their general functions? What are their general pathways?

Answer 2

1. Vestibulospinal: Facilitate Extensor Muscle Tone of Skeletal Muscles or Anti-Gravity Muscles
2. Rubrospinal: Modulate flexor muscle tone
3. Medullary Reticulospinal: Modulate extensor muscl tone
4. Pontine Reticulospinal: Modulate extensor muscle tone

Functions of regulation of facilitation and inhibition of muscle tone, posture and stance

• ​Brainstem (various nuclei) and descends
• To Anterior Aspects of Spinal Cord and synapses with
• Interneurons
• That synapse with Lower Motor Neuron (LMN) AKA
• Alpha Motor Neuron (AMN)
• That innervates Skeletal Muscle in Periphery

Question 3

What is the LCT and ACT? What is the path?

Answer 3

DESCENDING FROM Cerebral Cortex

• Lateral (and Anterior*) Corticospinal Tracts
  
  • Function of voluntary motor control (Spinal Nerves)
  • Pathway
    
    • Primary Motor Cortex and descends through Internal Capsule
    • To Cerebral Peduncles and DECUSSATES (LST) at Pyramidal Decussation in Medulla
    • To Anterior Horn of Spinal Cord and synapses with Lower Motor Neuron (LMN) AKA Alpha Motor Neuron (AMN)
• *ACT Fibers (80-85% DECUSSATE at cortex) 15% decussate at Anterior White Commissure in Spinal Cord

Question 4

What happens with a LCT lesion at the cortex? at the spinal cord?

Answer 4

• Corticospinal Tract Lesion
  
  • Loss of Voluntary Motor Control
  • Lesion in Right or Left Cerebral Cortex or Cerebral Hemisphere
• Contralateral Loss due to Pyramidal Decussation
• UMN Injury with resultant Hypertonicity or Spasticity on the affected side and Hyperactive DTRs
• Complete Lesion at Spinal Cord
  
  • Bilateral Loss
• Hemi-Lesion in the Spinal Cord
  
  • AKA Brown-Sequard Syndrome
  • Ipsilateral Loss

Question 5

What is the CBT? What does it do and what is it’s path?

Answer 5

DESCENDING FROM Cerebral Cortex

• Corticobulbar Tracts (CBT)
  
  • Function of voluntary motor control (Cranial Nerves)
  • Pathway
    
    • Primary Motor Cortex and descends through Internal Capsule
    • To Cerebral Peduncles
    • To Cranial Nerve Nuclei in Brainstem
      
      • Midbrain (CN 3, CN 4,CN 6)
      • Pons (CN 5, CN 7)
      • Medulla (CN 9, CN 10, CN 11, CN 12)

Question 6

What happens with a Vestibulospinal tract lesion?

Answer 6

• Vestibulospinal Tracts
  
  • Loss of modulation of Extensor Muscle Tone
  • Lesion in lower brainstem results in Decerebrate Posture (UES/LES extension)
  • Lesion in midbrain and higher results in Decorticate Posture (UES flexion and LES extension)

Question 7

What happens with a rubrospinal or the reticulospinal tract lesions?

Answer 7

DESCENDING Motor Tracts from the Brainstem (Extrapyramidal Tracts)

• Rubrospinal Tracts
  
  • Loss of modulation of Flexor Muscle Tone
  • Resultant increased Extensor Muscle Tone
• Medullary Reticulospinal Tracts and Pontine Reticulospinal Tracts
  
  • Loss of modulation of Extensor Muscle Tone or inhibition
  • Resultant Decerebrate Rigidity

Question 8

What is the presentation of a dorsal column lesion? Anterior cord?

Answer 8

• Specific Sites of Spinal Cord Lesions
• Posterior or Dorsal Column Lesions
  
  • Ipsilateral Loss of Proprioception, Vibration, Two-Point Discrimination BELOW Level of Lesion
  • Presents with Ataxic Movement
• Anterior Cord Lesions
  
  • Loss of Pain and Temperature Senses BELOW Level of Lesion
  • Resultant LMN Motor Weakness with affected Anterior Horn Cells

Question 9

Describe Brown-Sequard Syndrome

Answer 9

Brown-Sequard Syndrome (not so common) LEFT AND RIGHT lesion

• Hemi-Section or Hemi-Lesion at Spinal Cord
  
  • Contralateral Loss of Pain and Temperature BELOW Level of Lesion Due to Decussation in the Spinal Cord
  • Ipsilateral Loss of Pain and Temperature
  • Resultant Ipsilateral UMN Motor Weakness
• LCT damage-> ipsilateral UMN weakness
• Posterior column-> ipsilateral vibration and proprioception loss
• Antereolateral system-> contralateral pain and temperature loss

Question 10

Describe an UMN injury

Answer 10

UMN Injury from CVA, TBI or SCI

• Lesion in Descending Motor Tracts
• Resultant Hyperactive DTRs
• Resultant Hypertonicity or Spasticity
• Resultant Motor Paralysis or Paresis

Question 11

Decribe a LMN injury

Answer 11

LMN Injury from SCI or ALS

• Lesion in Anterior Horn of Spinal Cord
• Lesion in Spinal Nerves
• Resultant Hypoactive or Absent DTRs
• Resultant Motor Paralysis, Flaccidity