Brainstem Centers that Influence Motor Activity

Question 1

Rubrospinal Tract:

Primates & other non-humans

Answer 1

• Function in non-human primates & other mammals:
  
  • Contributes to control of forelimbs
• Description:
  
  • Cell bodies in red nucleus
  • Axons decussate in anterior tegmentum
  • Descends in lateral funiculus to cervical spinal cord

Question 2

Rubrospinal Tract:

Humans

Answer 2

• Function:
  
  • ​Provides feedback loop for cerebellum
  • Inferior olivary nucleus sends input to cerebellum
    
    • olivo-cerebellar tract
  • modulate cerebellum activity
    
    • participates in learning and memory functions of cerebellum

Question 3

Midbrain Lesions:

Answer 3

• Upper midbrain damage ⇒ Decorticate Posturing / Rigidity
  
  • Patient exhibits upper limbs flexed at the elbow, lower limbs extended
• Lower midbrain damage ⇒ Decerebrate posturing
  
  • Patient exhibits extension of both upper and lower limbs

Question 4

What is Benedikt’s Syndrome and what causes it?

Answer 4

• Unilateral lesion of red nucleus
• ipsilateral oculomotor palsy
• Contralateral tremor
  
  • ​usually occurs in conjunction with corticospinal tract lesions

Question 5

Tectospinal Tracts:

Answer 5

Motor Pathway:

• Input to Superior Colliculi:
  
  • visual cortex

1. Orgin: superior colliculi
2. Decussation: dorsal tegmentum
3. **Termination: **contralateral cervical spinal cord
   
   • CN XI nucleus – sternocleidomastoid m

• Function:
  
  • Coordinate reflexive turning movements of head and eyes
  • Facilitates upward gaze

Question 6

Parinaud’s Syndrome:

Dorsal Midbrain Syndrome/Collicular Syndrome

Answer 6

• lesion in the region of the superior colliculi or posterior commissure
• eye abnormalities
  
  • impaired vertical gaze
  • large, irregular pupils with light-near dissociation
    
    • pupils do not constrict with light but do constrict with accommodation
  • retraction or ptosis
  • convergence – retraction nystagmus
    (attempted upward gaze ⇒ eyes oscillate between convergence and retraction)

Question 7

Lateral Vestibulospinal Tract:

Answer 7

• Input to Vestibular Nuclei
  
  • Vestibular nerve (CN VIII)
  • Cerebellum
• LVST Description
  
  • Cell bodies in vestibular nuclei within brainstem (lateral vestibular nucleus)
  • Projects ipsilaterally within anterior funiculus to ALL LEVELS of spinal cord
• Function:
  
  • Innervates extensor (antigravity) muscles mainly in the trunk and lower limbs to maintain balance and posture

Question 8

Lateral Medullary Syndrome (of Wallenberg):

Answer 8

• Cause: vertebral artery or posterior inferior cerebellar artery (PICA) occlusion
• Ipislateral:
  
  • Dysphagia and dysarthria, diminished gag reflex
    
    • nucleus ambiguus – CN IX and X
  • Loss of pain and temperature from face
    
    • spinal tract of V descends ipsilaterally to spinal nucleus of V
  • Vertigo, nausea, vomiting and nystagmus
• Contralateral
  
  • Loss of pain and temperature sensation from body
  • anterolateral system [spinothalamic tract] – decussated in sp cd at or just above level of entry of sensory fibers

Question 9

Medial Vestibulospinal Tract:

Answer 9

• Input to Vestibular Nuclei:
  
  • Vestibular nerve
  • Cerebellum
• MVST Description:
  
  • Cell bodies in vestibular nuclei within brainstem (medial vestibular nucleus)
  • Projects bilaterally within anterior funiculus
    
    • cervical spinal cord
    • LMNs associated with the spinal accessory nerve
• MVST Function:
  
  • Adjusts head position in response to postural changes
  • Coordinate eye movements with each other
  • Vestibuloocular reflex
    
    • ​coordinates eye movements to compensate for head movements

Question 10

Reticulospinal Tracts:

Answer 10

• Input to Reticular Nuclei
  
  • Cortex
• Medullary / Lateral RST
  
  • Bilateral
  • Inhibits LMNs ⇒ inhibits extensor muscle contraction
• Pontine / Medial RST
  
  • Ipsilateral
  • Excites LMNs ⇒ stimulates extensor muscle contraction

Question 11

Decerebrate Posturing / Decerebrate Rigidity:

• Clincal Scenario:
• Description:
• Explanation:

Answer 11

• Clinical Scenario: Brainstem lesions caudal to the red nucleus
• Description: increased muscle tone, extension of upper and lower limbs with arms adducted and medially rotated
• Explanation:
  
  • removes excitatory cortical input to the INHIBITORY LRST
  • Ascending input to the MRST is still intact
  • Facilitory influence of the MRST is now unopposed
    
    • facilitation of extensor motor neurons