Corticobulbar Tract

Question 1

Corticonuclear / Corticobulbar Tract:
Function

Answer 1

• Function: Controls muscles of the head and face

Question 2

Where do corticonuclear/corticobulbar fibers originate?

Answer 2

Precentral gyrus

Question 3

Corticonuclear fibers pass with corticospinal tract fibers through which structures?

Answer 3

1. corona radiata
2. internal capsule (area 4 at genu)
3. cerebral peduncle

Question 4

Corticobulbar Tract Route:

• Projection:
• Termination:

Answer 4

• Cerebral cortex
• Corona radiata
• Internal capsule
• Projection: Corticonuclear fibers project through the posterior limb of the internal capsule (closer to genu than CST fibers)
  
  • ​bilateral
• Termination: CN motor nuclei
  
  • ​CNs V, VII (* contralateral)
  • XII (* contralateral)
  • nucleus ambiguus (CNs IX and X)
  • accessory nucleus (CN XI)

Question 5

Describe the precentral gyrus association with the corticospinal tract:

Answer 5

• Precentral gyrus projects in assoc. w/ corticospinal tract to CN motor nuclei in brainstem
  
  • UMN for brainstem CN nuclei
• Most of these are corticoreticular fibers:
  
  • relay information through the reticular formation to CN motor nuclei
• Those nuclei that receive DIRECT corticobulbar fibers include:
  
  • trigeminal, facial, and hypoglossal nuclei

Question 6

Describe the corticobulbar pathway to the facial nucleus (left cortex):

Answer 6

1. Left cortex projects to:
   
   • right lower & upper facial motor nuclei
   • left upper facial motor nuclei
2. Facial motor nuclei project to their repsective regions:
   
   • rt. lower facial motor nucleus ⇒ right lower face
   • rt. upper facial nucleus ⇒ right upper face
   • lt. upper facial motor nucleus ⇒ left upper face

Question 7

What would you expect with a cortical or internal capsule lesion?

Answer 7

• simultaneously affect the corticospinal tract and corticonuclear tract
• patients will exhibit contralateral hemiplegia accompanied by CN signs:
  
  • CN VII
  • CN XII

Question 8

Peripheral 7^th vs Central 7^th lesion (left):

Answer 8

1. Peripheral (Bell’s Palsy)
   
   • ​​Contralateral hemiplegia
   • Affects the entire right side of the face
     
     • ​Ex: ptosis, drooling, ect.
2. Central
   
   • ​​contralateral hemiplegia
   • Affects the lower side of the right face
     
     • Ex: drooling

Question 9

Why does a central 7^th lesion only affect the lower contralateral portion of the face?

Answer 9

Consider the left side:

• the right cortex also contributes directly to the right upper facial motor nucleus
• Thus, the right upper face is still receiving motor input via the right cortex
  
  • ​i.e. upper facial muscles receive motor input both ipsilaterally and contralaterally

Question 10

Describe the cotricnuclear pathway to the hypoglossal nucleus (left):

Answer 10

1. Lt. coticonuclear tract projects ⇒ rt. hypoglossal nucleus
2. Rt. hypoglossal nucleus ⇒ rt. CN XII

Question 11

What are the CN XII signs in a corticonuclear tract lesion?

Answer 11

• deviated tongue away from affected side
  
  • ​signals a contralateral corticonuclear lesion
  • Example:
    
    • lt. tongue deviation indicates a rt. corticonuclear tract lesion

Question 12

What are the CN XII signs in a peripheral CN XII lesion?

Answer 12

• Tongue deviates toward the affect side
  
  • ipsilateral CN XII lesion
  • Example:
    
    • ​rt. CN XII lesion ⇒ rt. sided tongue devation

Question 13

What is pseudobulbar palsy?

Answer 13

• bilateral lesion of corticobulbar tract
  
  • Dysphagia, dysarthria, paresis of the tongue, loss of emotional control
• Causes: brainstem infarcts, ALS, MS