Neuro 61: U & LMN for the head

Question 1

Head mvmnts are controlled by a 2 component system

Answer 1

1. UMN = corticobulbar fibers

2. LMN = motor cranial nerves

Question 2

Lesions in CN III, IV, or VI

Answer 2

• cause paralysis of the extrinsic eye m.
• eye will not have a central neutral position –> eye will move to the side of the functioning/contracted m. & move away from the damaged m.

Question 3

Lesions in CN V

Answer 3

-jaw deviates to the paralyzed side b/c some of these m. act to draw the jaw towards the midline

Question 4

Lesions in CN VII

Answer 4

-paralysis of face m.s ipsilaterally

Question 5

Lesions in Nuc. ambiguus

Answer 5

-loss of gag reflex/swallowing, hoarseness, uvula deviates to opposite side

Question 6

Lesions in CN XII

Answer 6

-tongue deviates to paralyzed side

Question 7

Lesions in CN XI

Answer 7

-wknss in shoulder shrug/head turn

Question 8

Corticobulbar fibers

Answer 8

• the UMN to the head
• travel with the corticospinal fibers
• arrise from the face area of the precentral gyrus
• supply cranial nerve motor nuclei BILATERALLY –> usually move both side of face together
• b/c bilateral innervation, most cranial motor nerves are NOT affected by damage to corticobulbars on one side of the CNS

Question 9

What 2 cranial nerves have corticobulbar exceptions

Answer 9

1. CN VII = lower facial m.s

2. CN XII = tongue

Question 10

UMN control of CN VII

Answer 10

• facial m. nucleus is in the caudal pons
• there are 2 groups of LMN to the face m.
  1. upper face= supplied bilaterally by corticobulbars
  2. lower face= supplied only contralaterally corticobulbars
• so lesions of corticobulbars on one side will cause wkness of paralysis of only the LOWER face on the OPPOSITE side

Question 11

UMN control of CN XII

Answer 11

• corticobulbars supply CN XII bilaterally but CONTRALATERAL is often STRONGER
• so lesions cause TRANSIENT contralateral wkness in tongue muscles –> tongue deviates to the opposite side