Cranial Nerves

Question 1

Describe the Corneal Blink Reflex

Answer 1

• Involves CN V & VII
• Initiated by touching cornea with sterile cotton
• Sensory = V1 (affereents to trigeminal ganglion) –> output is bilateral (to both eyes)
• Motor = VII (efferents to orbicularis oculi)

Question 2

What does corticobulbar fiber damage (CN VII) cause?

Answer 2

In upper half of the face, they cause weakness of only the contralateral lower quadrant.
–but spares upper quadrant since the corticobulbar fibers to the upper part of the face are distributed bilaterally.

Question 3

What happens if there is lower nerve or nucleus damage (CN VII)?

Answer 3

Entire side of ipsilateral face is paralyzed.

Question 4

What is Bells Palsy?

Answer 4

Paralysis of entire ipsilateral face due to LMN (lower motor neuron) lesion of facial nerve and/or its nucleus.

• Rapid onset
• May be associated with inflammation from herpes, Lyme Disease, diabetes, AIDS, sarcoid, or tumors
• Usually self resolves
• May also impact other roles of the facial nerve (taste, tear and saliva production)

Question 5

What is Leissaur’s tract?

Answer 5

Only associated with spinothalamic tract
-It is where entering 1deg pain and temperature nerves can ascend or descend a segment or two before ending the substantia gelatinosa

Question 6

What is the substantia gelatinosa?

Answer 6

Only associated with spinothalamic tract
It is areas at the entry of the dorsal horn that house most of the synaptic connections between first and second order pain/temp neurons in the dorsal horn.

Question 7

What does Lamina V have?

Answer 7

It contains some neurons that can add crude touch fibers to the pain/temp. fiber bundle crossing over to the STT on the contralateral side of the cord

Question 8

What is the significance of the Mesencephalic nucleus of V?

Answer 8

It is involved in proprioception in the mandible/jaw and participates in a two neuron monosynaptic jaw jerk reflex, similar to reflexes in the spinal cord. The pseudounipolar sensory neurons have their cell bodies in the mesencephalic nucleus (unique to this nucleus!) with their peripheral process in the gums and jaw and a central process projecting to the motor nucleus of V. Motor neurons in the motor nucleus of V innervate the jaw muscles and help to control the strength of the bite.