Corticobulbar Fibers And Cranial Nerves DLA

Question 1

Where does the corticobulbar tract terminate?

Answer 1

The corticobulbar tract terminates in the brain stem by synapsing on the various cranial nerve nuclei.

Question 2

Summarize the route corticobulbar tract?

Answer 2

• Cortex
• Corona radiata
• Internal capsule ( genu)
• Brainstem

Question 3

Does the corticobulbar decussate?

Answer 3

• Most of the innervation to the cranial nerve motor nuclei is bilateral, with a few exceptions
• There is contralateral (crossed) corticobulbar influence to the lower face, uvula, genioglossus muscle, and trapezius muscle

Question 4

What is the impact of hypoglossal nucleus damage?

Answer 4

Damage to corticobulbar fibers that project to the hypoglossal nucleus causes a contralateral deviation of the tongue during protrusion.

This lesion the right corticobulbar fibers will cause the tongue to deviate to the left

Question 5

How does a central lesion to corticobulbar fibers affect hypoglossal muscles?

Answer 5

A central lesion to corticobulbar fibers that project to the hypoglossal nucleus causes contralateral deviation of the tongue during protrusion

Damage to the hypoglossal nerve causes an ipsilateral deviation of the tongue during protrusion.

Question 6

What is the significance of the central (cortical) facial lesion ?

Answer 6

The upper motor neuron lesion (corticobulbar lesion) spares the upper face (“upper spares upper”) so that weakness is only seen in the contralateral lower face.

In a unilateral corticobulbar lesion, the patient is typically still able to wrinkle the forehead.

Question 7

What happpes in a peripheral facial lesion?

Answer 7

The lower motor neuron lesion (facial nerve lesion) does not spare the upper face. Weakness is seen on the ipsilateral upper and lower face.

In a lesion affecting the facial nerve, both upper and lower facial muscles are paralyzed (facial LMN syndrome –e.g., Bell’s palsy).