Corticobulbar Pathway

Question 1

what is the pathway of the corticobulbar tract?

Answer 1

pre-central gyrus motor cortex —–> corona radiata —–> genu of internal capsule ——> crus cerebri —–> correct cranial nerve nuclei

Question 2

Cranial nerve V3 has motor innervation to what muscles?

Answer 2

• muscles of mastication (temporalis, masseter, med and lateral pterygoids)
• tensor tympani
• tensor veli palatini
• mylohyoid
• anterior belly of digastric

Question 3

where does a motor signal originate if you clench your jaw or smile? what is the blood supply to this region?

Answer 3

• inferior lateral region of the precentral gyrus
• middle cerebral artery

Question 4

what is the CN V motor pathway?

Answer 4

UMN: motor cortex —–> internal capsule —–> crus cerebri —-> terminates bilaterally at CN V nuclei in the pons
LMN: motor nuclei of CN V —–> trigeminal ganglion —-> V3 —-> muscle

Question 5

what are the sensory modalities of CN V?

Answer 5

• proprioception
• touch
• pressure
• vibration
• pain
• temperature

Question 6

what is the sensory nuclei for proprioception and where is it located?

Answer 6

• mesencephalic nucleus
• midbrain

Question 7

what is the sensory nuclei for touch, pressure and vibration and where is it located?

Answer 7

• main sensory nucleus
• pons

Question 8

what is the sensory nuclei for pain and temperature and where is it located?

Answer 8

• spinal nucleus
• pons, medulla and spinal cord

**very long nucleus

Question 9

what is the basic CN V sensory pathway?

Answer 9

sensory receptors ——> trigeminal ganglion (1st order) —–> mesencephalic/main/spinal nucleus (2nd order) ——> decussation —–> VPM nucleus of thalamus (3rd order) ——> internal capsule ——> post central gyrus

Question 10

what is the CN V sensory pathway for touch, pressure and vibration?

Answer 10

1st order neuron
- trigeminal ganglion cells

2nd order neuron
- synapse in principal main nucleus (pons)
- fibers cross midline
- trigeminothalmic tract ( trigeminal lemiscus) ascends

3rd order neuron:
- synapse in the VPM of the thalamus
- axons enter internal capsule
- primary somatosensory cortex (post central gyrus)

Question 11

what is the CN V sensory pathway for pain and temperature?

Answer 11

1st order neuron
- trigeminal ganglion cells enter at pons
- fibers descend in the spinal trigeminal tract

2nd order neuron
- synapse at the spinal nucleus in the medulla
- fibers cross midline
- trigeminothalamic tract (trigeminal lemiscus) ascends

3rd order neuron
- synapse at the VPM of the thalamus
- axons enter internal capsule
- primary somatosensory cortex (post central gyrus

Question 12

what is the trigeminal pathway for proprioception?

Answer 12

• originates in the muscles of mastication and periodontal ligaments
• the sensory and motor feedback controls bite force
• both motor and sensory cell bodies are in the CNS
• motor nuclei of V (efferent) and mesencephalic nuclei for sensory (afferent)

Question 13

what would be the result of an upper motor neuron lesion and a lower motor neuron lesion to the proprioception pathway of CN V?

Answer 13

• UMN: hyperactive/ repeating reflex
• LMN: reflex is absent

Question 14

what are the efferent and afferent limbs of the corneal blink reflex?

Answer 14

touch or irritation to the cornea causes
- afferent limb: ophthalamic division of V for sensory information
- efferent limb: facial nerve motor for muscle that closes the eye (obicularus oculi)

Question 15

what is the shingles virus mode of action?

Answer 15

• virus within the dorsal root trigeminal ganglion
• unilateral (in ganglion not nucleus)
• hitches a ride with the nerve that innervates a certain dermatome

Question 16

what is trigeminal neuralgia?

Answer 16

chronic pain condition involving the trigeminal nerve of the face

**considered secondary neuralgia if caused by a tumor or MS

Question 17

what is the path of the facial nerve in order to innervate the muscles of facial expression?

Answer 17

ponto-medullary junction then exits at internal acoustic meatus then goes through the facial canal and exits at the stylomastoid foramen

Question 18

what facial muscles are innervated by the facial nerve?

Answer 18

• buccinator
• platysma
• orbicularis oculi
• zygomaticus major
• levator labii superiorus
• orbicularis oris
• mentalis
• depressor anguli oris

Question 19

what is the cranial nerve VII motor pathway?

Answer 19

UMN: precentral gyrus motor cortex —-> corona radiata —–> crus cerebri —–> terminates in the pons at facial nucleus

LMN: facial nucleus —–> muscles of facial expression

Question 20

what would happen with an UMN lesion and a LMN lesion of the facial nerve and why?

Answer 20

UMN: lack of movement only to the LOWER face due to the lower face only having contralateral projections and upper face having bilateral projections (supranuclear lesion)

LMN: would cause both upper and lower face to lack motor innervation (bells palsy; facial nerve lesion)

Question 21

what is the cranial nerve XII motor pathway?

Answer 21

UMN: motor cortex pre central gyrus —–> corona radiata —–> internal capsule ——> crus cerebri —–> terminates at medulla

LMN: synapse in contralateral hypoglossal nucleus

Question 22

what muscles does the hypoglossal XII nerve innervate?

Answer 22

genioglossus
hyoglossus
styloglossus

Question 23

the hypoglossal nerve comes out of what cranial opening?

Answer 23

hypoglossal canal

Question 24

what would happen with a LMN and UMN lesion of CN XII?

Answer 24

UMN: corticobulbar tract to the hypoglossal nucleus decussates before synapsing
** lesion would cause CONTRALATERAL tongue deviation

LMN: region below the nucleus innervates IPSILATERALLY
** lesion would cause same side tongue deviation