Lecture 9: Brainstem & Corticobulbar Pathways

Question 1

Describe the deficits that would be seen with occlusion of the lenticulostriate arteries on the right (i.e., extremities, face, uvula, tongue, trapezius/SCM)?

Answer 1

• Left spastic hemiparesis of the extremities (corticospinal damage)
• Central facial paralysis on the left
• Deviation of uvula to the right on phonation
• Deviation of tongue to the left when protruded
• Effects on the trapezius and SCM are variable (ipsilateral deficits)

Question 2

Which 3 CN and nuclei that are associated with only the medulla

Answer 2

1) Hypoglossal (CN XII)
2) Vagus (CN X)
3) Glossopharyngeal (CN IX)

Question 3

The Accessory nerve was historically described as having 2 parts, but where are the SE motor neurons that innervate the trapezius and SCM located; where do they travel?

Answer 3

• Located in the cervical SC ONLY (C1-C6)
• Ascend into cranial cavity via foramen magnum
• Exit via the jugular foramen (w/ CN IX)

Question 4

What is seen with a lesions of the CN XI root?

Answer 4

• Drooping of the shoulder (trapeizius paralysis) on ipsilateral side
• Difficult in turning head to the contralateral side (SCM paralysis) against resistance

Question 5

What is damaged in regards to CN XI with lesions to the internal capsule, what deficits produced?

Answer 5

• Damage to the corticobulbar fibers relaying to the accessory nucleus
• Drooping of shoulder (ipsilateral), trouble turning head (contralateral)
• Primarily uncrossed —> ipsilateral deficits

Question 6

Vagus nerve exits the cranial cavity via what foramen?

Answer 6

Jugular foramen

Question 7

Which 2 ganglia lie immediately external to jugular foramen and which cell bodies does each contain?

Answer 7

1. Superior ganglion contains the cell bodies of SA fibers
2. Inferior ganglion contains the cells bodies of VA fibers

Question 8

What 2 nuclei are supplying vagal motor fibers and to where?

Answer 8

1. Dorsal motor nucleus of the vagus:
   - VE parasympathetic preganglionic targeting terminal (intramural) ganglia
   - Visceral structures of the trachea/bronchi, heart, and digestive system
2. Nucleus ambiguus (SE): targeting pharyngeal and laryngeal targets + skeletal muscles in upper 1/2 esophagus

Question 9

The VE parasympathetic preganglionic fibers of the Dorsal Motor Nucleus of Vagus target what ganglia and structures?

Answer 9

• Terminal (intramural) ganglia
• Visceral structures of the trachea and bronchi, heart, and digestive system just prox. to splenic flexure of colon

Question 10

Somatic afferent input (pain and thermal) from a small area on the ear and part of the external auditory meatus, dura of the posterior cranial fossa innervated by Vagus have cell bodies where and utilize what tract?

Answer 10

• Cell bodies located in superior ganglion of the CN X
• Enter via medulla to join spinal trigeminal tract and synapse in spinal trigeminal nucleus

Question 11

Where are the cell bodies for the visceral afferent and taste fibers of Vagus and which tract do they utilize, which terminates where?

Answer 11

• Cell bodies are located in the inferior ganglion of the vagus nerve
• Central processes enter the solitary tract and terminate in the surrounding caudal solitary nucleus

Question 12

Lesion to the root of CN X results in?

Answer 12

• Dysphagia, owing to unilateral paralysis of pharyngeal and laryngeal musculature
• Dysarthria, owing to a weakness of laryngeal muscles and vocalis m.

Question 13

Motor fibers of the glossopharyngeal nerve originate from which 2 nuclei?

Answer 13

1. Inferior salivatory nucleus
2. Nucleus ambiguus

Question 14

The parasympathetic motor fibers of the glossopharyngeal nerve originiating from the inferior salivatory nucleus join which CN, synapse where, and supply what?

Answer 14

• Join w/ CN XI
• Synapse on VE postganglionic neurons (otic ganglion)
• Supply parotid gland

Question 15

The SE fibers of glossopharyngeal originating from the nucleus ambiguus innervate what?

Answer 15

• Stylopharyngeus m.
• Participate as efferent limb of gag reflex (MINOR)

Question 16

The SA fibers of glossopharyngeal originating from small area of the pinna, external auditory canal, and posterior 1/3 of tongue have cell bodies where and utilize which tract?

Answer 16

Cell bodies in superior ganglion –> Spinal trigeminal tract –> Spinal trigeminal nucleus

Question 17

The VA sensory fibers of glossopharyngeal conveying info from parotid gland, oropharynx, and carotid body have cell bodies where and use which tract?

Answer 17

Cell bodies in inferior ganglion —> Solitary tract —> Solitary nucleus

Question 18

What is glossopharyngeal neuralgia?

Answer 18

• Attacks of intense idiopathic pain arising from the sensory distribution of the nerve
• Pain in the oral cavity

Question 19

Which CN’s are at risk by tumors or lesions near the jugular foramen?

Answer 19

CN IX, X, XI

Question 20

Which CN’s are located at the Pons-Medulla junction?

Answer 20

• Vestibulocochlear (CN VIII)
• Facial (CN VII)
• Abducens (CN VI)

Question 21

Which 2 motor nuclei are located at the pons-medulla junction?

Answer 21

1. Abducens motor nucleus
2. Facial motor nucleus

Question 22

SE motor neurons from the Facial motor nucleus arch around what nucleus before exiting brainstem and are joined by axons from which nucleus?

Answer 22

• Arch around the abducens nucleus to exit brainstem
• Joined by axons from superior salivatory nucleus (VE preganglionic parasympathetic)

Question 23

Which 2 nerve fibers emerge from the brainstem as 2 nerve bundles, and both form CN VII?

Answer 23

1. Facial nerve fibers
2. Intermediate nerve fibers

Question 24

The taste fibers (VA) of the facial nerve from anterior 2/3 of tongue enter which tract and terminate where?

Answer 24

Solitary tract and terminate rostrally in the gustatory nucleus (of solitary nucleus)

Question 25

The cutaneous sensory fibers (SA) of the facial nerve from external ear and external auditory canal utilize which tract and terminate where?

Answer 25

**Spinal trigeminal tract** and terminate in the **spinal trigeminal nucleus**

Question 26

The abducens nucleus contains what 2 types of neurons; what do these neurons innervate?

Answer 26

1. **SE motor neurons** innervate **ipsilateral lateral rectus m.** 2. **Interneurons** send **contralateral** axons to the **medial longitudinal fasciculus (MLF) --\>** target the **contralateral** oculomotor nucleus

Question 27

The abducens, oculomotor, and trochlear nerves do NOT receive information from where?

Answer 27

Corticonuclear fibers

Question 28

Lesions to the Abducens nerve in the pons as in **medial pontine syndrome** results in what deficits?

Answer 28

- Flaccid paralysis of the **ipsilateral lateral rectus m.** - Affected eye is slightly introverted and does not abduct - Opposite eye adducts because **interneurons** are intact

Question 29

A lesion of the Abducens nucleus results in what deficits?

Answer 29

- Damages motor neurons and interneurons - Paralysis of the lateral rectus m. **ipsilateral** - Failure of **contralateral** medial rectus m. to contract on attempted gaze **toward the side of lesions** - Combines a LMN lesion w/ **internuclear opthalmoplegia**

Question 30

Damage only to interneurons in the MLF (as in MS) causes what deficit?

Answer 30

- Inability to **adduct** the ipsilateral eye on attempted gaze contralaterally - These neurons are targeting oculomotor nucleus

Question 31

What are the 2 CN's of the midbrain?

Answer 31

1. Trochlear (CN IV) 2. Oculomotor (CN III)

Question 32

The CN's of the midbrain are exclusively motor, which supplies somatic efferents and which visceral efferents?

Answer 32

- Somatic efferents (**both**) - Visceral efferents (**CN III**)

Question 33

What is the ONLY motor CN that is formed entirely by axons that decussate before exit?

Answer 33

Trochlear Nerve (CN IV)

Question 34

Where is the trochlear nucleus located and describe the route of the axons that leave here and what do they innervate?

Answer 34

- Situated posteriorly but **adjacent to the MLF** - Axons arch around the periaqueductal gray, decussate, exit from posterior surface of the midbrain ---\> innervate contralateral **Superior Oblique m.**

Question 35

Trochlear motor neurons innervate which eye muscle on which side?

Answer 35

The **contralateral** superior oblique m., because they **decussate** before exiting

Question 36

Lesions of the Trochlear nerve roots would cause what deficit?

Answer 36

- Paralysis of Superior Oblique m., **on that side** (peripheral) - If the lesion is on the left side, the left eye cannot rotate slightly downward and outward

Question 37

Lesions in the midbrain involving the RIGHT MLF/trochlear nucleus would produce what deficits?

Answer 37

- If lesions on RIGHT --\> paralysis of the LEFT superior oblique m., left eye cannot rotate downward and outward - Patient would also have internuclear opthalmoplegia on the right

Question 38

Motor innervation by the Oculomotor nucleus is ipsilateral, except for?

Answer 38

Superior Rectus m.

Question 39

Edinger-Westphal preganglionic nucleus sends fibers where, which gives off which nerves with what function?

Answer 39

- To the **ciliary ganglion** via **CN III** - Gives off **short ciliary nerves ---\>** innervate **sphincter pupillae and ciliary muscles**

Question 40

Lesions involving the oculomotor nucleus and oculomotor nerve produces SE motor and parasympathetic deficits, what are they?

Answer 40

- SE motor fibers paralyze ALL extraocular muscles in **ipsilateral** orbit, except for SO and LR - Produces **diplopia (double vision)** - **Parasympathetic** deficits: cause **pupil dilation** (**mydriasis**) and non-reactive to light - Lens in **ipsilateral** eye cannot **accomodate** --\> ciliary m. denervated

Question 41

Upper motor neurons of the Corticonuclear system influence what 3 nuclei and associated CN's?

Answer 41

1) **Motor nuclei** (CN V, VII, and XII) 2) **Nucleus ambiguus** (CN IX and X) 3) **Accessory nucleus** (CN XI)

Question 42

Describe the course of the Corticonuclear tract, including the anatomical sites and regions of CNS it passes through; terminates at which CN nuclei?

Answer 42

- Corticonuclear axons funnel in genu of the internal capsuel and continue into cerebral peduncles - Located **medial** to **CST fibers** - Descend into **pons** and **medulla** --\> exit bundle rostral to the cranial nerve nucleus --\> then terminate at **nuclei** of CN **V, VII, X, XII**

Question 43

Corticonuclear fibers terminate on which neurons for trigeminal motor nuclei and where are fibers sent?

Answer 43

- Terminate on interneurons adjacent to the nuclei - Send equal number of fibers bilaterally

Question 44

How do unilateral lesions/damage to corticonuclear fibers affect Trigeminal motor nuclei innervation of mastificatory muscles?

Answer 44

- Does **NOT** result in any discernible weakness on either side - Fibers are sent from each corticonuclear tract **bilaterally**

Question 45

How are muscles of the upper 1/2 of face vs. lower 1/2 of face controlled by Facial motor nuclei?

Answer 45

- Upper 1/2 of face controlled **equally** from **both hemispheres** - Lower 1/2 of face controlled **primarily** from **contralateral hemisphere**

Question 46

How does Supranuclear Facial Palsy (Central Facial Paralysis) differ from Bell (facial) Palsy?

Answer 46

- **Supranuclear facial palsy:** a lesion **rostral** to facial motor nucleus results in drooping of muscles at **corner of mouth and lower** face **contralaterally** - **Bell (facial) palsy:** a lesion of **root** of facial nerve will result in flaccid paralysis of facial muscles of **upper and lower** portions of face on the **ipsilateral side**

Question 47

Fibers distributed bilaterally to nucleus ambiguus, but motor innervation of soft palate/uvula is from the ________ side.

Answer 47

Contralateral

Question 48

How do lesions to root of vagus (jugular foramen syndromes) affect the palatal arch muscles and uvula?

Answer 48

- Weakness and slight drooping of the arch **ipsilateral** to lesion - Deviation of the uvula opposite the lesion at resk - Acute deviation on phonation **U GO AWAY**

Question 49

Fibers distributed bilaterally, but innervation of genioglossus muscles is primarily \_\_\_\_\_\_\_\_.

Answer 49

Contralateral

Question 50

Lesions to the hypoglossal nucleus cause the tongue to deviate to which side?

Answer 50

- Deviate toward lesion (**contralateral**) side, unopposed pull of intact muscle - This is an UMN lesion

Question 51

How will lesion of RIGHT corticonuclear fibers (UMN) targeting the hypoglossal nucleus affect the tongue?

Answer 51

- Tongue will deviate left (weak) side, opposite the lesion - This is because the lesion is to the UMN which is contralateral

Question 52

Injury to LEFT hypoglossal nerve (LMN) will affect the tongue in what ways, including LMN signs?

Answer 52

- Tongue will deviate left (weak) - LMN signs: muscle atrophy and flaccid paralysis

Question 53

A lesion of medial medulla would affect what CN and tract, producing what deficits?

Answer 53

- Root of the CN XII, pyramid (corticospinal), and medial lemniscus - Ipsilateral deviation of the tongue, contralateral hemiparesis (CST), contralateral loss of PCMLS - Inferior alternating hemiplegia (medial medullary or Dejerine syndrome)

Question 54

UMN lesions in fibers targeting nucleus ambiguus will cause what kind of deviation of palate/uvula?

Answer 54

- Deviation of palate/uvula **ipsilateral** to the lesion - **Uvula goes away from the side of lesion**, when a LMN is involved. - **BUT this is a UMN lesion**, and the UMN is contralateral the weak side, so the uvula is still deviating away from the weak side, but is toward the side of the UMN lesion