Lecture 12: Brainstem & Corticobulbar Pathways

Question 1

Name the CN’s that are associated with only the medulla

Answer 1

Hypoglossal (CN XII)
Vagus (CNX)
Glossopharyngeal (CNIX)

**Accessory nerve is unique and addressed separately

Question 2

Where are somatic efferent neurons of the spinal accessory nerve that innervate the SCM and trapezius mm located?

Answer 2

In the cervical SC only (C1-6) -> there is no cranial part to CN XI

Question 3

SE motor neurons of the spinal accessory nerve that innervate the SCM and trapezius mm are located in the cervical SC only. What is their corse into the head?

Answer 3

Axons exit the lateral aspect of the SC and join to form the nerve, ascend into the cranial cavity via foramen magnum and briefly join CN X, then exit cranial cavity via the jugular foramen with CN IX

Question 4

What Sx are seen with lesions of the CN XI root?

Answer 4

Drooping of the ipsilateral shoulder (trapezius paralysis), ossicle scapular winging

Difficulty in turning the head to contralateral side (SCM paralysis) against resistance

Question 5

What are the Sx of cervical cord lesions involving the accessory nerve?

Answer 5

Weakness of SCM and trapezius

**Not especially obvious bc hemiplegia is the overwhelmingly obvious deficit

Question 6

What are the Sx of lesions of the internal capsule invoving the accessory nerve?

Answer 6

Weakness/paralysis of SCM and trapezius

Damage to corticobulbar fibers relaying to accessory nucleus

Primarily uncrossed fibers therefore ipsilateral deficits

Question 7

Axons of the motor neurons of the hypoglossal nerve pass anteriorly in the _________ along the lateral aspect of the __________ and the ___________ and exits as CNXII

Answer 7

Medulla; medial emniscus and the pyramid

Question 8

The nucleus for the hypoglossal nerve is supplied by what artery?

Answer 8

Penetrating branches of the anterior spina artery

Question 9

The vagus nerve is located at an intermediate position between the midline and lateral aspect of the ___________ and exits the cranial cavity via the ___________ foramen

Answer 9

Medulla; jugular foramen

Question 10

The vagus nerve has 2 ganglia immediately externa to the jugular foramen, a superior and inferior ganglion. What does each contain?

Answer 10

Superior = cell bodies of SA fibers

Inferior = cell bodies of VA fibers

Question 11

What fibers are housed in the dorsal motor nucleus of the vagus nerve?

Answer 11

visceral efferent parasympathetic preganglionic fibers targeting the terminal (intramural) ganglia -> innervates visceral structures of the trachea and bronchi, heart, and digestive system to a level just proximal to the splenic flexure of the colon

Question 12

What fibers are housed in the nucleus ambiguus?

Answer 12

Axons of motor neurons of the vagus nerve that contact numerous pharyngeal and laryngeal targets, as well as skeletal muscle in upper half of esophagus

Question 13

What somatic afferent inputs does the vagus nerve carry?

Answer 13

Pain and thermal sensatioinfrom a small area on the ear and part of the external auditory meatus, dura of the posterior cranial fossa

Question 14

What is the course of somatic afferent inputs of the vagus nerve from a small area on the ear and part of hte external auditory meatus, dura of the posterior cranial fossa?

Answer 14

Enter via medulla to join spinal trigeminal tract and synapse in spinal trigeminal nucleus

Question 15

Where are the cell bodies of visceral afferent and taste fibers of the vagus nerve versus the somatic afferent input?

Answer 15

Somatic afferent = superior ganglion

Visceral afferent = inferior ganglion

Question 16

The central processes of visceral afferent & taste fibers of the vagus nerve enters the __________ Tract and terminate in the surrounding caudal ___________ nucleus

Answer 16

Solitary tract and solitary nucleus

Question 17

What are symptoms of a lesion to the root of CN X?

Answer 17

Dysphagia, owing to a unilateral paralysis of pharyngeal and laryngeal muscles

Dysarthria, owing to a weakness of laryngeal muscles and vocalis muscle

**No lasting Sx specifically related to visceromotor (ANS) dysfunction -> taste loss is not detectable and small somatosensory loss involving the ear has little consequence

Question 18

Where do motor fibers of the glossopharyngeal nerve originate from?

Answer 18

Inferior salivatory nucleus and nucleus ambiguous

Question 19

What is the course of motor fibers of the glossopharyngeal nerve from the inferior salivatory nucleus?

Answer 19

Parasympathetics project and join the CNXI -> synapse on visceral efferent postganglionic neurons in the otic ganglion to go supply the parotid gland

Question 20

What is the course of motor fibers of the glossopharyngeal nerve from the nucleus ambiguous?

Answer 20

Somatic efferent fibers from the nucleus ambiguus innnervat the stylopharyngeus m and participate as efferent limb of the gag reflex

Question 21

Where do SA fibers of the glossopharyngeal nerve originate?

Answer 21

Small area of the pinna and external auditory canal and posterior 1/3 of the tongue

Question 22

What is the course traveled by SA fibers of the glossopharyngeal n?

Answer 22

Superior ganglion -> spinal trigeminal tract -> spinal trigeminal nucleus

Question 23

Where do VA fibers of the glossopharyngeal nerve coney info to?

Answer 23

Parotid gland and oropharynx

Question 24

Where do VA fibers of the glossopharyngeal N receive input from?

Answer 24

Carotid body

Question 25

What is the course traveled by A fibers of the glossopharyngeal n?

Answer 25

Cell bodies in inferior ganglion -> solitary tract -> solitary nucleus

Question 26

What symptoms are seen with glossopharyngeal nerve lesions?

Answer 26

Diminished sense of taste from posterior tongue Loss of stylopharyngeus m contraction on side of lesion, may affect gag reflex Subject to glossopharyngeal neuralgia -> attacks of intense idiopathic pain arising from the sensory distribution of the nerve **Lesion may occur with vagal and accessory root lesions at jugular foramen

Question 27

What nerves are found at the pons-medulla junction?

Answer 27

Vestibulocochlear Facial Abducens

Question 28

What 2 nuclei are located at the pons-medulla junction?

Answer 28

Abducens motor nucleus | Facial motor nucleus

Question 29

T/F: Facial and vestibulocochlear nerves exit the skull via the same foramen

Answer 29

True

Question 30

The facial motor nucleus contains ___________ neurons. The fibers of these neurons are joined by axons from the ________________ nucleus

Answer 30

SE motor neurons; superior salivatory nucleus

Question 31

VA taste fibers of the CN VI enter the ___________ tract and terminate rostrally in the ___________________, which is the central receiving area for all taste sensory signals

Answer 31

Solitary tract; gustatory nucleus (of solitary nucleus)

Question 32

Cutaneous sensory fibers of the CN VII from the external ear and external auditory canal reach cell bodies in the ___________ ganglion. Central processes enter the _______________ tract and terminate in the ______________ nucleus.

Answer 32

Geniculate ganglion; Spinal trigeminal tract; spinal trigeminal nucleus

Question 33

Where is the nucleus of the abducens nerve located and what does it contain?

Answer 33

Located internal to facial colliculus surrounded by the internal genu of the facial nerve Contains motor neurons (innervate ipsilateral lateral rectus m) and interneurons (send contralateral axons into media longitudinal fasciculus (MLF) to target contralateral oculomotor nucleus)

Question 34

T/F: The abducens nucleus receives input from corticonuclear fibers

Answer 34

False -> it does NOT receive input from corticonuclear fibers

Question 35

What are the symptoms of injury to abducens fibers in the pons (AKA medial pontine syndrome)?

Answer 35

Flaccid paralysis of ipsilateral lateral rectus m Affected eye is slightly introverted and doesnt abduct Opposite eye abducts bc interneurons are intact

Question 36

What are the symptoms of a lesion of the abducens nucleus?

Answer 36

Damages motor neurons and interneurons causing paralysis of the ipsilateral lateral rectus m WITH failure of contralateral medial rectus m to contract on attempted gaze toward the side of the lesion **Combines a LMN lesion with internuclear opthalmopegia

Question 37

What does damage only to interneurons in the medial longitudinal fasciculus (MLF)cause?

Answer 37

Inability to adduct the ipsilateral eye on attempted gaze contralaterally

Question 38

The cranial nerves of the midbrain are ________ and ________, both of which are exclusively ________.

Answer 38

Trochlear and oculomotor; both exclusively motor -> both SE and CNIII is VE too

Question 39

T/F: The Trochlear N and oculomotor N do not receive input from corticonuclear fibers

Answer 39

True

Question 40

What is the only motor cranial nerve formed entirely by axons that decussate before they exit?

Answer 40

Trochlear N

Question 41

What is the course and action of the Trochlear N?

Answer 41

Situated posteriorly but adjacent to the MLF -> axons arch around the periaqueductal gray, decussate, exit from the post surface of the midbrain and innervates the superior oblique m -> directs the eye inferolateraly (downward and outward)

Question 42

Trochlear motor neurons innervate the ____________ (ipsilateral/contralateral) ____________ m

Answer 42

Contralateral superior oblique m -> bc they decussate before they exit!!

Question 43

What are the symptoms of a lesion of the Trochlear nerve root?

Answer 43

Paralysis of superior oblique m on that side Ex. If the lesion is on the left side, the left eye cant rotate slightly downward and outward

Question 44

What are symptoms of lesions in the midbrain involving the MLF/Trochlear nucleus?

Answer 44

Paralysis of superior oblique m contralateral to lesion Right MLF with Trochlear nucleus = paralysis of left sup. Oblique m Left eye cant rotate downward and outward Pt would also have internuclear ophthalmoplegia on the right

Question 45

The oculomotor nucleus is located within the ventral portion of the ___________________ and present in about the rostral half of the midbrain. Innervation is ipsilateral except for the ______________ m

Answer 45

Periaqueductal gray; superior rectus m -> axons decussate within the nucleus and enter the contralateral oculomotor n

Question 46

Edinger-Westphal nucleus sends ___________________ fibers to the ______________ ganglion via CN III

Answer 46

Preganglionic parasympathetic; ciliary ganglion

Question 47

What are symptoms of lesions involving the ocuomotor nucleus and oculomotor nerve?

Answer 47

Paralysis of all extraocular muscles in ipsilateral orbit except superior oblique and lateral rectus Produces diplopia bc image seen by each eye cant be directed to corresponding portions of each retina Pupil dilation and nonreactive to light Lens in ipsilateral eye cant accommodate

Question 48

Organized in parallel with the CST is the ________________ system

Answer 48

Corticonuclear (corticobulbar)

Question 49

How are the fibers from the facial motor nuclei dispersed?

Answer 49

Bilaterally Muscles in upper 1/2 of face are controlled equally by both hemispheres Muscles in lower 1/2 of face are controlled primarily by contralateral hemisphere

Question 50

What are the symptoms of a lesion rostral to the facial motor nucleus?

Answer 50

Drooping of muscles at corners of mouth and lower face contralaterally -> central facial paralysis (AKA supranuclear facial palsy)

Question 51

What are the symptoms of a lesion of the root of th facial nerve?

Answer 51

Flaccid paralysis of facial muscles of the upper and lower portions of the face on the ipsilateral side -> bell’s palsy

Question 52

What are the symptoms of a lesion of the corticonuclear fibers to CN X and IX on the right side of the body?

Answer 52

Weakness of the palate arch muscles on the left Slight drooping of palatal arch, failure to elevate on weak side Deviation of uvula on right on attempted phonation

Question 53

What are the symptoms of a lesion to the root of corticonuclear fiber to CN X?

Answer 53

Weakness and slight drooping of arch ipsilateral to lesion Deviation of uvula opposite the lesion at rest Acute deviation on phonation

Question 54

Corticonuclear fibers to CN XII pass __________ to reach hypoglossal nuclei. The fibers distribute bilaterally but innervation of genioglossus muscles is primarily ______________

Answer 54

Superiorly; contralateral

Question 55

What are symptoms of a lesion to the hypoglossal nucleus?

Answer 55

Tongue deviates toward contralateral side when protruded, unopposed pull of intact m

Question 56

What are the symptoms of a lesion of the right corticonuclear fibers to the CN XII?

Answer 56

Protruded tongue will deviate left **This is a lesion of UMNs

Question 57

What are the symptoms of injury to the left hypoglossal nerve?

Answer 57

Protruded tongue will deviate left LMN signs in the tongue = muscle atrophy and flaccid paralysis **This is a lesion of LMNs

Question 58

What are the symptoms of a lesion of the medial medulla?

Answer 58

- involves root of hypoglossal n, pyramid, and medial lemniscus - ipsilateral deviation of tongue, contralateral hemiparesis, contralateral loss of PCMLS - inferior alternating hemiplegia (medial medullary or Dejerine syndrome)

Question 59

Internal stabismus is another term used for what condition?

Answer 59

Abducens palsy (“sundown” eyes and papilledema)