Brainstem (uses other resources in addition to lecture)

Question 1

What are the four somatic motor nuclei and where in the brainstem are they?

Answer 1

III - Oculomotor - midbrain
IV - Trochlear - midbrain
VI - Abducens - pons
XII - Hypoglossal - medulla

Question 2

What does the oculomotor nucleus innervate and what will injury to it look like?

Answer 2

• Innervates all extra ocular eye muscles (except Superior Oblique and Lateral Rectus)
• Injury to oculomotor nucleus will cause eye to deviate DOWN and OUT due to unopposed actions of Lateral Rectus and Superior Oblique
• Lack of innervation to Levator Palpebrae Superioris will also result in ptosis

Question 3

What is special about the trochlear nerve?

Answer 3

The axon decussates to the contralateral side BEFORE exiting from the DORSAL midbrain

Question 4

What does the trochlear nucleus innervate and what will injury to it look like?

Answer 4

Innervates Superior Oblique

• Test clinically by asking patient to look MEDIAL and DOWN
• Injury of trochlear NUCLEUS produces deficit in CONTRALATERAL superior oblique
• Whereas injury of trochlear NERVE produces deficit in IPSILATERAL superior oblique

Question 5

What does the abducens nucleus innervate and what will injury to it look like?

Answer 5

Innervates Lateral Rectus

• Test clinically by asking patient to look laterally (ABduct)
• Injury to abducens nerve causes diplopia when looking laterally TOWARDS the side of the lesion
• However, injury to abducens NUCLEUS causes inability to look laterally with either eye towards the side of the lesion (due to lesion in MLF)

Question 6

What does the hypoglossal nucleus innervate and what will injury to it look like?

Answer 6

Innervates tongue muscles

• Exits brainstem ventrally in between the olives and the pyramids
• One of the muscles it innervates is the genioglossus muscle which protrudes the tongue out of the mouth
• With injury, protruded tongue deviates towards the side of the injury “lick your wounds”

Question 7

Name the three Branchio-Motor nuclei and where are they found?

Answer 7

Vc - Trigeminal Motor Nucleus - Pons
VII - Facial Motor Nucleus - Pons
IX and X - Nucleus Ambiguus - Medulla

Question 8

What does the Trigeminal Motor Nucleus innervate?

Answer 8

Muscles of mastication (temporalis, masseter, pterygoids)

Question 9

What does the Facial Motor Nucleus innervate and what is special about it?

Answer 9

Innervates facial muscles of expression.
CN VII axon courses around abducens nucleus prior to exiting pons. Therefore and abducens lesion may affect muscles of facial expression (CN VII)

Question 10

What does the Nucleus Ambiguus innervate and what would an injury look like?

Answer 10

Associated with CN IX and X

1) Innervates Levator Veli Palatini, elevating soft palate. In injury, uvula moves away from injured side
2) Innervates pharyngeal muscles for swallowing therefore injury can be very dangerous
3) Innervates laryngeal muscles for phonation. Injury can cause a hoarse voice.

Question 11

Name the four visceral motor nuclei and where they are found

Answer 11

III - Edinger Westphal Nucleus - Midbrain
VII - Superior salivatory Nucleus - Pons
IX - Inferior salivatory Nucleus - Medulla
X - Dorsal Vagal Nuclei - Medulla

Question 12

What does the Edinger-Westphal Nucleus do and what would injury look like?

Answer 12

Synapses in the ciliary ganglion and then goes on to innervate

• Pupillary constrictor sphincter muscle for pupil constriction due to the pupillary light reflex
• Ciliary muscles for lens accommodation

Injury to EWN causes mydriasis (excessively dilated pupil). Normally, injury to EWN would present with damage to adjacent CN III oculomotor nucleus (eye would be DOWN and OUT)

Question 13

What does the superior salivatory nucleus do and what would injury look like?

Answer 13

Associated with CN VII

• Parasympathetic via 2 nerves
  1) Chordates tympani innervates submandibular and sublingual glands
  2) Greater petrosal nerve innervates lacrimal gland and naso-palatal glands

Injury to superior salivatory nucleus results in dry mouth (submandibular/sublingual glands), dry eyes (lacrimal glands), dry mucous membranes (naso-palatal glands)

Question 14

What does the inferior salivatory nucleus do and what would injury look like?

Answer 14

Associated with CN IX

• Parasympathetic to parotid gland
• Injury to inferior salivatory nucleus won’t be that detrimental as parotid gland only makes a small fraction of the saliva

Question 15

What does the dorsal vagal nuclei innervate and what would injury look like?

Answer 15

Associated with CN X

• Parasympathetic to heart, lungs, foregut, midgut
• Injury won’t be that detrimental since foregut and midgut can act on their own and heart and lungs are innervated by other structures and circulating hormones also modulate them.
• Axon exits medulla laterally

Question 16

Which cranial nerves hitchhike on CN V’s sensory nucleus?

Answer 16

CN VII, IX and X

Question 17

What are the nuclei associated with the vagus nerve?

Answer 17

1) Spinal nucleus of trigeminal nerve - sensation from pharynx, larynx and external ear
2) Nucleus solitarius - general visceral afferents (GI, heart, lung)
3) Dorsal Motor Nuclei - Parasympathetic to GI, cardiovascular and resp systems
4) Nucleus ambiguus - motor to larynx, pharynx and soft palate

Question 18

What does the Nucleus Solitarius do?

Answer 18

(A visceral sensory nucleus)
Found in medulla
- Taste from VII and IX
- Cardiovascular baroreceptor input IX and X
- Respiratory receptor input IX and X
- Visceral afferents from GI tract IX and X

Question 19

Describe the trigeminal nucleus

Answer 19

(A general sensory nucleus)

• Sensation from face split into mesencephalic nucleus (proprioception), principal nucleus (light touch) and Spinal nucleus (pain and temperature)
• CN VII, IX and X hitchhike on the spinal nuclei

Question 20

What does CN VIII nucleus do?

Answer 20

Hearing and balance

Question 21

Name the 4 medial structures at risk of a brainstem stroke. What artery are they supplied by?

Answer 21

• Motor nuclei: CN III, IV, VI, XII – ocular or lingual palsy depending on level of lesion
• Medial longitudinal fasciculus – eye movements. No ipsilateral eye adduction on lateral gaze
• Medial lemniscus (=dorsal column). Contralateral, fibres have already decussated, loss of vibration and proprioception
• Motor Corticospinal – contralateral weakness of UL/LL
• These structures are all supplied by Anterior Spinal Artery

Question 22

Name the 4 lateral structures at risk of a brainstem stroke. What artery are they supplied by?

Answer 22

• Sensory nucleus (CN V) – ipsilateral facial pain + temp loss
• Sympathetic nerves – ipsilateral Horner’s syndrome
• Spinocerebellar tract – ipsilateral limb ataxia
• Spinothalamic tract – contralateral loss of limb pain and temp
• These structures are all supplied by PICA. Blockage of PICA can lead to PICA syndrome.

Question 23

Name all 14 brainstem nuclei

Answer 23

- Somatic motor nuclei - eye muscles and tongue muscles
CN III
CN IV
CN VI
CN XII

• Branchio-motor nuclei
  Vc - trigeminal motor to muscles of mastication
  VII
  Nucleus Ambiguus IX and X

- Visceral Motor Nuclei
Edinger-Westphal Nucleus (CN III)
Superior Salivatory Nucleus (CN VII)
Inferior Salivatory Nucleus (CN IX)
Dorsal Vagal Nucleus (CN X)

- Visceral Sensory Nuclei
Nucleus Solitarius (CN VII and IX)

- General Sensation
Trigeminal nucleus (split into three regions)

• Hearing and Balance
  CN VIII