CNs and Brainstem (Tutorial)

Question 1

What is another word for a ‘vascular lesion’?

Answer 1

Infarction, stroke

Question 2

Lesions on which pathways would lead for a patient to be almost entirely paralysed except for his eyelids, and moving his eyes up and down (vertically)?

Answer 2

Corticospinal and corticobulbar tract

Corticospinal = below the head, arms and legs

Corticobulbar = facial muscles, muscles of mastication, eye muscles

Question 3

Which 2 CNs come out of the cerebral hemisphere?

Answer 3

CN I - olfactory and CN II - optic

Question 4

Which one nerve is not in the brain? And where is it?

Answer 4

CN XI - in the spine

Question 5

Which nerves supply the eye movements?

Answer 5

Occulomotor, abducens and facial

Question 6

What muscle moves the eye out?

Answer 6

Abducens - innervates the lateral rectus muscle

Question 7

Which vessels supply these CNs with blood?

CN I, II and III are not affected in the patient because…?

Answer 7

Supplied by the carotid arteries

Question 8

Which would be the prime target that would lead you to believe where these set of symptoms could come from?

Answer 8

Basilar artery stroke / infarction

Question 9

Why is his sensation completely spared?

Answer 9

Tracts towards the back is still supplied by arteries - purely motor functions impaired, all sensation is still spared

Question 10

Which muscles control the closing of the eye? (blinking - active motion)

Answer 10

CN VII (facial nerve)

Question 11

Which muscles controls the opening of the eye?

Answer 11

CN III (occulomotor)

Question 12

55M - Over a few days, he developed total paralysis of his body and most of his face. He could not swallow or speak. Horizontal eye movements were impaired but vertical eye movements and eye blinks were maintained. Communication via a code of eye movements showed that he remained mentally alert and that sensation over his whole body remained intact. A brainstem vascular lesion was suspected.

1. Which pathway has been affected?
2. Why are vertical but not horizontal eye movements maintained?
3. Where in the brainstem is the lesion?
4. Why are sensation and consciousness not affected?
5. Which artery is most likely to have been involved?

Answer 12

1. Corticospinal and corticobulbar tracts projecting to spinal and brainstem motoneurones respectively
2. The lesion must be below the level of the oculomotor nucleus (vertical eye movements spared) but above that of the abducens (lateral eye movements lost) and all lower motor nuclei. The preserved “eyeblinks” are not true reflexes as the motor nucleus of the facial nerve is below the level of the lesion. They will be intermittent upward movements of the eyelid made by the oculomotor innervation of the levator palpebrae muscles
3. Basal part of the upper pons (locked-in syndrome – mercifully rare)
4. The lesion is confined to the ventral (anterior) part of the brainstem thus sparing the ascending sensory tracts and reticular formation which are more dorsally (posteriorly) located
5. Thrombosis of the basilar artery leads to this isolated lesion. The medulla is still supplied by branches of the vertebral arteries while the internal carotid arteries maintain the circle of Willis for supply of the forebrain and midbrain

Question 13

46F - presented with muscle weakness on the left side of her face, accompanied by reduced sensation in the same area. On examination she was found to have reduced hearing in the left ear. She thought the deafness had been present for several months and also admitted to occasional bouts of dizziness

1. These symptoms are all caused by a single lesion – where?
2. What type of lesion is it?
3. Explain the symptoms in terms of the structures involved.
4. How can the condition be treated?
5. What is likely to happen if the condition is left untreated?

Answer 13

1. In or near the left internal acoustic meatus
2. An acoustic schwannoma (also called acoustic neurinoma or neurofibroma) - a benign tumour which develops slowly on the vestibular part of the VIII cranial nerve
3. The first signs are usually sensorineural deafness due to pressure on the auditory part of the nerve, accompanied or followed by tinnitus and/or vertigo. As the tumour grows out into the posterior fossa, there may be impaired facial sensation (e.g. demonstrated by loss of the corneal reflex) due to distortion of cranial nerve V, and weakness of the facial muscles due to stretching of nerve VII
4. Removed surgically but there is usually residual deafness
5. Further growth of the tumour could put pressure on the cerebellum and brainstem, causing unilateral ataxia + signs of raised intracranial pressure

Question 14

What are the ascending and descending pathways and where do they travel? (i.e. dorsal or ventral)

Answer 14

Descending (motor) = ventral

Ascending (sensory) = dorsal

Question 15

What 2 major motor pathways contribute to movement?

Answer 15

Corticospinal (movement below the head)

and Corticobulbar (above the neck movement)

Question 16

How many motor neurons are there of the corticospinal tract?

Answer 16

2 - upper and lower

Question 17

Where are the cell bodies of the upper and lower motor neurons of the corticocpinal tract?

Answer 17

Primary motor cortex and Ventral horn respectively

Question 18

Where are the lower motor neurons of the corticobulbar tract found?

Answer 18

In the brainstem

Question 19

Where do the cortico- spinal and bulbar tracts innervate from in the brain?

Answer 19

Different areas of the primary motor cortex, depending on which area of the body it is supplying i.e. limbs, trunk etc.

Question 20

Motor tracts are generally more anterior or posterior in comparison to sensory tracts?

Answer 20

Anterior

Question 21

Why are vertical but not horizontal eye movements maintained?

Answer 21

CNs III and IV come out of the midbrain, CN VI comes out of the pons, so if the brainstem has a vascular lesion, then only CN VI is affected, and not CN III and IV

Question 22

What are the 2 arteriole systems supplying the brain?

Answer 22

Vertebral basilar and Internal carotid arteries

Question 23

If the vertebral basilar artery blood supply is cut off, which CNs does it affect?

Answer 23

CN VI, VII and VIII

Question 24

What is abduction vs adduction?

Answer 24

Abduction - move out, away from midline of the body

Adduction - move in, towards midline of the body

Question 25

If CNs VI, VII and VIII are non-functioning, why can a patient still move their eye inwards and appear to be blinking?

Answer 25

CN VI - supplies lateral rectus for outwards eye movement, which is impaired, but CN III and IV is still working for inward and vertical eye movement

CN VII - supplies active blinking, patient is actually opening their eyes using CN III, as gravity causes their eyelids ot fall down

Question 26

What is locked in syndrome?

Answer 26

Thrombosis in basilar artery = brainstem lesion

Descending pathways affected as anterior affected, ascending pathways still functioning as posterior unaffected

Cognitive ability working due to this (ascending pathways unaffected) - can feel, hear and see everything (i.e. sensation + consciousness), but cannot move except their eyes partially
Front of the brainstem not receiving blood

Question 27

What are the major roles of CN VII (facial nerve)?

Answer 27

lacrimal function, supplies muscles of mastication, 2/3 of tongue sensation, motor nerves of the face = facial expression etc.

Question 28

Which CN causes dizziness?

Answer 28

CN VIII, vestibulocochlear nerve - arises from an imbalance in the fluid movement in the ear canals - conflicting info about where the head is in space = dizziness

Question 29

Where does a lesion have to be to impact the 5th, 7th and 8th CNs?

Answer 29

Internal acoustic meatus - small hole from which these 3 nerves exit from

Treatment = excision (removal of lesion)