CN4 Trochlear nerve

Question 1

What is cranial nerve 4?

Answer 1

Trochlear nerve

Question 2

Where does the CN4 trochlear nerve originate from?

Answer 2

Brainstem
midbrain
dorsal surface

Question 3

What does the CN4 trochlear nerve innervate?

Answer 3

Superior oblique muscle

which is one of the extra-ocular muscles

Question 4

What is the function of the CN4 trochlear nerve?

Answer 4

Motor - superior oblique muscle

Question 5

What is the route of the CN4 trochlear nerve, from its origin to its innervation?

Answer 5

Runs through the cavernous sinus
through the superior orbital fissure
into the orbit

Question 6

What are the causes of damage to the CN4 trochlear nerve?

Answer 6

Head injury

Raised intracranial pressure

Congenital palsy

Question 7

How does damage to the CN4 trochlear nerve present?

Answer 7

Eye in superior and medial and extorted position

Diplopia

• normally subtle
• worse with downward gaze

Question 8

How are the functions of the CN4 trochlear nerve tested?

Answer 8

Eye movements

Question 9

Why is the eye in an superior and medial and extorted position with damage to the CN4 trochlear nerve?

Answer 9

Loss of innervation to superior oblique muscle
which moves eye inferiorly, laterally and intorts it
lose these movements

Question 10

How do patients with damage to the CN4 trochlear nerve compensate for the extortion of the affected eye?

Answer 10

Tilt head slightly

Question 11

Why is the diplopia worse with a downward gaze with damage to the CN4 trochlear nerve?

Answer 11

Because eye is in medial position, this is when superior oblique muscle is the main depressor of the eye