CN IV

Question 1

CN IV is which nerve?

Answer 1

the trochlear nerve?

Question 2

Where does it emerge from?

Answer 2

axons emerge from the neuron cell bodies in the trochlear nucleus within the midbrain, pass dorsally, cross in the dorsal aspect of the midbrain and them emerge from dorsal surface of the midbrain at the lower border of the inferior colliculus. The nerve then passes anteriorly, winding around the lateral surface of the cerbebral peduncles under the free edge of the tentorium cerebellai to the ventral surface of the brainstem where it then passes between the posterior cerebral and superior cerebellar arteries.

Question 3

does it pass through cavernous sinus?

Answer 3

Through lateral wall of caverbous sinus below CN III

Question 4

enters orbit through which fissure

Answer 4

superior orbital fissure

Question 5

CN IV lies where to the rigid free margin of tentorium cerebelli

Answer 5

adjacent

Question 6

how many muscles does CN 4 innervate? causing it to be what?

Answer 6

one. the longest intracranial course

Question 7

what muscle does it innervate?

Answer 7

the superior oblique. if only this muscles were functioning it would turn the eye down and out.

Question 8

read page 258

Answer 8

read pg 258

Question 9

compression of the CN 4 nerve would cause which clinical considerations?

Answer 9

1. head trauma

2. tumors compressing CN IV

Question 10

What three other things would CN IV cause?

Answer 10

ischemia of the trochlear nerve, cavernous sinus or superior orbital fissure syndromes and intracranial aneuryisms.

Question 11

What are two signs/symptoms of the trochlear nerve?

Answer 11

1. Vertical deviation. If the right superior oblique eye was not functioning and if the patient looked straight at you the eye would be slightly elevated compared to the left eye. Because the inferior oblique muscle is no longer opposed. this is called hyper deviation
2. Vertical diplopia