Trochlear Nerve. The trochlear nerve is purely a motor nerve and is the only cranial nerve to exit the brain dorsally. ... The trochlear nucleus gives rise to nerves that cross (decussate) to the other side of the brainstem just prior to exiting the brainstem.

Where does the trochlear nerve decussate?

The Trochlear Nerve (IV)

It decussates at the anterior medullary velum in the roof of the aqueduct before exiting from dorsal midbrain below the inferior colliculus (Fig. 4.7). The nerve is the only motor cranial nerve that leaves from the dorsal side of the brainstem. Figure 4.7.

Which cranial nerve is the only nerve to completely decussate?

The trochlear nerve is the longest and thinnest of all cranial nerves, making it susceptible to trauma. After leaving the trochlear nucleus, the axons pass dorsolaterally and caudally around the periaquaeductal gray, and decussate almost completely in the anterior medullary velum.