Cranial nerve IV, the trochlear nerve, is the smallest of the cranial nerves. These trochlear nerves arise from the mid-brain and carry motor impulses to a pair of external eye muscles, called the superior obliques, which are not supplied by the oculomotor nerves, but aid in moving the muscles of the eye. The trochlear nerves contain some sensory fibers to transmit information about the condition of certain eye muscles.