A3. The difference between cranial nerves and spinal nerves is that cranial nerves emerge from the brain while spinal nerves emerge from parts of the spine. Cranial nerves transmit messages between the brain and different parts of the body,  primarily from the neck and head region. Spinal nerves on the other hm, transfer messages between the spinal cord and the rest of the body. The trochlear nerve among the cranial nerves is the smallest nerve in human body.