Cranial nerves

If we consider the brain as a disproportionately developed part of the spinal cord, we can understand why the arrangement of symmetrical ladder-like emerging spinal nerves is lost there. In the brain however, there are the cranial nerves that arise there, and travel for a short distance within the central nervous system. They emerge at the periphery by eventually passing through small holes in the skull. There are twelve pairs of cranial nerves. They are concerned almost entirely with the senses and the sensory and motor properties of the organs of the head. The first cranial nerve is the olfactory. Like the second, the optical nerve, it is actually a direct projection of the brain.

The third, fourth and sixth cranial nerves innervate the small muscles of each eye. The fifth nerve is the trigeminal nerve. This is a large sensory nerve that supplies the skin of the face and the front part of the head, as well as the teeth. The seventh is the facial nerve, which innervates all small muscles of the face. Hearing and balance are controlled by the eighth nerve, the auditory nerve. The glossopharyngeal nerve, number nine, conveys taste and other sensations from the back of the tongue and the throat. The tenth nerve, the vagus nerve, is very large and passes to the heart and upper part of the stomach. It is an autonomic nerve. The eleventh is the accessory nerve, innervating some muscles of the shoulder, enabling us to shrug our shoulders. The twelfth nerve, the hypoglossal nerve, innervates the muscles of the tongue, and is essential in producing speech.