The Cranial Nerves - Introduction

Tutorial 17: The Cranial Nerves

Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test

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Twelve pairs of nerves leave the ventral surface of the brain. The majority of these "cranial nerves" are "mixed", and serve both sensory and motor functions of the neck and head. A few pairs are exclusively sensory, and associated with special senses such as vision and hearing. Others are involved in the control of muscles and glands.

A Roman numeral identifies each cranial nerve. This numeral indicates the order in which the nerve emerges from the brain stem moving from anterior to posterior. The name of each cranial nerve describes its distribution or function. Each cranial nerve originates from a cluster of neurons (called a nucleus) that integrates incoming sensory information and/or outgoing motor control. The nuclei for cranial nerves I through IV are found in the midbrain and forebrain, while nuclei for cranial nerves V through XII are found in the hindbrain's pons and medulla oblongata. Cell bodies of sensory fibers are located outside the brain in clusters called ganglia, whereas cell bodies of motor neurons are found in grey matter of the brain. The cranial nerves pass out of the skull to the parts of head, neck, and trunk they support.

Three cranial nerves (I, II, and VIII) are strictly sensory and carry this information to the central nervous system for interpretation. Five cranial nerves (III, IV, VI, XI, and XII) function primarily to move muscles. Each, however, has some sensory function that relays proprioception information about the state of each muscle to the central nervous system. The remaining cranial nerves (V, VII, IX, and X) are called mixed, having both sensory and motor functions.

Tutorial 17 illustrates the placement of cranial nerves II through XII, and describes the basic function of each. Cranial nerve I, the Olfactory nerve, is the only cranial nerve to send its information directly to the cerebrum and is discussed in Tutorial 30.

Advanced

Students often use mnemonic devices to recall the order and names of the cranial nerves. A couple of these devices are: 1) "On occasion, our trusty truck acts funny -- very good truck anyway." and 2) "Old oreos outrage true tasters and fritters vary greatly - taste anyway." You will note that the first letters of each word in the sentences is the first letter of the cranial nerves in sequence from I through XII, using one of the common approaches to labeling these important nerves. This method can be adapted to fit the variations you may find in the labeling of several of the cranial nerves.

Suggestions for further study

Tutorial 17: The Cranial Nerves

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