The cranial nerve is a part of the peripheral nervous system and primarily serves the head and the neck. There are about 12 pairs of cranial nerves where only one pair extends to the thoracic and the abdominal cavities.
Characteristics of the cranial nerves
- Cranial nerves are numbered and are in order.
- The names of the cranial nerve, in most cases, reveal the most significant structure that they contain.
- Most cranial nerves are mixed nerves, meaning they are both functioning as sensory and for motor function. Only three pairs of cranial nerves are purely sensory in function.
- To remember the cranial nerves in order take note and memorize this: Oh, Oh, Oh To Touch And Feel Very Good Velvet AH. The first letter of the words (capitalized letter) represents the name of the cranial nerves in order.
The Twelve Cranial Nerves
Cranial Nerve I: Olfactory
The first cranial nerve is purely sensory in function. The olfactory nerve is the one responsible for carrying the impulse for smelling things (sense of smell). Olfactory receptor fibers arise from the nasal mucosa and synapse with the olfactory bulbs. Olfactory bulb in turn, sends fibers to the adrenal cortex where the interpretation of stimuli is done. To know if this cranial nerve is functioning well, the subject is asked to identify substances by sniffing certain aromatic substances while his or her eyes are covered. Substances such as cloves or vanilla may be used; however, alcohol or irritating substances should be avoided.
Cranial Nerve II: Optic
Optic cranial nerve is the second nerve that is purely sensory in function. This is the nerve that carries the impulse of a person to see things or for vision. The fibers of this nerve surface from the retina of the eyes and form the optic nerve. There are two optic nerves and these two forms the optic chiasma by partial crossover of fibers. These fibers are branching continuously to the optic cortex through the optic tracts. To assess the functioning of this nerve, vision and visual field are tested with an eye chart. This is done by asking and testing the subject’s point in which he or she first saw the object moving into the visual field. The interior of the eye are viewed using special equipment called an opthalmoscope.