What are the Cranial Nerves?
The Cranial Nerves are made up of 12 pairs of nerves which are located on the ventral surface of
The brain. Some control muscles. Some transmit information from the sensory organs to the brain. Others still are connected to glands or organ such as the lungs and heart.
Examining the function of the cranial nerves will provide you with pertinent information about your patient's nervous system.
The cranial nerves are numbered using Roman Numerals I-XII. There are a number of mnemonics to help you remember the names of the nerves.
I. Olfactory Nerve Its modality is Special Sensory and its function is smell. In routine examinations this is not usually tested unless the patient complains of loss or changes in a sense of smell.
Each nostril should be patent. Have the patient occlude on and then the other during testing. With the eyes closed, a patient should be able to identify common smells such as cinnamon, coffee, vanilla or cloves.
II. Optic NerveIts modality is Special Sensory and its function is vision. To test visual acuity, have the patient read A Snellen eye chart from a distance of 20 feet (6 meters). The patient covers one eye at a time and reads to smallest line possible.
To test visual fields. Stand about 2 feet (60 cm) away from the patient. Ask the patient to concentrate his gaze on your nose or directly into your eyes. Spread your arms so that your hands are about 2 feet apart and lateral to the patient's ears. Wave your fingers as you slowly draw your hands in towards the patient's line of gaze. Ask him to tell you when he first visualizes your wiggling fingers. DO this from all quadrants of the visual field. The patient should see both hands simultaneously and from all directions.
Cranial Nerves III, IV and VI are tested together. They each control the extraoccular muscles involved in eye movement.
III. Oculomotor NerveIts modality is two-fold; Somatic Motor and Visceral Motor. The Somatic Motor function is eye movement and the Visceral Motor function is pupil dilation.
IV. Trochlear Nerve Its modality is Somatic Motor and its function is eye movement.
VI. Abducens Nerve Its modality is Somatic Motor and its function is eye movement.
To test these nerves, have the patient hold his head steady while you move your finger about 1 foot (30 cm) from his nose to watch his eyes move peripherally and up and down. First out to the right side then up and down; and back in towards the nose and up and down.
Then outward from the left side and up and down; back in towards the nose and up and down. Have the patient follow your finger with his eyes without moving his head.
