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 rhymes or mnemonicsto help you remember the names of the nerves. You might also find this graphic helpful.
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 Nerve Its 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 Nerve Its 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 move your finger 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. V. Trigeminal Nerve This nerve has two modalities Brachial Motor and General Sensory. Its function is also two-fold. The Brachial Motor controls the muscles of mastication (chewing). The General Sensory provides sensory information regarding touch and pain in the face to the brain.
To test this nerve first have the patient clench jaw muscles by clenching his teeth. Muscle strength in the temporal and masseter muscles of the face should be felt and should be symmetrical. Touch the patient's face at the forehead cheek and chin on each side. The patient should report the sensation as being symmetrical. You can use a clean safety pin or suitable sharp object) for testing pain sensation. A cotton swab can be used to test for dull sensation. You can also test for sensation of temperature using test tubes filled with warm water and ice water.
VII. Facial Nerve This nerve has four modalities and functions. The modalities are Brachial Motor, Visceral Motor, General Sensory and Special Sensory. The functions include taste on the anterior 2/3 of the tongue and salivary glands, transmission of somatosensory information from the ear to the brain, control of muscles used in facial expression.
To test this nerve, have the patient repeat a sentence. Observe his facial expression during normal conversation check for any asymmetry, tics, or other facial movements. Next ask the patient to smile, frown, puff out his cheeks. Look for symmetry especially in the nasolabial folds.
Ask him to close his eyes tightly and you try to open them by pulling upward on the eyebrows and downward on the cheeks just below the eyes checking for strength and symmetry. To test for taste, drop a few drops of sweet or salty water on the front part of the tongue and see how it tastes to your patient.
VIII. Acoustic Nerve (also known as Vestibulocochlear or Auditory Nerve) This nerve has one modality; Special Sensory. It has two branches; the Cochlear which transmits sound messages to the brain; and Vestibular which controls balance or equilibrium. To Test this nerve have the patient occlude one ear with a finger. Stand about 1 to 2 feet away (30-60 cm) and softly whisper a word with two distinct syllables such as football, baseball, or doorbell. Make sure the patient can't read your lips. Repeat with the other ear and a different word. Repeat the word slightly louder if necessary and observe for difficulties distinguishing words.
Equilibrium can be tested using the Romberg test: Have the patient stand erect with his feet close together and his eyes closed. He might sway slightly, but should not fall. (Stay close to the patient in case he does begin to fall.)
Cranial Nerves IX and X are tested together as they both have a function that innervates the pharynx.
IX. Glossopharyngeal Nerve This nerve has four mobilities Brachial Motor, Visceral Motor, General Sensory and Special Sensory. Its function includes taste on the posterior 1/3 of the tongue, some swallowing muscle function, and transmitting somatosensory information from the tongue, tonsils and pharynx.
X. Vagus Nerve This nerve also has four modalities: Brachial and Visceral Motor as well as Visceral Sensory and Special Sensory. Its functions include autonomic, sensory and motor functions of viscera such as glands, heart rate and digestion.
To test these nerves have the patient swallow some sweet or salty water and test for taste sensation as well as ability to swallow. Then ask the patient to open wide and say "ah" while you observe the uvula and palate. These should move symmetrically and without deviation to one side. Next tell the patient you're going to test his gag reflex. Lightly stimulate the back of the throat on each side with a swab or tongue depressor. The reflex should be present or symmetrically diminished. XI. Spinal Accessory Nerve (also known as Accessory Nerve) The modality is Brachial Motor and the function is control of the trapezius and sternocleidomastoid muscles in movement of the head.
Place your hands on the patient’s shoulders from the back. Have him shrug his shoulders upward while you exert slight resistance. The strength and contraction of the trapezius muscles should be symmetrical. Next place one hand on the side of the patient's jaw and the other on the opposite sternocleidomastoid muscle. Have the patient turn his head towards the hand on his jaw while you apply slight resistance. Observe the strength in both muscles. Repeat to the other side.
XII. Hypoglossal Nerve The modality is Somatic Motor and the function is control of the muscles of the tongue. This nerve is tested by listening to the patient's articulation as he speaks as well as observing for any atrophy or deviation of the tongue while speaking. Have the patient stick his tongue out and move it from side to side. Check for symmetry of movement. Have the patient push his tongue against the inside of each cheek and you palpate for strength from the outside of his cheek.
Document your assessment carefully and report all abnormal findings to the physician or other practitioner.
Resources: Lippincott Manual of Nursing Practice, 8th Edition. Philadelphia: Lippincott, Wilkins & Wilkins, 2006 "Assessing the Cranial Nerves" Nursing 2006 November 2006:47-49