©2008 By Kathy Quan RN BSN
All Rights Reserved
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 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 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.
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.
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.
"Assessing
the Cranial Nerves" Nursing 2006
November 2006:47-49
Neuroscience for
Kids- Cranial Nerves