Cranial Nerves and Assessment I Anatomy and Physiology
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Course
Anatomy and Physiology
Institution
University Of Santo Tomas
This text discusses the 12 cranial nerves, their function, assessment tests and common abnormalities. The key points are:
The olfactory nerve is responsible for smell. It can be assessed by asking the patient to identify different odor samples.
The optic nerve provides vision. Visual acuity a...
12 Cranial Nerves and Assessment
1) Nerve: Olfactory (I)
Type: Sensory
Function: Sense of smell
Test:
You’ll need three substances with distinctive but familiar odors;
for example, coffee, tobacco, and cloves. Ask your patient to close
his or her eyes, and occlude her left nostril with her finger. Hold
one of these substances under his / her right nostril, and ask her to
identify the odor. Follow the same procedure with the other two
substances. Then, repeat the entire test on the other nostril.
Normal findings:
Patient detects and correctly identifies all three odors.
Possible causes of abnormalities:
Temporary impairment from common cold; head trauma resulting
in Parosmia (perversion of sense of smell); compression of
Olfactory bulb by meningiomas or anterior fossa aneurysm; tumor
infiltration in frontal lobe; or temporal lobe lesions, resulting in
Olfactory hallucinations.
2) Nerve: Optic ( II )
Type: Sensory
Function: Vision
Test: Visual acuity
Use Snellen chart or an E chart to test your patient’s visual acuity.
Normal Findings:
Patient’s vision fields should be approximately the same as your
own ( provided your own vision is normal ).
Test: Internal eye structure
Examine your patient’s eyes with an opthalmoscope.
Normal Findings:
Optic disc appears yellowish-pink and is round or oval, with
clearly defined edges. Fundus appears uniformly orange, with optic
disc located one side. Blood vessels extend outward from optic
disc along borders of the fundus.
Possible causes of abnormalities:
Optic neuritis, toxic substances ( fro example, alcohol abuse ),
head trauma, chronic nephritis, Diabetes mellitus, anemia,
nutritional deficiencies, multiple sclerosis, chronic hypertension,
intracranial tumors or aneurysms, or increased intracranial
pressure.
, (2)
3) Nerve/s: - Oculomotor ( III )
- Trochlear ( IV )
- Abducens ( VI )
Type: Motor
Function: Oculomotor: Innervates extrinsic eyemuscles and ciliary muscle
Trochlear : Innervates superior oblique muscle
Abducens : Innervates external rectus muscle
Important: These three (3) nerves operate as a unit and
should be tested and evaluated together.
Test: Extrinsic Eye muscles
Ask the patient to open his or her eyes. Instruct him or her to focus
on a point directly in front of him / her. Observe her ability to
focus on one point effectively.
Normal Findings:
Lower edges of lids meet bottom edges of irises; upper lids cover
approximately 2mm of irises.
Test: Direct papillary response
Carefully note each pupil’s size. Darken the room, and check your
patient’s eyes with a penlight. To do this, shine the light directly
into one of your patient’s pupils, as she keeps his / her other eye
closed. Note the pupil’s reaction. Then, check the other eye.
Normal Findings:
Pupils constrict and remain constricted with light; pupils dilate
when light is removed.
Test: Consensual papillary responses
Darken the room, but make sure your patient keeps both eyes open.
Position the penlight directly in front of his / her right eye. Turn
the penlight ON, and observe the reaction of his or her left pupil.
Then, check the other eye.
Normal Findings:
Pupils constrict bilaterally and remain constricted with light.
Test: Extraocular eye movement
Begin by familiarizing yourself with the six cardinal fields of gaze. As
you know each of these fields corresponds to one of your patient’s
extraocular muscles. Check the field separately. First, hold a pencil 12”
(30 cm.) in front of your patient’s nose. Ask your patient to hold his / her
head still and follow the pencil’s movement with his / her eyes. Then,
slowly move the pencil to your right side, then to your left, then, when
the pencil’s approximately 24 “ ( 60 cm) from your starting point, or
your patient’s eye movement stops ( in either or both eyes ), hold the
pencil still. Note the position of the iris in relation to each eye’s midline.
Repeat this procedure, checking each vision field separately.
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