Cranial NervesGroup 6

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I. OLFACTORY

Type:•SensoryFunction:•The olfactory nerve is involved in the sense of smell. This nerve has access to the cerebral cortex, but does not pass through the thalamus like other cranial nerves.Test:•You’ll need three substances with distinctive but familiar odors;for example, coffee, tobacco, and cloves. Ask your patient to closehis or her eyes, and occlude her left nostril with her finger. Holdone of these substances under his / her right nostril, and ask her toidentify the odor. Follow the same procedure with the other twosubstances. 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 resultingin Parosmia (perversion of sense of smell); compression ofOlfactory bulb by meningiomas or anterior fossa aneurysm; tumorinfiltration in frontal lobe; or temporal lobe lesions, resulting inOlfactory hallucinations.

Type:•SensoryFunction:The optic nerve is involved in the sense of sight. Responsible for vision, damage to this nerve can result in temporary or permanent blindness. Ophthalmologists use the location of visual disturbances to determine if damage to the optic nerve is present.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 yourown ( provided your own vision is normal ).Test:(Internal eye structure)•Examine your patient’s eyes with an ophthalmoscope.

Normal Findings: Optic disc appears

yellowish-pink and is round or oval, with clearly defined edges. Fundus appears uniformly orange, with opticdisc 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,

III. OCCUMOTOR NERVE

Function:

The oculomotor

nerve is the third of

twelve paired cranial

nerves. It controls most

of the eye's movement

and constriction of the

pupil, and maintains an

open eyelid

Testing the nerve:

The examiner typically instructs the patient to hold his

head still and follow only with the eyes a finger or

penlight that circumscribes a large "H" in front of the

patient.

By observing the eye movement and eyelids, the

examiner is able to obtain more information about

the extra ocular muscles, the levator palpebrae

superioris muscle, and cranial nerves III, IV, and VI.

Since the oculomotor nerve controls most of the eye

muscles, it may be easier to detect damage to it.

Another test that can be done is by moving a finger

toward a person's face. It is a test used to

induce accommodation, as well as his going cross-eyed,

his pupils should constrict. Shining a light into his eyes

should also makes his pupils constrict. Both pupils

should constrict at the same time, independent of what

eye the light is actually shone on.

IV. TROCLEAR NERVEFunction:

The trochlear nerve is also called the fourth cranial nerve. It is a motor nerve which stimulates and supplies the superior oblique muscle of the eye. The trochlear nerve is also a part of the cranial nerves which stems from the brain and connects to the eyes. Trochlear nerve function is interconnected to the superior oblique muscle. Which is also responsible for the movement of the eyes as it is one of the six extra ocular muscles that together help in the movement and alignment of the eyes. It acts as a pulley to move the eyes down—toward the tip of the nose

Test:

(Masseter muscle strength)

•Instruct your patient to clench her teeth tightly. As he or she does, locate and palpate the masseter muscle bulges at his / her right and left jaw joints. Compare them.

Normal Findings:

•Patient can clench teeth tightly. Masseter muscles bulge when teeth

•are clenched. On palpation, both masseter muscles feel equal in

•size and strength.

Test:

(Temporal muscle strength)

•Instruct your patient to clench

his or her teeth tightly. As he

or she does, locate and

palpate the temporal muscles

at his or her temples.

Compare them.

Normal Findings:

•Patient can clench his / her

teeth tightly. On palpation,

temporal

•muscles feel equal in size

and strength.

Test:

( Pterygoid Muscle strength)

•Instruct your patient to clench his or her teeth. Ask your patient toresist your efforts to open his or her jaws. Then, grasp his or herlower jaw with one hand, and pull downward.

Normal Findings:

Patient keeps teeth tightly clenched, despite your efforts.

• Test:

(Corneal reflex)

• Instruct your patient to look up. Gently touch a cotton wisp to her right cornea. Repeat the test on her left cornea. Note: if yourpatient wears contact lenses, her corneal reflexes may bediminished.

Normal Findings :

Patient blinks and his or her eyes tear when cornea’s touched

Test:

( Facial sensation )

•Instruct your patient to close her eyes. Gently touch the point of apin to one side of his or her forehead. Ask him or her to tell you what she feels, and when and where she feels it. Wait about 2 seconds, then repeat the test on the opposite side ofthe forehead. Next, repeat the test, using the blunt end of the pin.Finally, try the entire test ( both ends of pin ) on both sides of your patient’s cheeks and jaw. Compare all findings.

Normal Findings :

•Patient identifies the same sensation bilaterally, and tells when and where she feels it.

Test:

(Temperature sensation )

•To test your patient’s hot / cold

perception, to do this, fill one test

tube ( or bottle ) with hot water

and another test tube ( or bottle )

with cold water. Then, touch the

one filled with hot water to your

patient’s face. Hold it there for

about 1 second. Then, touch the

cold one to his or her face for

about 1 second.

Normal Findings :

•Patient identifies the same

sensation bilaterally, and tells

when and where she feels it.

Possible causes of abnormalities:

•Trauma, tic douloureux ( Trigeminal Neuralgia ), intracranial tumor, meningeal infection, intracranial aneurysm; when only descending tract is affected, syringobulbia ( cavities in medullaoblongata ) and multiple sclerosis. Also, pons lesion producesmasticatory muscle paralysis and light touch sensation loss in face.Medulla lesion affecting descending tract causes pain and producesloss of temperature sensation and corneal reflex.

•

 

VI. ABDUCENS

Function :The abducens nerve or abducent nerve (the sixth cranial nerve, also called the sixth nerve or simply VI) is a “somaticefferent” nerve that controls the movement of a single muscle, the lateral rectus muscle of the eye. Homologous abducens nerves are found in all vertebrates except  lampreys and hagfishes .

The abducens nucleus is located in the pons, on the floor of the fourth ventricle, at the level of the facial colliculus . Axons from the facial nerve loop around the abducens nucleus, creating a slight bulge (the facial colliculus) that is visible on the dorsal surface of the floor of the fourth ventricle. The abducens nucleus is close to the midline, like the other motor nuclei that control eye movements (the oculomotor and trochlear nuclei).

Function

•Oculomotor : Innervates extrinsic eye muscles 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 focuson a point directly in front of him / her. Observe her ability tofocus 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. Turnthe 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. Asyou know each of these fields corresponds to one of your patient’sextra ocular 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 / herhead 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 theirs in relation to each eye’s midline. Repeat this procedure, checking each vision field separately.

Normal Findings : Eyes move smoothly and bilaterally in six cardinal fields of gaze.

Test: ( Accommodation and Convergence )

First, hold a pencil approximately 18” ( 45 cm ) in front of your

patient’s nose. Then, ask her to watch the pencil as you move it.

Instruct him or her to keep his / her head and eyes stationary

throughout the examination. Then, slowly move the pencil toward

the bridge of his / her nose. If everything’s OK, both your patient’s

eyes will converge on the pencil at the same level and distance. At

that point, expect his / her pupils to constrict and remain

constricted. When the pencil’s 2” to 3” ( 5 to 7.6 cm.) from the

bridge of his / her nose, your patient should be able to

comfortably

hold her gaze. Document all findings in your nurse’s notes.

Normal Findings :

Both eyes converge on pencil at same level and distance. Patient maintains gaze on pencil when it’s held 2” to 3” ( 5 to 7.6 cm.)

from the bridge of his / her nose. When your patient’s eyes

converge, both of her pupils constrict and remain constricted.

Abnormal findings : Eyeball deviated inward, diplopia, paralysis of lateral gaze.

Possible causes of abnormalities:

•Trauma, multiple sclerosis, tumor or aneurysm at base of skull,

•increased intracranial pressure, botulism, or lead poisoning.

VII. FACIAL

Test :Dr's hands arms length by each ear of pt.• Rub one hand's fingers with noise on one side, other hand noiselessly.• Ask pt. which ear they hear you rubbing.• Repeat with louder intensity, watching for abnormality.Weber's test: Lateralization• 512/ 1024 Hz [256 if deaf] vibrating fork on top of patients head/ forehead.• "Where do you hear sound coming from?"• Normal reply is midline.Rinne's test: Air vs. Bone Conduction• 512/ 1024 Hz [256 if deaf] vibrating fork on mastoid behind ear. Ask when stop hearing it.• When stop hearing it, move to the patients ear so can hear it.• Normal: air conduction [ear] better than bone conduction [mastoid].If indicated, look at external auditory canals, eardrums.

VIII. VESTIBULOCOCHLEARFunction :

The vestibulocochlear nerve has separate acoustic and vestibular divisions. The acoustic portion of the nerve allows for proper hearing. The vestibular division is essential for normal balance.

Function :

The vestibulocochlear nerve has separate acoustic and vestibular divisions. The acoustic portion of the nerve allows for proper hearing. The vestibular division is essential for normal balance

Test :Test :

Inspect facial droop or asymmetry.Facial expression muscles: pt. looks up and wrinkles forehead.• Examine wrinkling loss.• Feel muscle strength by pushing down on each side [UMNL preserved because of bilateral innervation].Pt. shuts eyes tightly: compare each side.Pt. grins: compare nasolabial grooves.Also: frown, show teeth, puff out cheeks.Corneal reflex already done.

IX. GLOSSOPHARYNGEAL

Function :

The glossopharyngeal nerve allows for taste on the back portion of the tongue, provides the sensations of pain and touch from the tongue and tonsils, and participates in the control of muscles used during swallowing

Assessment :

Voice: hoarse or nasal. Pt. swallows, coughs (bovine

cough: recurrent laryngeal). Examine palate for uvular

displacement. (unilateral lesion: uvula drawn to normal side).

Pt. says "Ah": symmetrical soft palate movement.

Gag reflex [sensory IX, motor X]:• Stimulate back of throat each side.• Normal to gag each time.

X. VAGUSFunction :

The vagus nerve plays an important role in the human body. It controls the sensory and motor functions of the heart and glands. It also participates in the process of digestion.

Assessment :Voice: hoarse or nasal.Pt. swallows, coughs (bovine cough: recurrent laryngeal).Examine palate for uvular displacement. (unilateral lesion: uvula drawn to normal side).Pt says "Ah": symmetrical soft palate movement.Gag reflex [sensory IX, motor X]:• Stimulate back of throat each side.• Normal to gag each time.

XI. ACCESORYFunction:

The spinal accessory nerve allows the trapezius muscle and sternocleidomastoid muscle to control the movements of the head.

Assessment : From behind,

examine for trapezius atrophy, asymmetry.

Pt. shrugs shoulders (trapezius).

• Pt. turns head against resistance: watch, palpate SCM on opposite side

XII. HYPOGLOSSAL

Assessment: Listen to

articulation. Inspect tongue in

mouth for wasting, fasciculation.

• Protrude tongue: unilateral deviates to affected side