Cranial Nerve Assessment 2-3_3

7/30/2019 Cranial Nerve Assessment 2-3_3

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Cranial Nerve Assessment


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Summary of Function of Cranial

Nerves

Figure 13.5b


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Cranial Nerve I: Olfactory

Arises from the olfactory epithelium

Passes through the cribriform plate of the

ethmoid bone

Fibers run through the olfactory bulb and

terminate in the primary olfactory cortex

Functions solely by carrying afferent impulsesfor the sense of smell


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Cranial Nerve I: Olfactory

Figure I from Table 13.2


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Olfactory nerve (CN I)

Located in the nose, cranial nerve (CN) I controls the senseof smell.

This nerve isnt frequently tested, even by neurologists.

However, suspect an abnormality in a neurologic patientwho has a poor appetite.

To assess the nerve, use soap and coffeeboth are easy tofind on a unit. Or take a trip to the kitchen for cloves andvanilla.

Dont use a substance with a harsh odor, such as ammonia,

because it will stimulate the intranasal pain endings of CNV.

Have the patient close both eyes, close one nostril, andgently inhale to smell the scent. Remember to do bothnostrils.


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C inica notes

Smells and the responses they can provokeEvidence of olfactory connections to thelimbic system are:

smells can trigger memories;

smells can provoke emotional responses;

smells have a role in sexual arousal.Anosmia

Head injuries which fracture the cribriform

plate may tear olfactory nerves resulting inpost-traumatic anosmia. Anosmia can alsobe caused by blockage of the nasal cavities,for example a nasal polyp or malignancy.

.


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Cranial Nerve II: Optic

Arises from the retina of the eye

Optic nerves pass through the optic canals and

converge at the optic chiasm

They continue to the thalamus where they synapse

From there, the optic radiation fibers run to the

visual cortex

Functions solely by carrying afferent impulses forvision


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Cranial Nerve II: Optic

Figure II Table 13.2


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Optic nerve (CN II)

Located in and behind the eyes, CN II controls central andperipheral vision.

The fovea in the center of the retina is responsible forvisual acuity in our central vision.

Test one eye at a time. Ask the patient to read his I.V.

bag. Then have him count how many fingers you are holding

up 6 inches in front of him.

Test peripheral vision one eye at a time, too.

Cover one eye and instruct the patient to look at yournose. Move your index fingers to check the superior andinferior fields one at a time.

Ask the patient to note any movement in the peripheralvisual fields


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Lesions of optic pathway

Optic nerve

Section of one optic nerve causes blindness in

one eye.


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Crossing fibres in chiasma

Destruction of crossing fibres in chiasma (e.g.

pituitary tumour) causes blindness in the

nasal retina of both eyes.

This gives a bitemporal hemianopia (field

loss).


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Pressure on lateral aspect of chiasma

Pressure on the lateral aspect of the chiasma

(e.g. internal carotid aneurysm) affects fibres

from the temporal retina of the ipsilateral eye,

giving an ipsilateral nasal hemianopia.

This is uncommon.

Bilateral internal carotid artery aneurysms

would cause a binasal hemianopia even

more uncommon


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Optic tract or geniculate body

Destruction of the right optic tract or LGBwould interrupt pathways from the temporalretina of the right eye and the nasal retina of

the left eye. This would cause blindness in the left side of

both visual fields. This is a homonymoushemianopia.

Thus, destruction of the right optic tractwould cause a left homonymous hemianopia


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Oculomotor nerve (CN III)

Also positioned in and behind the eyes, CN III controlspupillary constriction.

To test the patients pupils, dim the lights, bring the

light of the penlight from the outside periphery to thecenter of each eye, and note the response. Use themm chart to describe pupil size; descriptions such assmall, medium, and large are too subjective.

Also, check where the eyelid falls on the pupil.

If it droops, note that the patient has ptosis.

Its easy to check cranial nerves III, IV, and VI together


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3rd , 4th ,6th nerve

Functions:

Control of all the external muscles and elevators of thelid

Purpose of the test:

1. Inspect the pupils and to detect any abnormalities(localized disease, autonomic lesion, nuclearinvolvement in brainstem)

2. Evaluate the eye movement (muscular origin, lesion

in occulomotor nerve, nuclei in brainstem, pathway ofsupranuclear control)

3. Evaluate the nystagmus (vestibular dysfunciton)


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Inspection

Ptosis (absent/present)

Squit(absent/ present)

unilateral./ bilateral

Exopthalmos (thyrotoxicosis, hydrocephalus,craniosyostosis)

Enophthalmos (horners syndrome)

Conjuctival hemorrhage(cranial trauma,

subarachnoid haemorrhage) Telengiectases(louis bar syndrome)

Color of the eyes(vascular disease)


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Pupil size, shape equality, regularity of the

pupil.

Constricted pupil sympathetic dilatormuscle(hypothalamus, brainstem sympathetic

chain, pericarotid plexus,pontine tumor)

Dilated pupil parasympathetic fiberspretectal nuclei, edinger westphal nucleus


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Occular movement

Internal rectus

Superior rectus

Inferior oblique Inferior rectus

Superior oblique

External rectus


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Conjugate eye movement

Frontal lobe contralateral conjugate gaze

Brain stem ipsilateral gaze

Nystagmus1, detect nystagmus

2, rate, amplitude, direction

3,Peripheral, central, vestibular


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Central nystagmus occurs as a result of either

normal or abnormal processes not related to the

vestibular organ. For example, lesions of themidbrain or cerebellum can result in up- and down-

beat nystagmus.

Peripheral nystagmus occurs as a result of either

normal or diseased functional states of the

vestibular system and may combine a rotational

component with vertical or horizontal eye

movements and may be spontaneous,positional, orevoked.


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Gaze Induced nystagmus occurs or is exacerbated as aresult of changing one's gaze toward or away from aparticular side which has an affected vestibular apparatus.

Positional nystagmus occurs when a person's head is in aspecific position.An example of disease state in which thisoccurs is Benign paroxysmal positional vertigo(BPPV)

Post rotational nystagmus occurs after an imbalance iscreated between a normal side and a diseased side bystimulation of the vestibular system by rapid shaking or

rotation of the head.

Spontaneous nystagmus is nystagmus that occursrandomly, regardless of the position of the patient's head.


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5th nerve

Root pattern

Brainstem pattern

Corneal reflex 5th to 7th

Wasting of temporalis muscle

Jaw jerk


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8th nerve

Cochlear component:

Whispering numbers to each ear.

webers test ?

Conductive deafness

Perceptive deafness

Ri ?


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Rinnnes test?

Conductive deafness bone conduction > nerve conduction

Perceptive deafnessbone and air conductionimpaired


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9th and 10th

Vocal cord paresis voice high pitched

Swallowing difficulty

Nasal regurgitation of fluids

Open the mouth asymmetry of palatalmovements

Gag reflex:

Stimulate both side of the palate

Afferent X Efferent IX


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11th cranial nerve

Sternomastoid

Trapezius


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12th cranial nerve

Upper motor neuron lesion of 12th cranial nerve:

Weakness of opposite half of tongue and on protrusion

Tongue deviates to the side opposite to that of lesion

Lower motor neuron lesion of 12th cranial nerve:

Ipsilateral half of the tongue and on protrusion tongue

deviates towards the side of lesion due the unopposed

action of genioglossus of the healthy side


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Cerebrospinal fluid rhinorrhoea

Head injuries may tear the dura mater, leading to cerebrospinal fluid

(CSF) leaking into the nasal cavity and dripping from the anterior

nasal aperture. This should be considered if clear fluid issues from

the nose after a head injury


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Temporal lobe epilepsy

Diseases such as epilepsy in the areas to

which the olfactory impulses project (e.g. the temporal

lobe) may cause olfactory hallucinations.

The smells which are experienced are usually

unpleasant and are often accompanied by pseudo-

purposeful movements associated with tasting such as

licking the lips

Cranial Nerve Assessment 2-3_3

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