cranial nerve assessment 2-3_2

7/30/2019 Cranial Nerve Assessment 2-3_2

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Cranial Nerve Assessment


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Summary of Function of CranialNerves

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 sense

of smell. This nerve isnt frequently tested, even by neurologists. However, suspect an abnormality in a neurologic patient

who has a poor appetite. To assess the nerve, use soap and coffee both are easy to

find 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, and

gently inhale to smell the scent. Remember to do bothnostrils.


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C inica notesSmells 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.

AnosmiaHead injuries which fracture the cribriformplate 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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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 towhich the olfactory impulses project (e.g. the temporallobe) may cause olfactory hallucinations.The smells which are experienced are usuallyunpleasant and are often accompanied by pseudo-purposeful movements associated with tasting such aslicking the lips


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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 and

peripheral vision. The fovea in the center of the retina is responsible for

visual 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 thenasal retina of both eyes.

This gives a bitemporal hemianopia (fieldloss).


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Pressure on lateral aspect of chiasma

Pressure on the lateral aspect of the chiasma(e.g. internal carotid aneurysm) affects fibresfrom 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 evenmore 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 thelight 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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cranial nerve assessment 2-3_2

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