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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