Lab 14 Continued
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Transcript of Lab 14 Continued
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Lab 14 Continued
Cranial Nerves
Portland Community CollegeBI 232
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Cranial Nerves
• Nerves that originate from the brain rather than the spinal cord
• Part of the peripheral nervous system (not the central nervous system)
• May contain one or more of the following:• Sensory• Somatic Motor (voluntary movement)• Parasympathetic Motor (involuntary “rest and
digest” part of the autonomic nervous system)
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Cranial nerve origins • First 2 originate from the
forebrain• The next 10 pairs originate
from the brainstem.• Midbrain-CNIII, CNIV• Pons- CNV, CNVI, CNVII• Pons/medulla border-
CNVIII• Medulla-CNIX, CNX, XI,
XII
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Use Figure 14.5 to view all CNs
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Cranial Nerve Passageways• Cranial nerves must
leave the cranial cavity by passing through an opening (foramen, fissure, or canal) in the skull.
• Identify the openings for the cranial nerves (activity 14.8)
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CN I: Olfactory Nerve• Function:
• Sensory for smell• Exiting foramen=cribriform
plate• Origin forebrain
• Test: Have patient identify aromatic substances like vanilla or coffee
• Symptoms of nerve damage: Anosmia: diminished or absent sense of smell
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CN II: Optic Nerve• Function:
• Sensory for vision• Exiting foramen= optic canal• Origin=forebrain
• Tests: 1. Eye chart2. Check peripheral vision 3. Funduscopic exam
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CN II: Optic Nerve
• Optic chiasm: Fibers from the nasal half of each retina cross over to the opposite side of the brain.
• Symptoms of nerve damage:• Loss of vision (peripheral
or central)• Abnormal funduscopic
appearance
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CN II: Optic Nerve PathologyPapilledema. Note swelling of the disc, hemorrhages, and exudates, with preservation of the physiologic cup.
Proliferative Diabetic Retinopathy. Note the multiple hemorrhages throughout the retina.
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Cranial Nerves III, IV & VI(Control Eye Movements)
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CN III: Oculomotor nerve• Function:
• Somatic Motor to extraocular muscles (voluntarily move the eye)
• Parasympathetic (motor) to iris and lens (pupillary constriction)
• Exiting Foramen= superior orbital fissure• Origin= midbrain
• Tests: 1. Check pupils for size, shape and equality2. Shine light in each eye and check for pupil constriction 3. Have patient follow an object in all directions to check for symmetric eye
movements
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CN III: Oculomotor Nerve Injury
• Symptoms of nerve damage:• Double vision (diplopia): The affected eye
turns outward when the unaffected eye looks straight ahead
• The affected eye can move only to the middle when looking inward and cannot look upward and downward.
• Ptosis: eyelid droop• Pupil may be dilated and sometimes fixed
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Oculomotor Nerve Injury Right Eye
Normal side
Injured side
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Pupillary Reflex
Efferent Afferent
Consensual reflex: Both pupils should constrict at the same time
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CN IV: Trochlear Nerve• Function:
• Somatic motor to superior oblique muscle of the eye.• Exiting foramen= superior orbital fissure• Origin= midbrain
• Test: Check eye movements• Symptoms of nerve damage:
• Outward rotation of the affected eye • Vertical diplopia
Injured sideNormal side
Originates in the midbrain
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CN VI: Abducens Nerve• Function:
• Somatic Motor to lateral rectus muscle of the eye.Exiting foramen=superior orbital fissureOrigin= pons
• Test: Check eye movements• Symptoms of nerve damage:
• The affected eye will tend to be deviated inward because of the unopposed action of the medial rectus muscle.
• Cannot move eyeball laterally beyond the midpoint Injured
sideNormal
side
Originates in the pons
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CN V: Trigeminal Nerve
3 Branches1. Ophthalmic2. Maxillary3. Mandibular
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CN V: Trigeminal Nerve• Function:
• Somatic Motor (mandibular branch) to muscles of mastication (chewing)
• Sensory (all branches)to face and cornea.• Exiting foramen= Ophthalmic branch=superior
orbital fissure• Maxillary branch= foramen rotundum• Mandibular branch = foramen oval• Origin= pons
Originates in the pons
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CN V: Trigeminal NerveTest: Have patient bite down while you palpate the masseter muscle
Test: Touch patient with an open paperclip and ask “sharp or dull”
Test: Touch cornea with a wisp of cotton. Patient should blink
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CN V: Trigeminal Nerve• Symptoms of nerve damage:• Inability to firmly bite down (mandibular branch
only)• Loss of sensation (each branch can be affected
independently)• Loss of corneal reflex (may indicate brain stem
injury)• Trigeminal Neuralgia (Tic Douloureux):
debilitating intermittent pain on one side of the face
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CN VII: Facial Nerve 5 Branches
1. Temporal2. Zygomatic3. Buccal4. Mandibular5. Cervical
• Function: • Somatic Motor to muscles of facial expression• Parasympathetic (motor) to lacrimal and salivary
glands• Sensory taste to anterior 2/3 tongue
Originates in the pons
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CN VII: Facial Nerve
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CN VII: Facial Nerve Testing• Exiting foramen= enters internal acoustic
meatus exits via stylomastoid foramen• Origin= Pons• Tests:
1. Check taste on anterior 2/3 of tongue by having patient taste sugar, salt, sour and bitter
2. Check symmetry of facial muscles:• Close eyes, smile, whistle, puff out
cheeks (make funny faces)3. Check tearing with ammonia fumes
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CN VII: Facial Nerve
• Symptoms of nerve damage:• Mild weakness to total paralysis of facial
muscles (may include twitching),• Drooping eyelid• Drooping corner of the mouth• Drooling or dry mouth• Impairment of taste• Excessive tearing in the eye or dry eye
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CN VII: Facial Nerve Injury (Bell’s Palsy)
Paralyzed facial muscles
Patients can still feel their face because sensory is supplied by the trigeminal nerve
Injured side
Normal side
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CN VIII: Vestibulocochlear• Function: Sensory
• Vestibular system for balance & equilibrium• Cochlea for hearing• Exiting foramen= internal acoustic meatus• Origin= Pons-medulla border
• Tests:• Auditory component of the nerve:
• Hearing test• Vestibular control of balance and movement:
• Romberg test (tests equilibrium)
Originates in the medulla
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CN VIII: Vestibulocochlear Tests
• Simple hearing test:• Rub fingers together near the ear
and ask “right or left” If there is lateralization (hearing louder on one side) there is a problem
• Other hearing tests:• Performed by an audiologist with special
equipment to determine tones, frequencies and degree of hearing loss
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CN VIII: Vestibulocochlear TestsRomberg Test
• Have patient stand with arms at side and feet together
• Have patient stand with their eyes closed
• Stand close to prevent falls• Normally, they should maintain
position for 20 seconds with only minimal swaying• If they loose their balance, they have
failed the equilibrium test.
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CN IX: Glossopharyngeal• Function:
• Somatic Motor to muscles of pharynx• Parasympathetic (motor) to salivary glands• Sensory to pharynx and taste to posterior tongue• Exiting foramen= Jugular foramen• Origin= medulla oblongata
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CN IX: Glossopharyngeal• Tests:
• Gag reflex: Touch each side of the throat with the tongue depressor
• Evaluate swallowing movements • Say AHH, and watch the palate
and uvula elevate. • Evaluate taste on posterior 1/3 of tongue
• Symptoms of nerve damage: • Loss of gag reflex• Difficulty swallowing• Loss of taste
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CN X: Vagus Nerve• Function:
• Somatic Motor to muscles of pharynxand larynx
• Parasympathetic (motor) fibers of the heart and other viscera
• Sensory to pharynx and larynx
Originates in the medulla
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CN X: Vagus Nerve• Test:
• Inspect palate• Test gag reflex
• Symptoms of nerve damage: • Loss of gag reflex• Difficulty swallowing• Hoarse voice• Exiting foramen = Jugular foramen• Origin = Medulla oblongata
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CN XI: Accessory Nerve• Function: Somatic Motor to sternocleidomastoid
and trapezius muscles
Originates in the medulla
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CN XI: Accessory Nerve
• Exiting foramen = jugular foramen
• Origin = medulla oblongata• and spinal cord• Test:
• Shrug shoulders against resistance
• Turn head against resistance.
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CN XI: Accessory Nerve
• Symptoms of nerve damage:• Weakness• Uneven
shoulders• Winged
scapula
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CN XII: Hypoglossal Nerve• Function: Somatic Motor to tongue
Originates in the medulla
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Hypoglossal Nerve Injury• Exiting foramen = hypoglossal
canal• Origin = medulla oblongata• Test:• Ask patient to stick out tongue• Symptoms of nerve damage: • When paralyzed, the tongue will
point to the damaged side
Normal side
Injured side
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Lab Activities
• Identify cranial nerves on models• Perform cranial nerve tests• Identify cranial nerve passageways on the
skulls• Know origins of cranial nerves
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The End