Lab 14 Continued

Cranial Nerves

Portland Community CollegeBI 232

2

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)

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

3

Use Figure 14.5 to view all CNs

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)

4

5

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

6

CN II: Optic Nerve• Function:

• Sensory for vision• Exiting foramen= optic canal• Origin=forebrain

• Tests: 1. Eye chart2. Check peripheral vision 3. Funduscopic exam

7

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

8

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.

9

Cranial Nerves III, IV & VI(Control Eye Movements)

10

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

11

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

12

Oculomotor Nerve Injury Right Eye

Normal side

Injured side

13

Pupillary Reflex

Efferent Afferent

Consensual reflex: Both pupils should constrict at the same time

14

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

15

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

16

CN V: Trigeminal Nerve

3 Branches1. Ophthalmic2. Maxillary3. Mandibular

17

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

18

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

19

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

20

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

21

CN VII: Facial Nerve

22

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

23

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

24

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

25

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

26

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

27

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.

28

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

29

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

30

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

31

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

32

CN XI: Accessory Nerve• Function: Somatic Motor to sternocleidomastoid

and trapezius muscles

Originates in the medulla

33

CN XI: Accessory Nerve

• Exiting foramen = jugular foramen

• Origin = medulla oblongata• and spinal cord• Test:

• Shrug shoulders against resistance

• Turn head against resistance.

34

CN XI: Accessory Nerve

• Symptoms of nerve damage:• Weakness• Uneven

shoulders• Winged

scapula

35

CN XII: Hypoglossal Nerve• Function: Somatic Motor to tongue

Originates in the medulla

36

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

Lab Activities

• Identify cranial nerves on models• Perform cranial nerve tests• Identify cranial nerve passageways on the

skulls• Know origins of cranial nerves

37

38

The End