1. Portland Community College
Lab 14 Continued
Cranial Nerves
Portland Community College
BI 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)

3. 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
Use Figure 14.5 to view all CNs

4. 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)

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:
Eye chart
Check peripheral vision
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 Pathology
Papilledema. 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:
Check pupils for size, shape and equality
Shine light in each eye and check for pupil constriction
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
Injured side
Normal side

13. Pupillary Reflex Efferent Afferent
Consensual reflex: Both pupils should constrict at the same time

14. CN IV: Trochlear Nerve Originates in the midbrain Normal side
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
Normal side
Injured side

15. CN VI: Abducens Nerve Originates in the pons Function:
Somatic Motor to lateral rectus
muscle of the eye.
Exiting foramen=superior orbital fissure
Origin= 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 side
Normal side

16. CN V: Trigeminal Nerve
3 Branches
Ophthalmic
Maxillary
Mandibular

17. CN V: Trigeminal Nerve Originates in the pons 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

18. CN V: Trigeminal Nerve
Test: 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 Originates in the pons 5 Branches Temporal
Zygomatic
Buccal
Mandibular
Cervical
Function:
Somatic Motor to muscles of facial expression
Parasympathetic (motor) to lacrimal and salivary glands
Sensory taste to anterior 2/3 tongue

21. CN VII: Facial Nerve

22. CN VII: Facial Nerve Testing
Exiting foramen= enters internal acoustic meatus exits via stylomastoid foramen
Origin= Pons
Tests:
Check taste on anterior 2/3 of tongue by having patient taste sugar, salt, sour and bitter
Check symmetry of facial muscles:
Close eyes, smile, whistle, puff out cheeks (make funny faces)
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
Normal side
Injured side
Patients can still feel their face because sensory is supplied by the trigeminal nerve

25. CN VIII: Vestibulocochlear
Originates in the medulla
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)

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 Tests Romberg 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 Originates in the medulla Function:
Somatic Motor to muscles of pharynx and larynx
Parasympathetic (motor) fibers of the heart and other viscera
Sensory to pharynx and larynx

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 Originates in the medulla
Function: Somatic Motor to sternocleidomastoid and trapezius muscles

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
Originates in the medulla
CN XII: Hypoglossal Nerve
Function: Somatic Motor to tongue

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

37. Lab Activities Identify cranial nerves on models
Perform cranial nerve tests
Identify cranial nerve passageways on the skulls
Know origins of cranial nerves

38. The End
The End