Lab 14 Continued
Cranial Nerves
Portland Community College
BI 232
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)
2
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 borderCNVIII
• Medulla-CNIX, CNX, XI,
XII
Use Figure 14.5 to view all CNs
3
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
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
5
CN II: Optic Nerve
•
•
Function:
•
Sensory for vision
•
Exiting foramen= optic canal
•
Origin=forebrain
Tests:
1. Eye chart
2. Check peripheral vision
3. Funduscopic exam
6
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
7
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.
8
Cranial Nerves III, IV & VI
(Control Eye Movements)
9
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 equality
2. 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
10
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
11
Oculomotor Nerve Injury
Right Eye
Injured
side
Normal
12
side
Pupillary Reflex
Efferent
Afferent
Consensual reflex: Both pupils should constrict at the same time
13
Originates in the midbrain
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
Normal side
Injured side
14
Originates in the pons
CN VI: Abducens Nerve
• 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
15
side
CN V: Trigeminal Nerve
3 Branches
1. Ophthalmic
2. Maxillary
3. Mandibular
16
Originates in the pons
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
17
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
18
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
19
Originates in the pons
CN VII: Facial Nerve
5 Branches
1. Temporal
2. Zygomatic
3. Buccal
4. Mandibular
5. Cervical
• Function:
• Somatic Motor to muscles of facial expression
• Parasympathetic (motor) to lacrimal and
salivary glands
20
• Sensory taste to anterior 2/3 tongue
CN VII: Facial Nerve
21
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
22
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
23
CN VII: Facial Nerve Injury
(Bell’s Palsy)
Normal
side
Injured
side
Paralyzed facial muscles
Patients can still feel their face because sensory is supplied by the
24
trigeminal nerve
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)
25
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
26
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
27
the equilibrium test.
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
28
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
29
Originates in the medulla
CN X: Vagus Nerve
• Function:
• Somatic Motor to
muscles of pharynx
and larynx
• Parasympathetic
(motor) fibers of
the heart and other
viscera
• Sensory to pharynx
and larynx
30
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
31
Originates in the medulla
CN XI: Accessory Nerve
• Function: Somatic Motor to sternocleidomastoid
and trapezius muscles
32
CN XI: Accessory Nerve
• Exiting foramen = jugular
foramen
• Origin = medulla oblongata
• and spinal cord
• Test:
• Shrug shoulders against
resistance
• Turn head against
resistance.
33
CN XI: Accessory Nerve
• Symptoms of
nerve damage:
• Weakness
• Uneven
shoulders
• Winged
scapula
34
Originates in the medulla
CN XII: Hypoglossal Nerve
• Function: Somatic Motor to tongue
35
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
36
Lab Activities
• Identify cranial nerves on models
• Perform cranial nerve tests
• Identify cranial nerve passageways on the
skulls
• Know origins of cranial nerves
37
The End
38