The document outlines the 12 pairs of cranial nerves, detailing their origin, innervation, functions, and clinical evaluations to identify dysfunctions. Each nerve is associated with sensory, motor, or mixed functions, with specific tests recommended for assessing various conditions, such as visual loss, facial asymmetry, or hearing issues. Key nerves discussed include the olfactory, optic, oculomotor, trigeminal, facial, acoustic, glossopharyngeal, vagus, accessory, and hypoglossal nerves.

1. CRANIAL NERVES
 The 12 pairs of cranial nerves are part of the
peripheral nervous system.
 The Roman numeral is based on descending order
of the cranial nerve's attachment to the CNS.
 As a rule, cranial nerves do not cross in the brain.
 Cranial nerves may be sensory, motor both
somatic or parasympathetic, or have mixed
function.
General Characteristics:

2. CN I - OLFACTORY
 Use aromatic substances,
i.e. coffee, lemon, garlic,
etc.
 Test each nostril separately.
ORIGIN: Cerebral hemisphere
INNERVATION: Nasal mucous membranes.
FUNCTION: Sense of smell
DYSFUNCTION: Anosmia
CLINICAL EVALUATION

3. CN II - OPTIC
 Blurred vision or complete blindness.
 Ipsilateral vision loss - Optic atrophy, retinal/optic nerve lesions, trauma.
 Visual loss (one or both eyes) - Optic chiasm or occipital lobe lesions.
 Cortical blindness - Lesion of occipital cortex bilaterally, pupil reflexes intact.
 Papilledema - Optic nerve tumor, venous obstruction, chronic increased ICP.
 Optic atrophy - MS, optic neuritis, increased ICP.
 Scotomas- (Abnormal blind spots on visual fields) - optic neuritis or atrophy.
 Hemianopia - (loss of half of visual field in one or both eyes) - Lesions of optic
chiasm, tracts, or radiations.
CLINICAL EVALUATION
VISUAL ACUITY: Snellen chart for distant
vision, newspaper or fingers for near vision.
VISUAL FIELDS: Confrontation.
FUNDI AND OPTIC DISCS:
Visualization of the termination of
the optic nerve by looking through
pupil with ophthalmoscope.
SPECIFIC DYSFUNCTIONS

4. CN III - OCULOMOTOR
CLINICAL EVALUATION
 Observe for eye opening and symmetry.
 Direct light response - brisk, sluggish, or non-reactive.
 Consensual response - present or absent.
 Pupil size and shape.
 Accommodation.
 Extraocular movement (EOM's) (Abducens).
ORIGIN: Midbrain
INNERVATION: EOM's; eyelid; ciliary; and sphincter of iris.
FUNCTION: Eye movement inward (medially), upward, downward, and outward; pupil
constriction, shape and equality; elevates upper eyelid; accommodation
reflex.
DYSFUNCTION:Unable to look up, down, or medial (dysconjugate gaze); ptosis, pupil
dilatation - bilateral or ipsilateral, and loss of accommodation reflex.

5. CRANIAL NERVE FUNCTION & MUSCLE INNERVATION
RELATIVE TO EYE MOVEMENT
Superior rectus
CN III
Inferior oblique
CN III
Lateral rectus
CN VI
Medial rectus
CN III
Superior oblique
CN IV
Inferior rectus
CN III

6. CN IV - TROCHLEAR
 Extraocular movements (EOM's)
 CN IV (Trochlear) and CN VI tested with CN III (Oculomotor)
ORIGIN: Midbrain
INNERVATION: Superior oblique muscle.
FUNCTION: Down and inward movement of
the eye.
DYSFUNCTION: Loss of downward, inner
movement of eye, dysconjugate gaze.
CN VI - ABDUCENS
ORIGIN: Pons
INNERVATION: Lateral rectus muscle.
FUNCTION: Outward, lateral movement of
eye.
DYSFUNCTION: Loss of lateral eye
movement, dysconjugate gaze.
CLINICAL EVALUATION

7. CN V - TRIGEMINAL
ORIGIN: Pons. The sensory nucleus extends from the pons to the midbrain, and
also to the medulla and spinal cord.
INNERVATION: Three branches of CN V:
Ophthalmic, maxillary, & mandibular. Motor
innervation to masseter & temporal muscles.
Sensory innervation to skin & mucous
membranes in head; teeth, tongue, external
auditory canal, and cornea.
FUNCTION: Sensation of pain, touch, hot, &
cold; motor movement of masseter & temporal
muscles.
Brain Stem = Onion skin
sensory deficit
DYSFUNCTION: Loss of sensation - if affecting all three branches, indicative of peripheral
injury. Brainstem or upper cervical cord injury may result in loss of sensation to one or more
branches of the trigeminal nerve.
- Loss of corneal reflex.
- Paresthesia and/or severe pain indicative
of nerve compression or irritation (Trigeminal neuralgia)
-Deviation of jaw, loss of sensation.
Inability to bite down and chew, inability to close jaw.
Nerve Root Patterns

8. CN V - TRIGEMINAL
 SENSATION: Test with patients eye closed. Evaluate pain, temperature, & light
touch to jaw, cheeks, and forehead. Observe response and symmetry.
 MOTOR: Open jaw, check for deviation. Have patient bite down, palpate masseter
and temporal muscles. Move jaw laterally against resistance to evaluate weakness
or paralysis.
CLINICAL EVALUATION
CORNEAL REFLEX: Cotton wisp across cornea, observe for
blink (function of CN III)
JAW JERK: Tap lower jaw with mouth open - check for slight
elevation of mandible.

9. CN VII- FACIAL
ORIGIN: Pons & medulla.
INNERVATION: Anterior two-thirds of tongue; facial muscles, scalp, ear, and neck.
FUNCTION: - Control of facial muscles (expressions)
- Motor limb of blink & corneal reflexes
- Secretion of salivary & lacrimal glands
- Sensation of taste, anterior two-thirds tongue.
DYSFUNCTION:
Motor = Facial asymmetry - Ipsilateral weakness/paralysis, right or left, indicative of
damage to motor nucleus or peripheral component (lower motor neuron lesion) EX:
Bell's palsy
Contralateral weakness/paralysis of lower face indicative of contralateral motor
cortex damage (upper motor neuron lesion) or hemispheric lesion, i.e. massive CVA.
Bilateral weakness or paralysis , E.g. myasthenia gravis or Guillian Barre.
Parasympathetic -Loss or excessive tearing or salivation
Sensory= Loss of taste
Combined problem = speech difficulty and drooling/difficulty handling food

10. CN VII - FACIAL
 Observe for facial symmetry
 Ask patient to wrinkle forehead, puff cheeks,
smile, show teeth, open eyes against
resistance, and whistle.
 Test each side of tongue separately.
 Test for sweet (tip of tongue); sour (sides of
tongue); salty (over most of tongue, but
concentrated on sides).
 Give sip of water between tastes.
CLINICAL EVALUATION
MOTOR FUNCTION:
SENSORY FUNCTION:

11. CN VIII - ACOUSTIC
ORIGIN: Pons and medulla
INNERVATION: Cochlear - ear
Vestibular - ear
FUNCTION: Cochlear - Hearing
Vestibular - Balance, maintenance of body position, and proprioception.
DYSFUNCTION (Cochlear)
- Unilateral deafness
- Loss of sound appreciation
- Tinnitis
- (Rinne Test) AC >BC or both diminished indicative of nerve damage,
BC> AC middle ear disease.
- (Weber Test) Lateralization to good ear is nerve damage, lateralization to
bad ear is, middle ear disease.
DYSFUNCTION (VESTIBULAR)
- Vertigo
- Balance disturbances
Vestibular branch normally not tested unless patient gives history of vertigo or balance
Disturbance history is positive, caloric testing is done by physician.

12. CN VIII - ACOUSTIC
CLINICAL EVALUATION
 HEARING: Test bilaterally, whisper or watch tick
 CONDUCTION: Weber and Rinne tests (Differentiate between conduction
deafness and nerve deafness)
Rinne Test: Evaluates air (AC) and bone
conduction (BC). Place the base of a vibrating
tuning fork on the mastoid process until patient
can no longer hear sound; then quickly move
tuning fork near ear canal. Ask the patient if he
hears it, compare hearing times.
Rinne test: AC > BC normal result.
Weber Test: Evaluates lateralization. Use
vibrating tuning fork on top of patient's head,
ask patient where he hears it (one or both
sides).

13. Glossopharyngeal (IX) Vagus (X)
ORIGIN: Medulla Medulla
INNERVATION:
Mucous membranes of tonsils,
pharynx, posterior one-third of
tongue, pharyngeal muscles,
carotid sinus and carotid body
Muscles of larynx, pharynx, and
soft palate. Parasympathetic
innervation of thoracic and
abdominal viscera.
FUNCTION:
Taste from posterior one-third of
tongue - Afferent limb of gag,
swallow, and cardiac reflexes.
Muscles of larynx, pharynx, and
soft palate;- Sensation conveyed
from the heart, lungs, digestive
tract, carotid sinus, & carotid
body; Efferent limb of gag and
swallow
DYSFUNCTION: Loss of taste; Neuralgia
Loss of gag & swallow reflex;
Loss of carotid sinus &
oculocardiac reflex; Dysphagia
CN IX- GLOSSOPHARYNGEAL
and CN X - VAGUS

14. CN IX and X considered jointly, actions are seldom compared separately; they are
always tested together.
CLINICAL EVALUATION
- Evaluate voice quality (hoarseness or dysarthria)
- Ask patient to open mouth, say "ah", observe for
elevation of soft palate, midline position of uvula.
- Gag reflex, bilaterally
- Swallowing
- Taste (bitter) posterior one-third tongue*
CN IX- GLOSSOPHARYNGEAL
and CN X - VAGUS
Negative Findings
- Loss of voice quality, (dysarthria or hoarseness)
- Deviation of uvula toward non-paralyzed side
- Swallowing difficulty or nasal regurgitation
- Vagal irritation (bradycardia)
*usually not tested

15. CN XI - SPINAL ACCESSORY
 Palpate trapezius muscle as patient shrugs
shoulders against resistance; evaluate strength.
 Ask patient to turn head to one side and push
against examiners hand, palpate and evaluate
strength of sternocleidomastoid muscle.
 Evaluate both right and left side, compare for
symmetry.
ORIGIN: Medulla
INNERVATION: Sternocleidomastoid & trapezius muscles
FUNCTION: Motor function sternocleidomastoid & trapezius
DYSFUNCTION: Muscle weakness.
CLINICAL EVALUATION

16. CN XII -Hypoglossal
ORIGIN: Medulla
INNERVATION: Muscles of the tongue
FUNCTION: Movement of the tongue
Unilateral
Flaccid paralysis (peripheral lesion)
- Tongue deviates to side of lesion.
- Isilateral atrophy
- Fasciculation
Spastic paralysis (cortical pathways)
- Tongue deviates to opposite side of lesion
- No atrophy
- Dysarthria and ataxia of tongue
DYSFUNCTION:
Bilateral
Flaccid paralysis (medullary lesion, MG)
- Dysphagia
- Dysarthria
- Difficulty chewing food

17. IV Trochlear
III Oculomotor
VII Facial
VI Abducens
V Trigeminal
CEREBRAL
HEMISPHERE
MIDBRAIN
PONS
MEDULLA
CRANIAL NERVES
II Optic
I Olfactory
VIII Acoustic
XII Hypoglossal
XI Accessory
X Vagus
IX Glossopharyngeal