Clinical Neurology

Cranial Nerves: Introduction | El Paso, TX.


Human Cranial nerves are a set of 12 paired nerves that come directly from the brain. The first two (olfactory and optic) come from the cerebrum, with the remaining ten come from the brain stem. The names of the these nerves relate to what function they perform and are also numerically identified in roman numerals (I-XII). The nerves serve in functions of smell, sight, eye movement, and feeling in the face. These nerves also control balance, hearing, and swallowing.

Cranial Nerves: Review

  • CN I – Olfactory
  • CN II – Optic
  • CN III – Oculomotor
  • CN IV – Trochlear
  • CN V – Trigeminal
  • CN VI – Abducens
  • CN VII – Facial
  • CN VIII – Vestibulocochlear
  • CN IX – Glossopharyngeal
  • CN X – Vagus
  • CN XI – Accessory
  • CN XII – Hypoglossal

Location Of Nerves


[caption id="attachment_64865" align="aligncenter" width="556"] with_labels_en.svg/424px-Brain_human_normal_inferior_view_with_labels_en.svg.png synopsis-of-cranial-nerves-of-the-brainstem-clinical-gate/

CN I – Olfactory

CN I Clinically

  • Lesions resulting in anosmia (loss of the sense of smell) can be caused by:
  • Trauma to the head, especially patient’s hitting the back of their head
  • Frontal lobe masses/tumors/SOL
  • Remember that loss of the sense of smell is one of the first symptoms seen in Alzheimer’s and early dementia patients

Testing CN I

  • Have the patient close their eyes and cover one nostril at a time
  • Have them breathe out through their nose, THEN place the scent under the nostril while they breathe in.
  • Ask them “do you smell anything?”
  • This tests if the nerve is functioning
  • If they say yes, ask them to identify it
  • This tests if the processing pathway (temporal lobe) is functional

Cranial Nerve II – Optic

Cranial Nerve II Clinically

Lesions to this nerve can be the result of:

  • CNS disease (such as MS)
  • CNS tumors and SOL
  • Most problems with the visual system arise from direct trauma, metabolic or vascular diseases
  • FOV lost in the periphery can mean SOL affecting the optic chiasm such as a pituitary tumor

Testing Cranial Nerve CN II






Associated Testing For Visual System

  • Ophthalmoscopic/Funduscopic exam
  • Assessment of A/V ratio and vein/artery health
  • Assessment of cup to disc ratio
  • Field of vision testing
  • Intraoccular pressure testing
  • Iris shadow test

Cranial Nerve III – Oculomotor

Cranial Nerve III Clinically

  • Diplopia
  • Lateral strabismus (unopposed lateral rectus m.)
  • Head rotation (yaw) away from the side of the lesion
  • Dilated Pupil (unopposed dilator pupillae m.)
  • Ptosis of the eyelid (loss of function of levator palpebrae superioris m.)
  • Lesions to this nerve can be the result of:
  • Inflammatory diseases
  • Syphilitic and tuberculous meningitis
  • Aneurysms of the posterior cerebral or superior cerebellar aa.
  • SOL in the cavernous sinus or displacing the cerebral peduncle to the opposite side

Testing Cranial Nerve CN II & III

  • Pupillary reflex testing
  • Move the light in front of the pupil from the lateral side and hold 6 seconds
  • Watch for direct (ispilateral eye) and consensual (contralateral eye) pupillary constriction

Testing Cranial Nerve CN II & III

[caption id="attachment_64884" align="aligncenter" width="700"]

Cranial Nerve IV – Trochlear

Cranial Nerve IV Clinically

  • Patient has diplopia & difficulty in downward gaze
  • Often complain of difficulty walking down stairs, tripping,falling
  • Extortion of the affected eye (unopposed inferior oblique m.)
  • Head tilt (roll) to the unaffected side
  • Lesions to this nerve can be the result of:
  • Inflammatory diseases
  • Aneurysms of the posterior cerebral or superior cerebellar aa.
  • SOL in the cavernous sinus or superior orbital fissure
  • Surgical damage during mesencephalon procedures

Head Tilt In Superior Oblique Palsy (CN IV Failure)

[caption id="attachment_64880" align="aligncenter" width="700"] Pauwels, Linda Wilson, et al. Cranial Nerves: Anatomy and Clinical Comments. Decker, 1988.

Cranial Nerve VI – Abducens

Cranial Nerve VI Clinically

  • Diplopia
  • Medial strabismus (unopposed medial rectus m.)
  • Head rotation (yaw) toward the side of the lesion
  • Lesions to this nerve can be the result of:
  • Aneurysms of the posterior inferior cerebellar or basilar aa.
  • SOL in the cavernous sinus or 4th ventricle (such as a cerebellar tumor)
  • Fractures of the posterior cranial fossa
  • Increased intracranial pressure

Testing Cranial Nerve CN III, IV & VI

  • H-Pattern testing
  • Have the patient follow an object no larger than 2 inches
  • Patient’s can have focus difficulty if the item is too large
  • It’s also important not to hold the object too close to the patient.
  • Convergence and accommodation
  • Bring object close to the bridge of the patient’s nose and back out. Perform at least 2 times.
  • Look for pupillary constriction response as well as convergence of the eyes

Cranial Nerve V – Trigeminal

Cranial Nerve V Clinically

  • Decreased bite strength on the ipsilateral side of lesion
  • Loss of sensation in V1, V2 and/or V3 distribution
  • Loss of corneal reflex
  • Lesions to this nerve can be the result of:
  • Aneurysms or SOL affecting the pons
  • Specifically tumors at the cerebellopontine angle
  • Skull fractures
  • Facial bones
  • Damage to foramen ovale
  • Tic doloureux (Trigeminal neuralgia)
  • Sharp pain in V1-V3 distributions
  • Tx with analgesic, anti-inflammatory, contralateral stimulation

Testing Cranial Nerve CN V

  • V1 – V3 pain & light touch testing
  • Testing is best done toward the more medial or proximal areas of the face, where V1, V2 &V3 are better delineated
  • Blink/Corneal reflex testing
  • Puff of air or small tissue tap from the lateral side of the eye on the cornea, if normal, the patient blinks
  • CN V provides the sensory (afferent) arc of this reflex
  • Bite strength
  • Have patient bite down on tongue depressor & try to remove
  • Jaw jerk/Masseter Reflex
  • With patient’s mouth slightly open place thumb on patient’s chin and tap your own thumb with a reflex hammer
  • Strong closure of the mouth indicates UMN lesion
  • CN V provides both the motor and sensory of this reflex

Cranial Nerve VII – Facial

Cranial Nerve VII Clinically

  • As with all nerves, symptoms describe the location of the lesion
  • Lesion in the lingual nerve will result in loss of taste, general sensation in tongue & salivary secretion
  • Lesion proximal to the branching of the chorda tympani such as in the facial canal will result in the same symptoms without the loss of general sensation of the tongue (because V3 has not yet joined the CN VII)
  • Corticobulbar innervation is asymmetric to the upper and lower parts of the Facial Motor Nucleus
  • If there is an UMN lesion (lesion to the corticobulbar fibers) the patient will have paralysis of the muscles of facial expression in the contralateral lower quadrant
  • If there is a LMN lesion (lesion to the facial nerve itself) the patient will have paralysis of the muscles of facial expression in the ipsilateral half of the face
  • Bell’s Palsy

Testing Cranial Nerve CN VII

  • Ask the patient to mimic you or follow instructions to make certain facial expressions
  • Be sure to assess all four quadrants of the face
  • Raise eyebrows
  • Puff cheeks
  • Smile
  • Close eyes tightly
  • Check for strength of the buccinator muscle against resistance
  • Ask patient to hold air in their cheeks as you press gently from the outside
  • Patient should be able to hold air in against resistance

Cranial Nerve VIII – Vestibulocochlear

Cranial Nerve VIII Clinically

  • Changes in hearing alone are most often due to
  • Infections (otitis media)
  • Skull fracture
  • The most common lesion to this nerve is caused by an acoustic neuroma
  • This affects CN VII and CNVIII (cochlear AND vestibular divisions) due to proximity in the internal auditory meatus
  • Symptoms include nausea, vomiting, dizziness, hearing loss, tinnitus, and bell’s palsy etc.

Testing Cranial Nerve CN VIII

  • Otoscopic Exam
  • Scratch Test
  • Can the patient hear equally on both sides?
  • Weber Test
  • Tests for lateralization
  • 256 Hz tuning fork placed on top of the patient’s head in the center, is it louder on one side than the other?
  • Rinne Test
  • Compares air conduction to bone conduction
  • Normally, air conduction should last 1.5-2 as long as bone conduction

Testing Cranial Nerve CN VIII

Cranial Nerve IX – Glossopharyngeal

Cranial Nerve IX Clinically

  • This nerve is rarely damaged alone, due to it’s proximity to CN X & XI
  • Look for signs of CN X & XI damage as well if CN IX involvement is suspected

Cranial Nerve X – Vagus

Cranial Nerve X Clinically

  • Patient may have dysarthria (difficulty speaking clearly) and dysphagia (difficulty swallowing)
  • May present as food/liquid coming out their nose or frequent choking or coughing
  • Hyperactivity of the visceral motor component can cause hypersecretion of gastric acid leading to ulcers
  • Hyper-stimulation of the general sensory component can cause coughing, fainting, vomiting and reflex visceral motor activity
  • The visceral sensory component of this nerve only provides general feelings of un-wellness, but visceral pain is carried on the sympathetic nerves

Testing Cranial Nerve IX & X

  • Gag reflex
  • CN IX provides the afferent (sensory) arc
  • CN X provides the efferent (motor) arc
  • ~20% of patients have a minimal or absent gag reflex
  • Swallowing, gargling, etc.
  • Requires CN X function
  • Palatal elevation
  • Requires CN X function
  • Is it symmetrical?
  • Palate elevates and uvula deviates contralateral to damaged side
  • Auscultation of the heart
  • R CN X innervates SA node (more rate regulation) and L CN X the AV node (more rhythm regulation)


Cranial Nerve XI – Accessory

Cranial Nerve XI Clinically

  • Lesions may result from radical surgeries in the neck region, such as removal of laryngeal carcinomas

Testing Cranial Nerve XI

  • Strength test SCM m.
  • Patient will have difficulty turning head against resistance toward the side opposite of the lesion
  • Strength test trapezius m.
  • Patient will have difficulty with shoulder elevation on the side of the lesion

Cranial Nerve XII – Hypoglossal

Cranial Nerve XII Clinically

  • On tongue protrusion, the tongue deviates toward the side of the inactive genioglossus m.
  • This could be contralateral to a corticobulbar (UMN) lesion OR ipsilateral to a hypoglossal n. (LMN) lesion







Testing Cranial Nerve XII

  • Ask patient to stick out their tongue Look for deviation as in above slide
  • Have patient place tongue inside cheek and apply light resistance, one side at a time
  • Patient should be able to resist moving the tongue with pressure

Clinical Examination – CN’s I – VI (Lower CN’s)

Clinical Examination – CN’s VII – XII


Blumenfeld, Hal. Neuroanatomy through Clinical Cases. Sinauer, 2002.
Pauwels, Linda Wilson, et al. Cranial Nerves: Anatomy and Clinical Comments. Decker, 1988.

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