Cranial Nerves

Cranial Nerve I –  Olfactory Nerve
Olfactory Nerve Information – TeachMe Anatomy

Olfactory Examination – NeuroExam
Cranial Nerve 1 – Olfaction: Normal Test
This CN is tested one nostril at a time by using a nonirritating smell such as tobacco, orange, vanilla, coffee, etc. Detection of the smell is more important than the actual identification.

Cranial Nerve 1- Olfaction: Abnormal Test
This patient has difficulty identifying the smells presented. Loss of smell is anosmia. The most common cause is a cold (as in this patient) or nasal allergies. Other causes include trauma or a meningioma affecting the olfactory tracts. Anosmia is also seen in Kallman syndrome because of agenesis of the olfactory bulbs.


Cranial Nerve II – Optic Nerve
​Optic Nerve Information – TeachMe Anatomy
Cranial Nerve 2
This cranial nerve has important localizing value because of its "x" axis course from the eye to the occipital cortex. The pattern of a visual field deficit indicates whether an anatomical lesion is pre- or postchiasmal, optic tract, optic radiation or calcarine cortex.

Cranial Nerve 2 – Visual acuity: Normal Test
The first step in assessing the optic nerve is testing visual acuity. This can be done with a standard Snellen chart or with a pocket chart (Rosenbaum). Have the patient use their glasses if needed to obtain best-corrected vision. Have the patient hold the pocket chart at the focal length that is best for them which is usually 14 inches. Have them recite the line with the smallest letters that they can read and record the acuity.

Cranial Nerve 2 – Visual fields: Normal Test
There are several different screening tests that can be used to assess visual fields at the bedside. First hold up both hands superiorly and inferiorly and ask the patient if they can see both hands and do they look symmetric. Then test each eye individually using your fingers in the four quadrants of the visual field and ask the patient to count fingers held up or point to the hand when a finger wiggles using yourself as a control. A second screening test is to use a grid card. Have the patient focus on the dot in the center of the grid then ask if any part of the grid is missing or looks different. A third method is to use a cotton tip applicator. Testing one eye at a time ask the patient to say “now” as soon as they see the applicator come into their side vision as they focus on the examiner’s nose. All of these tests are screening tests. Formal perimetry is the most accurate way of assessing visual fields.

Cranial Nerve 2 – Fundoscopy: Normal Test
Direct visualization of the optic nerve head is an important and valuable part of assessing CN 2. Systematically look at the optic disc, vessels, retinal background and fovea.

Images are courtesy Dr. Kathleen Digre, The University of Utah.


Cranial Nerve 2- Visual acuity: Abnormal Test
This patient’s visual acuity is being tested with a Rosenbaum chart. First the left eye is tested, then the right eye. He is tested with his glasses on so this represents corrected visual acuity. He has 20/70 vision in the left eye and 20/40 in the right. His decreased visual acuity is from optic nerve damage.

Cranial Nerve 2- Visual fields: Abnormal Test
The patient’s visual fields are being tested with gross confrontation. A right sided visual field deficit for both eyes is shown. This is a right hemianopia from a lesion behind the optic chiasm involving the left optic tract, radiation or striate cortex.

Video is without sound.


Cranial Nerve 2- Fundoscopy: Abnormal Test
The first photograph is of a fundus showing papilledema. The findings of papilledema include
1. Loss of venous pulsations
2. Swelling of the optic nerve head so there is loss of the disc margin
3. Venous engorgement
4. Disc hyperemia
5. Loss of the physiologic cup and
6. Flame shaped hemorrhages.
This photograph shows all the signs except the hemorrhages and loss of venous pulsations.

The second photograph shows optic atrophy, which is pallor of the optic disc resulting form damage to the optic nerve from pressure, ischemia, or demyelination.

Images are courtesy Dr. Kathleen Digre, University of Utah.


Cranial Nerve III, IV, VI – Oculomotor Nerve, Trochlear Nerve, Abducens Nerve
Oculomotor Nerve Information – TeachMe Anatomy
Trochlear Nerve Information – TeachMe Anatomy
Abducens Nerve Information – TeachMe Anatomy
Cranial Nerves 3 and 4
These cranial nerves give us a view of the midbrain. The 3rd nerve in particular can give important anatomical localization because it exits the midbrain just medial to the cerebral peduncle. The 3rd nerve controls eye adduction (medial rectus), elevation (superior rectus), depression (inferior rectus), elevation of the eyelid (levator palpebrae superioris), and parasympathetics for the pupil.
The 4th CN supplies the superior oblique muscle, which is important to looking down and in (towards the midline).
Cranial Nerve 6
This cranial nerve innervates the lateral rectus for eye abduction. Remember that cranial nerves 3, 4 and 6 must work in concert for conjugate eye movements; if they don’t then diplopia (double vision) results.
The medial longitudinal fasciculus (MLF) connects the 6th nerve nucleus to the 3rd nerve nucleus for conjugate movement.




Normal Testing for Cranial Nerves II, III, IV, and VI.
Cranial Nerves 2 & 3 – Pupillary Light Reflex
The afferent or sensory limb of the pupillary light reflex is CN2 while the efferent or motor limb is the parasympathetics of CN3. Shine a flashlight into each eye noting the direct as well as the consensual constriction of the pupils.
The swinging flashlight test is used to test for a relative afferent pupillary defect or a Marcus Gunn pupil. Swinging the flashlight back and forth between the two eyes identifies if one pupil has less light perception than the other. Shine the flashlight at one eye noting the size of both pupils. Then swing the flashlight to the other eye. If both pupils now dilate then that eye has perceived less light stimulus (a defect in the sensory or afferent pathway) than the opposite eye.

Cranial Nerves 3, 4 & 6 – Inspection and Ocular Alignment
Before checking ocular movements it is important to inspect the eyes. Look for ptosis. Note the appearance of the eyes and check for ocular alignment (the reflection of your light source should fall on the same location of each eyeball).

Cranial Nerves 3, 4 & 6 – Versions
Testing extraocular range of motion with both eyes open and following the target (conjugate gaze) is called versions. The patient is asked to follow a target through the six principle positions of gaze. Note any misalignment of the eyes or complaint of diplopia (double vision).

Cranial Nerves 3, 4 & 6 – Ductions
If there is any misalignment of the eyes or diplopia on versions it is important to then examine each eye with the other covered (this is called ductions). The patient should follow an object through the six principle positions of gaze so each extraocular muscle’s function is tested.

Abnormal Testing for Cranial Nerves II, III, IV, and VI.

Cranial Nerves 2 & 3- Pupillary Light Reflex
The swinging flashlight test is used to show a relative afferent pupillary defect or a Marcus Gunn pupil of the left eye. The left eye has perceived less light stimulus (a defect in the sensory or afferent pathway) then the opposite eye so the pupil dilates with the same light stimulus that caused constriction when the normal eye was stimulated.

Video is courtesy of Dr. Daniel Jacobson, Marshfield Clinic and Dr. Kathleen Digre, University of Utah.


Cranial Nerves 3, 4 & 6- Inspection & Ocular Alignment
This patient with ocular myasthenia gravis has bilateral ptosis, left greater than right. There is also ocular misalignment because of weakness of the eye muscles especially of the left eye. Note the reflection of the light source doesn’t fall on the same location of each eyeball.

Video is courtesy of Dr. Daniel Jacobson, Marshfield Clinic and Dr. Kathleen Digre, University of Utah.


Cranial Nerves 3, 4 & 6- Versions

• The first patient shown has incomplete abduction of her left eye from a 6th nerve palsy.

• The second patient has a left 3rd nerve palsy resulting in ptosis, dilated pupil, limited adduction, elevation, and depression of the left eye.

Part 2 of the video is courtesy of Dr. Daniel Jacobson, Marshfield Clinic and Dr. Kathleen Digre, University of Utah.


Cranial Nerve V – Trigeminal Nerve
Trigeminal Nerve Information – TeachMe Anatomy
Cranial Nerve 5
The entry zone for this cranial nerve is at the mid pons with the motor and main sensory (discriminatory touch) nucleus located at the same level. The axons for the descending tract of the 5th nerve (pain and temperature) descend to the level of the upper cervical spinal cord before they synapse with neurons of the nucleus of the descending tract of the 5th nerve. Second order neurons then cross over and ascend to the VPM of the thalamus.

Cranial Nerve V – Normal Testing
Cranial Nerve 5 – Sensory
Test for both light touch (cotton tip applicator) and pain (sharp object) in the 3 sensory divisions (forehead, cheek, and jaw) of CN 5.

Cranial Nerve 5 – Motor
The motor division of CN 5 supplies the muscles of mastication (temporalis, masseters, and pterygoids). Palpate the temporalis and masseter muscles as the patient bites down hard. Then have the patient open their mouth and resist the examiner’s attempt to close the mouth. If there is weakness of the pterygoids the jaw will deviate towards the side of the weakness. The last test for this nerve is testing for a jaw jerk, which is a stretch reflex. Have the patient slightly open their mouth then place your finger on their chin and strike your finger with a reflex hammer. Normally there is no movement. If there is a jaw jerk it is said to be positive and this indicates an upper motor neuron lesion.

Cranial Nerve V – Abnormal Testing
Cranial Nerve 5- Sensory
There is a sensory deficit for both light touch and pain on the left side of the face for all divisions of the 5th nerve. Note that the deficit is first recognized just to the left of the midline and not exactly at the midline. Patients with psychogenic sensory loss often identify the sensory change as beginning right at the midline.

Cranial Nerve 5- Motor

• The first patient shown has weakness of the pterygoids and the jaw deviates towards the side of the weakness (without sound).

• The second patient shown has a positive jaw jerk which indicates an upper motor lesion affecting the 5th cranial nerve (with sound).

Part 1 of the video is without sound.
Part 1 of the video is courtesy of Alegandro Stern, Stern Foundation.


Cranial Nerve VII – Facial Nerve
Facial Nerve Information – TeachMe Anatomy
Cranial Nerve 7
 This cranial nerve has a motor component for muscles of facial expression (and, don’t forget, the stapedius muscle which is important for the acoustic reflex), parasympathetics for tear and salivary glands, and sensory for taste (anterior two-thirds of the tongue).
Central (upper motor neuron-UMN) versus Peripheral (lower motor neuron-LMN) 7th nerve weakness– with a peripheral 7th nerve lesion all of the muscles ipsilateral to the affected nerve will be weak whereas with a "central 7th ", only the muscles of the lower half of the face contralateral to the lesion will be weak because the portion of the 7th nerve nucleus that supplies the upper face receives bilateral corticobulbar (UMN) input.

Facial Nerve Normal Testing
Cranial Nerves 5 & 7 – Corneal reflex
The ophthalmic division (V1) of the 5th nerve is the sensory or afferent limb and a branch of the 7th nerve to the orbicularis oculi muscle is the motor or efferent limb of the corneal reflex. The limbal junction of the cornea is lightly touched with a strand of cotton. The patient is asked if they feel the touch as well as the examiner observing the reflex blink.

Cranial Nerve 7 – Motor
The motor division of CN 7 supplies the muscles of facial expression. Start from the top and work down. Have the patient wrinkle forehead (frontalis muscle), close eyes tight (orbicularis oculi) show their teeth (buccinator), and purse lips or blow a kiss (orbicularis oris). If there is weakness especially in a bilateral upper motor neuron distribution, get the patient to smile by telling a joke or funny story. With a pseudobulbar palsy automatic or emotional facial expression will be more complete than movements to command.

Cranial Nerve 7 – Sensory, Taste
Taste is the sensory modality tested for the sensory division of CN 7. The examiner can use a cotton tip applicator dipped in a solution that is sweet, salty, sour, or bitter. Apply to one side then the other side of the extended tongue and have the patient decide on the taste before they pull their tongue back in to tell you their answer.

Facial Nerve Abnormal Testing

Cranial Nerves 5 & 7 – Corneal reflex
A patient with an absent corneal reflex either has a CN 5 sensory deficit or a CN 7 motor deficit. The corneal reflex is particularly helpful in assessing brainstem function in the unconscious patient. An absent corneal reflex in this setting would indicate brainstem dysfunction.

Video is audio only.


Cranial Nerve 7- Motor

• The first patient has weakness of all the muscles of facial expression on the right side of the face indicating a lesion of the facial nucleus or the peripheral 7th nerve.

• The second patient has weakness of the lower half of his left face including the orbicularis oculi muscle but sparing the forehead. This is consistent with a central 7th or upper motor neuron lesion.

Video is without sound.
Video is courtesy of Alegandro Stern, Stern Foundation.


Cranial Nerve 7- Sensory, Taste
The patient has difficulty correctly identifying taste on the right side of the tongue indicating a lesion of the sensory limb of the 7th nerve.

Cranial Nerve VIII – Vestibulocochlear Nerve
Vestibulocochlear Nerve Information – TeachMe Anatomy
Cranial Nerve 8
This nerve is a sensory nerve with two divisions- acoustic and vestibular. The acoustic division is tested by checking auditory acuity and with the Rinne and Weber tests.
The vestibular division of this nerve is important for balance. Clinically it be tested with the oculocephalic reflex (Doll’s eye maneuver) and oculovestibular reflex (ice water calorics).

Vestibulocochlear Nerve Normal Testing
Cranial Nerve 8 – Auditory Acuity, Weber & Rinne Tests
The cochlear division of CN 8 is tested by screening for auditory acuity. This can be done by the examiner lightly rubbing their fingers by each ear or by using a ticking watch. Compare right versus left. Further screening for conduction versus neurosensory hearing loss can be accomplished by using the Weber and Rinne tests. The Weber test consists of placing a vibrating tuning fork on the middle of the head and asking if the patient feels or hears it best on one side or the other. The normal patient will say it is the same in both ears. The patient with unilateral neurosensory hearing loss will hear it best in the normal ear while the patient with a unilateral conductive hearing loss will hear it best in the abnormal ear. The Rinne test consists of comparing bone conduction (placing the tuning fork on the mastoid process) versus air conduction (placing the tuning fork in front of the pinna). Normally, air conduction is greater than bone conduction. For neurosensory hearing loss air conduction is still greater than bone conduction but for conduction hearing loss bone conduction will be greater than air conduction.

Cranial Nerve 8 – Vestibular
The vestibular division of CN 8 can be tested for by using the vestibulo-ocular reflex as already demonstrated or by using ice water calorics to test vestibular function. The later test is usually reserved for patients who have vertigo or balance problems or in the comatose patient when one is testing brainstem function.

Vestibulocochlear Nerve Abnormal Testing
Cranial Nerve 8- Auditory Acuity, Weber & Rinne Tests
This patient has decreased hearing acuity of the right ear. The Weber test lateralizes to the right ear and bone conduction is greater than air conduction on the right. He has a conductive hearing loss.

Cranial Nerve 8- Vestibular
Patients with vestibular disease typically complain of vertigo – the illusion of a spinning movement. Nystagmus is the principle finding in vestibular disease. It is horizontal and torsional with the slow phase of the nystagmus toward the abnormal side in peripheral vestibular nerve disease. Visual fixation can suppress the nystagmus. In central causes of vertigo (located in the brainstem) the nystagmus can be horizontal, upbeat, downbeat, or torsional and is not suppressed by visual fixation.

Video is audio only.


Cranial Nerve IX – Glossopharyngeal Nerve & Cranial Nerve X – Vagus Nerve
Glossopharyngeal Nerve Information – TeachMe Anatomy
Vagus Nerve Information  – TeachMe Anatomy 
Cranial Nerves 9 and 10
 These two nerves are clinically lumped together. Motor wise, they innervate pharyngeal and laryngeal muscles. Their sensory component is sensation for the pharynx and taste for the posterior one-third of the tongue.


Cranial Nerve IX and X Normal Testing
Cranial Nerves 9 & 10 – Motor
The motor division of CN 9 & 10 is tested by having the patient say “ah” or “kah”. The palate should rise symmetrically and there should be little nasal air escape. With unilateral weakness the uvula will deviate toward the normal side because that side of the palate is pulled up higher. With bilateral weakness neither side of the palate will elevate and there will be marked nasal air escape.

Cranial Nerves 9 & 10 – Sensory and Motor: Gag Reflex
The gag reflex tests both the sensory and motor components of CN 9 & 10. This involuntary reflex is obtained by touching the back of the pharynx with the tongue depressor and watching the elevation of the palate.

Cranial Nerve IX and X Abnormal Testing

Cranial Nerve 9 & 10- Motor
When the patient says "ah" there is excessive nasal air escape. The palate elevates more on the left side and the uvula deviates toward the left side because the right side is weak. This patient has a deficit of the right 9th & 10th cranial nerves.

Video is Spanish language.
Video is courtesy of Alejandro Stern, Stern Foundation.


Cranial Nerve 9 & 10- Sensory and Motor: Gag Reflex
Using a tongue blade, the left side of the patient’s palate is touched which results in a gag reflex with the left side of the palate elevating more then the right and the uvula deviating to the left consistent with a right CN 9 & 10 deficit.

Video is without sound.
Video is courtesy of Alejandro Stern, Stern Foundation.


Cranial Nerve XI – Spinal Accessory Nerve
Spinal Accessory Nerve Information – TeachMe Anatomy
Cranial Nerve 11
This nerve is a motor nerve for the sternocleidomastoid and trapezius muscles. The UMN control for the sternocleidomastoid (SCM) is an exception to the rule of the ipsilateral cerebral hemisphere controls the movement of the contralateral side of the body. Because of the crossing then recrossing of the corticobulbar tracts at the high cervical level, the ipsilateral cerebral hemisphere controls the ipsilateral SCM muscle. This makes sense as far as coordinating head movement with body movement if you think about it (remember that the SCM turns the head to the opposite side). So if I want to work with the left side of my body I would want to turn my head to the left so the right SCM would be activated.

Spinal Accessory Nerve Normal Testing
Cranial Nerve 11 – Motor
CN 11 is tested by asking the patient to shrug their shoulders (trapezius muscles) and turn their head (sternocleidomastoid muscles) against resistance.

Spinal Accessory Nerve Abnormal Testing

Cranial Nerve 11- Motor
When the patient contracts the muscles of the neck the left sternocleidomastoid muscle is easily seen but the right is absent. Looking at the back of the patient, the left trapezius muscle is outlined and present but the right is atrophic and hard to identify. These findings indicate a lesion of the right 11th cranial nerve.

Video is without sound.
Video is courtesy of Alejandro Stern, Stern Foundation.


Cranial Nerve XII – Hypoglossal Nerve
Hypoglossal Nerve Information – Teach Me Anatomy
Cranial Nerve 12
The last of the cranial nerves, CN 12 supplies motor innervation for the tongue.

Hypoglossal Nerve Normal Test
Cranial Nerve 12 – Motor
The 12th CN is tested by having the patient stick out their tongue and move it side to side. Further strength testing can be done by having the patient push the tongue against a tongue blade. Inspect the tongue for atrophy and fasciculations. If there is unilateral weakness, the protruded tongue will deviate towards the weak side.
By having the patient say lah-pah-kah, the examiner is testing the motor components of CN 12, 7, and 9&10.

Hypoglossal Nerve Abnormal Test
Cranial Nerve 12- Motor
Notice the atrophy and fasciculation of the right side of this patient’s tongue. The tongue deviates to the right as well because of weakness of the right intrinsic tongue muscles. These findings are present because of a lesion of the right 12th cranial nerve.