List of Cranial Nerves and their functions.
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Cranial Nerves

Video


Exam Summary


1. Introduction

  • Introduce yourself and the exam
  • Hand hygiene

2. Observations

  • Heart Rate
  • Temperature
  • Respiratory Rate

3. General Inspection

Note:
  • Alertness
  • Neck Stiffness which may be caused by meningitis, ankylosing spondylitis, cervical fusion, Parkinson's disease or increased Intracranial Prssure.
  • Handedness - ask the patient which hand is dominant
  • Orientation - ask the patient for their name, the place they are at and the date.

4. Face Inspection

Look for:
  • Structural abnormalities (eg acromegaly and Paget's Disese)
  • Ptosis
  • Proptosis (eye bulging)
  • Pupil differences
  • Eye deviation
  • Face droop
  • Herpes Zoster infection
Ptosis.jpg
Ptosis

Proptosis.jpg
Proptosis of a patient with Grave's Disease
Trigeminal_herpes_with_uveitis_and_keratitis.jpg
Herpes Zoster (shingles) of the Ophthalmic Division.

Bellspalsy.JPG
Face drop in a patient with Bell's Palsy.

5. Olfactory Nerve (CNI)
  • Ask the patient if they have had any difficult with smell or taste recently.
  • To test this nerve properly assess each nostril separately. Use familiar smells that are not repulsive. In hospital isopropyl alcohol wipes can be used.

  • Inability to smell this is known as anosmia which may be caused by:

6. Optic Nerve (CNII)

  • To test the optic nerve assess the patient's Visual Acuity using a Snellen Chart. Assess each eye individually.
    • Without Visual aid
    • With Visual Aid
    • Using a pinhole to correct for refractive errors.
  • Assess Visual fields using a red hat pin
    • Sit opposite the patient
    • Ask patient to look at you eyes
    • Cover one eye
    • Screen all four quadrants by bringing in the red pin at 45ยบ all the way to the centre.
    • Ask when the pin appears red
    • Ask if the pin ever disappears
    • Assess other eye
  • Also assess the light reflex by shining a light in the pupil and looking for:
    • Direct constriction
    • Consensual constiriction
    • Rapid Afferent Pupillary Defect (RAPD) in a swinging light test
  • Assess accommodation
    • Ask the patient to look at your finger and then a distant object.
    • Ask the patient to continuously look at your finger as you bring it closer
  • See Vision Loss for causes

7. Eye Movements (CNIII, IV, VI)

  • Test the movements of the eye by getting the patient to follow your finger and making an H-shape.
  • Ask the patient if they ever experience eye pain or double vision while doing so. Look for any movement the patient can't do as well as nystagmus (involuntary eye movements)
Eye2.png
Isolating the different eye muscles. Superior Oblique (CNIV), Lateral Rectus (CNVI). All others CNIII

8. Trigeminal Nerve (CNV)

  • Test the corneal reflex by using a wisp of cotton wool and touching the cornea (not the sclera). This should elicit a reflex blink in both eyes. No blinking suggests an afferent trigeminal problem (in the ophthalmic division) or a facial nerve problem while blinking on only the ipsilateral side indicates a facial nerve palsy.
  • Assess soft touch and pain of the three divisions of the face.
  • Assess the strength of the muscles of mastication by asking the patient to bite and open their mouth.
  • If there is a facial palsy, Request the jaw jerk or masseter reflex by placing two fingers on the tip patient's mandible and getting the patient to open their mouth a little. Using a tendon hammer and assess if the patient closes their mouth. An exaggerated response suggest an upper motor neuron lesion. No response is also normal.
Trigem.png
Trigeminal Dermatome distribution
Jawjerk.PNG
Jaw Jerk

9. Facial nerve (CNVII)

  • Assess muscle strength by getting the patient to:
    • Raise eyebrows (look for wrinkles)
    • Close their eyes
    • Puff out cheeks
    • Show their teeth
    • An upper motor neuron lesion will not affect forehead muscles while a lower motor neuron lesion will. Look for facial asymmetry at this time. Look at the nasolabial folds which will be absent in a lesion.
  • Assess the taste of the anterior two-thirds of the tongue on both sides (use vinegar, sugar, salt and quinine)
  • The most common cause of a CNVII lesion is Bell's Palsy which is often idiopathic.
Bellspalsy.JPG
Bell's Palsy

10. Vestibulocochlear Nerve (CNVIII)

  • Assess each ear by whispering three numbers or works while standing behind the patient.
  • If there is a deficit:
    • Rinne's Test: Assess air and bone conductance of each ear using a 256Hz tuning fork.
      • Place the vibrating fork on bone behind the ear
      • Ask the patient to tell you when they stop hearing the vibration
      • Move the tuning fork in front of the patient's ear on the same side and ask them if they can still hear the vibrations. If the patient cannot hear then this suggests there is a problem with transmission from the outer ear to the cochlea (ie conduction problem).
    • Weber's Test
      • Put tuning fork in centre of head and ask which ear hears the sound loudest
      • A unilateral conductive defect will cause the sound to be loudest in the ipsilateral ear
      • A unilateral sensorineural defect will cause the sound to be loudest in the contralateral ear

11. Glossopharyngeal Nerve (CNIX)

  • Request the gag reflex using a tongue depressor and placing it on the posterior 1/3 of the tongue. Ask the patient if they can feel the depressor. Lack of sensation suggests a glossopharyngeal lesion.
  • Ask the patient to cough. A bovine cough may be due to a defect in CNIX or CNX.

12. Vagus Nerve (CNX)

  • If there is no gag reflex but the tongue depressor is felt then it suggests a problem with CNX.
  • Also assess for uvula deviation. It will deviate to the side of the lesion
  • Ask the patient to speak and assess if for a hoarse voice. A hoarse voice suggests problems with the recurrent laryngeal nerve.

13. Accessory Nerve (CNXI)

  • Assess the trapezius muscle by asking the patient to shrug their shoulders. Push down on their shoulders asking the patient to resist.
  • Ask the patient to turn their head to the side and push against your hand. This assesses the strength of the contralateral sternocleidomastoid muscle.

14. Hypoglossal Nerve (CNXII)

  • Ask the patient to poke their tongue out straight. The tongue will deviate to the side of a lesion.
  • Also ask the patient to push against the inside of their cheek with their tongue. Place your fingers on the outside of the cheek and push against their tongue.
Hypoglossal_Nerve_Palsy_.jpg
Hypoglossal nerve palsy. Patient was asked to poke tongue out straight.


15. Conclude

Thank the patient and offer assistance.

See also

Eye movements
Cranial Nerves

Citation

Proptosis photo: By Jonathan Trobe, M.D. - University of Michigan Kellogg Eye Center (The Eyes Have It) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
Ptosis image: By Andrewya (Own work) [Public domain], via Wikimedia Commons
Shingles image: "Trigeminal herpes with uveitis and keratitis" by Jonathan Trobe, M.D. - University of Michigan Kellogg Eye Center - The Eyes Have It. Licensed under CC BY 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Trigeminal_herpes_with_uveitis_and_keratitis.jpg#/media/File:Trigeminal_herpes_with_uveitis_and_keratitis.jpg
Bell's Palsy image: "Bellspalsy" by James Heilman, MD - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Bellspalsy.JPG#/media/File:Bellspalsy.JPG
Trigeminal Dermatomes image: "Gray784" by Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 784. Licensed under Public Domain via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Gray784.png#/media/File:Gray784.png
Hypoglossal nerve palsy image: http://www.exodontia.info/Hypoglossal_Nerve_Damage.html
Jaw Jerk image: By semiologiaclinicas from https://www.youtube.com/watch?v=UESIyXicsc0
Cranial nerves image: "Brain human normal inferior view with labels en-2" by Brain_human_normal_inferior_view_with_labels_en.svg: *Brain_human_normal_inferior_view.svg: Patrick J. Lynch, medical illustratorderivative work: Beaoderivative work: Dwstultz (talk) - Brain_human_normal_inferior_view_with_labels_en.svg. Licensed under CC BY 2.5 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Brain_human_normal_inferior_view_with_labels_en-2.svg#/media/File:Brain_human_normal_inferior_view_with_labels_en-2.svg
Eye movements image: By Alex Miles, author's own
Hypoglossal nerve palsy image: http://www.exodontia.info/Hypoglossal_Nerve_Damage.html
By Andrewya (Own work) [Public domain], via Wikimedia Commonshttp://www.exodontia.info/Hypoglossal_Nerve_Damage.html
  • A unilateral conductive defect will cause the sound to be loudest it the ipsilateral ear.