Cranial nerve examination

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Cranial nerve examination
Eye dilation
One component of the examination (III) uses the pupillary light reflex to assess the status of the oculomotor nerve (CNIII).
Purposepart of the neurological examination

The cranial nerve exam is a type of neurological examination. It is used to identify problems with the cranial nerves by physical examination. It has nine components. Each test is designed to assess the status of one or more of the twelve cranial nerves (I-XII). These components correspond to testing the sense of smell (I), visual fields and acuity (II), eye movements (III, IV, VI) and pupils (III, sympathetic and parasympathetic), sensory function of face (V), strength of facial (VII) and shoulder girdle muscles (XI), hearing and balance (VII, VIII), taste (VII, IX, X), pharyngeal movement and reflex (IX, X), tongue movements (XII).

Components

CN I

The first test is for the

aging. Unilateral loss indicates a possible nerve lesion or deviated septum. This test is usually skipped on a cranial nerve exam.[1]

The short axons of the first cranial nerve regenerate on a regular basis. The neurons in the olfactory epithelium have a limited life span, and new cells grow to replace the ones that die off. The axons from these neurons grow back into the CNS by following the existing axons—representing one of the few examples of such growth in the mature nervous system. If all of the fibers are sheared when the brain moves within the cranium, such as in a motor vehicle accident, then no axons can find their way back to the olfactory bulb to re-establish connections. If the nerve is not completely severed, the anosmia may be temporary as new neurons can eventually reconnect.[2]

CN II

Vision via the optic nerve is examined both in fields of vision, and in clarity of vision.

  • optic pathway between the orbit and the diencephalon. For example, loss of peripheral vision may be the result of a pituitary tumor pressing on the optic chiasm. The pituitary, seated in the sella turcica of the sphenoid bone, is directly inferior to the optic chiasm. The axons that decussate in the chiasm are from the medial retinae of either eye, and therefore carry information from the peripheral visual field.[2]

CN III, CN IV, CN VI

The three nerves that control the

lateral rectus is controlled by neurons of the abducens nucleus in the superior medulla, whereas the medial rectus is controlled by neurons in the oculomotor nucleus of the midbrain.[2]

  • PERRLA
    (pupils equal, round and reactive to light and accommodation).
  • dilation
    will occur during the swing between.

CN V

Testing the trigeminal nerve involves testing its three branches.

  • Light touch is tested in each of the three divisions of the trigeminal nerve and on each side of the face using a cotton wisp or tissue paper. The ophthalmic division is tested by touching the forehead, the maxillary division is tested by touching the cheeks, and the mandibular division is tested by touching the chin. Be careful not to test the mandibular division too laterally, as the mandible is innervated by the great auricular nerve (C2 and C3). A common mistake is to use a stroking motion, which will trigger pain and temperature nerves. Instead, a point stimulus should be applied. For pain and temperature repeat the same steps as light touch but use a sharp object and a cold tuning fork respectively.

CN VII

The facial nerve is tested by inspecting for facial asymmetry and involuntary movements. The individual is asked to:

  1. Raise both eyebrows
  2. Frown
  3. Close both eyes tightly so that you can not open them. Test muscular strength by trying to open them
  4. Show both upper and lower teeth
  5. Smile
  6. Puff out both cheeks

The sensory component is tested for taste. Testing this is as simple as introducing salty, sour, bitter, or sweet stimuli to either side of the tongue. The patient should respond to the taste stimulus before retracting the tongue into the mouth. Stimuli applied to specific locations on the tongue will dissolve into the saliva and may stimulate taste buds connected to either the left or right of the nerves, masking any lateral deficits.[2]

CN VIII

The vestibulocochlear nerve is tested for hearing and balance.

  • Hearing is tested by whispering numbers in one ear as patient covers the other and ask the patient to repeat the numbers. Alternatively, have patient close their eyes and say "left" or "right" depending on the side from which they hear the sound. Vigorously rub fingers together in one ear at a time to produce rustling sound.[3]

More sensitive hearing tests are

mastoid process and the patient indicates when the sound produced from this is no longer present. Then the fork is immediately moved to just next to the ear canal so the sound travels through the air. If the sound is not heard through the ear, meaning the sound is conducted better through the temporal bone than through the ossicles, a conductive hearing deficit is present.[2]

The Weber test also uses a tuning fork to differentiate between conductive versus sensorineural hearing loss. In this test, the tuning fork is placed at the top of the skull, and the sound of the tuning fork reaches both inner ears by travelling through bone. In a healthy patient, the sound would appear equally loud in both ears. With unilateral conductive hearing loss, however, the tuning fork sounds louder in the ear with hearing loss. This is because the sound of the tuning fork has to compete with background noise coming from the outer ear, but in conductive hearing loss, the background noise is blocked in the damaged ear, allowing the tuning fork to sound relatively louder in that ear. With unilateral sensorineural hearing loss, however, damage to the cochlea or associated nervous tissue means that the tuning fork sounds quieter in that ear.[2]

  • Vestibular Function

CN IX, CN X

The glossopharyngeal nerve (CN IX) and vagus nerve (CN X) are tested for:

  • Gag response
  • Visualizing uvula deviation away from affected side on articulating "AHH" with tongue depressor.
  • Palatal articulation "KA"
  • Guttural articulation "GO"

CN XI

The accessory nerve is tested for:

CN XII

The hypoglossal nerve has a sole motor function for most of the muscles of the tongue:

  • Stick out tongue and move it to one side, then the other[4]
  • Inspect for tongue atrophy, fasciculations or asymmetry in movement or appearance.

See also

References

  1. . Retrieved 27 June 2011.
  2. ^ a b c d e f g  This article incorporates text available under the CC BY 4.0 license. Ju, William (November 11, 2023). Neuroscience. Toronto: University of Toronto. 1.6 The Neurological Exam.
  3. ^ "Examination of the Cranial Nerves". 22 April 2016.
  4. ^ "Examination of the Cranial Nerves". Archived from the original on 2021-03-09. Retrieved 2014-06-26.

External links

  • NeurologyExam.com Free neurology exam videos by Cleveland Clinic trained neurologist.