Cranial nerve examination
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Cranial nerve examination | |
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Purpose | part 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
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]
- ophthalmoscope.[2]
CN III, CN IV, CN VI
The three nerves that control the
- Eye movements are tested by standing one meter in front of the patient and asking the patient to follow a target with eyes only, and not the head. The target is moved in an "H" shape and the patient is asked to report any diplopia. Then, the target is held at the lateral ends of the patient's visual field. Nystagmus is tested for. One or two beats is a normal finding. The accommodation reflexis tested by moving the target towards the patient's nose. As the eyes converge, the pupils should constrict. The optokinetic nystagmus test is optional and involves asking the patient to look at a strip of vertical lines moving horizontally across visual field. Nystagmus is normally observed.
- PERRLA(pupils equal, round and reactive to light and accommodation).
- dilationwill 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.
- Corneal reflex is conducted along with the facial nerve section of the test. Note the sensory innervation of the cornea is provided by the trigeminal nerve while the motor innervation for blinking the eye is provided by the facial nerve.-
- masseter) should be inspected for atrophy. Palpate the temporalis and masseter as the patient clenches the jaw. The pterygoids can be tested by asking the patient to keep the mouth open against resistance, and move from side to side against resistance. A jaw jerk reflexcan be tested by placing a finger over the patient's chin and then tapping the finger with a reflex hammer. Normally the jaw moves minimally.
CN VII
The facial nerve is tested by inspecting for facial asymmetry and involuntary movements. The individual is asked to:
- Raise both eyebrows
- Frown
- Close both eyes tightly so that you can not open them. Test muscular strength by trying to open them
- Show both upper and lower teeth
- Smile
- 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
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:
- Shrug shoulders (trapezius muscle)
- Turn head from side to side (sternocleidomastoid muscle)
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
- ISBN 978-1-4051-0432-6. Retrieved 27 June 2011.
- ^ 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.
- ^ "Examination of the Cranial Nerves". 22 April 2016.
- ^ "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.