Cranial nerves examination

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There are 12 pairs of cranial nerves although the optic nerve is really an extension of the brain rather than a peripheral nerve. The ability to test them swiftly, efficiently and to interpret the findings should be a core competency for general practitioncer.

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Nội dung Text: Cranial nerves examination

Cranial nerves examination There are 12 pairs of cranial nerves although the optic nerve is really an extension of the brain rather than a peripheral nerve. The ability to test them swiftly, efficiently and to interpret the findings should be a core compe tency for general practitioncer.
I). Cranial nerve I – Olfactory nerve: 1). Anatomy: The olfactory nerves (CN I) have sensory fibers concerned with the special sense of smell. The olfactory receptor neurons are in the olfactory epithelium (olfactory mucosa) in the roof of the nasal cavity. The central process es of the olfactory receptor neurons ascend through foramina in the cribriform plate of the ethmoid to reach the olfactory bulbs in the anterior cranial fossa. These nerves synapse on neurons in the bulbs, and the processes of these neurons follow the olfa ctory tracts to the primary and associated areas of the cerebral cortex.
2). Examination: Test the sense of smell by presenting the patient with familiar and nonirritating odors. First be sure that each nasal passage is open by compressing one side of th e nose and asking the patient to sniff through the other. The patient should then close both eyes. Occlude one nostril and test smell in the other with such substances as cloves, coffee, soap, or vanilla. Ask if the patient smells anything and, if so, what. Test the other side. A person should normally perceive odor on each side, and can often identify it. 3). Olfactory disorder: Hyperosmia is an increased ability to smell. Hyposmia is a reduced ability to smell and to detect odours Anosmia - loss of smell has many causes, including nasal disease, head trauma, smoking, aging, and the use of cocaine. It may be congenital. Dysomia is the impairment of olfactory stimuli processing leading to an altered sense of smell.
II). Cranial nerve II – Optic nerve: 1). Anatomy: The optic nerves (CN II) have sensory fibers concerned with the special sense of vision. The nerve fibers arise from ganglion cells in the retina. They exit the orbit via the optic canals; fibers from the nasal half of the retina cross to the contralateral side at the optic chiasm. The fibers then pass via the optic tracts to the geniculate bodies of the thalamus, where they synapse on n eurons whose processes form the optic radiations to the primary visual cortex of the occipital lobe.
2). Examination: Visual acuity: To test the acuity of central vision use a Snellen eye chart, if possible, and light it well. Position the patient 20 feet from the chart. Patients who use glasses other than for reading should put them on. Ask the patient to cover one eye with a card (to prevent peeking through the fingers) and to read the smallest line of print possible. Coaxing to attempt the next line may improve performance. A patient who cannot read the largest letter should be positioned closer to the chart; note the intervening distance. Determine the smallest line of print from which the patient can identify more than half the letters. Record the visua l acuity designated at the side of this line, along with use of glasses, if any. Visual acuity is expressed as two numbers (e.g., 20/30): the first indicates the distance of patient from chart, and the second, the distance at which a normal eye can read th e line of letters. Testing near vision with a special handheld card helps to identify the need for reading glasses or bifocals in patients over age 45. You can also use this card to test visual acuity at the bedside. Held 14 inches from the patient’s eyes, the card simulates a Snellen chart. You may, however, let patients choose their own distance.