The optic nerves from both sides enter the cranium through the respective optic canals and meet at the optic chiasm at which fibers sort such that the two halves of the visual field are processed by the opposite sides of the brain. The examiner's visual fields should be normal, since it is used as the baseline. The examiner wiggles the finger in each of the four quadrants and asks the patient to state when the finger is seen in the periphery. Visual fields are assessed by asking the patient to cover one eye while the examiner tests the opposite eye.Vision via the optic nerve is examined both in fields of vision, and in clarity of vision. If the nerve is not completely severed, the anosmia may be temporary as new neurons can eventually reconnect. 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. 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. The neurons in the olfactory epithelium have a limited life span, and new cells grow to replace the ones that die off. The short axons of the first cranial nerve regenerate on a regular basis. This test is usually skipped on a cranial nerve exam. Unilateral loss indicates a possible nerve lesion or deviated septum. Bilateral loss can occur with rhinitis, smoking, or aging. Loss of the sense of smell is called anosmia and can be either unilaateral or bilateral. Some example stimuli include cinnamon, cloves, and toothpaste. The stimuli used should be non-irritating and identifiable. Smell is tested in each nostril separately by placing stimuli under one nostril and occluding the opposing nostril. ![]() The first test is for the olfactory nerve. 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). Each test is designed to assess the status of one or more of the twelve cranial nerves (I-XII). It is used to identify problems with the cranial nerves by physical examination. ![]() The cranial nerve exam is a type of neurological examination. One component of the examination (III) uses the pupillary light reflex to assess the status of the oculomotor nerve (CNIII).
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