The examination of the cranial nerves tests motor, sensory, and mixed functions of the twelve cranial nerves
| CN | Name | Motor | Sensory | Autonomic |
|---|---|---|---|---|
| I | Olfactory | x | ||
| II | Optic | x | ||
| III | Oculomotor | x | ||
| IV | Trochlear | x | ||
| V | Trigeminal | x | x | |
| VI | Abducens | x | ||
| VII | Facial | |||
| VIII | Vestibulocochlear | |||
| IX | Glossopharyngeal | |||
| X | Vagal | x | x | x |
| XI | Spinal Accessory | x | ||
| XII | Hypoglossal | x |
CN I
The olfactory nerve - obviously confers smell. Close the patient's eyes. Occlude a nostril. Test with a non-irritating powerful scent (such as coffee?). Can the patient identify the substance? Then, as a control, cap the vial or bag and try again. Repeat contralaterally.
Interpretation: most patients will not be able to identify the specific odor (normal), but can sense the presence of the odor (the important part).
CN II, III
CN III, IV, VI
- CN III
- Innervates the medial rectus muscle - which brings the eye to the midline
- Innervates the superior and inferior rectus and the inferior oblique muscles
- Innervates the pupil -
- CN IV
- Innervates the superior oblique (SO) muscle - which turns the eye downwards and in, with the help of the superior and inferior rectus and the inferior oblique muscles
- CN VI
- Innervates the lateral rectus muscle
Six cardinal positions of gaze are determined by the innervation and function of the extraocular muscles. Only the medial and lateral recti operate in a single plane. All other EOMs have components of adduction/abduction, depression/elevation, and internal/external rotation.
Internuclear ophthalmoplegia (INO) - indicates a CNS issue. Bilateral INO is often seen in MS, unilateral INO typically occurs after vascular injury to the medial longitudinal fasciculus (MLF). The MLF connects the abducens (VI) on one side with the oculomotor (III) nucleus on the contralateral side. A unilateral MLF lesion leads to ipsilateral adduction deficit on lateral gaze with preserved convergence, as well as a contralateral monocular nystagmus when looking contralaterally.