Cranial nerves 1, 3–6

Published on 10/04/2015 by admin

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Last modified 10/04/2015

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Cranial nerves 1, 3–6

Traditionally the examination of the cranial nerves is reported according to their numerical order (Box 1). However, during the examination it is easier to group them according to their function – for example, considering the 3rd, 4th and 6th together as eye movements.

Box 1 The cranial nerves

8 Vestibulocochlear (auditory)

9 Glossopharyngeal

Olfactory nerve (1st)

This nerve is usually only tested formally in patients with specific complaints regarding the sense of smell. The examination consists of the presentation of a range of smells such as peppermint, camphor and rose water to each nostril while closing off the other and asking the patient to identify them. Ammonia is also tested: this is not perceived by the olfactory nerve but is a direct irritant to the nasal mucosa, stimulating the trigeminal nerve. Failure to respond suggests non-organic anosmia.

Olfactory nerve lesions are usually post-traumatic, but can occur rarely in patients with frontal lesions, and subtle abnormalities are found in degenerative conditions such as Parkinson’s disease. Anosmia occurs commonly with nasal blockage (e.g. colds).

Eye movements (3rd, 4th, 6th)

Eye movements are controlled in several ways. They can be moved as follows:

Voluntarily (e.g. look right) – movement is initiated from the frontal eye fields. These are also called saccadic movements.

On pursuit – following objects (e.g. follow my finger); this is controlled by the occipital lobe.

Under vestibular control, reflex movements maintain eye posture with the head and other movements. This is tested as the vestibulo-ocular reflex, which subserves the doll’s head phenomenon.

With convergence, to look at close objects (rarely of clinical importance).

These movements are integrated in the brain stem with the 3rd and 4th nuclei in the midbrain, and the parapontine reticular formation and 6th nerve nucleus in the pons. These are connected by the median longitudinal fasciculus (MLF). Eye movements result from contraction of the extraocular muscles. All but two of the extraocular muscles are supplied by the 3rd nerve, the superior oblique and lateral rectus being supplied by the 4th and 6th nerves, respectively (Fig. 1

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