Page 116 - Edited - Webster HEAD AND NECK - part 2-Merge PDF

HN 310

CRANIAL NERVES

The peripheral distributions of the 12 pairs of cranial nerves can seem more bewildering than their
names. This note and attached Tables and figure are intended to help clarify matters.

NAMES and NUMBERS

Olfactory (Ⅰ); Optic (II); Oculomotor (III); Trochlear (IV); Trigeminal (V); Abducent (VI); Facial (VII);
Vestibulo-Cochlear (or auditory-vestibular) (VIII); glossopharyngeal (IX); Vagus (X); Accessory (XI);
Hypoglossal (XII).
The names (the origins of the names are noted in Table 2) all reflect some feature of the peripheral
organisation or course and/or function of the nerve: unfortunately, which feature caught the attention of the
original nominator is not always obvious. You will doubtless at first use a mnemonic to help to match name to
number - a few are given below - but your aim should be to be able to use either name or number of any
individual cranial nerve without recourse to chanting/counting under your breath. All mnemonics begin with
the first nerve and end with the twelfth. The twelfth nerve is nearest the spinal cord, the first farthest from it,
with the rest strung out in between more or less in sequence.
Mnemonics

“On Old Olympus’s Towering Top A Finn And (a) German Viewed A Hop”.
“Old Oppenheimer Often *Pinches Three Aspidistras From Audrey’s Glass Vase”. (This second version has
the disadvantage of stopping at Vagus; the old name for Oculomotor nerve was the *Pathetic nerve.)
One for the smutty-minded: “O, Orgasmic Onan: Tight Trousers’ Amorous Frottage Always Gives Virgins
Ardent Hours”
And one for those among you who can use a dictionary: “Olid optation! Oculate, treating tribades abjure
facile, audacious glances (of) vaguely accentuated hypocrisy”.
Notice that in all these, the eighth cranial nerve is identified as “auditory-vestibular".

PERIPHERAL DISTRIBUTIONS

If you read and understood my earlier notes (Segmentation. The Peripheral Nervous System) you will
know that in principle a peripheral nerve may contain up to four basic components: somatic / autonomic /
sensory / motor.

This applies no less to cranial nerves than to spinal. The autonomic components may be further
subdivided into sympathetic and parasympathetic, but cranial nerves contain only parasympathetic axons (the
postsynaptic sympathetic fibres to the head arise in the superior cervical sympathetic ganglion and travel in the
adventitia of the carotid arterial tree - see Segmentation. The Peripheral Nervous System, pp 12-13 ). Thus, in
1
principle, a cranial nerve may contain axons in four categories:
sensory somatic (general sensation - touch, pain, temperature, etc.)
sensory parasympathetic (normal visceral function - chemo-reception or stretch reception)
motor somatic (i.e. skeleto-motor)

motor parasympathetic (to viscera - secretomotor to exocrine glands; modulating activity of smooth and
cardiac muscle)

All spinal nerves contain all four components - although of the autonomic components, the
parasympathetic fibres are limited to spinal nerves S2, 3, 4. The bad news is that cranial nerves exhibit no
regular pattern: only nerves VII (facial), IX (glossopharyngeal) and X (vagus) contain all four basic

1 Note: The distinction is not quite complete: postsynaptic sympathetic axons to the eye enter the orbit in the adventitia of the
ophthalmic artery, but enter the eyeball itself in the cillary nerves, which are the parasympathetic component of the oculamator
nerve (cranial nerve III) and reach the muscle which lifts the upper lid-the levator palpebrae superioris - in the frontal branch of
the ophthalmic division of the trigeminal nerve (cranial nerve V). These are, however, details which you can safely ignore. The
parasympathetic component of the vagus nerves (cranial nerve X) mingle, of course, with sympathetic axons in the autonomic
nerve plexuses of the chest and belly.
\NewCMedPhysSc\28 HN 310 CranNerves.