Cranial Nerves 1664 – A Monumental Study of the Brain

Unlike spinal nerves, which emerge from the spinal cord, cranial nerves emerge from the brain and are distinctive in connecting directly to it. Humans have 12 pairs of cranial nerves entering and leaving the cranium (the part of the skull surrounding the brain).

The 12 pairs of cranial nerves, with some of their functions, are:

1. olfactory (sense of smell from the nose),
2. optic (sense of sight from the eye),
3. oculomotor (control of eye movement),
4. trochlear (eye movement control),
5. trigeminal (facial sensations; control of chewing muscles),
6. abducens (eye movement control),
7. facial (taste sensations from the front of the tongue; facial and neck muscle control),
8. auditory (hearing and sense of balance),
9. glossopharyngeal (taste from the back of the tongue; neck muscle control),
10. vagus (interface with the heart, lungs, intestines, larynx and other organs),
11. accessory (neck muscle control) and
12. hypoglossal (tongue muscle control).

In 1664, English physician Thomas Willis published “Cerebri Anatome,” a monumental study of the brain. His classification of cranial nerves was used for more than 100 years, and he numbered the first six nerves fully and correctly as we do today. Willis cut nerves and vessels at the base of the brain to examine the cranial nerves carefully. His fascination with the brain arose partly from an attempt to understand the soul through brain research. Striking differences between the cerebral cortex (the outer layer of the brain composed of nerve cells) of humans and other animals led Willis to propose that the upper part of the brain was the primary seat of the human “rational soul.” He also hypothesized that the higher functions of the human brain arose from the folds of the cerebral cortex (a remarkably accurate prediction).

Description of the Article Image: A depiction of some cranial nerves beneath the brain from Andreas Vesalius's De Humani Corporis Fabrica (1543). The olfactory nerves at the top are highlighted in bright yellow, and the optic nerves are shown in green.

Historical Figures Mentioned in the Article: Thomas Willis (1621–1675)

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