1. What is the nervous system?

1.1 Central nervous system (CNS)

The CNS is made up of three parts: the brain, the spinal cord and the ganglion system.

• The brain contains around a hundred billion neurons. At the base of the brain emerge twelve pairs of cranial nerves (one left and one right), numbered I to XII, each of which innervates a particular region of the body. For example, cranial nerve I transmits signals from the nasal area (sense of smell) to the brain. The encephalon is surrounded in the cranium by two membranes (the meninges) and the encephalic fluid, which protect it...