Twelve pairs of cranial nerves originate at the underside of the brain. In order from front to back these are the olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, spinal accessory and hypoglossal nerves. These are essential in vision, smell, eye and facial movements, salivation and tongue movements.