The sympathetic division responds to stress and the parasympathetic division calms the nerves. There are many nerves in the brain that these divisions must communicate with, but knowing them can be helpful. They can be classified by sensory motor or both. The sensory nerves are the olfactory nerve which processes sent stimuli, the optic nerve processes visual stimuli and the auditory nerve processes audio inputs. The motor nerves are the oculomotor which controls 4/6 eye muscles, the trochlear controls 1/6 eye muscles, the abducens controls certain eye movements, the spinal accessory nerve moves the head and shoulders, the hypoglossal nerve allows swallowing and to speak. Some nerves can be both sensory and motor. There are only three: the facial nerve which moves the facial muscle, the glossopharyngeal nerve which moves the tongue and pharynx, the vagus nerve controls the digestion of the heart.