Final answer:
The major parasympathetic outflow from the head routes through the vagus nerve, which is part of the parasympathetic nervous system responsible for 'rest and digest' activities.
Step-by-step explanation:
The route of major parasympathetic outflow from the head is primarily through the vagus nerve (cranial nerve X). This nerve is part of the parasympathetic nervous system, which is responsible for stimulating 'rest and digest' activities when the body is at rest. Neurons in the dorsal nucleus of the vagus nerve project through the vagus nerve to terminal ganglia in the thoracic and abdominal cavities, influencing organs such as the heart, bronchi, esophagus, stomach, liver, pancreas, gall bladder, and small intestine. These parasympathetic preganglionic fibers help to decrease heart rate, encourage digestion, and perform other functions that help conserve and restore energy during peaceful times.