Vagus nerve

The Vagus nerve is tenth of twelve cranial nerves and the only nerve that starts in the brainstem (somewhere in the medulla oblongata) and extends way down past the head, all the way down to the abdomen.

It was for this reason that it was so named, for "the wanderer" (the words "vagrant" and "vagabond" come from the same Greek word).

This nerve supplies motor and sensory parasympathetic fibres to pretty much everything from the neck down to the first third of the transverse colon. In this capacity, it is involved in, amongst other things, such varied tasks as heartrate, gastrointestinal peristalsis and sweating.

As if those rather important functions weren't enough, Vagus also controls a few skeletal muscles, namely:

levator veli palatini muscle
salpingopharyngeus muscle
stylopharyngeus muscle
palatoglossus muscle
palatopharyngeus muscle
superior, middle and inferior pharyngeal constrictors
muscles of the larynx (speech).

This means that Vagus is responsible for quite a few muscle movements in the mouth and also is vitally important for speech and in keeping the larynx open for breathing.

It also receives some sensation from the outer ear and part of the meninges.

Arguably the single most important nerve in the body.