Archive for February 9th, 2013

February 9, 2013

Recurrent Laryngeal Nerve

The recurrent [ri-kur-uhntlaryngeal [luh-rin-jee-uhlnerve is a branch of the vagus nerve (tenth cranial nerve) that supplies motor function and sensation to the larynx (voice box). It is referred to as ‘recurrent’ because the branches of the nerve innervate the laryngeal muscles in the neck through a rather circuitous route: it descends into the thorax before rising up between the trachea and esophagus to reach the neck.

The extreme detour of this nerve (about 15 feet in the case of giraffes)  is cited as evidence of evolution as opposed to intelligent design. The nerve’s route would have been direct in the fish-like ancestors of modern tetrapods, traveling from the brain, past the heart, to the gills (as it does in modern fish). Over the course of evolution, as the neck extended and the heart became lower in the body, the laryngeal nerve was caught on the wrong side of the heart. Natural selection gradually lengthened the nerve by tiny increments to accommodate, resulting in the circuitous route now observed.