Fibre size in the left and right recurrent laryngeal nerves (RLNs) in the man

Some morphological data of the right and left human RLNs were evaluated with the aim of verifying possible differences in the fibre composition of the two nerves. The following parameters were evaluated in the right and left RLNs of five human cases: 1) the maximum diameter of the fibres; 2) the axon diameter and area; 3) the myelin sheath area obtained substracting the axon area from the total area of each fibre. The obtained data were plotted on histograms for each case: moreover, histograms of all fibres of both left and right nerves of all five cases were made. The results show that the values of the maximum diameter of the fibres and of the myelin sheath area are always greater in a statistically significant way in the left RLNs than in the right RLNs. On the other hand the axon diameter is nearly the same in the nerves of both sides. These data suggest that the greater calibre of the myelin sheath in the fibres of the left inferior laryngeal nerve can be responsible of the faster conduction speed in this nerve. This fact might explain the simultaneous arrival of the impulses to the laryngeal muscles of the two sides in spite to the different length of the two nerves.