Ultrastructural Changes With Age in the Human Superior Laryngeal Nerve

Análise quantitativa das fibras mielínicas dos nervos laríngeos em humanos de acordo com a idade

“…We found five papers dealing with this theme in the literature; two of these papers used animal models 16,17 and three were studies on human beings. [18][19][20] The SLN was studied in three papers 17,18,20 and the RLN was investigated in two. 16,19 We found no published paper that evaluated both laryngeal nerves (SLN and RLN) in humans and correlated findings with the aging process.…”

“…16,17 Many published papers have described the laryngeal nerve morphometry; there were differences in methods, however, which have constrained the comparison of results. In our method we used previously reported parameters, such as the level at which SLNs were seccioned, 18,34 the preparation of material and the morphometric analysis. The choice of site for harvesting the RLN was based on anatomical studies 22,35 and on proof of altered morphometric features, depending on the section level.…”

“…18,34 The RLN fragment was harvested 4cm from the lower border of the cricoid cartilage; this site was chosen due to the increased possibility of harvesting all of the branches that innervate the larynx. 22,35 The harvesting procedure included sectioning the nerve fragments cross-sectionally (perpendicular to the length axis of the nerve), making it possible to quantify the following morphometric measures: intraperineural cross-sectional area (representative of the number of myelin fibers) and the number and diameter of myelin fibers.…”

“…These include laryngeal receptors, general visceral afferent pathways, nervous system brainstem nuclei, special visceral efferent pathways and intrinsic laryngeal muscles. 15 There are few studies on the effect of aging on laryngeal nerves; [16][17][18][19][20] most of the papers on laryngeal innervation restrict themselves to purely anatomical issues. [21][22][23][24] Generally speaking, these papers state that the larynx is innervated by the vagus nerve through the following branches: the superior laryngeal nerve (SLN) and the recurrent laryngeal nerve (RLN).…”

“…The SLN is predominantly composed of smaller diameter afferent myelin fibers that course in the inner branch and are responsible for supraglottic and hypopharyngeal sensitivity, 17,18,20,25,26 and by medium diameter efferent myelin fibers that course in the outer branch and that innervate the cricothyroideus muscle and part of the thyroarytenoid muscle. 23,25,26 The RLN is composed by afferent and efferent myelin fibers and is responsible for subglottic sensitivity and for the innervation of the intrinsic laryngeal muscles, 25,27,28 the superior region of the esophagus and part of the cricopharyngeus muscle.…”