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Some of the muscles innervated by the laryngeal nerves are so close to the surface mucosa that they can indirectly be visualized. Others are deeper, and only their effects can be visualized. Near-direct visualization includes the ability to see the muscle contract and thicken or shorten. Atrophy and fasciculations can be visualized.

Indirect visualization includes the ability to see joint and structure movement.

Some activities, such as respiration, are rhythmic and symmetric. Inappropriate timing and asymmetric motion can be utilized to infer innervation status.

Muscles observed during a typical endoscopic evaluation include:

•Lingual muscles – genioglossus

•Palatal muscles – levator veli palatini

•Pharyngeal constrictors

•Laryngeal muscles: thyroarytenoid (TA); lateral cricoarytenoid (LCA); posterior cricoarytenoid (PCA); interarytenoid (IA); cricothyroid (CT)

Near-direct visual findings include the following (along with the muscles in which they can be endoscopically observed):

•Atrophy – TA, PCA

•Fasciculation – TA, PCA

Indirect visual findings utilized to infer muscle function include the following (along with the muscles in which they can be endoscopically observed):

•Oscillation – TA, CT

•Tension – TA, CT

•Range of motion – LCA, PCA

•Lengthening – CT

•Respiration

•Inspiration – PCA

•Expiration – LCA

Observe timing of motion for evidence of inappropriate reinnervation. Remove compensation by unmasking vocal tasks.

Larynx motion appears to be complex, at least on superficial examination, and reference articles may fail to discriminate among the various types of motion. I frequently hear the statement, “The vocal cords do not move.” I do not know whether the speaker is referring to abduction and adduction or intrinsic stiffness of the vocal cord affecting oscillation. I also do not know whether there is a lack of abduction and adduction or whether there is inappropriate or simultaneous attempted abduction and adduction leading effectively to no, reduced or inappropriate motion.

There are 5 types of mobility:

•Opening – abduction – PCA

•Closing – adduction – initially TA, then mostly LCA (and for maintaining closure – IA)

•Intrinsic tensioning (isometric) – TA

•Extrinsic tensioning by lengthening – CT

•Oscillation – passive flexibility