Figure 17 - Role of UES closure and opening muscles during the three phases of vomiting.

Schematic illustration of typical pattern of activation of most pharyngeal, hyoid, and laryngeal muscles during vomiting derived from EMG data of chronically instrumented dogs stimulated to vomit by apomorphine. Note that during the pre-retch phase the tone of the CP and esophagus increase, significantly closing the UES. During retching the muscles pulling the UES open in a superior direction (superior hyoid muscles, HP and SP) are all activated in concert 180 degrees out of phase with the UES opening muscles that open the UES in an inferior direction (inferior hyoid muscles). However, the UES does not open during superior movement because all of the UES closure muscles are activated as well. During vomiting, the superior and inferior hyoid and pharyngeal UES opening muscles are activated concomitantly with relaxation of all of the UES closure muscles, thereby causing maximum opening of the UES. MH, mylohyoideus; GH, geniohyoideus; TH, thyrohyoideus; HG, hyoglossus; HP, hyopharyngeus; SP, stylopharyngeus; TP, thyropharyngeus; CP, cricopharyngeus; E#, esophagus number of centimeters from UES; SH, stenohyoideus; ST, sternothyroideus; CT, cricothyroideus; TA, thyroarytenoideus; CD, cricoarytenoideus dorsalis; DH, diaphragm hiatus. (Source: Lang et al.,¹⁰³ with permission of the American Physiological Society.)