The primary muscles involved in propelling the food bolus down the pharynx and esophagus are:

1. Pharyngeal Muscles:

a) Superior pharyngeal constrictor: This muscle generates the initial force to move the food bolus from the oral cavity into the pharynx.

b) Middle pharyngeal constrictor: It continues the propulsive movement of the bolus.

c) Inferior pharyngeal constrictor: This is the most powerful pharyngeal constrictor and helps propel the bolus forcefully into the esophagus.

2. Esophageal Muscles:

a) Upper esophageal sphincter: It relaxes to allow the bolus to enter the esophagus.

b) Esophageal smooth muscles: These muscles generate a wave-like motion known as peristalsis. Peristaltic contractions push the food bolus along the entire length of the esophagus.

c) Lower esophageal sphincter: This sphincter relaxes to allow the bolus to enter the stomach and contracts to prevent backflow of stomach contents into the esophagus.

The coordinated contraction and relaxation of these muscles create a synchronized wave that moves the food bolus from the pharynx to the stomach.