Voluntary stage of deglutition is:
**Core Concept**
The voluntary stage of deglutition is a crucial phase of swallowing that involves the coordinated movement of muscles in the oral cavity, pharynx, and larynx. This stage is characterized by the formation of a bolus and its propulsion through the pharynx by the actions of the tongue and the muscles of mastication.
**Why the Correct Answer is Right**
During the voluntary stage of deglutition, the bolus is formed in the oral cavity through the actions of the tongue and the teeth. The bolus is then propelled through the pharynx by the action of the pharyngeal constrictor muscles, which are innervated by the cranial nerves IX (glossopharyngeal) and X (vagus). The voluntary stage of deglutition is initiated by the contraction of the superior constrictor muscle, which is the first stage of swallowing. The bolus then passes through the oropharynx, where it is further propelled by the action of the middle and inferior constrictor muscles.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the involuntary stage of deglutition is the stage where the bolus is propelled through the pharynx by the action of the pharyngeal constrictor muscles, but it is not initiated by voluntary action.
* **Option B:** This option is incorrect because the oral preparatory stage of deglutition is the stage where the food is chewed and mixed with saliva, but it is not the stage where the bolus is formed and propelled through the pharynx.
* **Option C:** This option is incorrect because the pharyngeal stage of deglutition is the stage where the bolus is propelled through the pharynx by the action of the pharyngeal constrictor muscles, but it is not the stage where the bolus is formed.
**Clinical Pearl / High-Yield Fact**
The voluntary stage of deglutition is initiated by the contraction of the superior constrictor muscle, which is the first stage of swallowing. This muscle is innervated by the cranial nerve IX (glossopharyngeal) and is responsible for the initiation of the swallowing reflex.
**Correct Answer:** C.