Swallowing is a complex act involving both voluntary and involuntary neural circuits and the co-ordination of multiple small muscles in the neck.
A disruption of a part of this circuit may lead to compensation from other structures. The patient may be unaware of the compensation, but barium swallow will often reveal it. This may eventually become decompensated, prompting symptoms (such as aspiration), and barium swallow is again useful for diagnosis.
It is useful to get a feel for the normal structures in a barium swallow in order to help determine what may be causing a patient's compensated or decompensated swallowing.
Always remember to image the entirety of the oesophagus when performing an assessment of swallowing, as pharyngeal symptoms may have an oesophageal origin, and since there is an association between pharyngeal and oesophageal pathologic processes (e.g. GERD/GORD).