Final answer:
Dysphagia refers to the difficulty in swallowing which can be caused by neurological conditions such as stroke and Parkinsonism, or by decreased salivary production due to aging or disease.
Step-by-step explanation:
The difficulty in swallowing, associated with conditions such as stroke, Parkinsonism, or decreased salivary production, is known as dysphagia. Regulation of salivation is under the control of the autonomic nervous system, which adjusts the level of saliva based on various stimuli and conditions. Issues with salivation, whether overproduction or underproduction, can affect the voluntary phase of deglutition, impacting the ability to swallow comfortably and efficiently. During aging or in certain diseases, the production of saliva may decrease, the muscles involved in swallowing can become weaker, and the ability to control swallowing can diminish, all contributing to symptoms of dysphagia.