Oral Preparatory Phase - food is chewed and manipulated in the mouth
Oral Phase - the tongue moves to push food toward the back of the throat to "trigger" the swallow
Pharyngeal Phase - after the swallow is triggered, the food (also known as a bolus) moves down the upper portion of the throat known as the pharynx
Esophageal phase - the food moves past the pharynx and enters the esophagus where it moves further down into the stomach
A person with a swallowing disorder has a problem at one or more of these phases.
How "the swallow" works:
The best way to explain it is by stating that we have 2 "tubes" in our throat.
The trachea (or the airway)-this is where air goes in and out of our lungs and past our vocal cords (which we use for speech); AKA: The air tube
The esophagus- this is where food and liquid go down into the stomach; AKA: The food tube
A normal swallow follows the 4 phases of swallowing.
We place food in our mouth and our tongue, lips, teeth, and jaw all work together to chew the food until it's ready to be swallowed. We then use our tongues to push the food backwards towards our throat. When we move our tongues back it sets in motion the epiglottis.
The epiglottis is one of the most important things you need to know about to understand the swallow. The epiglottis is the little "flap" that will lower down and cover your airway when you are swallowing food. The epiglottis can't always be lowered or we wouldn't be able to get any air in and out of our lungs! So, during the swallow our tongue pushes back, the hyoid bone is elevated which pulls the larynx up and then the epiglottis flaps down to cover the trachea and direct the food to go into the esophagus and safely down into our stomach.
Now the problem:
Most everyone has hear the expression "it went down the wrong pipe." Anyone who has ever breathed in food or liquid in your mouth or has swallowed too quickly, has experienced this. You probably coughed uncontrollably, your face may have turned red, and your eyes watered.
Coughing is a good thing! It's the body's natural response to getting food, liquid, and any other object out of the airway and away from the lungs. When this experience occurs you experienced one of the following:
Penetration- food or liquid goes into the trachea (airway tube) and stays above the vocal cords (speech tools)
Aspiration- food or liquid goes into the trachea (airway tube) and goes below the vocal cords (speech tools)
The problem is when a person experiences food going into the airway and doesn't cough. In these instances the person does not feel the food or liquid going into the airway and the body can't trigger that "coughing reaction" or gag reflex. This is called silent aspiration.
Silent aspiration can only be observed via a modified barium swallow study (MBS) which is essentially an x-ray of the swallow.
Picture Below: Video fluoroscopic swallow study demonstrating (A) no penetration or aspiration, (B) penetration (black arrow indicates contrast above the level of the vocal cords), and (C) aspiration (black arrow indicates contrast below the level of the vocal cords).