Stages of the Typical Swallow Flashcards
Describe the Pre-Oral Stage of the Typical Swallow
This is the sensory input stage.
The hypothalamus helps to signal when we are feeling hungry or thirsty. We see food using the Optic Nerve (CN II) and the Occipital Lobe will help to process this information. You also smell food via the Olfactory nerve (CN I). Our knowledge of food is stored in the amygdala and the hippocampus. The amygdala helps us decide if we want to eat the food or not and the hippocampus helps us to remember if we enjoy that food or not. At this stage Salivation will begin. The parotid, sublingual and submandibular glands will be working to release saliva into the Oral Cavity in preparation for the food arriving. Food is also moved and place centrally in the mouth. We need to have good posture and proprioception in tact for this.
Describe the Oral Preparatory Stage of the Typical Swallow
The Oral Preparatory Stage is concerned with the mastication (chewing) of food / holding the fluid in the correct position. In order to masticate the food we need to have a sufficient lip seal. The Orbicularis Oris and Buccinators innervated by the Facial Nerve (VII) help to seal the lips and close off the lateral and anterior sulci. The muscles of mastication (Masseter, Temporalis and Pterygoid muscles) also kick in at this point. The Trigeminal Nerve (CN V) innervates these muscles. The jaw and the tongue will also move innervated by the Hypoglossal Nerve (CN XII) and this helps to keep the position of food in-between the teeth. This allows the teeth to breakdown the food. Food and drink in the mouth stimulate pressure, taste and temperature receptors in the Oral Cavity. The food is mixed with the saliva. The Soft Palate is pulled down and forward so that food is prevented from spilling into the Oropharynx. The Oral Preparatory Stage ends with the formation of a Bolus, this is held between the tongue and the hard palate. The tongue tip is also lifted so that the food is kept in a safe manner in the Oral Cavity
Describe the Oral Stage of the Typical Swallow
The bolus is delivered to the oropharynx. It does this via the movement of the tongue. The tongue forms a central trough via the intrinsic muscles of the tongue (CN XII)
Genioglossus- Draw the tongue forward from the root
Hyoglossus- Retracts the tongue and depresses its side
Styloglossus- Draws the tongue upward
which acts as a ‘chute’. There is then a ‘wave-like’ contraction of the tongue and a posterior movement of the bolus. At the same time the base of the tongue retracts towards the posterior pharyngeal wall via contraction of the hyoglossus and styloglossus (muscles of the tongue). The Bolus is pulled down into an area of low pressure (the Pharynx). The nasal cavity is sealed off by the elevation of the Soft Palate (via contraction of the Levator Veli Palatini (Trigeminal Nerve V) and the Uvulae ( Vagus Nerve X). This prevents any backwards movement of the bolus up in preparation for the Pharyngeal Stage. Breathing also stops at this stage.
Describe the Pharyngeal Stage of the Typical Swallow
The bolus is sitting at the top of the Pharynx and now needs to work it’s way down into the oesphagus.
The Pharyngeal Stage begins when the bolus arrives at the level of the vallecula. As the bolus moves down the Pharynx the superior, middle and inferiror constrictor muscles of the Pharynx (innervated by the Vagus nerve X) are activated and narrow and shorten the Pharynx. This helps to move the Bolus down to the Laryngeal/ Oesophageal area
The airway needs to be closed off. During the Pharyngeal stage Hyolaryngeal Excursion occurs. The Suprahyoid muscles contract (Innervated by the Facial Nerve VII) and the Hyoid bone and the larynx are directed up and forward.
As this happens we get airway protection at 3 key places:
- The True Vocal folds come together (innervated by the Vagus Nerve X)
- The False Vocal Folds (and the arytenoids) come together
- The Epiglottis and Aryepiglottic folds come together via epiglottis inversion (the epiglottis flips down to protect the airway and larynx) via innervation from the Trigeminal Nerve V
This means that the bolus can only move down into the oesophagus
This stage ends when the UES opens to allow the bolus to pass into the oesophagus
Describe the Oesophageal Stage of the Typical Swallow
The bolus enters the oesophagus and there is a relaxation of the UES. The Larynx has lowered and the airway is open. The UES resumes its contracted state. The Bolus moves via peristalsis (wave like constrictions).
The Oesophageal stage stops when the bolus reaches the stomach. 8-13 seconds in healthy adults
