The Normal Mechanism of Swallowing

Abstract

An account is given of the observed normal mechanism of swallowing, in which it is maintained that the bolus is carried from the back of the tongue to the clavicular level largely by negative pressure. The mechanism by which the negative pressure in the pharynx is produced is by a combined action of raising the larynx and backward movement of the tongue, which together completely obliterate the pharyngeal space for a fraction of a second. With mouth, nose, and larynx closed, the reopening of the pharynx produces a negative pressure that is largely responsible for the act of swallowing. Except for fluids, gravity plays a very minor part in the normal act of swallowing. The mechanism by which the larynx is cut off during the act is by a dragging up of the laryngeal pharynx behind the larynx to form contact with the epiglottis, possibly about a quarter of an inch below the tip of the epiglottis. The phases of swallowing may be summed thus:— 1. The mouth and nose are closed. 2. The larynx is raised and closed and its upper part is obliterated by the back of the tongue. 3. The pharyngeal space is obliterated by (a) raising the larynx, and (b) retraction of the tongue. (The posterior wall of the pharynx does not come forward; the pharynx is not constricted but is compressed from before backward against the posterior wall, that is, against the vertebræ.) 4. The pharynx is opened up, and with the three outlets closed a negative pressure is obtained by (a) dropping the larynx and (b) allowing the tongue to go forward. 5. During this movement the laryngeal pharynx still remains high, in close relation to the epiglottis. It is in an open-mouthed condition. 6. Food is tipped over the back of the tongue. 7. Food is sucked into the open mouth of the laryngeal pharynx, which,as it receives the bolus, drops from the epiglottis down to its normal position, thus opening up the larynx again, after the food has passed. 8. The food is probably sucked some distance down the esophagus.