2. The hyoid bone and the larynx are elevated. A ﬂ
structure attached to the larynx, called the
is) closes off the top of the trachea so that
food is less likely to enter the trachea.
3. The tongue is pressed against the soft palate and uvula,
sealing off the oral cavity from the nasal cavity.
4. The longitudinal muscles in the pharyngeal wall
contract, pulling the pharynx upward toward the food.
5. The lower portion of the inferior constrictor muscles
relaxes, opening the esophagus.
6. The superior constrictor muscles contract, stimulating
a peristaltic wave to begin in other pharyngeal muscles.
This wave forces the food into the esophagus.
The swallowing reﬂ
ex momentarily inhibits breathing. Then,
during the third stage of swallowing, peristalsis transports
the food in the esophagus to the stomach.
Although the pharyngeal muscles are skeletal muscles,
they are under voluntary control only in the sense that swal-
lowing (deglutition) can be voluntarily initiated. Complex
exes control the precise actions of these muscles during
Swallowing can be divided into three stages. In the first
stage, which is voluntary, food is chewed and mixed with
saliva. Then, the tongue rolls this mixture into a mass, or
and forces it into the pharynx.
The second stage of swallowing begins as food reaches the
pharynx and stimulates sensory receptors around the pharyn-
geal opening. This triggers the swallowing reﬂ ex, illustrated in
f gure 17.14
, which includes the following actions:
1. The soft palate (including the uvula) raises, preventing
food from entering the nasal cavity.
The tongue forces food into the pharynx.
The soft palate, hyoid bone, and larynx are raised,
the tongue is pressed against the palate, the epiglottis
closes, and the inferior constrictor muscles relax so
that the esophagus opens.
Superior constrictor muscles contract and
force food into the esophagus.
Peristaltic waves move food through the esophagus
to the stomach.
Steps in the swallowing ref
ex. (The mucosa in (
), and (
) has been removed to reveal the underlying muscles.)