Swallowing, slow wave mechanisms
- GI motility begins and ends with skeletal muscle
- Remainder is smooth muscle
- GI muscle exhibits spontaneous slow wave potentials
- Tonic contractions (sphincters) are sustained for minutes to hours,
and keep bolus from moving backwards (backflow)
- Phasic contractions (longitudinal and circular smooth muscle)
exhibit cycles of contraction and relaxation; they last a few seconds,
peristalsis moves bolus forward (longitudinal muscle), segmentation mixes (circular muscle)
- Slow waves (Basal electrical rhythm) are spontaneous cycles of depolarization and repolarization of
GI smooth muscle - Interstitial Cells of Cajal are pacemaker cells of the gut
- Force of contraction directly related to the amplitude and frequency of action potentials
- ICC are located between the nerve endings and smooth muscle cells in the GI tract
- Excitatory compounds of smooth muscle include Ach, substance P
- Inhibitory compoinds of smooth muscle include VIP, epinephrine, nitric oxide
- Peristaltic contractions move bolus forward, segmental contractions mix
- Stages of swallowing - oral prepatory, oral (1s), pharyngeal (1s), esophageal (8-20s)
- Swallowing reflex is coordinated by the medulla, during which fibers
in the glossopharyngeal and vagus nerves carry information
- Oral prepatory phase - voluntary cortical control, duration is variable, formation of
the bolus, anterior tongue elevated, posterior tongue elevated - airway open, nasal breathing continues
- Oral phase - voluntary cortical control, duration is 1s, bolus
pushed backwards against hard palate by posterior tongue (contraction of stylopharyngeus muscle);
the bolus passes through anterior faucial arches and crosses inferior mandible through
use of palatoglossus muscle (CN X) until pharyngeal wall stimulated - requires intact labial
(orbicularis oris and zygomaticus) and buccinator muscles for adequate mouth closure (CN VII)
- Pharyngeal phase - involuntary control, 1s duration, requires simultaneous airway closure;
phase begins when bolus is moved through the pharynx and ends with opening of UES -
sensory information from stimulated receptors at the posterior oropharyx travels to the swallowing center
(nucleus ambiguous) of the medulla oblongata via CN VII, IX, X
- Pharyngeal phase cont. - motor impulses transmit through CN IX, X, XII to stimulate contractions;
palatopharyngeal folds pull medially and form a slit in the upper pharynx where the bolus passes -
velum is raised by the palatoglossal (X), levator (X), and tensor veli palatini (V) muscles to prevent food from entering nasopharynx
- Contraction of the superior constrictor muscle allows for closure of the
velopharyngeal port
- Laryngeal substage - protection of airway and inhibition of inspiration;
the larynx and hyoid bone are pulled upwards and enlarge the pharynx, create a vacuum for the bolus,
and relax the cricopharyngeus muscles; true and false vocal folds adduct, epiglottis drops down over the top
of the larynx to protect the airway and divert the bous into the pyriform sinuses
- Four factors move food down the pharynx - downward movement of posterior tongue, stripping
action of pharyngeal constrictors, negative pressure in laryngopharynx, gravity
- Esophageal phase - involuntary control, 8-20 seconds, bolus moves through esophagus via peristaltic wave motion and gravity through the LES;
the larynx lowers and returns to normal positioning, cricopharyneus muscle contracts to prevent reflux
- Odynophagia - pain on swalling - can be due to infection (herpes, candidiasis, pharyngitis) or inflammatory (GERD, eosinophilic esophagitis)