Swallowing, slow wave mechanisms

  1. GI motility begins and ends with skeletal muscle
  2. Remainder is smooth muscle
  3. GI muscle exhibits spontaneous slow wave potentials
  4. Tonic contractions (sphincters) are sustained for minutes to hours, and keep bolus from moving backwards (backflow)
  5. 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)
  6. 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
  7. Force of contraction directly related to the amplitude and frequency of action potentials
  8. ICC are located between the nerve endings and smooth muscle cells in the GI tract
  9. Excitatory compounds of smooth muscle include Ach, substance P
  10. Inhibitory compoinds of smooth muscle include VIP, epinephrine, nitric oxide
  11. Peristaltic contractions move bolus forward, segmental contractions mix
  12. Stages of swallowing - oral prepatory, oral (1s), pharyngeal (1s), esophageal (8-20s)
  13. Swallowing reflex is coordinated by the medulla, during which fibers in the glossopharyngeal and vagus nerves carry information
  14. Oral prepatory phase - voluntary cortical control, duration is variable, formation of the bolus, anterior tongue elevated, posterior tongue elevated - airway open, nasal breathing continues
  15. 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)
  16. 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
  17. 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
  18. Contraction of the superior constrictor muscle allows for closure of the velopharyngeal port
  19. 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
  20. Four factors move food down the pharynx - downward movement of posterior tongue, stripping action of pharyngeal constrictors, negative pressure in laryngopharynx, gravity
  21. 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
  22. Odynophagia - pain on swalling - can be due to infection (herpes, candidiasis, pharyngitis) or inflammatory (GERD, eosinophilic esophagitis)