Coordination of peristalsis in pharynx and esophagus

When a swallowed liquid bolus is followed from mouth to stomach in man by contrast studies or manometry, it traverses its course without hesitation even though the bolus is propelled by striated muscle contraction in the first part of its journey and smooth muscle in the latter part. The striated muscle is innervated by excitatory cholinergic nicotinic cranial nerves whereas the smooth muscle of the esophagus is innervated by the enteric nervous system (ENS) through excitatory and inhibitory nerves. These differences can be demonstrated by observing the inhibitory effects of curare and atropine, the first blocking nicotinic receptors and the second muscarinic receptors. Early students of esophageal motility recognized that peristalsis could be initiated in two ways. The first is initiated by a swallow and is called primary peristalsis and the second called secondary peristalsis is initiated by distension of the esophagus. It was proposed that primary peristalsis was initiated by a single sensory input activated by the bolus entering the pharynx which in turn activated a motor program in the brain stem. Secondary peristalsis was believed to be stimulated by multiple afferent impulses arriving from the esophagus as the bolus passed down the esophagus. More recent studies using manometric techniques have suggested that the only difference between primary and secondary peristalsis is the afferent stimuli and the effector mechanism is the same. Subsequent studies of carefully timed, paired swallows, transection of vagus nerves and esophagus, and single nerve recordings suggest that the answer lies between the two extremes noted above.(ABSTRACT TRUNCATED AT 250 WORDS)