<P> If this channel is open, conductance changes in cell are reflected in smooth muscle; post-junctional integrated responses are triggered by neuroeffector junctions and interstitial cells . </P> <P> Based on anatomic location and function, two main types of ICC have been described: myenteric ICC (ICC - MY) and intramuscular ICC (ICC - IM). ICC - MY are present around the myenteric plexus and thought to be pacemaker cells for slow waves in the smooth muscle cells . Calcium imaging studies in the colon have shown that ICC - MY is innervated by nitrergic and cholinergic nerve terminals, though the nature of the contacts has not been well defined . ICC - IM is located in between the smooth muscle cells . Enteric nerves have been reported to make synaptic contacts with ICC - IM . These contacts include areas of electron dense lining on the inner aspect of the varicosity membrane without any postsynaptic density on the membrane of ICC . Such contacts were not reported between the nerves and the smooth muscles . If ICC are important intermediaries in motor neurotransmission, then loss of these cells could reduce communication between the enteric nervous system and the smooth muscle syncytium, resulting in reduced neural regulation of motility . </P> <P> Classical excitatory and inhibitory neurotransmitters are concentrated and released from neurovesicles located in enteric nerve terminals or varicose regions of motor nerves, whereas nitric oxide is probably synthesized de novo as calcium concentration increases in nerve terminals upon membrane depolarization . Enteric nerve terminals make intimate synapses with ICC - IM, which are situated between the nerve terminals and neighbouring smooth muscle cells . ICC - IM play a critical role in the reception and transduction of cholinergic excitatory and nitrergic inhibitory neurotransmission . ICC - IM form gap junctions with smooth muscle cells and post-junctional electrical responses generated in ICC are conducted to the smooth muscle syncytium . By this contact, ICC can regulate the neuromuscular responses observed throughout the GI tract . Recent morphological evidence using anterograde tracing methods, has shown close apposition between vagal and spinal afferents and ICC - IM within the stomach wall (Fig. 5) and their absence in mutant animals that lack ICC - IM also supports a role for ICC - IM as possible integrators for in - series stretch - dependent changes in this organ . </P>

Similarities between autonomic neuroeffector synapses and the neuromuscular junction include